MHN 413.pptx

MHN 412
NEURO ANATOMY
&PHYSIOLOGY

INTRODUCTION
The nervous system (NS) is the
most complex and highly developed of all
the systems because, it is the master
controlling and communicating system of
the body. Every thought, action and
emotion reflects its activity. The cells of
nervous system communicate by electrical
and chemical between the nervous system
of the body.

It is just like the telephone system with the
brain comparable to the central switchboard
and operators, the spinal cord like the main
cable and the nerves like the telephone
wires, ending in receivers and dischargers of
message in the body tissues.
The nervous system is one of the
regulating system with endocrine.
Electrochemical impulses of the nervous
system make it possible to obtain information
about external and internal environment and
process, interprets and do whatever is

Some of these activities are conscious but
much of it happens without our awareness.
For descriptive purposes, the parts of
the NS are grouped as follows:
•The Central nervous system (CNS)
consisting the brain and spinal cord that
serves as the integrating and command
centre of the NS
•The Peripheral nervous system (PNS)
consisting mainly of the 12 cranial nerves
and 31 paired spinal nerves which connects
CNS to all parts of the body

The PNS has 2 functional subdivisions:
a) Sensory or afferent division: this consists
of nerves fibres that convey impulses to
the CNS from sensory receptors located in
the skin, skeletal muscles and joints
[somatic afferent fibres] and those
receptors from the visceral organs
[visceral afferent fibres]. The sensory
division keeps the CNS constantly
informed of events going on both inside
and outside the body.
b) The motor or efferent division: this

are muscles and glands to cause contraction
of muscles and secretion of glands. The
motor division also has 2 main parts.
The somatic or voluntary nervous system
which composed of motor nerves conducting
impulses to skeletal muscle to cause
contraction at conscious level.
The autonomic or involuntary nervous
system (ANS/INS) consisting of motor fibres
to smooth muscles, cardiac muscles and
glands of the at un- conscious level. The ANS
has 2 functional subdivision i.e sympathetic
and parasympathetic

which typically work in opposition
to each other to maintain body
homeostasis.

EMBRYONIC DEVELOPMENT OF NS
 The NS develops from the outermost of the
three primary germs layer of an embryo, the
ectoderm. By 3rd week of embryonic
development, a dorsal streak called
neuroectoderm appears along the entire
length of the embryo and thickens to form a
neural plate, destined to give rise to all
neurons and glia except microglia.
As development progresses, the neural plate
sinks and forms a neural groove, while the
cells

along its margin continue to proliferate and
form a neural fold on each side. The neural
folds eventually meet and fuse along the
midline, somewhat like closing zipper.
By 4weeks, this creates a hollow
channel called the neural tube. The neural
tube separates from the overlying ectoderm,
sinks a little deeper and grows lateral
processes that later form motor nerve fibres.
The lumen of the neural tube develops into
the central canal and ventricles of the CNS

• Some ectodermal cells separate from the
neural tube and form a longitudinal column on
each side called the neural crest. Some
neural crest cell develop processes and
become sensory neurons, while some others
migrate to other locations and become
sympathetic neurons, schwann cells and
other cell types.
By the 4th week, the neural tube exhibits 3
anterior dilatation or primary vesicle, called
the forebrain (proencephalon), midbrain
(mesencephalon) and hindbrain
(rhombencephalon)

By the 5th week, the neural tube undergoes
further flexion and subdivision and exhibits 5
secondary vesicles. The forebrain divides
into 2 secondary vesicles – the
telencephalon and diencephalon, the
midbrain remains undivided and retains the
same name; and hindbrains divides into 2
secondary vesicles – mesenphalon and
myelencephalon, and the remains taper
processes formed the spinal cord. The
telencephalon is marked by a pair of lateral
outgrowth that later become the cerebral
hemisphere, and the diencephalon exhibit a

of small cuplike optic vesicles that becomes
the retinas of the eye.

COMPONENTS OF THE NS
 The NS consists mostly of nervous tissue which
is highly cellular. Although it is very complex, the
nervous tissue is made up of just 2 principal
cells
1. A vast number of units called neurones or
nerves cells that transmit electrical signals
2. Supporting cells with a special type of
connective tissue called neuroglia, smaller
cells that surround and wrap the more delicate
neurones

Each of the nerve cells is special in structure
compared with other cells in the body. Each
has the body called the nerve cell and
attached appendages arising from the nerve
cell called the nerve fibres. The cell and its
fibres formed the neurones.
The nerve cells are grouped together to
form the gray matter of the NS. The gray
matter is found in the brain peripherally
forming the cortex, inwardly in the spinal
cord and in the ganglia [small isolated mass
of nerves]. The nerve fibres are grouped
together to form the white matter of the NS.

White matter is found in the brain inwardly, in
the spinal cord outwardly and in all parts of
PNS. A nerve is simply referred to as a
bundle of nerve fibres bound together by
connective tissue.
The nerve cells vary considerably in size
and shape but they are all too small to be
seen by the naked eye but only seen by a
microscope.

NEURONES
 There are about a trillion neurones in the NS
which are the unit on which NS is built up.
The neurones are highly specialized cells
that conduct messages in form of nerve
impulses from one part of the body to
another. Neurones are complex cells, though
are vary in structure but they all have a cell
body and one or more slender processes i.e
axon and dendrites which are extension of
the cell bodies

•Cell Body: is the control centre of the
neurone. It has a single centrally located
nucleus with a large nucleolus surrounded by
cytoplasm which contains the typical
organelles such as lysosome, mitochondria, a
golgi body, endoplasmic reticulum etc.
Clusters of cell bodies in the CNS are called
nuclei whereas those that lie along the
nerves in PNS are called ganglia
•Axon: each nerve cell has only one axon
arising from a cone-shaped area of the cell
body carrying nerve impulses away from the
cell body called the axon hilock

They are usually longer than the dendrites.
Sometimes as long as 10cm. Structurally,
large axons and those of the PNS are
surrounded by a myelin sheath which
functions as insulator to the axon, protector
from pressure and injury and source of
nutrition. The myelin sheath consists of series
of Schwann cells arranged along the length of
the axon. Each one is wrapped around the
axon so that it is covered by a number of
concentric layer of Schwann cell membrane.
Between the layers of plasma membrane,
there is about 20% protein and 80% lipid

The outermost layer of schwann cell plasma
membrane is called neurilemma. There are
tiny areas of exposed sarcolemma between
adjacent schwann cells called node of
Ranvier which assist the rapid transmission
of nerve impulses. Post ganglionic fibres and
some small fibres in the CNS are non-
myelinated. In this type a number of axons
are invaginated into a series of schwann cell
membranes so that adjacent ones are in
close association and there is no exposed
sarcolemma, hence transmission of impulses
are not faster.

NEURONES
 Dendrites ; These are the processes of
nerve fibres that provide an enormous
surface area for receiving signals from
other neurones toward the body because
they have receptors for neurotransmitter.
They have almost the same structure as
axons but they are usually shorter and
branching. They are usually many between
2-200 on a neurone. They form synapses
with dendrites of other

NEURONES
neurones or terminate in specialized sensory
receptor such as those in the skin.
The CNS contains both the cell bodies
and their processes (white matter) whereas
the PNS for the most parts’ consists chiefly
of the processes alone. Bundles of neurone
processes are called tract in the CNS but
they are referred to as nerves in the PNS.

NEURONES
 Neurones have 3 main characteristics
(properties).
a) irritability; This is the ability of neurone to
initiate nerve impulses in response to
stimuli from outside the body (e.g touch,
light waves) and inside the body (e.g
change in the concentration of oxygen in
the body alters respiration). In the body, this
stimulation may be described as partly
electrical and partly chemical.

NEURONES
b) Conductivity; This means that the
neurone has the ability to transmit an
impulse from one part of the brain to
another, from brain to skeletal muscles,
from muscles and joint to the brain, brain to
organ of the body and vice versa, from
outside world to the brain through special
senses(eye, nose, ear, tongue) and sensory
nerve ending in the skin

NEURONES
C) Secretion; neurones communicate
with other cells by secreting
neurotransmitters and other chemical
messengers.

