Nervous system anatomy and physiolog.ppt

Anatomy

1. ANATOMY AND PHYSIOLOGY OF
NERVOUS TISSUE
Dr. MUMENA C.H

2. Introduction
•Organization of nervous system
•Histology
•CNS: Structure (External & Internal)
•Function

3. Introduction
•Nervous tissue forms the rapid response body
control
•Nervous system is a complex, highly organized
network of billions of neurons
•Structures that makes nervous system
includes: Brain, cranial nerves & their
branches, spinal cord, spinal nerves & their
branches, ganglia, enteric plexuses and
sensory receptors

4. Nervous system functions
•It has 3 basic function;
–Sensory function
–Senses changes (stimuli) within body (internal) and outside body
(external),
–monitors internal & external environment through presence of
receptors
–Integrative function
–interpretation of sensory information (information processing);
complex (higher order) functions
–Analysis of the information, store and make decisions on appropriate action
–Motor function
–Response to stimuli by initiating action after interpretation in form of
–muscular contraction or
–glandular secretions

5. Division of nervous system
•Nervous system: two principal divisions:
–Central Nervous System-CNS
–Brain
–Spinal cord
–Peripheral Nervous System-PNS
–Consists of Cranial Nervous (CN 1-12) & Spinal Nervous-SN
–CN arises from the brain
–SC arises from the spinal cord
–All the neural tissue outside CNS
–Afferentdivision (sensory input)
–Efferent division (motor output)
–Somatic nervous system (Voluntary)
–Autonomic nervous system (Auto-self, Nomos-law): Involuntary

6. General Organization of the nervous system
Brain & spinal
cord

7. General organization of the nervous
system
•ANS: the motor portion of the ANS consist of
two branches:
–Sympathetic division: fight-or-flight response
–Parasympathetic division:rest-and-repair
•These two division have opposing action
•Sympathetic speeds the heart, parasympathetic
slows it
•The viscera receive both

8. Histology of neural tissue
Two types of neural cells in the nervous system:
Neurons-For processing,transfer, and storage
of information
Neuroglia–For support, regulation & protection
of neurons

9. Neuroglia (glial cells): 6 types of cells
CNS neuroglia: (Only 4 types)
•astrocytes
•oligodendrocytes
•microglia
•ependymal cells
PNS neuroglia: (only 2 types)
•Schwann cells (neurolemmocytes)
•satellite cells

10. Astrocytes
•create supportive
framework for neurons
•create “blood-brain
barrier”
•monitor & regulate
interstitial fluid surrounding
neurons
•secrete chemicals for
embryological neuron
formation
•stimulate the formation of
scar tissue secondary to
CNS injury

11. Oligodendrocytes
•create myelin sheath
around axons of neurons
in the CNS. Myelinated
axons transmit impulses
faster than unmyelinated
axons
Microglia
•“brain macrophages”
•phagocytize cellular
wastes & pathogens

12. Ependymal cells
•line ventricles of brain &
central canal of spinal cord
•produce, monitor & help
circulate CSF
(cerebrospinal fluid)

13. Schwann cells
•surround all axons of neurons in
the PNS creating a neurilemma
around them. Neurilemma allows
for potential regeneration of
damaged axons
•creates myelin sheatharound
most axons of PNS
Satellite cells
•support groups of cell bodies
of neurons within gangliaof the
PNS

14. Neuron structure

15. •Most axons of the nervous system are
surrounded by a myelin sheath
(myelinated axons)
•The presence of myelin speeds up
the transmission of action potentials
along the axon
•Myelin will get laid down in segments
(internodes) along the axon, leaving
unmyelinated gaps known as “nodes
of Ranvier”
•Regions of the nervous system
containing groupings of myelinated
axons make up the “white matter”
•“gray matter”is mainly comprised of
groups of neuron cell bodies, dendrites
& synapses (connections between
neurons)
of Ranvier

