A complete guide about neurons.

1. Neurons

2. Neurons
Types of neurons according to structure
Types of neuron according to function
Structure of neuron
Functions of neurons
The neuron: Neuronal Characteristics, Types, Transmission and
Communication systems.
Neurotransmitteers, types. functions
Glial cells

3. The Neuron
The neuron is the basic building
block of the nervous system
They are often grouped in bundles
called nerves.

4. Mechanism of action
 Neurotransmitters transmit signals across a synapse at various locations, such
as:
 From one neuron to another target neuron
 At the neuromuscular junction (NMJ), that is from a neuron to a target
muscle cell
 From a neuron to a target gland.
 A synapse is a junction through which a neuron relays information to another
neuron; it has three main components:
 The axon terminal, or pre-synaptic side where information is transmitted from
 The synaptic cleft
 The dendrite, or post-synaptic side, receiving the information.

5.  When an electrical signal reaches the end of a neuron, it
triggers the release of small sacs called vesicles that contain
the neurotransmitters. These sacs spill their contents into
the synapse, where the neurotransmitters then move across
the gap toward the neighboring cells. These cells contain
receptors where the neurotransmitters can bind and trigger
changes in the cells.
 After release, the neurotransmitter crosses the synaptic gap
and attaches to the receptor site on the other neuron, either
exciting or inhibiting the receiving neuron depending on
what the neurotransmitter is.

7. What do Neurons Do…..

8. Types of neurons…
Sensory neurons do not have true dendrites. They
are attached to sensory receptors and transmit
impulses to the central nervous system, which then
stimulate the interneurons, and then motor neurons.
Interneurons are located entirely within the central
nervous system. They intercept the impulses from
the sensory neurons and transmit the signals to
the motor neurons.
NERVE RECEPTORS
SENSORY NEURONS
INTERNEURONS
MOTOR NEURONS

9. Fundamental Types of Neurons
 Sensory (afferent) neurons
 receptors detect changes in body and external environment
 this information is transmitted into brain or spinal cord
 Interneurons (association neurons)
 lie between sensory & motor pathways in CNS
 90% of our neurons are interneurons
 process, store & retrieve information
 Motor (efferent) neuron
 send signals out to muscles & gland cells
 organs that carry out responses called effectors

10. Fundamental Types of Neurons

11. Types of neurons according to Shapes
 Multipolar neuron
 Neurons come in many shapes, but the "typical" neuron has multiple
dendridic projections and one axon from the soma. This is called a
multipolar neuron,
 Bipolar
 There are also neurons that have only one dendridic projection and
these are called bipolar, and
 unipolar
Some that only have one projection that includes both the dendrite and
axon and these are called unipolar.
To some extent the shape represents the function in that unipolar and
bipolar neurons are more typically sensory neurons, while multipolar
neurons are more typically motor or interneurons.

12. Parts of the Neuron - Terminals

13. 4 parts of the neuron
1. Dendrites are specialized to receive signals from neighboring
neurons and carry them back to the cell body
 Thin, bushy-like structures that receive information from outside
the neuron
 Relays the information into the cell body

14. The Neuron
2. The Cell body
contains the
cell nucleus
 The cell body
relays the
information
down to the
axon

15. The structure of a neuron
3. Axon: A thin, long structure that
transmits signals from the cell body
to the axon terminal.
4. Axon Terminal is the last step for the
relay of information inside the
neuron.

16. The cell
body is
covered
with Axon
Terminals

17. Once the information hits the
terminal, it is transmitted
outside the cell by
neurotransmitters, which
reside in the axon terminal.

22. -Electrical Communication
-Chemical Communication
How do Neurons
Communicate?

24. The Electrical Part
 Action potential is an electrical current sent down the axon.
 The activity within the neurons is electrical. This current causes the
neuron to “fire”
 This is an “all-or-none” process
 Na= sodium ions
 K+= potassium ions
 CL= chloride (remains inside) negatively charged

25. Neuron Communication
All-or-None Principle
The principle that if a neuron
fires it will always fire at the
same intensity
All action potentials are of
the same strength.
A neuron does NOT fire at
30%, 45% or 90% but at
100% each time it fires.

26. Action potentials travel down the axon
like a wave of energy

27. Synaptic transmission
 The Synapse is the space between neurons
 The synaptic gap or cleft
• Information must be transmitted across the synapse to other
neurons via the neurotransmitters.
• This is an electrochemical process

29. Presynaptic Neuron
________________________
__________
________
________
____________

30. Electrical Potentials
& Currents
 Neuronal communication is based on
mechanisms for producing electrical
potentials & currents
 electrical potential - difference in concentration
of charged particles between different parts of
the cell
 electrical current - flow of charged particles from
one point to another within the cell
 Living cells are polarized
 resting membrane potential is -70 mV with a
relatively negative charge on the inside of nerve
cell membranes

31. Resting Membrane Potential
 Unequal electrolytes distribution
 diffusion of ions down their concentration gradients(difference)
 selective permeability of plasma membrane
 Explanation for -70 mV resting potential
 membrane very permeable to K+ (potassium)
 leaks out until electrical gradient created attracts it back in
 membrane much less permeable to Na+ (sodium)
 Na+/K+ pumps out 3 Na+ for every 2 K+ it brings in
 works continuously & requires great deal of ATP
 necessitates glucose & oxygen be supplied to nerve tissue