CLASSIFICATIONS OF NEURONES
On the basis of structural differences,
neurones are classified according to the
number of processes extending from their
cell body as follow;
1) Multipolar neurones; they have 3 or more
nerve fibres one of which is an axon. They
are the major neurones in the CNS, about
99% of neurones in the body are multipolar.

CLASSIFICATIONS OF NEURONES
2) Bipolar neurones; They have only 2
nerve fibres. One of them is an axon and
other is a dendrite. They are found in some
of the special sense organs such as retina
of the eye and olfactory mucosa.
3) Unipolar neurones; They have a single
nerve fibre that extends from the cell body
and then divides into 2 branches, one
connected to a peripheral body part and

CLASSIFICATION OF NEURONES
functioning as a dendrite and other entering
the brain and spinal cord and functioning as
an axon. The cell bodies of some unipolar
neurones aggregate in specialized masses
of nervous tissue called ganglia located
outside CNS.
On the basis of functional differences,
neurones are grouped according to the
direction in which the nerve impulse travels

relative to the CNS as follow;
a) sensory/afferent neurones; These
transmit impulses to the CNS from
peripheral body tissues. Their cell bodies
are located in sensory ganglia outside the
CNS. The impulses may be passed to
connector neurones of the reflex arcs in the
spinal cord. They gave rise to sensation
such as touch,

pain, heat or cold. Changes that occur inside
or outside the body stimulate receptor ends
triggering sensory nerve impulses, which
travel along the sensory neurone fibres to
CNS. Most sensory neurones are unipolar.
b) Motor/efferent neurones; These transmit
impulses away from the CNS and
autonomic ganglia to the effector organs
(muscle and glands) of the body periphery.
Except for

some neurones of ANS, their cell bodies are
located in the CNS. Most of motor neurones
are multipolar. There are 2 types of motor
neurones;
 Somatic nerves; involved in voluntary &
reflex skeletal muscle contraction.
 Autonomic nerves; involved in involuntary
or smooth muscle contraction and glandular
secretion. This is also called secretory
neurones.

c) Mixed/interneurones ; also called
internuncial or association neurones.
These lie between motor and sensory in
neural pathways and shuttle signals
through CNS pathway where integration
occurs. They are multipolar confined
with CNS. They may direct incoming
sensory impulses to appropriate part for

processing and interpretation.
Outside the CNS, sensory and
motor neurones are enclosed with
the same sheath of connective
tissue and they are called mixed
neurones.

NEUROGLIA
The neurones of the CNS are protected
and supported by non-excitable glial cells
that outnumbered as much as 50 to a
neurone called neuroglia. Unlike neurones,
they continue to replicate throughout life
and aid the functions of the neurones. The
neuroglia are named by their shapes,
number of processes they posses and
where found. They are;

NEUROGLIA
1) Astrocytes ; They are most abundant and
important glial cells. They are star- shaped
that cover the entire brain surface and most
regions of the neurones. They are adjacent
to blood vessels with their foot processes
forming a sleeve round them. This means
that the blood is separated from the
neurones by the capillary wall and a layer

NEUROGLIA
of astrocyte foot processes which together
constitute the blood brain barrier. This is a
selective barrier that protect the brain from
chemical variations in the blood, e.g after a
meal, oxygen, carbon dioxide, alcohol,
barbiturates, glucose and lipophilic
substances quickly cross the barrier into the
brain. Some large molecules, drugs,
inorganic

NEUROGLIA
ions and amino acids pass slowly from the
blood to the brain. Astrocytes also form scar
tissue that fills spaces following injury to
the CNS.
2) Oligodendrocytes ; These cells occur in
rows along nerve fibres. They are smaller
than astrocytes and are found in clusters
round the neurone cell wall in CNS. The
cells form myelin sheath around nerve
fibres of CNS

NEUROGLIA
but do not form a nuerilemma like schwann
cells. The myelin sheaths formed around
the portion of the nerve fibres produce
insulating covering for them.
3) Microglia ; These cells are scattered
throughout the CNS. They are small ovoid
cells with relatively long processes. They
are derived from monocytes that migrate
from

NEUROGLIA
the blood into NS before birth. Like all
macrophages, they arise from embryonic
mesoderm. Microglia phagocytize dead
nervous tissue, micro-organisms and other
foreign matter. This protective role is
important because cells of immume system
are denied access to the CNS.
4) Ependymal cells ;The cells range in
shape

NEUROGLIA
from squamous to columnar and many
ciliated, arranged in single layer. They line
the ventricles of the brain and central canal
of spinal cord where they form a fairly
permeable barrier between the
cerebrospinal fluid (csf) that fills these
cavities and the tissue fluid bathing the cells
of CNS. They also assists in the circulation
of CSF.

NEUROGLIA
5) Neurolemmocytes ; These are flatten
cells arranged and form myelin sheath
around the axon of large fibres in PNS.
They are functionally similar to
oligodendrocytes, and are vital to
regeneration of damaged peripheral
nerve fibres.

THE SYNAPSE
The word "synapse" is from the
Greek word synapsis, meaning
"conjunction", in turn from words such
as," together" and "to fasten“. It was
introduced in 1897 by English
physiologist Michael Foster . This is the
site of functional contact between 2
neurones or between neurone and
effector (muscle or glands).

It is a junction that mediates information
transfer from one neurone to the next.
Synapses between the axon endings of
one neurone and dendrites of other
neurones are axodendritic synapse.
Those between axon endings of one
neurone

THE SYNAPSE
and cell bodies (soma) of other neurones are
axosomatic synapses. There are some
others but these two are the common ones.
The neurones conducting impulses
toward the synapse releases the
neurotransmitter i.e information sender are
called presynaptic neurones, while the
neurones transmitting the signal away from
the synapse respond to the

THE SYNAPSE
neurotransmitter i.e information receiver
are called postsynaptic neurones. Most
neurones in the body function as both
pre and post synaptic neurones.
Outside the CNS, the postsynaptic cell
may be either another neurone or an
effector cell (a muscle cell or gland cell).
There are 2 varieties of synapses. They
are;

THE SYNAPSE
1) Electrical synapse; These are less
common variety, consist of gap junction.
They contain protein channels, called
connexons that intimately connect the
cytoplasm of adjacent neurones and allow
ions and small molecules to flow directly
from one neurones to the next. Neurones
joined in this way are said to be electrically
coupled and transmission across

THE SYNAPSE
these synapses is very rapid. Depending on
the nature of the synapse communication
may be unidirectional or bidirectional.
In adult, electrical synapse are found in
regions of the brain responsible for certain
stereotyped movements and in the
hippocampus, a brain region involved in
emotion and memory. Electrical synapses
are

THE SYNAPSE
far more abundant in embryonic nervous
tissue to allow proper neurone connection
with one another. As the nervous system
develops, some electrical synapses are
replaced by chemical synapses.
2)Chemical synapses ; These are specialized
for release and reception of chemical
neurotransmitters. A typical chemical
synapse

THE SYNAPSE
is made up of 2 parts;
1) A knoblike axon terminal of presynaptic
neurone which contains many tiny,
membrane-bounded sacs called synaptic
vesicles, each containing thousand of
neurotransmitter molecules.
2) A neurotransmitter receptor region on the
membrane of a dendrite or the cell body
of

THE SYNAPSE
the postsynaptic neurones.
Although close to each other, presynaptic
and postsynaptic membrane are always
separated by the synaptic cleft, a fluid filled
space. Because the current from the
presynaptic membrane dissipates in the
fluid-filled cleft, chemical synapses
effectively prevent a nerve impulse from
being directly

THE SYNAPSE
transmitted from one neurone to another.
Instead, transmission of signals across
the synapses is a chemical event that
depends on the release, diffusion and
receptor binding of neurotransmitter
molecules and results in unidirectional
communication between neurones.