16. Classification of neurons
Structural classificationbased on number of
processes coming off of the cell body:

17. Anaxonic neurons
•no anatomical clues to
determine axons from
dendrites
•functions unknown

18. Multipolar neuron
•multiple dendrites & single
axon
•most common type

19. Bipolar neuron
•two processes coming off cell
body –one dendrite & one
axon
•only found in eye, ear & nose

20. Unipolar (pseudounipolar)
neuron
•single process coming
off cell body, giving rise
to dendrites (at one end)
& axon (making up rest of
process)

21. Classification of neurons
Functional classificationbased on type of information &
direction of information transmission:
•Sensory (afferent) neurons–
•transmit sensory information from receptors of PNS towards the CNS
•most sensory neurons are unipolar, a few are bipolar
•Motor (efferent) neurons–
•transmit motor information from the CNS to effectors
(muscles/glands/adipose tissue) in the periphery of the body
•all are multipolar
•Association (interneurons)–
•transmit information betweenneurons within the CNS; analyze inputs,
coordinate outputs
•are the most common type of neuron (20 billion)
•are all multipolar

22. Sensory neurons
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24. Classification of neurons; Motor or efferent
neurons
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25. Classification of neurons:
Interneurons
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26. Conduction across synapses
Most synapses within the nervous system are
chemicalsynapses, & involve the release of a
neurotransmitter
In order for neural control to occur, “information”
must not only be conducted along nerve cells, but
must also be transferred from one nerve cell to
another across a synapse

27. The Structure of a Typical Synapse

28. Examples of neurotransmitter &
neurons manufacturing them
3-Neurotransmitter production classification :Neurons
differ in the type of neurotransmitter they manufacture.
Some examples are :
•Cholinergic neurons—acetylcholine.
•ABAergic neurons—gamma amino butyric acid
•Glutamatergic neurons—glutamate
•Dopaminergic neurons—dopamine
•Serotonergic neurons—serotonin
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29. Neuronal Pools

30. Anatomical organization of neurons
Neurons of the nervous system tend to group together into
organized bundles
The axonsof neurons are bundled together to form nervesin
the PNS & tracts/pathwaysin the CNS. Most axons are
myelinated so these structures will be part of “white matter”
The cell bodiesof neurons are clustered together into
gangliain the PNS & nuclei/centersin the CNS. These are
unmyelinated structures and will be part of “gray matter”

31. Neural Tissue Organization

32. Anatomical structure of Nerves
Fig. 14.6

33. NERVE CELL FIBER
-Epineurium: A sheath of
dense connective tissue
surrounds the nerve. Blood
vessels of various sizes can
be seen in the epineurium.
-Perineurium: A sheath
penetrates the nerve to
form the perineurium
which surrounds bundles of
nerve fibers.
-Endoneurium: which
consists of a thin layer of
loose connective tissue,
surrounds the individual
nerve fibers.
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34. 10 minutes break

35. The Central Nervous
System
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36. CNS
•The central nervous system(CNS)
It is the part of the nervous system that
integrates the information that it receives and
coordinates the activity of all parts of the body.
It contains the majority of the nervous system
and consists of the brainand the spinal cord.
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37. CNS
•Grey matter.
–Areas containingnerve cell bodies, their myelinated and
unmyelinated processes and supporting (glial) cells are
called
–It appears grayish rather than white because the Nissl
bodies impart a gray color and there is little or no myelin in
these areas.
•White matter
–Areas containing predominantly myelinated axons but also
some unmyelinated axons and glial cells are referred to as.
The whitish color of myelin gives white matter its name.
•Blood vessels are present in both white and gray
matter.
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38. In the brain, the grey matter is exterior to the
white matter, the reverse is the case in the
spinal cord.
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39. The Peripheral Nervous
System
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40. PNS
•The peripheral nervous system(PNS)
–consists of the cranial and spinal nerves and
gangliaoutside of the brainand spinal cord.
–The main function of the PNS is to connect the
central nervous system(CNS) to the limbs and
organs.
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41. PNS
•The sensory Division : ( afferent):
–contains Somatic and visceral sensory nerve fibers
and conducts impulses from receptors to the CNS.
•The Motor Division : ( efferent) :
–contains motor nerves fibers and conducts
impulses from the CNS to effectors ( muscles and
glands ).
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42. PNS
•The Somatic nervous system : SNS :
–contains somatic motor nerves .
–Its actions are largely voluntaryand conducts
impulses from the CNS to skeletal muscles only.
•The Autonomic nervous system : ANS :
–contains visceral motor nerves .
–Its actions are largely involuntaryand conducts
impulses from the CNS to cardiac muscles ,
smooth muscles and glandular epithelium.
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43. 43

