Nervous system: part I

Lecture Notes in Medical Physiology for Pharmacy Students

1. The Nervous System
Dr. FawazA. Mustafa
PhD in Medical Physiology and Pharmacology

2. Central nervous
system (CNS)
Brain
Spinal cord
Peripheral nervous
system (PNS)
Cranial nerves
Ganglia outside
CNS
Spinal nerves
The Nervous System: (NS)

3. The Nervous System: (NS)
•Include all the neural tissue in the body.
•Neural tissue with supporting blood vessels &
connective tissue forms the organs of the NS:
the brain, the spinal cord& the receptorsin
complex sense organs & the nervesthat
interconnect those organs & link the NS with
other organs.

4. The Nervous System: (NS)
•The basic functional units of the NS are the
neurons. The neurons are supported by
supporting cells ( neuroglia, glial cells), these
separate & protect the neurons.
•Processing of information takes place in simple
clusters of neurons called gangliaor inmore
complexcircuits in thebrain

5. The Nervous System: (NS)

6. The Nervous System: (NS)
•Human bodies have a complex nervous system
that consists of
–A central nervous system (CNS)where
integration takes place; this includes the brain
and a spinal cord
–A peripheral nervous system (PNS), which
carries information into and out of the CNS
–The axons of neurons of the PNS, when
bundled together, form nerves

7. The Nervous System: (NS)
Sensory input
Motor output
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Effector
Integration

8. The Nervous System: (NS)

9. The Nervous System: (NS)
•PNS:includealltheneuraltissueoutsidethe
CNS.ThePNSdeliverssensoryinformationto
theCNS&carriesmotorcommandstothe
peripheraltissue&systems.
•AfferentdivisionofPNSbringssensory
informationtoCNSfromreceptorsinperipheral
tissue&organs.
•EfferentdivisionofPNScarriesmotor
commandsfromtheCNStomuscles&glands
(effectors).

10. The Nervous System: (NS)
Neuron Structure and Function
•Neurons are nerve cells that transfer
information within the body
•Most of a neuron`s organelles are in the cell
body
•Most neurons have dendrites, highly branched
extensions that receive signals from other
neurons
•The axon is typically a much longer extension
that transmitssignals to other cells at synapses
•The cone-shaped base of an axon is called the
axon hillock

11. The Nervous System: (NS)

12. Nucleus
Dendrites
Stimulus
Axon hillock
Cell
body
Presynaptic
cell
Signal
direction
Axon
Synapse
Neurotransmitter
Synaptic terminals
Postsynaptic cell
Synaptic
terminals
The Nervous System: (NS)

13. The Nervous System: (NS)
Functional classification of the neuron:
1. Sensory neurons: from the afferent division of the
PNS, the cell bodies of the sensory neurons are found
in peripheral sensory ganglia (a ganglion is a collection
of neuron cell bodies in the PNS).
-somaticsensory neurons ( monitor the outside world
& our position within it).
-visceralsensory neurons ( monitor internal conditions
& the status of other organ system).
2. Motor neurons: or efferent neurons, which carries
instructions from the CNS to peripheral effectors
(Somatic, visceral).

14. The Nervous System: (NS)
Dendrites
Axon
Cell
body
Portion
of axon
Sensory neuronInterneuronsMotor neuron

15. The Nervous System: (NS)
•Neurons use two types of signals to
communicate: electrical signals (long-distance)
and chemical signals (short-distance)
•Interpreting signals in the nervous system
involves sorting a complex set of paths and
connections

16. The Nervous System: (NS)
The big question:
What is the language of the nervous
system? How can one neuron communicate
with the other?

17. The Nervous System: (NS)

18. The Nervous System: (NS)

19. The Nervous System: (NS)

20. The Nervous System: (NS)

21. The Nervous System: (NS)

22. The Nervous System: (NS)

23. The Nervous System: (NS)

24. The Nervous System: (NS)

25. The Nervous System: (NS)

26. The Nervous System: (NS)
•The speed of an action potential increases with
the axon`s diameter
•In vertebrates, axons are insulated by a myelin
sheath, which causes an action potential`s
speed to increase
•Myelin sheaths are made by glia—
oligodendrocytes in the CNS and Schwann
cells in the PNS

27. The Nervous System: (NS)

28. The Nervous System: (NS)
•Action potentials are formed only at nodes of
Ranvier, gaps in the myelin sheath where
voltage-gated Na+channels are found
•Action potentials in myelinated axons jump
between the nodes of Ranvier in a process
called saltatoryconduction