THE SYNAPSE
After being released, some
neurotransmitters are decomposed by
enzymes in the synaptic cleft. Others are
transported back into the synaptic knob that
released them (reuptake) or into nearby
neurones or neuroglial cells. Decomposition
of the neurotransmitter prevents continuous
stimulation of postsynaptic neurones

NEUROTRANSMITTERS &
NEUROMODULATORS
The nerve impulses are transmitted to
nerve terminals which travel across the
synaptic cleft, hence the concept of
neuro-humeral transmission was given
to explain the mode by which nerve
transmit their effect across the cleft.
This concept states that nerve mediate
its effect through the release of specific
chemical

NEUROTRANSMITTERS &
NEUROMODULATORS
substances called Neurotransmitters
(NT). Neurotransmitters, also known
as chemical messengers, are
endogenous chemicals that enable
neurotransmission. They transmit
signals across a chemical synapse,
such as a neuromuscular junction, from
one neuron (nerve cell) to another
"target" neuron, muscle cell, or gland
cell.

NEUROTRANSMITTERS & NEUROMODULATORS
 NTs are the means by which each
neurone communication with others to
process and send messages to the rest
of the body. They are synthesized by
nerve cells, actively transported along
the axons and stored in the synaptic
vesicles. They are released by

NEUROTRANSMITTERS &
NEUROMODULATORS
exocytosis in response to the action
potential and diffuse across the synaptic
cleft. They act on specific receptor sites
on the postsynaptic membrane. Their
action is short lived as they are
inactivated immediately they have
stimulated the postsynaptic neurones.

NEUROTRANSMITTERS &
NEUROMODULATORS
The sensitivity of post synaptic
neurones may be increased or decreased
by substances modulating them rather
than transmitting the message, hence they
are called Neuromodulators. They are
messengers that indirectly influence
synaptic communication. They include
hormones and neuropeptides released by

NEUROTRANSMITTERS &
NEUROMODULATORS
endocrine and nerve cells respectively.
Neuromodulators alter the rate of
synthesis, release, reuptake or enzymatic
degeneration of neurotransmitters.
At present, more than 50
neurotransmitters or neuromodulators
have been identified. Although some
neurones produce and release only one
kind of neurotransmitters, most make two
or more

NEUROTRANSMITTERS &
NEUROMODULATORS
and may release any one or all of them
depending on the action potentials.
Neurotrnsmitters are classified chemically
and functionally.
Functionally, NTs that increase
postsynaptic membrane permeability to
Na++ may trigger nerve impulse and they are
called excitatory NTs [cause depolarization]
e.g. Glutamate is a typical excitatory. Other
NTs decrease

NEUROTRANSMITTERS &
NEUROMODULATORS
membrane permeability to Na++, thus
making it less likely that threshold will be
reached [cause hyperdepolarization] and
they are called inhibitory NT because they
lessen the chance that a nerve impulse will
occur e.g. GABA and glycine are usually
inhibitory. Others exert both effects
depending on the specific receptor type with
which they interact e.g. acetycholine,
catecholamines etc

NEUROTRANSMITTERS &
NEUROMODULATORS
NTs fall into several chemical
compositions based on molecular structure
as follows:
1 Acetylcholine (Ach); this was the first NT
identified. It is synthesized from acetic acid
and choline obtained from diet. Ach is
employed as NT at the neuromuscular
junction, at the post ganglionic
parasympathetic nerve endings, all
preganglionic nerve ending of the ANS. In
the

NEUROTRANSMITTERS &
NEUROMODULATORS
In the CNS, Ach is employed as a NT by
Betz cells of the motor cerebral cortex and
neurones of brain stem and hippocampus. It
is implicated in a form of dementia called
Alzheimer disease
2 Biogenic Amines: These are synthesized
from amino acids by replacing the COOH
group with another functional group. They
include the catecholamines such as
dopamine, nor-epinephrine(NE), and
epinephrine, and

NEUROTRANSMITTERS &
NEUROMODULATORS
indolamines such as serotonin and histamine.
(a) Dopamine: is an intermediate in the
biosynthesis of NE, but can itself also serve as
a NT. The best dopaminergic neurones are
those of sustantia nigra of the mid brain,
hypothalamus, extra pyramidal system, and
some sympathetic ganglia. Loss of these
neurones is associated with Parkinson’s disease
and excess of them is associated with
schizophrenia.

NEUROTRANSMITTERS &
NEUROMODULATORS
(b) Nor epinephrine(NE) is
synthesized from tyroxine or
phenylalanine via dopamine
through hydroxylation. It is secreted
in the brain stem especially locus
coeruleus of mid brain, limbic
system, cerebral cortex, cerebellum
and serves as main NT of
ganglionic neurones in the SNS.

NEUROTRANSMITTERS &
NEUROMODULATORS
(c) Histamine: This is released by mast cells of
connective tissue from histidine, secreted
mainly in the hypothalamus. It is involved in
wakefulness, appetite control, learning and
memory.
(d) 5-hydroxytryptamine {5-HT, Serotonin}:
this is derived from tryptophan. It is secreted
in the brain stem,[mid brain], hypothalamus,
limbic system, cerebellum, pineal gland and
spinal cord.

NEUROTRANSMITTERS &
NEUROMODULATORS
It is involved in sleep and implicated in Bi-
polar affective disorders.
3 Amino Acids: it is difficult to prove amino
acids as NTs because they occur in all body
cells. But there are some that their roles as
NT is certain such as GABA, glycine
aspartate and glutamate.
(a)GABA: this is synthesized from glutamic
acid. It is generally inhibitory NT which acts
by increasing chloride conductance. It is

NEUROTRANSMITTERS &
NEUROMODULATORS
secreted in the cerebral cortex, hypothalamus,
cerebellum, spinal cord, granule cells of
olfactory bulb, cells of retina.
Glutamate, Glycine and aspartate are
considered putative small molecule NT in
several areas of CNS.
4. Neuroactive peptides: This group
comprises of many small peptides. They are
described by non-commital term because
their status

NEUROTRANSMITTERS & NEUROMODULATORS
as NT is not well established (putative NT).
They act as neuromodulators rather than NT.
They include enkephalins, endorphines,
substance P, Thyrotropin, neurotensin,
Bradykinin, Somatostatin and other peptide
hormones.
5.Others: these group are purine such as ATP,
Gases and Lipids, such as Nitric oxide,
carbon monoxide and other
endocannabinoids.

PROTECTIVE COVERINGS OF CNS
The CNS lies inside the skull and vertebral
column. In addition to the hard bony
protection provided by the axial skeleton, the
brain and spinal cord are completely
surrounded by three membranes which are
connective tissue called meninges. The
meninges are found lying between the skull
and the brain and between the vertebrae and
the spinal cord.

Named from without inwards, they are:
•Dura mater
•Arachnoid mater
•Pia mater
THE DURA MATER
This is strongest meninx, with a tough, fibrous
coat consisting largely of white collagen fibres.
It consist of 2 layers of dense fibrous tissue
and irregular connective tissue. The outer layer
takes the place of the periosteum i.e it lines the
interior of cranium and the vertebral canal
while the inner layer provides a protective

The two dural layers are fused together except
in certain areas, where they separate to
enclose dural venous sinuses that collects
venous blood from the brain and directs it into
the internal jugular vein. The brain inner layer
sweeps inward between the cerebral
hemisphere to form the falx cerebri, between
the cerebellar hemisphere to form the falx
cerebelli and between the cerebrum and
cerebellum to form the tentorium cerebelli.

These rigid folds of the inner layers of the
dura mater which project into the cranial
cavity help to support the brain and to
maintain it in position.
The falx cerebri is a large sickle-shaped
fold lining vertically in the midline and
separating the right and left hemisphere.
The superior sagittal sinus is formed by the
falx cerebri.