44. 44

45. PNS
•ANS:
–It also differs from the sensory-somatic system by
using two groups of motor neurons to stimulate
the effectors instead of one.
–The first is the preganglionic neuronsthat arise
in the CNS and run to a ganglionin the body.
•Here they synapsewith postganglionic neuronswhich
run to the effector organ (cardiac muscle, smooth
muscle, or a gland).
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46. PNS:ANS
•Sympathetic Division :
–mobilizes body systems during activity and the stimulation
of the sympathetic branch of the ANS prepares the body
for emergencies: for "fight or flight" (and, perhaps,
enhances the memory of the event that triggered the
response).
•Parasympathetic Division :
–conserves energy and returns the body functions to
normal after they have been altered by sympathetic
stimulation.
N.B: In times of danger, the sympathetic system prepares
the body for violent activity. The parasympathetic
system reverses these changes when the danger is
over.
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48. The Synapses
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49. Synapses
•The synapse
•is a specialized junctional complex by which axons
and dendrites emerging from different neurons
intercommunicate.
•Synapses are essential to neuronal function:
neurons are cells that are specialized to pass
signals to individual target cells, and synapses
are the means by which they do so.
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50. Synapses
•At a synapse, the plasma membrane of the signal-
passing neuron (the presynapticneuron) comes
into close apposition with the membrane of the
target (postsynaptic) cell.
•Both the presynaptic and postsynaptic sites
contain extensive arrays of molecular machinery
that link the two membranes together and carry
out the signaling process.
•In many synapses, the presynaptic part is located
on an axon, but some presynaptic sites are
located on a dendrite or soma.

51. Synapses are :
1.axodendritic : from axon to dendrite.
2.axosomatic : from axon to cell body.
3.axoaxonic : from axon to axon.
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52. Synapses
•The two types of synapses :
–Electrical
–Chemical
•Both differs structurally and
functionally:

53. Chemical Synapses
•Presynaptic neuron releases a chemical
neurotransmitterthat binds to receptorson
the postsynaptic cell, usually embedded in the
plasma membrane.
•The neurotransmitter may initiate an
electrical response or a secondary messenger
pathway that may either excite or inhibit the
postsynaptic neuron.
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54. Chemical Synapses
•The connection at chemical synapse contains a
small synaptic cleft between the connect
neurons.
•The AP may not be conveyed across the cleft
as there is no membrane in the cleft.

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56. 56

57. Chemical Synapses
•AP at the pre-synaptic neuron.
–Opening of voltage-gated calcium channels
–increase in [ca2+]
–migration and fusion of vesicles containing the
neurotransmitter
–neurotransmitter release
–diffusion of the neurotransmitter in the synaptic cleft
–binding of neurotransmitter to receptors on the post-
synaptic cell
–change in the permeability ( membrane potential ) of
the post-synaptic cell.
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58. Electric synapses
•AP conduct directly between adjacent cells
through structures called Gap junctions.
•Each gap junction contains a hundred or so
tubular connexons.
•As ions flow from one cell to the next one
through connexons the AP spreads from cell
to cell.
•We find electrical synapses in the CNS.
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59. 59

