Nervous system Sisay A..pdf

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THE BRAIN
NEUROANATOMY
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Nervous system Sisay A.
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Nervous system
Nervous system
 The nervous system is composed of organs, principally the
brain, spinal cord, nerves, and ganglia.
 The various activities of the nervous system can be
grouped together as three general, overlapping functions:
 Sensory
 Integrative
 Motor
 The nervous system is composed of organs, principally the
brain, spinal cord, nerves, and ganglia.
 The various activities of the nervous system can be
grouped together as three general, overlapping functions:
 Sensory
 Integrative
 Motor
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Types of cells in the nervous system
 Two main types of cells
 The actual nerve cell is the neuron
 It is the "conducting" cell that transmits impulses and the
structural unit of the nervous system
 The other type of cell is neuroglia,or glial cell.
 These cells are nonconductive and provide a support system for
the neurons.
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Neurons
 Structure
 Most neurons consist
of three parts
 The dendrites
 The cell body, or
perikaryon
 The axon
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Types of nerve cells
•Based on the size and shape of
their processes
•Multipolar neurons
•E.g- Motor neurons
•Bipolar neurons
•Found in the retina of the
eye
•Pseudounipolar neurons
•Most sensory neurons
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Types of nerve cells
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Types of glial cells
Glial Cell Type Origin Location Main Functions
Oligodendrocyte Neural tube Central nervous
system
Myelin
production,
electric insulation
Schwann cell Neural tube Peripheral nerves Myelin
production,
electric insulation
Astrocyte Neural tube Central nervous
system
Structural
support, repair
processes
Ependymal cell Neural tube Central nervous
system
Lining cavities of
central nervous
system
Microglia Bone marrow Central nervous
system
Macrophagic
activity
Ganglionic
gliocytes
Neural tube Peripheral nerves
ganglia
Support ganglia in the
PNS
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Covering & protection of CNS
Includes
 The skull –protects the brain
 The vertebral column - protects
the spinal cord
 The meninges and cerebrospinal
fluid protect the central nervous
system.
Meninges
Three connective tissue membranes
that lies external to the CNS
 Dura Mater
 Arachnoid Mater
 Pia Mater
Covering & protection of CNS
Includes
 The skull –protects the brain
 The vertebral column - protects
the spinal cord
 The meninges and cerebrospinal
fluid protect the central nervous
system.
Meninges
Three connective tissue membranes
that lies external to the CNS
 Dura Mater
 Arachnoid Mater
 Pia Mater
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Dura Mater Dura Mater
 Three dural septa extend
inward and limit excessive
movement of the brain
 Falx cerebri – fold that
dips into the longitudinal
fissure
 Falx cerebelli – runs
along the vermis of the
cerebellum
 Tentorium cerebelli –
horizontal dural fold
extends into the transverse
fissure
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Arachnoid Mater
 It is separated from the dura mater by the subdural space
 Beneath the arachnoid is a wide subarachnoid space filled with CSF
and large blood vessels
Pia Mater
 Between the arachnoid and the pia mater is the subarachnoid space.
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Organization of nervous system
Organization of nervous system
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Subdivisions of Nervous System
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THE BRAIN
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Regions of the Brain
• The four main regions of
the brain are:
Cerebral hemispheres
Diencephalon
• Thalamus
• Hypothalamus
Brain stem
• Midbrain
• Pons
• Medulla
Cerebellum
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Development of Brain
 Beginning of the 3rd week ectoderm-neural tube- 3 swellings are
formed
 The three primary brain vesicles
– forebrain (prosencephalon)
– midbrain (mesencephalon)
– hindbrain (rhombencephalon)
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• During the 5th week:
Consequently, there are five secondary brain vesicles.
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Gray & White Matter
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 Microscopically, the CNS
contains 2 neural elements:
 Neuron cell bodies (clusters are
known as nuclei)
 Nerve fibers (axons) in bundles
called tracts.