The Falx cerebelli continues inferiorly
form the posterior falx cerebri, this small
midline partition runs along the vermis of
the cerebellum.
The Tentorium cerebelli is a
crecentric hatched sheet which lies
horizontally and forms a tent-like roof for
the posterior cranial fossa, thereby
separating the cerebrum from the
cerebellum below. The straight and
transverse sinuses are formed by the

In the spinal cord, the dura mater forms
a loose sheath round cord, extending from the
foramen magnum to the 2nd sacral vertebra.
Thereafter, it invests the filum terminale and
fuses with the periosteum of the coccyx. The
spinal dura mater is an extension of the inner
layer of the brain dura mater and is
separated from the periosteum of the
vertebrae and ligaments within the neural
canal by the epidural or extradural space
containing blood vessels and areolar tissue.

Nerves entering and leaving the spinal cord
pass through the epidural space.
THE ARACHNOID MATER
This is a delicate transparent serous
membrane that form the middle meninx i.e.
situated between the dura and pia maters. It is
separated from the dura mater by a narrow
serous cavity the subdural space, which
contain a thin fluid, and from the pia mater by
the subarachnoid space containing CSF.
The arachnoid mater loosely covers the brain,
never dipping into the sulci of the cerebral
surface but dipping down

With the dura between the main portion i.e., it
accompanies the inner layer of dura mater in
formation of the falx cerebri, falx cerebelli and
tentorium cerebelli. It continues downwards to
envelop the spinal cord and ends by merging
with dura mater at the level of the 2nd sacral
vertebra.
The name arachnoid means like a spider
web is given because of the microscopic
appearance of the tissue. Between the under-
surface of cerebellum and the medulla
oblongata, the subarachnoid space is
enlarged to form the cisternal magna where

may be passed between the occiput and the
atlas vertebra to withdraw CSF. The
procedure is called cisternal puncture.
In the arachnoid mater, there are
knoblike projection that protrude superiorly
through the dura mater and into the superior
sagittal called arachnoid villi through which
the CSF is absorbed into the venous blood.
THE PIA MATER
This is the inner most meninx. It is
composed of delicate, thin, translucent layer
of loose connective tissue. It is richly vascular

THE PIA MATER
supplied with numerous small blood
vessels which supply the surface of the
brain and spinal cord. It closely invests
the brain, completely covering the
convolutions and dipping into each sulci
and fissure like a sheet of cellophane.
The pia mater continues downwards to
invest the spinal cord. Beyond the end
of the cord, it

THE PIA MATER
continues as the filum terminale, a long
slender filament which pierces the
arachnoid tube and goes on with the
dura mater to fuse with the periosteum
of the coccyx.

THE VENTRICLES OF THE BRAIN
The ventricles are 4 hallow irregular
shaped cavities or chambers with the
brain that are lined by ependymal cells
and contain the CSF. They arise from
expansions of the lumen of the
embryonic neural tube. The 4 link with
one another and continue with central
canal of the spinal cord. They are;

 Right and left lateral ventricles
 Third ventricle
 Fourth ventricle
lateral ventricles
The paired lateral ventricle i.e right & left
or first & second are located deep within
each cerebral hemisphere forming a
butterfly shape in cross sections of the
brain just below

the corpus callosum. They reflect the pattern
of cerebral growth. Anteriorly, they lie close
together and only separated by a thin
median membrane called septum
palludium and are lined with ciliated
epithelium. Each lateral ventricle
communicates with the 3rd ventricle via a
channel called an interventricular
foramen (foramen of Monro)

The Third ventricle
This is a little more than a length-wise slit in
the diencephalon beneath the mid-portion
of the corpus callosum and longitudinal
fissure, just between the 2 parts of the
thalamus. It communicates with the 4th
ventricle by a canal called cerebral
aqueduct that runs

through the midbrain hence aqueduct of the
midbrain or aqueduct of Sylvius.
The fourth ventricle
This is a small triangular and diamond
shaped chamber lies in the hindbrain
between the cerebellum posteriorly and the
medulla and pons varolli anteriorly below
and behind the 3rd ventricle. It is an
expansion of

the central canal of the cord after the cord
enters the cranial cavity and become
enlarged to form the medulla three
openings mark the walls of the 4th
ventricle; the paired lateral apertures in
its side walls and the median aperture in
its roof. This apertures connect the
ventricle to the subarachnoid space for

The flow of CSF and through the opening
at distal end of the central canal of the
spinal cord.

CEREBROSPINAL FLUID (CSF)
In addition to the bony and membranous
coverings, nature has further fortified the
CNS against injury by providing a Cushing
of fluid both around them and within them
[i.e. The brain and spinal cord]. The fluid is
called cerebro-spinal fluid (csf), which is
clear, colourless liquid similar in
composition to blood plasma, from which it
is formed and the spaces containing it are:

CEREBROSPINAL FLUID (CSF)
 The subarachnoid space around the
brain
 The subarachnoid space around the
spinal cord
 The ventricles and aqueducts inside the
brain
 The central canal inside the cord.

FORMATION , CIRCULATION AND
ABSORPTION
 The formation of the CSF occurs by the secretions
by the choroid plexuses which are network of blood
capillaries covered by ependymal cells that project
from the pia mater into the roof of each lateral
ventricles. These capillaries covered by a simple
cuboidal epithelium are fairly permeable, and tissue
fluid filters continuously from the blood stream.
From each lateral ventricle, the CSF passes into 3rd
ventricles then into the 4th ventricle.

From the roof of the 4th ventricle, Csf flow through
foramen into the subarachnoid space and completely
surrounds the brain and spinal cord. It also circulate
into the central canal of the cord.
There is no intrinsic system of CSF circulation
but its movement is aided by pulsating blood vessels,
respiration and changes of posture. The CSF passes
back into blood through tiny diverticular of arachnoid
called arachnoid villa a finger-like extension that
project into the dural venous sinuses especially
superior saggital sinuses.

The movement of CSF from the subarachnoid space
to venous sinuses depends upon the difference in
pressure on each side of the walls of the villi. When
CSF passes into the blood and vice versa. There
may also be some re-absorption of CSF by cells in
the wall of the ventricles. The rate of about 20ml/hour
(i.e. 480ml/day) is reabsorbed.
CSF is secreted continuosly at the rate of
about 0.5ml/minute i.e 720mls/day. The amount
around the brain and spinal cord remain fairly
constant at about 140ml in adult [23mls in the
ventricles and 117ml in the subarachnoid space].

Which means that the absorption keeps pace with
secretion. CSF pressure may be measured using a
vertical tube attached to the lumber puncture needle.
It remains fairly constant at about 10cmH2O when
the individual is lying on his side and about
30cmH2O when sitting.

CHARACTERISTICS AND CONTENTS
 CSF is a clear, colourless watery fluid,
slightly alkaline with a specific gravity of
1004-1008. It has an organic salt similar to
that of blood plasma. CSF consists of mainly
waters, some WBC, glucose, plasma protein
[small amounts of albumin and globulin],
small amount of creatinine and urea, and cat
ions such as Na+, K+, Ca2+, Mg2+ and
anions such as Cl- HCO3-

 The glucose concentration of CSF is
abnormally high in uncontrolled diabetic
mellitus but reduced in pyrogenic meningitis.
The protein content of the CSF is elevated in
many pathogenic conditions because of
increased permeability of the walls of the
blood vessels in the choroid plexus i.e. A
reduced blood brain barrier. Blockage in the
route of flow and re absorption of CSF can
result into abnormal accumulation of CSF,
expansion of the ventricles and compression
of nervous tissue.

 The condition is the called
Hydrocephalus in infant, which can be
treated by inserting a shunt into the
ventricle to drain excess CSF into the
abdominal cavity.

FUNCTIONS
 It protects and support the brain and
spinal cord by forming a liquid cushion that
gives buoyancy to the CNS structure.
 It acts as a water bed between the
delicate nerve tissue and the bony walls of
the cavities in which these structures lie.
 It nourishes, cleanses and washes away
waste and toxic substances including
exchange of nutrients into the blood
stream

FUNCTIONS
 It keeps the brain and spinal cord moist and
maintains a uniform pressure around these
delicate structures.
 It homeostatically regulates the chemical
environment of the CNS neurones e.g
regulating the pH to prevent dizziness and
fainting.