60. SPINAL CORD

62. A. External Structure of the spinal cord
•Spinal cord is roughly cylindrical but flattened
slightly in its anterior-posterior dimension
•In adults extends from medulla oblongata (the
most inferior part of the brain) to the superior
border of L2 vertebra
•In new born it extends to the L3 or L4 vertebra
•In adult the length ranges from 42 to 45 cm,
diameter is about 2 cm in mid thoracic, larger in
lower cervical & lumbar regions, smallest at
inferior tips

65. Structure of the spinal cord
•Viewed externally two conspicuous enlargement
can be seen:
–Superior enlargement: Cervical enlargement; C4 to T1
–Inferior enlargement: lumbar enlargement: T9 to T12
•Spinal cord has two grooves that divide the cord:
–Anterior median fissure: it is deep, wide groove
located on the ventral surface
–Posterior median sulcus: Shallower, narrow groove on
the dorsal surface

66. Structure of the spinal cord
•Conus medullaris:
–inferior to the lumbar enlargement, spinal cord
tapers to conical portion conus medullaris,
•Filum terminale:
–arises from the conus medullaris, it an extension
of pia matter that extends inferiorly and achors
the spinal cord to the coccyx

67. Structure of the spinal cord
•Spinal cord
–has bony covering: Vertebrae, and tough meninges
–Has cushioning CSF
–Spinal cord is located in the Vertebra column (Canal),
•Meninges: are connective tissue coverings of the
spinal cord and brain.
–The part of meninges covering spinal cord: Spinal
meninges
–The part of meninges covering the brain: cranial
meninges

68. Structure of the spinal cord
•Meninges are of three types:
•Most superficial: Dura mater, (Dura-tough, Mater-
mother)
–Composed of dense, irregular connective tissue.
–It forms a sac from the level of foramen magnum of
the occipital bone,
–It continuous with the duramater of the brain
–It is closed at level of sacral vertebra
–Between duramater and vertebral column there is
epidural space: contains fats & connective tissues

69. Structure of the spinal cord
•Second meninge is
•Arachnoid (means spider)
–Avascular
–Spider web arrangement of collagen & elastic
fibers
–It lies inside dura mater and continuous with
arachnoid of the brain
–There is a space between dura and arachnoid:
subdural space-contains interstitial fluid

70. Structure of the spinal cord
•Third-innermost meninx;
•Pia mater: pia means delicate
–Thin transparent connective tissue layer that
adheres to the surface of the spinal cord and brain
–Contains many blood vessels that supply nutrients
to the spinal cord
–Space between arachnoid and pia mater:
Subarachnoid space: CSF
–NB: Meningitis is inflammation of the meninges

71. B: Internal Structure of the spinal cord
•N.B: in a freshly dissected brain & spinal cord
note that some regions appear white and
glistering whereas others appear gray
•White matter is aggregations of myelinated
and unmyelinated axons of many neurons-
called white because of myelin
•Gray mater: contains neurons cell bodies,
dendrites, unmyelinated axons, axons
terminals and neuroglia

73. Structure of the spinal cord
•There are two grooves that penetrates white matter of the
spinal cord and divide into right and left sides.
•AMF: deep, wide groove on anterior aspect (Ventral)
•PMS: Shallower, narrow furrow on the posterior (Dorsal)
•Gray matter of spinal cord is shaped like the letter H,
•Grey commissure forms the cross bar of the H
•In the centreof the gray commissure is the central canal
•Superiorly the central canal is continuous with the 4
th
ventricle (contains CSF) in the medulla oblongata
•Anterior to gray commissure is the anterior white
commissure-connects white matter of the right and left
sides

74. Structure of the spinal cord
•In the grey matter of the spinal cord and
brains: clusters of neuronal cell bodies form
functional groups-Nuclei
•Sensory nuclei: receives inputs from receptors
via sensory neurons
•Motor nuclei: provide output to effector
tissues via motor neurons