 Viewed macroscopically,
CNS tissues can be
distinguished by color:
 Gray matter consists of
somata, dendrites, and
unmyelinated axons
 White matter consists
primarily of myelinated axons
and dendrites
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 The pattern of white & gray
matter changes with descent
thru the brain stem
 The cortex disappears, but
scattered gray matter nuclei
are seen within the white
matter
 At the caudal end of the brain
stem the basic pattern is
evident
Cerebrum
 it is divided into two halves
called cerebral
hemispheres by
longitudinal cerebral fissure.
 They are connected by
corpus callosum
 Separated from cerebellum
posteriorly by transverse
fissure called tentorium
cerebelli.
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Cerebrum
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Insula
Each hemisphere has a covering of gray matter, the cortex and internal
masses of white matter, the basal nuclei, and a lateral ventricle.
Cerebrum

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The Cerebral Hemispheres
 The cerebral hemispheres
form the superior part of
the brain
 These two structures
account for about 80% of
the mass of the brain
 The two hemispheres
cover & obscure the
diencephalon & the top of
the brain stem
 Nearly the entire surface
of the cerebral
hemispheres is marked by
elevated ridges of tissues
called gyri separated by
shallow grooves called
sulci
 The transverse fissure
separates the cerebral
hemispheres from the
cerebellum below
Lobes of Cerebral Hemispheres
 Deeper sulci divide
each hemisphere
into five lobes
 Frontal lobe
 Temporal lobe
 Parietal lobe
 Occipital lobe
 Insula (located
within the lateral
sulcus)
Insula
Cerebrum
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Boundaries of the lobes
of the hemisphere
 The Frontal Lobe lies :
 in front of the central
sulcus
 above lateral sulcus
 The Parietal Lobe
bounded :
 Anteriorly: by the central
sulcus
 Posteriorly: parieto
occipital sulcus
 Inferiorly: lateral sulcus
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 The temporal lobe is bounded:
 Superiorly: lateral sulcus
 Posteriorly: parieto-occipital sulcus
 The occipital lobe: lies behind parieto-occipital sulcus
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Sulci & Gyri of the Cerebral hemisphere
• The surfaces of the hemisphere is formed of grey matter & called
cerebral cortex
• Each surface is divided by sulci (grooves) into gyri (convolutions)
• These infoldings result in marked increase in the surface area of the
cerebral cortex without increasing the size of the cerebral hemisphere.
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Sulcus of Cerebral Hemispheres
 Sulci divide lobes
of the hemispheres
 Central sulcus
 Parieto-
occipital sulcus
 Lateral sulcus
 Transverse fissure
The sulci & Gyri of the lateral surface
Frontal lobe
Important sulci:
Precentral sulcus:
Sup. frontal sulcus
Inf. frontal sulcus:
Important Gyri:
precentral gyrus:
superior frontal gyrus:
middle frontal gyrus:
inferior frontal gyrus
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Parietal lobe
Important Sulci:
 The postcentral sulcus:
 The intra parietal sulcus:
Important Gyri
 The postcentral gyrus:
 The superior parietal gyrus:
 The inferior parietal gyrus:
 The supramarginal gyrus:
 The angular gyrus :
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Temporal lobe
Sulci:
• The superior temporal sulcus:
• The middle temporal sulcus :
Gyri:
• The sup temporal gyrus:
• The middle temporal gyrus:
• The inferior temporal gyrus
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Occipital lobe
 The main part of the occipital lobe lies on the medial surface
 Only a small part appears on the lat surface & presents one sulcus called
the transverse occipital sulcus
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The Insula
 is hidden in the bottom of the lateral sulcus
 Function-Memory; integration of other cerebral activities
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White matter of cerebral hemispheres
 Composed of myelinated nerve fibers of different
diameters
 The nerve fibers classified in to three groups.
