bsu unversity russia

1. NERVOUS SYSTEM
PHISIOLOGY OF NERVOUS TISSUES.
SYNAPSES.
LECTURE

2. Lecture outline
1. Organization of nervous system
2. Neuron, neuroglia, classification and properties of
nerve fiber
3. Electrophysiology, action potential, nerve impulse,
synapse, neurotransmitters
4. Central nervous system: structure and functions of
brain (cerebrum, brain stem, cerebellum)
5. Central nervous system: spinal cord (gross
structure, functions of afferent and efferent nerve
tracts, reflex activity)
6. Peripheral nervous system
7. Autonomic nervous system

3. Nervous System
• Master controller and communicating system
in the body
• Every thought, action and emotion reflects its
activity.
• It signals the body through electrical impulses
that communicate with the body cells.

4. Neural Organization

5. • complex nervous system that consists of
– A central nervous system (CNS) where
integration takes place; this includes the brain
and a nerve cord
– A peripheral nervous system (PNS), which
carries information into and out of the CNS
– The neurons of the PNS, when bundled
together, form nerves

6. The Nervous System Is Composed of
Cells
• Types of cells in the nervous system:
– Neurons, or nerve cells
– Glial cells provide support for neurons
• Microglia
• Astrocytes
• Oligodendrocytes
• Schwann cells

7. NEURON
About how many neurons are in the human brain? 100 billion
1 billionAbout how many neurons are in the spinal cord?

8. Nervous Tissue: Neurons
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
 Neurons = nerve cells
-Cells specialized to transmit messages
Major regions of neurons
-Cell body – nucleus and metabolic center
of the cell
-Processes – fibers that extend from the
cell body (dendrites and axons)
-Axonal terminals

9. Neuron Anatomy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

10. Neuron cells are specialized to…
1. Receive information from the another
neurons.
2. Process the information
3. Pass on information to the next neuron
or effector cell
3 main tasks of neurons

11. Classifications of Neurons
1. According to Function
a. sensory neurons (afferent neurons)
b. motor neurons (efferent neurons)
c. interneurons

12. THE THREE FUNCTIONAL CLASSES OF NEURONS

13. Classifications of Neurons
2. According to Structure
1. unipolar
2. pseudounipolar
3. bipolar
4. multipolar ( M. can be pyramidal,
stellate, basket, granule, etc.)

14. Structural Classification of Neurons
According to amount of processes
 1. Unipolar neurons – are found during
early embryogenesis. They have one
axon

15. Structural Classification of Neurons
 2. Pseudounipolar neurons – have a
short single process leaving the cell
body

16. Structural Classification of Neurons
3. Bipolar neurons – one axon and one
dendrite

17. Structural Classification of Neurons
 4. Multipolar neurons – many extensions
from the cell body

20. Classifications of Neurons
3. According to Effect
4. According to Axon length
a. excitatory neurons
b.
-inhibitory neurons
-excitatory neurons
-projection neurons (Golgi Type I)
-local neurons (Golgi Type II)
5. According to Neurochemical identity
e.g., cholinergic, dopaminergic,
GABAergic, etc.

21. Nerve cell action potential

22. How are neurons connected?
Synapses!!

23. What is a synapse?
Synapse is a specialized junction that
transfers nerve impulse information
between neurons or between neuron
and an effector cell

25. Functional classification
or types of communication
Chemical synapses
Electrical synapses

26. CHEMICAL SYNAPSE
• Almost all synapses used for signal
transmission in the CNS of human being
are chemical synapses.
• First neuron secretes a chemical
substance called neurotransmitter at the
synapse to act on receptor on the next
neuron to excite it, inhibit or modify its
sensitivity.

27. Classification according to anatomical
types of synapses
• Axo-dendritic – synapses between the axon
of one neuron and the dendrite of another
• Axo-somatic – synapses between the axon
of one neuron and the soma of another
• Axo-axonic - synapses between the axon of
one neuron and the axon of another

28. Axo-dendritic synapse Axo-somatic synanpse Axo-axonic synapse

29. How many synapses
are in one neuron?
1,000 to 10,000!!

30. Structure of a chemical synapse
A synapse consists of 3 elements:
Presynapse or presynaptic part: The
part that elicits the stimulus.
Postsynapse or postsynaptic part: The
part that receives the stimulus.
Synaptic cleft: The space between the
two structures.