29. The Nervous System: (NS)

30. The Nervous System: (NS)
How does action potential (impulse) is
propagated?
Neurons communicate with other cells at synapses

31. Neurons communicate with other
cells at synapses
•At electrical synapses, the electrical current
flows from one neuron to another
•At chemical synapses, a chemical
neurotransmitter carries information across the
gap junction
•Most synapses are chemical synapses

32. Neurons communicate with other
cells at synapses
•The presynaptic neuron synthesizes and
packages the neurotransmitter in synaptic
vesicles located in the synaptic terminal
•The action potential causes the release of the
neurotransmitter
•The neurotransmitter diffuses across the
synaptic cleft and is received by the
postsynaptic cell

33. Neurons communicate with other
cells at synapses

34. The Synaptic Transmission
Events that occur at a cholinergic synapse
following the arrival of an AP at the synaptic knob
may be summarized by four steps:
Step I:
-arriving AP depolarized the synaptic knob & the
presynaptic membrane.

35. The Synaptic Transmission
Step II:
-Ca2+ions enter the cytoplasm of the synaptic
knob.
-acetylcholine (ACh) release occurs by exocytosis
of neurotransmitter vesicles.

36. The Synaptic Transmission
Step III:
-AChbinds to receptor on postsynaptic membrane.
-chemically regulated Na+channels activated (graded
depolarization).
-AChrelease stops because Ca2+ions are removed
from the cytoplasm.
Step IV:
-depolarization ends as AChis broken down into
acetate & choline by AChE.
-the synaptic knob reabsorbs choline from synaptic
cleft & resynthesize ACh.

37. Neurotransmitters
•Chemicals in the junction which allow impulses
to be started in the second neuron
•There are more than 100 neurotransmitters,
belonging to five groups: acetylcholine, biogenic
amines, amino acids, neuropeptides, and gases
•A single neurotransmitter may have more than a
dozen different receptors

38. Neurotransmitters
•Acetylcholine is a common neurotransmitter in
human
•It is involved in muscle stimulation, memory
formation, and learning
•Vertebrates have two major classes of
acetylcholine receptor, one that is ligand gated
and one that is metabotropic

39. Neurotransmitters
•Amino acid neurotransmitters are active in the
CNS and PNS
•Known to function in the CNS are
–Glutamate
–Gamma-aminobutyric acid (GABA)
–Glycine

40. Neurotransmitters
•Biogenic amines include
–Adrenaline
–Noradrenaline
–Dopamine
–Serotonin
•They are active in the CNS and PNS

41. Neurotransmitters
•Several neuropeptides, relatively short chains
of amino acids, also function as
neurotransmitters
•Neuropeptides include substance Pand
endorphins,which both affect our perception of
pain

42. The Spinal Cord
•The central canalof the spinal cord and the
ventriclesof the brain are hollow and filled with
cerebrospinal fluid
•The cerebrospinal fluid is filtered from blood and
functions to cushion the brain and spinal cord as
well as to provide nutrients and remove wastes

43. The Spinal Cord
•Every spinal segment is associated with
1.A pair of dorsal root ganglia (that contain the
cell bodies of sensory neurons). The dorsal
roots which contain the axons of these sensory
neurons.
2.A pair of ventral roots that contains the axons
of motor neurons which extend to the periphery
controlling somatic & visceral effectors.

44. The Spinal Cord

45. The Spinal Cord
•On either sides the dorsal & ventral roots of
each segment pass through the inter-ventral
foramen.

46. The Spinal Cord
•Distal to each dorsal ganglion, the sensory &
motor roots are bound together into a single
spinal nerve, spinal nerves are mixed nerves
because they contain both afferent (sensory) &
efferent (motor) fibres, there are 31 pairs of
spinal nerves.

47. The Spinal Cord
•The spinal nerves takes
the name of the segment of
the vertebrae,
e.g. T1, T2, C1, L3, S2…

48. The Spinal Cord
•Cervical spinal nerves:C1 –C8
•Thoracic spinal nerves:T1 –T12
•Lumber spinal nerves:L1 –L5
•Sacral spinal nerves:S1 –S5

49. The Spinal Cord
•Spinal Meningesprovide the physical stability &
shock absorption & blood vessels branching
within these layers also deliver oxygen &
nutrients to the spinal cord, there are 3 meningeal
layers
1.The dura mater
2.The arachnoid
3.The pia mater
These are continuous with the cranial meninges of
brain.

50. The Spinal Cord

51. The Spinal Cord
•The anterior median fissure & the posterior
median sulcus mark the division between left &
right sides of the spinal cord.

