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Nervous system
Lecture for medical students
Department of histology,
cytology and embryology KhNMU
Nervous system
Includes:
 Central nervous system (CNS)
 --Brain
 --Spinal cord
 Peripheral nervous system (PNS):
(outside the brain and spinal cord)
Peripheral Nervous System
• - consists of groups
of neurones (ganglion
cells),
• feltworks of nerve
fibres,
• and bundles of
parallel nerve fibres
called ganglia,
called plexuses,
that form the nerves
and nerve roots.
Neurones in the central nervous system
form Gray matter.
- Gray matter – cell bodies and unmyelinated
fibers
(- the white matter – fibers )
- Central Gray matter – Spinal Cord
-- Nuclei – clusters of cell bodies within the
white matter of the brain stem,
--- Cortex – in the cerebellum and cerebrum
Neuron Cell Body
Location
 In Peripheral NS:
 Ganglia – collections of cell bodies
outside the central nervous system,
sensory or sympathetic/
parasympathetic
Neuron location
Development of the SNS
Late Gastrulation
Axial organs
formation
Ectoderm
Amniotic Cavity
Paraxial mesoderm
Somite
Intermediate mesoderm
Lateral plate mesoderm
Yolk Sac
Endoderm
Notochord
Development of the Neural Tube
by the invagination of ectoderm
Development of the Neural
Tube
Development of the Neural
Tube
Development of the Neural
Tube
Development of the Neural Tube
Surface Ectoderm
Neural Crest Cells
Neural Tube
Neural tube formation
Neural tube formation
Neural tube formation.
Gastrulation is finished with the formation of axial organs –neural tube,
notochord, somites
Development of the Neural Tube
Surface Ectoderm
Neural Crest Cells
Neural Tube
Development of CNS
Neural tube – CNS
• Cranial part – brain
• Caudal part – spinal cord
Development of CNS
•Neural crest – 1. sensory bipolar
NEURONS of cranial ganglia, spinal ganglia,
• 2. motor NEURONS of autonomic ganglia,
• 3. - And:
neuroendocrine cells (APUD),
Shwann cells of neuroglia,
adrenal medulla, melanoblast of skin
Development of CNS
• Radial migration process
Layers of NT from inside:
• Primitive ependimal or germinal;
• Mantle layer – developmental cells;
• Marginal layer – fibers of neuroglial cell
GANGLIA
GANGLIA
• Ganglia are aggregations of nerve cells
(ganglion cells) outside the CNS:
• Sensory neurons (Cranial nerve and
dorsal root ganglia) and …
• … motor neurons (ANS only, s/ps ganglia)
Sensory GANGLIA
• Neurones in cranial nerve and dorsal root
ganglia are pseudounipolar. They have a
T-shaped process.
GANGLIA
• The branches of the T connect the
ganglion cell with the CNS (central branch,
axon) and the periphery (peripheral
branch, dendrite).
GANGLIA
• Cranial nerve and
dorsal root ganglia
are surrounded by a
connective tissue
capsule, which is
continuous with the
dorsal root epi- and
perineurium.
GANGLIA
GANGLIA
• Individual ganglion cells are surrounded by
a layer of flattened satellite cells.
Spinal cord
Spinal Cord
 Extends from the
medulla oblongata to
the region of T12
Figure 7.18
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Slide 7.52
Spinal Cord
 Below T12 is the cauda
equina (a collection of
spinal nerves)
Figure 7.18
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Slide 7.52
Spinal Cord
 Enlargements occur in
the cervical and lumbar
regions
 Meninges cover the spinal cord
Figure 7.18
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Slide 7.52
Spinal Nerves
 There is a pair of spinal nerves at the
level of each vertebrae.
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Slide 7.63
Spinal Cord Anatomy
 Nerves begin:
Dorsal root + …
 … Ventral root
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Slide 7.54
Spinal Nerves
Figure 7.22a
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Slide 7.64
• Afferent, sensory fibres enter the spinal
cord via the dorsal roots,
• efferent, motor fibres leave the spinal cord
via the ventral roots.
Spinal Cord
Spinal Cord
Spinal Cord Anatomy
 Internal gray matter - mostly cell bodies
 Dorsal (posterior) horns
 Anterior (ventral) horns
Figure 7.19
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Anterior horn:
• two motor nuclei: medial and lateral.
• The axons of motor neurons form anterior
root.
Spinal Cord
Posterior horn
two integrative (Intecalated) nuclei of
somatic nervous system:
• proper nucleus and Klark’s nucleus.