32. Steps of the synaptic transmission

33. Excitatory Postsynaptic Potential (EPSP)
Excitatory Neurotransmitters:
ACh and glutamate

34. Inhibitory Postsynaptic Potential (IPSP)
Inhibitory Neurotransmitters:
Glycine and GABA

35. Neurotransmitter Recovery and
Degradation
• Neurotransmitters must be cleared from the
synapse to permit another round of synaptic
transmission.
• Methods:
– Diffusion
– Enzymatic degradation in the synapse.
– Presynaptic reuptake followed by degradation
or recycling.
– Uptake by glia
– Uptake by the postsynaptic neuron and
desensitization.

36. Neurotransmitters
• There are dozens of different neurotransmitters
(NT) in the neurons of the body.
• NTs can be either excitatory or inhibitory
• Each neuron generally synthesizes and releases
a single type of neurotransmitter

37. Major Neurotransmitters in the Body
Neurotransmitter Role in the Body
Acetylcholine A neurotransmitter used by the spinal cord neurons to control muscles and
by many neurons in the brain to regulate memory. In most instances,
acetylcholine is excitatory.
Dopamine The neurotransmitter that produces feelings of pleasure when released by
the brain reward system. Dopamine has multiple functions depending on
where in the brain it acts. It is usually inhibitory.
GABA
(gamma-aminobutyric acid)
The major inhibitory neurotransmitter in the brain.
Glutamate The most common excitatory neurotransmitter in the brain.
Glycine A neurotransmitter used mainly by neurons in the spinal cord. It probably
always acts as an inhibitory neurotransmitter.
Norepinephrine Norepinephrine acts as a neurotransmitter and a hormone. In the
peripheral nervous system, it is part of the flight-or-flight response. In the
brain, it acts as a neurotransmitter regulating normal brain processes.
Norepinephrine is usually excitatory, but is inhibitory in a few brain areas.
Serotonin A neurotransmitter involved in many functions including mood, appetite,
and sensory perception. In the spinal cord, serotonin is inhibitory in pain
pathways.
NIH Publication No. 00-4871

38. FACTORS EFFECTINF SYNAPATIC
TRANSMISSION: DRUGS
Many drugs are known to increase the excitability
of neurons, and others are known to decrease
excitability.
For instance,
Caffeine,
Theophyline,
Theobromine, which are found in coffee, tea, and
cocoa, respectively.
All increase neuronal excitability, presumably by
reducing the threshold for excitation of neurons.

39. Electrical Synapses
• Pre- and postsynaptic neurons
joined by gap junctions
– allow local current to flow
between adjacent cells.
Connexons: protein tubes in
cell membrane.
• Rare in CNS or PNS
• Found in cardiac muscle and
many types of smooth
muscle. Action potential of
one cell causes action
potential in next cell, almost
as if the tissue were one cell.
• Important where contractile
activity among a group of
cells important.

40. Two principal kinds of synapses: electrical and chemical

41. Central Nervous System
• Consists of brain and spine
• Functions:
– Receives sensory signals and determines
appropriate response
– Stores memory
– Carries out thought

42. Brain

43. The Complex Brain
• The mammalian brain is highly complex,
containing many specialized regions that
carry out specific functions.
• Generally, the brain is divided into hindbrain,
midbrain, and forebrain.

44. Brain: Structure
• Forebrain
processes
signals,
stores
memories,
creates
thought.
• Midbrain
coordinates
signals.
• Hindbrain
carries out
the most
basic
functions.

45. Forebrain
• Thalamus: relay
station channeling
sensory
information.
• Limbic system: basic
emotions, drives,
and behaviors.
• Cortex: higher
thought

46. Limbic system
• Hypothalamus:
master controller of
the endocrine
system.
• Amygdala: sensations
of pleasure or fear,
recognition of fear in
others.
• Hippocampus:
formation of
memories.

47. Cortex
• Various areas
control sensory
processing, motor
control, thought,
memory.
• Wiring is plastic:
people blind from
birth, for example,
use parts of the
visual cortex to
process auditory
signals.