THE BRAIN
 The Brain when fully developed is a large
organ filling the cranial cavity. It is about
1/50 of the body weight i.e. Average adult
man’s brain has a mass of about 1600g
while that of a woman has 1450g. The
adult brain is a complicated organ made of
about 100 billion multipolar neurones and
innumerable nerve fibres. Early in its
development, the brain is divided into 3
parts:

THE BRAIN
Which are the fore brain, midbrain and
hindbrain.
From the walls of the 3, the brain is fully
developed to consist of 5 main parts:
 The forebrain which consists of the 2
cerebral hemisphere (the cerebrum) and
the diencephalon or interbrain.
 The mid-brain or mesenphalon
 The hindbrain comprising.

THE BRAIN
• The pons
• The medulla Oblongata
• The Cerebellum
The midbrain, cerebellum, pons and
medulla oblongata are together often
called the brainstem as they are
comparatively small and occupy the
back lower part of the cranial cavity
only the cerebrum completely
overlapping them.

THE CEREBRUM
This is the largest part of the brain that
accounts for about 83% of total brain
mass and are the most conspicuous parts
of an intact brain. It occupies all the vault
of the cranium from the eyebrows in front
to the occiput at the back.
The cerebrum consist of 2 larger masses
called cerebral hemisphere which are
separated by a fold of dura mater the falx
cerebri.

THE CEREBRUM
Below the falx cerebri, the cerebral
hemisphere are joined by a bridge of
matter called corpus callosum of about
10cm in length. The corpus callosum
serves to convey over 200million nerve
fibres from one hemisphere to the others.
It serves to integrate the activities of the
2hemispheres which is a complementary
to each other.

THE CEREBRUM
Each hemisphere contains a small cavity
(ventricle) known as the left and right
lateral ventricles. These hemispheres
control the opposite side of the body so
that disease of the right side of the
cerebrum paralyses the left of the body,
and vice versa. The left hemisphere is
believed to be dominant and associated
with right handedness. It is associated
with verbal linguistic, mathematics,
sequential and analytic activities.

THE CEREBRUM
Nearly the entire surface of the cerebral is
marked by elevated ridges of tissue or
convolutions called gyri separated by shallow
grooves called sulci. Deeper grooves are
called fissure which separate large regions of
the brain. The median longitudinal fissure
separates the 2 cerebral hemisphere while the
transverse fissure separates the cerebral
hemisphere from the cerebellum below.

THE CEREBRUM
Several sulci divide each hemisphere into 5
lobes which corresponds roughly with the
bones of the cranium, the chief lobes are:
 The frontal lobe
 The parietal lobe
 The temporal [temporosphenoidal] lobe
 The occipital lobe
 The insular

THE CEREBRUM
The important sulci are:
 The central sulcus: (sulcus of Rolando)
which runs downwards and forward sfrom
the midline separating the frontal from the
parietal lobes. Bordering the central sulcus
are the precentral gyrus anteriorly and
postcentral gyrus posteriorly.
 Parieto-occipital sulcus: more posteriorly,
this is located on the medial surface of the
hemisphere separating the occipital lobe
from parietal lobe.

THE CEREBRUM
 The lateral cerebral sulcus: (sulcus of
Sylvius) which outlines the flaplike
temporal lobe and separates the frontal
and perietal lobes above from the
temporal lobe below. Burried in the lateral
sulcus is a portion of the cerebal cortex
called the insula and covered by parts of
the frontal, parietal and temporal lobes.
Stimulation of this insula causes increased
salivation, nausea, gastric movement,
belching and abdominal sensation.

THE CEREBRUM
each cerebral hemisphere has some basic
regions such as superficial (peripheral) parts
consisting of gray matter or nerve cell bodies
called cerebral cortex, an internal white
matter or nerve fibre, the basal ganglia/nuclei
and limbic system which are islands of gray
matter situated deep within the white matter.
The cerebrum

CEREBRAL CORTEX
This is thin layer of about 2-3cm thick in
the outermost portion if the cerebrum, i.e.
A layer of gray matter covering the surface
of the cerebral hemisphere. The cerebral
cortex constitutes about 40% of the mass
of the brain. It contains nearly 75% of all
the neurones cell bodies in NS, dendrites,
associated glial and blood vessels, but no
fibre tracts.

CEREBRAL CORTEX
It contains billions of neurones arranged in
six layers with a surface areas of about
2,500cm2. It has many convolutions
effectively triple its surface area. It is
composed of the principal types of
neurones which are;
 Stellate cells; they are concerned
largely with receiving sensory input and

CEREBRAL CORTEX
processing information on a local level.
 Pyramidal cells; are tall and conical their
apex points towards the brain surface
and has thick dendrites with many
branches which are small knobby
dendrites spines

FUNCTIONAL REGIONS OF THE CEREBRAL CORTEX
Specific regions of the cerebral cortex
perform specific functions. Although functions
overlap among regions, the cortex can be
divided into motor, sensory and association
areas.
 A) Motor Areas: lies in the frontal lobes just in
front of the central sulcus, [precentral motor
area], to control voluntary movement. The
motor areas composed of 4 specific areas:

 1) Primary motor(somatic) cortex: this is
located in the precentral gyrus of the frontal lobe
of each hemisphere. The nervous tissue in
these regions contains numerous large
pyramidal cells named for their pyramid-shaped
cell bodies. The pyramidal cells allow conscious
control skilled voluntary movement of skeletal
muscles. Their long axons projects to the spinal
cord to form the massive voluntary motor tract
called pyramidal tracts or corticospinal tracts.

Most of the nerve fibres in these tracts cross over
from one side to another within the brain stem.
As a result, the motor area of the right cerebral
hemisphere generally controls the skeletal
muscles on the left side of the body and vice
versa. The entire body is represented spatially
in the cortex of each hemisphere. In the
arrangement, the pyramidal cells that control the
lower limbs are at the top; next come those of
the trunk, upper limbs, neck, and head
extending outward and downward in front of the
central sulcus. The motor centres for the eyes
lies farther forward.

 2) Pre motor cortex: Just anterior to the
precentral gyrus in the frontal lobe is the
pre motor cortex. This region controls
learned motor skills of a repetitions or
patterned nature, such as playing a
musical instrument and typing. Think of
this region as the memory bank for skilled
motor activities.

 3) Broca’s area or speech Area: This lies
anteriorly to the interior region of the
premotor area and superior to the lateral
sulcus. It coordinates the complex
muscular actions of the mouth, tongue
and larynx, which makes speech possible.
The area lies on the left side of the frontal
lobe in a right handed person and vice
versa.

 4) Frontal Eye field: is located partially in
and anterior to the premotor cortex and
superior to Broca’s area. The area
controls voluntary movement of the eyes
and eyelid.

 B) Sensory Area: these areas are concerned
with conscious awareness of sensation, the
areas occur in the parietal, insular, temporal and
occipital lobes. The functional sensory areas
are;
1) Primary somatosensory cortex; This is
located in the posterior to the central sulci
(postcentral sulci) of the parietal lobe, just
posterior to the primary motor cortex. Neurones
in this gyrus receive information from the
general sensory receptor

FUNCTIONAL REGIONS OF THE CEREBRAL
CORTEX
in the skin and from proprioceptors in the
skeletal muscles, joint and tendons. As with
the primary motor cortex, the body is
represented spatially and upside –down
according to the site of stimulus input, and
the right hemisphere receives input from
the left side of the body.
2) Somatosensory association cortex;
This lies just posterior to the primary
somatosensoy

CORTEX
cortex and has many connections with it. Its
function is to integrate sensory input
relayed to it via the primary somatosensory
cortex to produce an understanding of an
object being felt; its size, texture and the
relationship of its part without seeing it.
3)Visual areas(striate cortex); The primary
visual cortex is seen on the extreme tip of
the

CORTEX
occipital lobe, but most of it buried deep
in the medial aspect of the lobe. As the
largest cortical sensory area, it receives
visual information from the retina of eye.
The primary visual cortex is surrounded
by visual association area which uses
past visual experiences to interpret
visual stimuli

CORTEX
4) Auditory areas; Each primary auditory
cortex is located in the superior margin of the
temporal lobe abutting lateral sulcus. Sound
energy is transmitted to the primary auditory
cortex for interpretation. Also posteriorly,
there is auditory association area which
allows storage of sound memories in the
past. The Wernicke’area which contributes
to understanding of language is part of the
auditory cortex.