 Commissural
 Association
 Projection fibers
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 Association fibers
 confined to a given cerebral hemisphere and conduct
impulses between neurons within that hemisphere
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 Commissural fibers
 Connect the neurons and gyri of one hemisphere with those of the other
 They are corpus callosum, anterior commissure, posterior commissure,
fornix
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 Projecting fibers
 Form the ascending and descending tracts that transmit
impulses
 From the cerebrum to other parts of the brain and
spinal cord
 From the spinal cord and other parts of the brain to
the cerebrum
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Structure of the cerebral cortex
 Cerebral cortex forms a complete covering of the cerebral
hemispheres
 Composed of gray matter
 probably contains in excess of 10 billion neurons
 The cerebral cortex consists of a mixtures of
 Nerve cells
 Nerve fibers
 Neuroglia
 Blood vessels
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Cerebral Cortex
• Research on the structure & function of the brain reveals that there are
both specialized & diffuse areas of function
• Motor & sensory areas are localized in discrete cortical areas called
domains
• Many higher mental functions such as memory & language appear to
have overlapping domains & are more diffusely located
• Broadmann areas are areas of localized function
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Cerebral Cortex - Generalizations
 The cerebral cortex has three types of functional areas
 Motor areas / control voluntary motor function
 Sensory areas / provide conscious awareness of sensation
 Association areas / act mainly to integrate diverse information for
purposeful action
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functional areas of cerebral hemispheres
Cortical areas controlling motor functions lie in the
posterior part of the frontal lobes
Motor areas include the
 primary motor cortex
 premotor cortex
 Broca’s area
 front eye field
 Prefrontal cortex
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Frontal Lobe
 The primary Motor area
(area 4)
 occupies the precentral
gyrus
 Control voluntary
contraction of specific
muscle
 Premotor area (area 6):
 Planning based on past
experience
 Damage results in the loss of
the motor skills in that region
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 Broca’s Speach area (area 44,45)
 in the post part of inf. frontal gyrus
 formation of words
 Injury causes loss of ability to produce speech, or expressive aphasia
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Frontal eye field (area 8):
 controls the voluntary
movements of the eyes
 inability to turn the eyes to
the opposite side
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 Prefrontal cortex (areas 9, 10, 11 & 12)
for abstract ideas, reasoning & judgment, impulse control, persistence, long
term planning
Injury may cause mental & personality disorders
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Sensory Areas
 Areas concerned with the conscious awareness of sensation in the
parietal, temporal & occipital lobes
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Parietal Lobe
 Primary somatosensory cortex (Main sensory area ): area 3,1,2
 occupies the postcentral gyrus
 It receives pain, touch, proprioception, temperature & taste sensations from
the opposite ½ of the body
 Lesion to this area results in loss of tactile discrimination from the
opposite ½ of the body
• Somatosensory association
cortex (areas 5&7 )
integrate & analyze different
somatic sensory inputs
This loss of integration of
sensory impulses is called
astereognosis
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Temporal Lobe
 The primary auditory area (41 & 42- reception of sound
 The secondary auditory or auditory association areas (21 & 22)=
interpretation
sensory speech area
of Wernicke
understanding of the
written and spoken
language
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The occipital Lobe
 The primary visual area (17)-reception of vision
 The secondary visual areas (18 & 19)= recognize and appreciate
what he or she is seeing.
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Basal ganglia (basal nuclei)
Is applied to a collection of masses of gray matter
They are
o Corpus striatum,
o Amygdaloid nucleus and
o Claustrum
 control unconscious
contractions of certain
skeletal muscles
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The Diencephalon
 Extends posteriorly to the cerebral aqueduct & anteriorly to
Interventricular foramen.
 includes;
 the thalamus
 the hypothalamus,
 the sub thalamus,
 the epithalamus.