52. The Spinal Cord
•Superficial white matter contain large number of
myelinated & non myelinated axons. It can be
divided into three regions called columns:
Posterior white column, Anterior white column
and Lateral white column
•The gray matter contain the cell bodies of
neurons & the projections of gray matter toward
the outer surface of the spinal cord are called
horns.

53. The Spinal Cord
Gray Matter: the cell bodies of neurons in the gray matter
of the spinal cord are organized into functional groups
called nuclei.
•Sensory nuclei:receive & rely sensory information from
peripheral receptors.
•Motor nuclei:issue motor commands to peripheral
effectors.
•The posterior or dorsal gray horns contain somatic &
visceral sensory nuclei.
•The anterior or ventral gray horns contain somatic motor
nuclei.
•The lateral gray horns (located only in the thoracic &
lumber segments) these contain visceral motor nuclei

54. The Spinal Cord

55. The Autonomic Nervous System:
(ANS)
•The autonomic nervous system has
sympathetic, parasympathetic, and enteric
divisions
•The sympathetic divisionregulates arousal
and energy generation (lfight-or-flightz
response)
•The parasympathetic division has antagonistic
effects on target organs and promotes calming
and a return to lrest and digestzfunctions

56. The Autonomic Nervous System:
(ANS)
•The enteric division controls activity of the
digestive tract, pancreas, and gallbladder

57. The Autonomic Nervous System
•This system works by itself, or it works
subconsciously. It interposed between the CNS
& the peripheral effectors
•This system is responsible for regulating:
1.All the smooth muscles in the body
2.Cardiac muscle
3.The exocrine glands which contain acini and
ducts

58. The Centre of ANS
•The ANS is motor, its centreshould be present
in the CNS.
a.In the brainstem, there are nuclei belong to
ANS
b.In the thoracic, lumbar or sacral segments of
spinal cord but not in the cervical ones

59. The Autonomic Nervous System
•The sympathetic nervous system originates from
thoracic and lumbar part of spinal cord, so, it is
anatomically called “thoracolumbar system”.
•The parasympathetic nervous system comes
from cranial nerves (axons of oculomotor nerve
(III), facial nerve (VII), glossopharyngeal nerve
(IX) and vagusnerve (X) and sacral region of
spinal cord, it is called “craniosacral system”.

60. The Autonomic Nervous System
•The nerve fibres before entering ganglion are
called “preganglionic sympathetic nerve fibres”
and these fibres make synapse with cell bodies
in ganglion.
•The action potential is initiated in the cell bodies
to which the preganglionic nerve fibres belong.

61. The Autonomic Nervous System
•Then the impulse travels from cell body through
the axon to reach at the end of axon where there
is enlargement containing vesicles or sacs filled
with neurotransmitter, which is acetylcholine in
ganglia and preganglionic nerve fibre of the
sympathetic system.
•The action potential (in preganglionic nerve fibre)
makes the vesicles to empty their contents of
acetylcholine in the space between preganglionic
neuron and postganglionic neuron.

62. The Autonomic Nervous System
The nerve fibresthat secret ACh
1.The preganglionic sympathetic nerve fibresin
the space between them and the
postganglionic sympathetic neurons.
2.The preganglionic parasympathetic nerve fibres
in the space between them and the
postganglionic parasympathetic neurons.

63. The Autonomic Nervous System
The nerve fibresthat secret ACh
3.The postganglionic parasympathetic nerve
fibresin the space between them and the cells
of the affecter organ.
4.In the end-plate between nerve and muscle in
the neuromuscular junction.
5.In many areas in CNS (e.g. cortex, spinal
cord,…etc.)
Any fibresecretes AChis cholinergic nerve fibre.

64. The Autonomic Nervous System
The nerve fibresthat secrete Noradrenaline
(NA)
•These nerve fibresare called “adrenergic nerve
fibre” which secrete either adrenaline or
noradrenaline. These fibresare either: the
postganglionic sympathetic nerve fibrethat
secrete noradrenaline in the space between
them and the effector organ, and there may
found in many parts of the CNS (e.g. cerebral
cortex, brainstem, spinal cord,…etc.).

65. The Autonomic Nervous System
•Is the parasympathetic always
stimulatory or inhibitory to a certain
organ? And is the sympathetic always
stimulatory or inhibitory?

66. The Autonomic Nervous System
•Why we have sympathetic and
parasympathetic nervous system in our
bodies?

67. The Autonomic Nervous System

68. The Autonomic Nervous System

69. The Autonomic Nervous System