CORTEX
5) Olfactory cortex; The primary olfactory
cortex lies on the medial aspect of the
temporal lobe in a small region called the
piriform lobe. It controls the conscious
awareness of different odours from
olfactory tracts.
6) Gustatory cortex; this is located in the
insula just deep to the temporal lobe. The
region is involved in the perception of taste
stimuli.

CORTEX
7) Visceral sensory area; This is located at
insula just posterior to the gustatory cortex.
It is involved in conscious perception of
visceral sensations such as full bladder,
upset stomach etc.
8) vestibular(equilibrium )cortex; this is
located in the posterior part of the insula
and adjacent to parietal cortex. It is
responsible for conscious awareness of
balance i.e position of the head in space.

CORTEX
C) Association Areas
Association areas occupy the anterior
portions of the frontal lobes and are
widespread in the lateral portion of temporal
and occipital lobes. They connect with one
another and with other brain structures.
These areas analyse and interpret sensory
experiences and oversee memory,
reasoning , verbalizing, judgement and
emotions.

CORTEX
Association areas of the frontal lobes
control a number of higher intellectual
processes. These include concentrating,
planning, complex problem solving,
cognition, personality, working memory,
abstract ideas and judging the possible
consequences of behaviour.
Association areas of parietal lobes help
in understanding speech and choosing
words to express thought and feelings.

CORTEX
Association areas of the temporal
lobes and regions at the posterior ends
of the lateral fissures interpret complex
sensory experiences such as those
needed to understand written and
spoken languages. The regions also
provide memory of visual scenes, music
and other complex sensory patterns

CORTEX
Association areas of the occipital
lobe that are adjacent to the visual
centres are important in analyzing visual
pattern and combining visual images
with other sensory experiences as when
one recognizes other person or an
object.

THE CEREBRAL WHITE MATTTER
The white matter of the cerebrum is not a
decision- making centre like the cortex but
constitutes most of the cerebral volume.
The white matter is internal and deep to the
cortical gray matter which responsible for
communication between cerebral areas and
between the cerebral cortex and lower CNS
centres. White matter consists largely of
myelinated fibres bundled into large tract.
The

fibres and tracts are classified according to
the direction in which they run as follow;
1)Commissural tract ; These connect
corresponding gray areas of one cerebral
hemisphere to the other through bridges
called commissures, to enable them to
function as a coordinated whole. The
largest commissure is the corpus
callosum which lies superior to the lateral
ventricles deep

within the longitudinal fissure. Less prominent
i.e a few tracts pass through the much
smaller anterior and posterior
commissures.
2) Association tracts; These connect
different regions within the same
hemisphere, they do not cross from one
side of the brain to the other. The lobes of a
cerebral hemisphere are interconnected by
long association fibres whereas short
association fibres connect

adjacent gyri within a single lobe. eg
association tracts link perceptual and
memory centres of the brain which enables
one to smell something and pictures what it
looks like.
3) Projection tracts; These extend vertically
from higher to lower brain or spinal cord
centres and carry information between the
cerebrum and the rest parts of the body.

Superior to the brainstem, they form a
dense band called the internal capsule
that lies between the thalamus and
basal nuclei. They then radiate in a
diverging, fanlike array the corona
radiata to specific areas of the cortex.

GENERAL FUNCTIONS OF CEREBRUM
The cerebrum above all other bodily
structures deserves the title “the most
important organ” because it can claim
distinct functions not share by any other
organ. It is the top executive of the world’s
most complex organization, the human
being.
In addition, the cerebrum provide the
functions that endow us with our unique
human qualities. It performs sensory, motor

and integrative functions such as;
1) The motor centres of the cortex control all
the voluntary muscles of the muscular
system.
2) The sensory centres of the cortex gives
sensation to the skin and to a lesser
extent to the muscles, bones and joints
3) The centres of special senses control
sensory perception including the
perception

of pain, touch, temperature, sight,
hearing, taste and smell.
4) The centres of the higher mental power
coordinates mental activities involved in
memory, intelligence, sense of
responsibility, thinking, reasoning, moral
sense and learning

5) Cerebrum receives all sensory stimuli
and convey most of them to
consciousness.
6) Cerebrum exercises control over many
functions of the body especially the
lower parts of the brain.

BASAL NUCLEI/GANGLIA
These are compact masses of cerebral
gray matter that are situated deep in the
white matter, lateral to the thalamus.
There are 5 basal nuclei in each
cerebral hemisphere; caudate nucleus
and putmen which form the corpus
striatum. Other 3 are globus pallidus,
amygdala and claustrum.

BASAL NUCLEI/GANGLIA
The basal nuclei are functionally
associated with the subthalamic nuclei
of the diencephalon and the substantia
nigra of the midbrain to influence
skeletal muscle tone and cognition.
They receive input from the entire
cerebral cortex and then issue output
fibres back to the cerebrum by the way
of the thalamus.

THE BASAL NUCLEI /GANGLIA
Damage to the basal nuclei tend
to cause slow jerky, clumsy and
uncoordinated movement.
Neurones of the basal ganglia
respond to the inhibitory
neurotransmitter dopamine,
released from nearby cells.

THE LIMBIC SYSTEM (LS)
This is a group of cortical structures
located on the medial border of the
temporal lobes of each cerebral
hemisphere and diencephalon. Its
structures surround the corpus callosum,
thalamus and the upper part of the brain
stem.
In the cerebral hemisphere, the LS is
formed by the structures such as cingulate
gyrus, septal nuclei, amagdala,
hippocampus,

and parahippocampus. Also the LS is made
up of structures such as anterior thalamic
nuclei, hypothalamus mammilary body in
the diencephalon. The two areas are
connected by fornix and anterior
commisure. There are connections between
the LS and higher brain regions which allow
the system to integrate and respond to a
variety of environmental

stimuli. Most LS output is relayed through the
hypothalamus. The LS also interacts with
prefrontal lobes to intimate relationship
between feelings and thoughts.
The LS controls emotional experience
and expression. It modifies the way a
person acts by producing such feelings as
fear, anger, pleasure and sorrow. The LS
recognizes upset

in a person’s life. By causing pleasant
or unpleasant feelings about
experiences, the LS guides a person
into behaviour that is likely to increase
the chance of survival. Disorders
associated with the LS are;
 Anxiety of various intensities
 Memory loss especially in chronic
alcohol

alcoholism due to damage to the
hippocampus
 Emotional upset due to damage to the
amagdala.
 Sleep disturbance and or excessive
sleep

DIENCEPHALON
This is located between the cerebral
hemispheres and above the midbrain it
is composed largely of grey matter
areas collectively enclose to the 3rd
ventricle. The major areas of
diencephalon are the thalamus,
hypothalamus and epithalamus.

THALAMUS
This consists of 2 oval masses of gray
matter each of which underlies the cerebral
cortex and lateral ventricle on one side of
the brain. The 2 masses bulge medially into
and form the lateral wall of the 3rd ventricle.
They extend from the interventricular
foramen in front to the midbrain behind and
just below the corpus callosum. The 2
masses are joined together at the midline
by a narrow

THALAMUS
Intermediate mass. The thalamus constitutes
about 4/5 (i e 80%) of the diencephalon and
is supplied by posterior cerebral artery.
The thalamus is largely composed of
relay nuclei, named according to their
relative location which forward impulses
either from the main sensory pathway or
from supra- segmental levels on the
cerebral cortex.