Lateral horn
• medial and lateral nuclei.
• intercalated neurons of ANS (mostly sNS).
Spinal Cord Anatomy
 Exterior white mater – conduction tracts
(myelinated fibers )
Figure 7.19
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Spinal Cord Anatomy
 Central canal filled with cerebrospinal
fluid
Figure 7.19
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Somatic reflex arc
•
•
•
•
1-st neuron – sensory ganglion
2-d neuron – dorsal horn
3-d neuron – ventral horn
Target – skeletal muscle
Testing Patellar Reflexes
Testing Achilles Reflexes
Testing Plantar Reflexes
Peripheral Nervous System
Peripheral Nerves
Peripheral Nerves
 Nerve = bundle of neuron fibers,
 fibers - myelinated and un-…
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Slide 7.55
Nerve fibers may be:
• Nerve fibres, which originate from
neurones within the CNS and pass out of
the CNS in cranial and spinal nerves, are
called efferent or motor fibers.
Nerve fibers may be:
• Nerve fibres which originate from nerve
cells outside the CNS but enter the CNS
by way of the cranial or spinal nerves are
called afferent or sensory nerve fibres.
Classification of Nerves
 Afferent (sensory) nerves – carry
impulses toward the CNS
 Efferent (motor) nerves – carry impulses
away from the CNS
 Mixed nerves – both sensory and motor
fibers
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Slide 7.57
Structure of a Nerve
Figure 7.20
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Slide 7.56
Peripheral nerves contain a considerable amount
of connective tissue.
• The space between individual nerve fibres is
filled by loose connective tissue, the
endoneurium.
• Nerve fibres are frequently grouped into distinct
bundles, fascicles, within the nerve. The layer of
connective tissue surrounding the individual
bundles is called perineurium.
• The entire nerve is surrounded by a thick layer
of dense connective tissue, the epineurium.
Structure of a Nerve
 Endoneurium
surrounds each fiber
 Groups of fibers are
bound into fascicles
by perineurium
 Fascicles are bound
together by
epineurium
Figure 7.20
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Slide 7.56
Brain Stem
Brain Stem
• Diencephalon
 Midbrain
 Pons
 Medulla oblongata
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• Grey matter (neurones) – nuclei
• White matter -- tracts
Autonomic Nervous System
--- The involuntary branch of the nervous
system
 Divided into two divisions
 Sympathetic division
 Parasympathetic division
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Slide 7.67
Anatomy of the Autonomic Nervous
System
Figure 7.25
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Slide 7.73
Sympathetic reflex arc
• 1-st: sensory neuron - in the spinal ganglion)
• 2-d: intercalated (preganglionic) neuron – in the lateral
horn of the thoracic and upper lumbar segment of spinal
cord.
• !!! Impulse leaves the spinal cord by way of the axon of
intercalated neuron. It is also called preganglionic fiber.
• 3-d, motor (efferent) neuron is located in the sympathetic
ganglion. The axon of the ganglion cell is called the
postganglionic fiber.
• An axon of the motor cell carries impulse to the effector,
namely, to the smooth muscle of the gut.
Parasympathetic reflex arc
• 1-st: sensory neuron (in the spinal
ganglion)
• 2-d neuron: is located in the sacral spinal
cord segments and in the brain stem.
• 3-d neuron is located in the
parasympathetic ganglia, which lie close to
the viscera or into wall of viscera.
Comparison of Somatic and
Autonomic Nervous Systems
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Figure 7.24
Slide 7.69
Autonomic Functioning
 Sympathetic – “fight-or-flight”
 Response to unusual stimulus
 Takes over to increase activities
 Remember as the “E” division = exercise,
excitement, emergency, and
embarrassment
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Autonomic Functioning
 Parasympathetic – housekeeping
activites
 Conserves energy
 Maintains daily necessary body functions
 Remember as the “D” division - digestion,
defecation, and diuresis
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Autonomic GANGLIA
Autonomic GANGLIA
GANGLIA
• Autonomic ganglia do contain synapses, and the
ganglion cells within them do have dendrites.
They receive synapses from the first neurone of
the two-neurone chain, which characterises
most of the efferent connections of the
autonomic nervous system. The second
neurone is the ganglion cell itself. Some
autonomic ganglia are embedded within the
walls of the organs which they innervate
(intramural ganglia - e.g. GIT and bladder).