48. Midbrain
• Reticular
formation: the
“traffic cops” of
the brain.
• Filters sensory
input, which
allows us to
concentrate.
• Filtering can be
affected by higher
thoughts.

49. Midbrain
• Mostly composed of tracts of nerve fibers
• Has two bulging fiber tracts –
cerebral peduncles
• Has four rounded protrusions –
corpora quadrigemina
– Reflex centers for vision and hearing

50. Try this:
• Stop and think: What have you been
paying attention to for the last ten
minutes?
• Pay attention to the feel of your shirt
on your arms. Had you been noticing it
during the last ten minutes? That’s the
reticular formation in action.
• What else have you not been paying
attention to?

51. Hindbrain
Medulla:
controls
autonomic
fuctions.
Pons: controls
sleep stages.
Cerebellum:
coordinates
movement,
stores some
motor memory.

52. Spine: structure
• The spinal cord is
protected by the
vertebrae.
• Gray matter
contains cell bodies;
white matter
contains myelinated
fibers.
• PNS nerves extend
outside of the
vertebrae.

53. The Reflex Arc
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
 Reflex – rapid, predictable, and
involuntary responses to stimuli
 Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector

54. Types of Reflexes and Regulation
• Autonomic reflexes
– Smooth muscle regulation
– Heart and blood pressure regulation
– Regulation of glands
– Digestive system regulation
• Somatic reflexes
– Activation of skeletal muscles

55. Peripheral Nervous System
• Nerves, neurons, and sensory organs
outside the central nervous system
• Functions:
– Sends signals to the CNS
– Receives and transmits motor signals from the
CNS
– Stimulates effectors

56. Somatic Nervous System
• Motor neurons that control voluntary
movements by activating skeletal muscles.
• Also involved in what we perceive as
involuntary movements, such as reflexes
(though voluntary control of the muscles
involved, such as tensing them, can reduce
the response).

57. Autonomic Nervous System
• Motor neurons that control involuntary
responses involving the organs, glands, and
smooth muscles.
• Some voluntary control over the responses
can come from relaxation, meditation, etc.,
which reduce perceptions of stress and in
turn reduce the stress response.

58. Sympathetic Division
• Portion of the autonomic nervous system
that produces the “fight or flight” response:
– Dilation of pupils
– Increased heart and breathing rates
– Constriction of blood vessels
– Inhibits digestion

59. Parasympathetic Division
• Portion of the autonomic nervous system
that produces the “rest and ruminate”
response:
– Constricts pupils
– Dilates blood vessels
– Reduces heart and breathing rates.
– Stimulates digestion.

60. Freeman 45-20

61. Autonomic Nervous System
• The involuntary branch of the nervous system
• Consists of only motor nerves
• Divided into two divisions
– Sympathetic division
– Parasympathetic division

62. Differences Between Somatic and
Autonomic Nervous Systems
• Nerves
–Somatic – one motor neuron
–Autonomic – preganglionic and
postganglionic nerves
• Effector organs
–Somatic – skeletal muscle
–Autonomic – smooth muscle, cardiac
muscle, and glands

63. Differences Between Somatic and
Autonomic Nervous Systems
• Nerurotransmitters
–Somatic – always use acetylcholine
–Autominic – use acetylcholine, epinephrine,
or norepinephrine

64. Comparison of Somatic and
Autonomic Nervous Systems

65. QUESTIONS
1. Functions and Divisions of the Nervous System.
2. Neurons. The important structural components and their functional role.
3. Classification of Neurons. Structural and functional classification.
4. Synapses. Classification of synapses.
5. Structure of a chemical synapse.
6. Steps of the synaptic transmission.
7. Types of neurotransmitters.
8. Excitatory postsynaptic potential. Inhibitory postsynaptic potential.
9. Electrical synapses.
10. Central nervous system: structure and functions of brain (cerebrum, brain stem,
cerebellum)
11. Central nervous system: spinal cord (gross structure, functions of afferent and
efferent nerve tracts, reflex activi
12. Peripheral Nervous System.
13. Autonomic Nervous System: sympathetic and parasympathetic components.