THALAMUS
Within the thalamus, information is
sorted out and edited. Impulses having
to do with similar functions are relayed
as a group via the internal capsule to
the appropriate area of the sensory
cortex as well as to specific cortical
association areas. It receives all
sensory impulses except for smell.

THALAMUS
In summary, the thalamus play a key
role in mediating sensation, motor
activities, cortical arousal, learning and
memory. It is truly the “gateway” to the
cerebral cortex.

HYPOTHALAMUS
This composed of a number of group
of nerve cells. It forms part of the walls
and floor of the 3rd ventricle, capping the
brain stem. It is situated below and in
front of the thalamus immediately above
the pituitary glands. The structure that
form the hypothalamus are;

HYPOTHALAMUS
 The optic chiasma, where optic nerves
meet.
 The tuber cinereum in the main part
 The infundibular stalk between optic chiasma
and mamillary bodies that connect the
hypothalamus to the posterior lobe of
pituitary.
 The mamillary bodies, the pea like nuclei that
bulge anteriorly from hypothalamus which
relay signals from the limbic system.

HYPOTHALAMUS
 The posterior perforated substance.
In each of these, there is a number of cell
masses or nuclei surrounded by a fibre
pathway which run throughout the length of
the hypothalamus and serves to link it with
midbrain posteriorly and the basal fore
brain area anteriorly. Through the
infundibular stalk, the hypothalamus control
the output of hormones from both lobes of
the hypophysis.

HYPOTHALAMUS
The hypothalamus is small but
functionally mighty area of the brain. It
weighs ¼ ounce, yet it controls the ANS
and endocrine system and plays an
essential role in the homeostatic regulation
of nearly all organs in the body both for
survival and for the enjoyment of life i.e it
links the psyche (mind) and the soma
(body) together. The function can be
summarized as follow;;

HYPOTHALAMUS
 It controls synthesis of vasopressin(ADH)
and oxytocin by the nuclei which are
subsequently stored in the posterior lobe of
pituitary gland prior to their release into the
blood stream.
 It controls the anterior pituitary secretion by
means of characteristic agent
(hypothalamic hormones or releasing
factors) which serves to inhibit or release
the anterior pituitary hormones through
feedback mechanism.

HYPOTHALAMUS
 It controls the appetite by directing both
the feeding centres and satiety centres
the function of this is to inhibit the
feeding or hunger centre after ingestion
of food.
 It controls the thirst, osmoreceptor cells
in the hypothalamus are stimulated by
an increased osmolarity pressure
(plasma hyperosmolarity) to provoke
thirst.

HYPOTHALAMUS
 It regulates the body temperature.
Constant body temperature is
necessary and this is maintained by the
integration of reflex thermoregulatory
response of hypothalamus' thermostat.
 Hypothalamic centres are involved in a
variety of emotional responses including
anger, fear, pleasure and contentment.

HYPOTHALAMUS
 It participates in autonomic (sympathetic
and parasympathetic) responses. The
hypothalamus is involved in any
autonomic activity affecting heart rate,
cardiac output, vasomotor tone
,ventilation, pupillary size and motility
and sensory activity of GIT.

HYPOTHALAMUS
 It also controls sexual behaviour such as
mating, sexual drive, copulation, child
bearing and orgasm with the limbic system.
 Hypothalamus controls biological clock or
circadian rhythms e.g. sleeping and
wakefulness and other various fluctuating
bodily functions within a period of about
24hours.

EPITHALAMUS
This is the most dorsal portion of the
diencephalon that consists mainly of the
pineal gland/body which extends from its
posterior border and visible externally. The
gland is an endocrine gland that secretes
the hormone melatonin. Another part of the
epithalamus is habenula, a relay from the
limbic system to the midbrain, and form a
thin roof over the third ventricle.

BRAIN STEM
The brain stem is a bundle of nervous
tissue that connects the cerebrum to the
spinal cord. It consists of numerous tracts
of nerve fibres and several nuclei. From
superior to inferior, the brain stem regions
are midbrain, pons and medulla oblongata.
Each roughly an inch, collectively they
account for only 2.5% of total brain mass.
Histologically, the organizatn

BRAINSTEM
of the brain is similar (but not identical) to
that of the spinal cord i.e with exception
of medulla oblongata, the rest part of
the brainstem have gray matter
peripherally but white matter inwardly.
Brainstem centres produce the rigidly
programmed, automatic behaviour
necessary for survival

MIDBRAIN
This is also called mesencephalon. It is
the shortest part of the brainstem i.e about
2.5cm long. It contains bundles of
myelinated nerve fibres that connect the
pons and cerebellum to the diencephalon. It
lies in the gap of the tentorium cerebelli,
and contains the cerebral aqueduct which
connects the 3rd and 4th ventricles. The 4
principal regions of the midbrain are the
cerebral peduncles, substantia nigra,
tegmentum and tectum.

MIDBRAIN
 cerebral peduncles; view from the ventral
aspect, there are 2 cerebral peduncles
which emerge from the substance of the
cerebral hemisphere and pass downwards
and medially connecting the internal
capsule to the pons.
 Substantia nigra; this is a bandlike dark
gray to black nucleus pigmented with
melanin and located between the
peduncles and

MIDBRAIN
tegmentum. The melanin pigment, a
precursor of the neurotransmitter
(dopamine) is released by the neurones.
The substantia nigra is functionally linked to
the basal nuclei and is considered part of
the basal nuclear complex. Degeneration of
the dopamine-releasing neurones of the
substantia nigra is the ultimate cause of
Parkinson’s disease.

MIDBRAIN
 Tegmentum; This lies deep to the
substantia nigra and contains the oval red
nucleus because of its high density of blood
supply and presence of iron pigment in its
neurones. The red nuclei serve as relay
nuclei in some descending motor pathways.
 Tectum; This consists of 4 nuclei called
the corpora quadrigemina, which bulge
from the midbrain roof. The superior pair,
the superior

MIDBRAIN
colliculi which are visual reflex centres that
coordinate head and eye movements when
we visually follow a moving object. The 2
inferior colliculi which receive all afferent
signal from the inner ear and relay them to
other parts of the brain , especially the
thalamus.
The midbrain contains some gray matter
which lie between the cerebellum behind and
the Pons and medulla in front. It contains

MIDBRAIN
the white matter which consists of motor
and sensory fibres running from and to
the nerve centres of cerebral cortex and
the basal ganglia to serve as a relay
station. In addition to this, nuclei of 3rd ,
4th and parts of 5th cranial nerves are
located in the gray matter of midbrain.

THE PONS
The Pons arises from the metencephalon
and it is the bulging brain stem region
wedged between the midbrain and the
medulla oblongata and connected to the
cerebellum by the middle cerebellar
peduncle. It is 25mm in length and 38mm in
width. Dorsally, it forms part of the anterior
wall of the 4th ventricle. Its ventral surface
presents a

THE PONS
shallow median groove and numerous
transverse ridges which are continuous
laterally with the middle cerebellar
peduncle.
The Pons is chiefly composed of
conduction tract, i.e forms the link joining
the various parts of the brain to another. It
consists of 2 main parts, that are oriented in
2 directions;

THE PONS
1) The deep projection fibres that run
longitudinally and complete the pathway
between higher brain centres (cerebral
cortex and midbrain) above and under
the bridge-like portion to the medulla,
cerebellum and spinal cord below.
2) The more superficial ventral fibres that
are oriented transversely and dorsally to
form the middle cerebellar peduncles
and

THE PONS
connects the Pons bilaterally with the 2
sides of the cerebellum dorsally. The
bridge-like portion joins one hemisphere of
cerebellum to the other.
The 2 above consist of motor and
sensory fibres running from and to the
nerve centres of the cortex. The gray matter
of the Pons has the nuclei that are
concerned with sleep,

THE PONS
posture, respiration (pneumostatic
centre), swallowing and bladder control.
The gray matter also comprises the
nuclei of the 5th, 6th, 7th and 8th cranial
nerves at junction with the medulla.