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 Thalamus
 Relay center for all sensory impulses, except smell, to the cerebral cortex and
performs some sensory interpretation
 The hypothalamus acts as an autonomic nervous center
 Cardiovascular regulation
 Body-temperature regulation
 Regulation of water and electrolyte balance
 Regulation of hunger and control of gastrointestinal activity
 Regulation of sleeping and wakefulness
 Sexual response
 Emotions
 Control of endocrine functions
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The ventricles (cavities) of the brain
 Are series of interconnected, fluid-filled cavities found
within the brain
 Two lateral ventricles, the third ventricle, and the fourth
ventricle
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Ventricles of the Brain
 Lateral
 Third
 Fourth
Lateral Ventricle
 Lie within each cerebral
hemisphere
 C-shaped cavity has
 Body in parietal lobe
 Anterior horn in
frontal lobe
 Posterior horn in
occipital lobe
 Inferior horn in
temporal lobe
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Third ventricle
 Slit like cleft between two thalami
 Derived from forebrain vesicle
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Aqueduct of Sylivius
 channel connecting 3rd to
4th ventricle
 Surrounded by a layer of
gray matter called central
gray
 no choroid plexus
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Fourth Ventricle
 Anterior to cerebellum and posterior to pons and cranial
half of medulla oblongata
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Communication between ventricles
Interventricular
foramina (of Monro)
Aqueduct of Sylivius
 Cerebrospinal fluid
exits from the fourth
ventricle into the
subarachnoid space via
Foramina of
Magndie
Foramina of Luschka
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CSF
 Formed in choroid
plexus
 The cerebrospinal fluid
then circulates in and
around the CNS
 Reabsorbed through
arachnoid villi into the
blood in cranial venous
sinuses .
 Formed in choroid
plexus
 The cerebrospinal fluid
then circulates in and
around the CNS
 Reabsorbed through
arachnoid villi into the
blood in cranial venous
sinuses .
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Brain stem
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Brain stem
 is made up of:- Medulla
oblongata, Pons and Midbrain
 It occupy the posterior cranial fossa
 Connect spinal cord with
forebrain
Function:-
 serves as a conduit for
ascending and
descending tract
connecting spinal cord
to forebrain
 It contain important
reflex center(
respiratory ,cvs &
consciousness)
 It contain important
nuclei of CN
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Medulla oblongata
Gross appearance;- connect pons superiorly & s.c inferior
- its upper half expand to the cavity of 4th v.
Anterior surface- is a median fissure
 Pyramid:- contain the motor fibers ; corticobulbarand corticospinal
fibers
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Medulla oblongata
The olive – oval elevation produced by inf. Olivary nuclei. CN XII
emerge b/n pyramid & olive
 Inf .cerebellar peduncles- lie post to olives
- connect medulla with cerebellum
- CN IX, X & XI emerge b/n ICP and olive.
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Medulla oblongata
Posterior surface:- sup. half form floor of 4th v.
-inf. half is continuous with s.c and posses post. median sulcus
 Gracile tubercle:- produced by gracile nucleus on each side of
median sulcus.
 Cuneate tubercle:- produced by cuneate nucleus , lateral to Gracile
tubercle.
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PONS
- is a bridge connecting Rt.
and Lt. cerebellar
hemispheres
 Lei ant. to cerebellum,
connect MO with
midbrain
 Has many transverse fiber
and basilary groove
CNV emerge in its
anterolateral surface.
 CNVI:- lei in the most
inf. Part of pons
 CNVII :- motor nuclei in
the most inf. Part of pons
 CNVIII :- sensory root in
the most inf. Part of pons
 Post surface form floor of
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Midbrain
 It connect Diencephalons to the Pons & Cerebellum.
 Topographically it lies in posterior fossa .
 Traversed by cerebellar aqueduct
 Posteriorly has -sup colliculus –visual &-inf colliculus -
auditory
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Midbrain
on its lateral side :-
- sup brachium pass from sup colliculus to lateral geniculate body
- inf brachium connect inf colliculus to medial geniculate body
On its anterior part is interpedencular fossa
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Midbrain
INTERPEDUNCULAR FOSSA
 Boundaries:- -Optic chiasma anteriorly,anterolaterally optic
tract, posterolaterally crus cerebri & posteriorly Pons.