75. Structure of the spinal cord

76. Structure of the spinal cord
•Gray matter:
–Is divided into horns
–Anterior gray horn (ventral): contains cell bodies of
somatic motor neurons and motor nuclei
–Posterior gray horn (Dorsal): contains somatic &
autonomic sensory nuclei
–Lateral gray horn: between the anterior and posterior
gray horns; present only in the thoracic, upper lumbar
and sacral segments of SC,
–Lateral horns: contain cell bodies of autonomic motor
neurons that regulate activities of smooth, cardiac
muscles and glands

77. Structure of the spinal cord
•White matter:
–Like gray matters is also organized into regions
–AGH & PGH divide the white matter on each side
into three broad areas: Columns
–Anterior (ventral) white columns
–Posterior white columns
–Lateral white columns
–Each columns contains distinct bundles of axons
having a common origin or destination and
carrying similar information

78. Structure of the spinal cord
•White matter cont…
–These bundles are Tracts
–Sensory tracts: ascending tracts: consists of axons
that conduct nerve impulses toward the brain
–Motor tracts: descending tracts: Consists of axons
that carry nerve impulses down the spinal cord

81. Physiology of spinal cord
•Focus on two major areas:
–Sensory and motor pathways: tracts
–Reflex arc

82. Physiology of spinal cord
•Physiology of SC:
–SC has two principal functions in maintaining
homeostasis
•Nerve impulses propagation
•Information integration

83. Physiology of spinal cord
•Sensory and motor tracts:
–Names of tracts indicates where it begins and it ends
–Anterior spinothalamic tract: located in anterior white
column, begins in spinal cord and ends in thalamus
–From sensory receptors there are two tracts for
impulses: Spinothalamic tracts and posterior columns
–Anterior and lateral spinothalamic tracts: pain,
warmth, coolness, itching, tickling, deep pressure &
crude poorly localized sense of touch

84. Physiology of spinal cord
•Sensory and motor tracts cont…
–Posterior columns (R&L):
•Proprioception-positions and movement of muscles,
tendons & joints.
•Discriminative touch-feel what part of the body is
touched
•Two point discrimination-distinguishing the touching of
two different points in the skin
•Light pressure sensations
•Vibrations
•

85. Physiology of spinal cord
•Descending pathways:
–Cerebral cortex plays major role in controlling
voluntary muscular movements
–Motor output to skeletal muscles travel down the
spinal cord in two types of descending pathways:
direct and indirect
–Direct: lateral corticopinal, anterior corticospinal,
and corticobulbartracts
–Indirect: rubrospinal, tectospinaland
vestobulospinal

86. Physiology of spinal cord
•Reflexes and reflex arcs;
–Spinal cord serves as integration centrefor some
reflexes
–A reflex is a fast, involuntary, unplanned sequence of
actions that occurs in response to a particular
stimulus.
–If integration takes place in spinal cord (gray matter):
spinal reflex
–If integration takes place in the brain: Cranial reflex-
using eyes to follow something
–The path followed by nerve impulses that produce
reflex is a reflex arc (reflex circuit)

87. Physiology of spinal cord
•Reflexes and reflex arcs cont…
–Examples of reflexes: stretch reflex causes muscles to
contracts as a response to stretching of muscles
–Sensory receptor in the muscle: muscle spindle is
stimulated by stretch
–Response to stretch muscle spindle generates
impulses that propagates through the posterior root
of spinal nerve into spinal cord
–In spinal cord integration
–Impulses arise in motor neuron & propagates along
anterior spinal root to stimulated muscles

88. SPINAL NERVES
•Components & branches of spinal nerves
•Plexus & distribution of nerves of the cervical,
brachial, lumbar & sacral plexuses
•Clinical significance of demartomes