THE MEDULLA OBLONGATA
The medulla oblongata simple called
medulla is a conical shaped structure
develops from the embryonic
myelencephalon. It is the most inferior part
of the brain stem that blends imperceptibly
into the spinal cord at the level of the
foramen magnum of the skull. It is about
25mm in length and 18mm in diameter,
extending from

the Pons above and continuous below with
spinal cord. Posteriorly, it is connected with
the cerebellum by way of the inferior
cerebellar peduncle and the posterior
flattened surface form the floor of the 4th
ventricle. Its ventral surface is marked by
the corticospinal tract. It is shaped like a
pyramid with its base upward because
flanking the

midline on the medulla’s ventral aspect
are 2 longitudinal ridges called pyramids
descending from the motor cortex. Just
above the medulla-spinal cord junction,
most of the fibres cross over to the
opposite side before continuing into the
spinal cord. The cross over point is
called the decussation of the pyramids.

The medulla is often called the spinal bulb
as it is similar to the spinal cord in structure
but slightly thicker than the cord. Its anterior
and posterior are marked by fissures as in
cord (eg anterior median fissure which
continuous with that of the cord). Also , the
medulla consists of white matter on the
surface and gray matter in the centre as
does the cord.

The white matter of the medulla
resembles branching tree called arbor vital
(tree of life) and consists of ;
1) Efferent or motor fibres running out from
the cerebrum to the spinal cord.
2) Afferent or sensory fibres running in from
the spinal cord to the cerebrum, i e it is a
relay station by crossing over to the other
side of the body (decussation).

The medulla also contains the gray
matter that houses a major neuronal pools
knows as vital and reflex centres of the
medulla.
The vital centres include;
1) Respiratory centres; these generate the
respiratory rhythm and in concert with the
centre in the Pons to control the rate and
depth of breathing by stimulating the
diaphragm and intercostal muscles through

phrenic and intercostal nerves respectively.
2) Cardiac centre; this adjusts the force and
rate of heart contraction to meet the body
need through sympathetic &
parasympathetic nerve fibres.
3) Vasomotor centre; this adjusts blood
vessel diameter to regulate blood pressure
and reroute blood from one part of the body
to another through the ANS.

The vital centre are essential to the
continuance of life hence injury to them
therefore causes instant death.
The reflex centres regulate or control the
food and air passages. Such reflex actions
include activities like vomiting, swallowing,
coughing, hiccupping, sneezing and
sweating. All these activities are below the
conscious level controlled by the cerebrum.

Also, the gray matter of the medulla
houses several other nuclei. The
prominent ones are;
 The nuclei of last 4 cranial nerves i.e
9th, 10th,11th and 12th cranial nerves.
 Inferior olivary nuclei which are the relay
centres of the state of stretch of
muscles and joints to the cerebellum.

 Nucleus gracilis and nucleus cuneatus
associated with a tract called the medial
lemniscus a relay nucleus in a pathway
by which general somatic sensory
information ascends from the spinal
cord to the somatosensory cortex.

RETICULAR FORMATION
This is a complex network of nerve fibres
associated with tiny islands of gray matter
forming group of more than 100 nuclei
scattered throughout the core of the region.
It extends through the central core of the
medulla oblongata, Pons, and midbrain.
The neurones of reticular formation have
unusual branched axons, with one branch
extending down into the spinal cord and the
other

RETICULAR FORMATION
extending up to the thalamus, hypothalamus
or cerebral cortex, with fibres in all the
major ascending and descending tracts,
making the reticular neurones ideal for
governing the arousal of the brain as a
whole.
The important arm of the reticular
formation is the reticular activating system
(RAS). Impulses from all the great
ascending sensory tracts synapse with RAS
nuerones

RETICULAR FORMATION
keeping them active and enhancing their
arousing effect on the cerebrum. It also acts
like a filter for this flood of sensory inputs.
The drug LSD interferes with this sensory
dampers, promoting the often
overwhelming sensory overload. The RAS
is inhibited by sleep centres located in the
hypothalamus and other neural regions,
and is depressed by alcohol, sleep-inducing
drugs & tranquilizers

RETICULAR FORMATION
The reticular formation also has a motor
arm, with its motor nuclei projecting to
motor neurones in the spinal cord via the
reticulospinal tracts, and help in control of
limbs skeletal muscle contraction.
The functions of the nuclei of reticular
formation are then fall into 4 categories
1) Somatic motor control; some upper
motor neurones of the cerebrum project to
reticular

RETICULAR FORMATION
formation nuclei to modulate the action of the
skeletal muscles. They stimulate
antagonists or fixator muscles and
suppress stretch reflexes, it also stimulates
muscle tone and aid in posture.
2) Autonomic control; some of the nuclei
are cardiovascular and respiratory centres
that alter HR, BP, and rate & depth of
respiration.

RETICULAR FORMATION
3) Arousal ; some nuerones send fibres to
synapse in the thalamus which relays their
signals to the cerebral cortex. These fibres
modulate activity of the cortex in various ways
such as enhancing or suppressing its
response to sensory input.(selective
awareness)
4) Pain modulation; fibres that descend from
the reticular formation through the spinal cord
can block pain messages from reaching the
brain.

CEREBELLUM
This is the largest part of the hindbrain
that occupies most of the posterior cranial
fossa. It accounts for about 11% of total
brain mass. It is located below the occipital
lobes of the cerebrum and posterior to the
Pons and medulla oblongata. It protrudes
under the occipital lobe from where it is
separated by the transverse cerebral
fissure. It is made up

CEREBELLUM
of 2 lateral cerebellar hemispheres which
look like 2 apple sized and are connected
by the wormlike vermis. Inferiorly the vermis
is clearly separated from the 2 hemispheres
and lies at the bottom of a deep cleft, the
vallecula. Its surface is heavily convoluted
with fine transversely oriented pleat like gyri
known as folia. It is also divided by a few
deep

CEREBELLUM
fissures into a number of lobules, (anterior,
posterior and flocculonodular lobules)
Like the cerebrum, the structure of the
cerebellum is remarkably uniform. It
consists of a cortex of gray matter covering
a mass of white matter, in which deep
nuclei of gray matter are buried. Of these,
the dentate nuclei are the most familiar and
the largest that occupy the central area of
each

CEREBELLUM
hemisphere. The other nuclei are
emboliformis, globosus and fastigii .
The cerebellum is connected to the
brainstem by way of 3 pairs of cerebellar
peduncles.
1)The superior cerebellar peduncles connect
the cerebellum and midbrain carrying
instruction from neurones in the deep
cerebellar nuclei to the cerebral motor
cortex via thalamic relays

CEREBELLUM
2)The middle cerebellar peduncles carry one-
way communication from the Pons to the
cerebellum advising the cerebellum of
voluntary motor activities initiated by the
motor cortex.
3) The inferior cerebellar peduncles connect
medulla oblongata and cerebellum to
convey sensory information to the
cerebellum from

CEREBELLUM
muscle proprioceptors throughout the body
and the vestibular nuclei of the brainstem,
which are concerned with equilibrium and
balance.
Functionally, the cerebellum is a reflex
centre for integrating sensory information
concerning the position of the body parts
and for coordinating complex skeletal

CEREBELLUM
muscle movements. It also helps to
maintain posture. The flocculonodular lobe
is the simplest part that coordinates
activities associated with the maintanance
of the balance and equilibrium of the body
and eye movement. The sensory input for
these functions is derived from the muscles
and joints, the eyes and ears.

CEREBELLUM
The vermis are involved in controlling
posture, locomotion and fine motor
coordination to produce smooth flowing
movement.
Damages to the cerebellum is likely to
result in clumsy uncoordinated muscular
movement, staggering gait and inability to
carry out smooth steady, precise movement
called ataxia.

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