Brain Stem
Figure 7.15a
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Diencephalon
 Sits on top of the brain stem
 Enclosed by the cerebral hemispheres
 Made of three parts
 Thalamus
 Hypothalamus
 Epithalamus
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Thalamus
 Surrounds the third ventricle
 The relay station for sensory impulses
 Transfers impulses to the correct part of
the cortex for localization and
interpretation
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Hypothalamus
 Under the thalamus
 Important autonomic nervous system
center
 Helps regulate body temperature
 Controls water balance
 Regulates metabolism
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Hypothalamus
 An important part of the limbic system
(emotions)
 The pituitary gland is attached to the
hypothalamus
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Epithalamus
 Forms the roof of the third ventricle
 Houses the pineal body (an endocrine
gland)
 Includes the choroid plexus – forms
cerebrospinal fluid
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Slide 7.37
Midbrain
 Mostly composed of tracts of nerve
fibers
 Reflex centers for vision and hearing
 Cerebral aquaduct – 3rd-4th ventricles
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Slide 7.39
Pons
 The bulging center part of the brain
stem
 Mostly composed of fiber tracts
 Includes nuclei involved in the control of
breathing
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Slide 7.40
Medulla Oblongata




The lowest part of the brain stem
Merges into the spinal cord
Includes important fiber tracts
Contains important control centers
 Heart rate control
 Blood pressure regulation
 Breathing
 Swallowing
 Vomiting
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Cerebellum
Cerebellum
 Two hemispheres with convoluted
surfaces
 Provides involuntary coordination of
body movements
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Cerebellum
Figure 7.15a
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Cerebellar cortex
1)Molecular layer
2)Purkinje cell
layer
3)Granular layer
Cerebellum
Cerebellum
Cerebral cortex
Cerebral cortex:
1)molecular layer.
2)external granular
layer.
3 )pyramidal layer.
4)internal granular layer.
5)ganglionic layer.
6)multiform layer.
• I. The molecular (or
plexiform) layer
consists of fibers,
most of which travel
parallel to the surface,
and horizontal cells.
• II. The outer granular
layer contains small
pyramidal cells and
stellate cells.
• III. The layer of medium
pyramidal cells (or outer
pyramidal layer) is not
sharply demarcated from
layer II, but cells larger
and possess a typical
pyramidal shape.
• IV. The inner granular
layer contains many small
stellate cells and granule
cells.
• V. The layer of large
pyramidal cells (inner
pyramidal layer). In motor
area they are extremely
large and are called Betz
cells.
• VI. The layer of
polymorphic cells
contains cells with
diverse shapes, many of
which have a spindle or
stellate shape. The main
cells of this layer are
called fusiform cells.
Cerebral Hemispheres (Cerebrum)
 Paired (left
and right)
superior parts
of the brain
 Include more
than half of
the brain
mass
Figure 7.13a
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Cerebral Hemispheres (Cerebrum)
 The surface
is made of
ridges (gyri)
and grooves
(sulci)
Figure 7.13a
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Lobes of the Cerebrum
Fissures (deep grooves) divide the
cerebrum into lobes.
 Surface lobes of the cerebrum
 Frontal lobe
 Parietal lobe
 Occipital lobe
 Temporal lobe
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Lobes of the Cerebrum
Figure 7.15a
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Specialized Areas of the Cerebrum
 Somatic sensory area – receives
impulses from the body’s sensory
receptors
 Primary motor area – sends impulses to
skeletal muscles
 Broca’s area – involved in our ability to
speak
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Sensory and Motor Areas of the
Cerebral Cortex
Figure 7.14
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Specialized Area of the Cerebrum
 Cerebral areas involved in special
senses
 Gustatory area (taste)
 Visual area
 Auditory area
 Olfactory area
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Specialized Area of the Cerebrum
 Interpretation areas of the cerebrum
 Speech/language region
 Language comprehension region
 General interpretation area
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Specialized Area of the Cerebrum
Figure 7.13c
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Layers of the Cerebrum
 Gray matter
 Outer layer
 Composed
mostly of neuron
cell bodies
Figure 7.13a
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Layers of the Cerebrum
 White matter
 Fiber tracts
inside the gray
matter
 Example:
corpus callosum
connects
hemispheres
Figure 7.13a
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Layers of the Cerebrum
 Basal nuclei – internal
islands of gray matter
 Regulates voluntary
motor activities by
modifying info sent to
the motor cortex
 Problems = ie unable
to control muscles,
spastic, jerky
 Involved in
Huntington’s and
Parkinson’s Disease
Figure 7.13a
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