32. Be clear on vocabulary
 Polarize = to increase the difference in ion concentration. To move away from
0mV.
 Resting potential is polarized (-70mV).
 There’s a difference in Na+/K+ conc.
 Depolarize = To move toward no electrical potential.
 Allowing Na+/K+ to go where they want.
 “Opening flood gates”
 Repolarize = To go back to original potential

33.  Unlike Neurons, glial cells do not conduct Electrical Impulse. The glial cells
surround neurons and provide support for and insulation between them.
Glial cells are the most abundant cell types in the central nervous system.
 Composition of Nerves Tissue and neurons
 Supporting cells :
 CNS : neuroglia (glia)
 PNS : Schwann cells and satellite cells
 Functions :
 physical support
 electrical insulation
 metabolic exchange (Astrocytes may increase glucose utilization and release lactate,
which is taken up and consumed by neurons to generate ATP by oxidative metabolism).
 Astrocytes form the blood-brain barrier (a structure that blocks entrance of toxic
substances into the brain)
Glial Cells

34. Role of Glial Cells
 The role of glia cells:
1. Glial cells support neurons, providing the brain with structure,
they also separate and sometimes insulate neuronal groups
and synaptic connections from each other.
2. Two types of glial cells (oligodendrocytes and Schwann cells)
produce the myelin used to insulate nerve cell axons, the cell
outgrowths that conduct electrical signals.
3. Some glial a scavengers (cells that can ingest bacteria, foreign
particles and other cells), removing debris (scattered pieces of
rubbish or remains) after injury or neuronal death.
4. Glial cells perform important housekeeping chores that
promote efficient signaling between neurons. some glia also
take up chemical transmitters released by neurons during
synaptic transmission.
5. During brain development certain classes of glial cells (radial
glia) guide migrating neurons and direct the outgrowth of
axons.
6. In some cases, as at the nerve-muscle synapse

35. Types and Functions of Glia
Name of Glial
Cell
Function
Astrocyte
(Astroglia)
Star-shaped cells that provide physical and
nutritional support for neurons: 1) clean up
brain"debris"; 2) transport nutrients to neurons; 3)
hold neurons in place; 4) digest parts of dead neurons;
5) regulate content of extracellular space
Microglia Like astrocytes, microglia digest parts of dead
neurons.
Oligo-
dendroglia
Provide the insulation (myelin) to neurons in the
central nervous system.
Satellite Cells Physical support to neurons in the peripheral
nervous system.
Schwann Cells Provide the insulation (myelin) to neurons in the
peripheral nervous system.

36. Neuroglia
in the CNS

37.  Able to replicate!
 Importance in nervous system function is
VASTLY underestimated!
 Evidence is mounting:
1. Nurturing role (provide nutrients to your neurons,
including oxygen).
2. Destroy pathogens.
3. Provide a general support structure on which
neurons can sit.
4. Signaling role (Memory?)
5. Inflammation
6. Pain
7. Many more to come!
Neuroglia:
Distinguishing Features

38. 1. Presence of tight junctions between the endothelial cells (a thin layer of single flat
cells that line the interior surface of blood vessels and lymphatic vessels)
2. One of the notable features of endothelial cells in comparison to other cell is the lack
of pinocytic vesicles
3. Selective permeability to molecules based on their molecular weight and lipid
solubility
4. Presence of specific markers
• Rich in two enzymes: gamma glutamyl transpeptidase (GGTP) (for amino acid
transport) and alkaline phosphatase (transport of phsopahte ions) used as marker for
BBB.
• Others: glucose transporter (GLUT-1); endothelial barrier antigen (EBA; unknown
function) and antigen recognized by the MRC OX-47 monoclonal antibody
(important for cell-to-cell adhesion); transferrin receptor (transport of ferric ions).
There are certain areas of the brain, which have greater capillary density and the endothelial
cells lack of tight junctions. The blood vessels in these areas also demonstrate absence or
week presence of specific BBB markers. These areas are located close to the ventricles of
the brain, particularly the third ventricle, they also called as circumventricular organs. But
there is the presence of tight junctions between these organs and the rest of the brain
thereby preventing an indiscriminate access of substances from the circumventricular
organs to the rest of the brain
Properties of Blood Brain Barriers

39. BBB

40. 1. Neurons have TWO "processes" called axons and
dendrites. Glial cells only have ONE.
2. Neurons CAN generate action potentials. Glial cells
CANNOT, however, do have a resting potential.
3. Neurons HAVE synapses that use neurotransmitters.
Glial cells do NOT have chemical synapses.
4. Neurons do NOT continue to divide. Glial cells DO
continue to divide.
5. There are many MORE (10-50 times more) glial cells in
the brain compared to the number of neurons.
Glia are different from neurons:

41. Nerve Cells

42. Neurons, Glia,
Extracellular Space,
and Blood

43. Bidirectional Communication Partners
in the CNS
• Receiving signals from neighboring neurons and
responding to them with release of neuroactive
substances
• Express receptors for almost all neurotransmitters
and neuromodulators
• Increase of intracellular calcium concentration
• Membrane depolarization in astrocytes are common
responses to neural activity
• Metabolically coupled to neural activity

44. Three Types of Metabolic
Cooperation of Astrocytes and
Neurons
1. Supply of the energy substrate lactate
to neurons
2. The recycling of neuronal glutamate by
the glutamate-glutamine cycle
3. The supply by astrocytes of precursors
for neuronal glutathione (GSH)
synthesis