 Contents - occulomotor nerve - mammilary body
-posterior cerebellar aa - tuber cinerium
- posterior perforated substance - infundibulum
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Cerebellum (Little Brain)
 Location
 Posterior cranial fossa
 Posterior to 4th ventricle,
pons & medulla
Has two hemispheres &
vermis
Connected to posterior part
of brain stem by three
symmetrical bundles of
nerve fibers (cerebellar
peduncle)
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cerebellum
Each cerebellar
hemisphere has 3
anatomical lobes
 Anterior
 Posterior
 Flocculonodular
Has fissures
 Primary
 Horizontal
 Uvulonodula
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Structure of Cerebellum
 Has outer gray and inner white matter
 Intracellebellar nuclei embedded in white matter
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Intracerebellar Nuclei
 Four masses of gray matter embedded in white matter on
each side of the midline
 Dentate, emboliform, globose and fastigial
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CEREBELLAR PEDUNCLES
 Afferent & efferent bundles of nerve fibers
 Link cerebellum with other parts of CNS
Superior CP- Midbrain
Middle CP -Pons
Largest of the peduncles
 Inferior CP - M.oblongata, vestibular nuclei, cells of
the reticular formation
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Functions of cerebellum
 It serves as:
1. A coordinator of motor activity
2. A regulator of muscle tone
3. Functions to maintain balance and equilibrium
4. Participates in motor planning
5. Plays a role in controlling visceral activity
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Functional Areas of Cerebellar Cortex
1. Cortex of Vermis
 Influence movement of long axis of the body
 Spinocerebellar tracts
 sends projections to the fastigial nucleus of the
cerebellum, which then sends output to the
vestibular nuclei
2. Intermediate Zone CH
 Receives input from the
corticopontocerebellar fibers
 Receives sensory feedback from the muscles
 Muscles of distal parts of limbs e.g. hands &
feet
3. Lateral Zone CH
 Receives input from the parietal cortex via
pontocerebellar mossy fibers
 Information regarding the location of the body
in the world
 The large numbers of feedback circuits allow
for the integration of this body position
information with indications of muscle position,
strength, and speed.
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Blood supply of brain
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 Circle ofWillis
 The anterior communicating
 anterior cerebral
 internal carotid
 posterior communicating
 posterior cerebral
 basilar arteries
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ARTERIES OF SPECIFIC BRAIN AREAS
1. The corpus striatum and the internal capsule are supplied by middle
cerebral artery& anterior cerebral artery
2. The thalamus
posterior communicating
basilar
Posterior cerebral
3. The midbrain
posterior cerebral
superior cerebral
basilar arteries
4. Pons
basilar
anterior, inferior and superior cerebellar arteries
5. Medulla oblongata
vertebral, anterior and posterior spinal, posterior inferior cerebellar& basilar
6. Cerebellum
Superior cerebellar,anterior inferior cerebellar and, posterior inferior cerebellar arteries
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Cranial Nerves
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There are 12 pairs of cranial nerves
- Cranial nerves I and II attach to the forebrain
/telencephalon & diencephalon respectively/
- All others attach to the brain stem
There are 12 pairs of cranial nerves
- Cranial nerves I and II attach to the forebrain
/telencephalon & diencephalon respectively/
- All others attach to the brain stem
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Functional group of cranial nerves
Functional group of cranial nerves
Types of cranial nerves
 I, II,VIII are entirely sensory.
 III, IV,VI, XI, XII are entirely motor.
 V,VII, IX, X are mixed.
Types of cranial nerves
 I, II,VIII are entirely sensory.
 III, IV,VI, XI, XII are entirely motor.
 V,VII, IX, X are mixed.
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Cranial nerve I :Olfactory nerve
Cranial nerve I :Olfactory nerve
 Functions- sense of smell
 Location of Cell Bodies -Within Sensory Organ or Ganglia
(Olfactory mucosa)
- Major connections - Mucosa projects to olfactory bulb
 Functions- sense of smell
 Location of Cell Bodies -Within Sensory Organ or Ganglia
(Olfactory mucosa)
- Major connections - Mucosa projects to olfactory bulb
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Cranial Nerve II: Optic Nerve
 Contains myelinated axons that arise from the ganglion cells
in the retina and passes through the optic papilla to the
orbit.
 The nerve changes its name to optic tract when the fibers
have passed through the optic chiasm
 Contains myelinated axons that arise from the ganglion cells
in the retina and passes through the optic papilla to the
orbit.
 The nerve changes its name to optic tract when the fibers
have passed through the optic chiasm
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 Optic tract axons project
to the superior colliculus
and to the lateral geniculate
nucleus within the
thalamus, which relays
visual information to the
cortex.
Function - vision
 Optic tract axons project
to the superior colliculus
and to the lateral geniculate
nucleus within the
thalamus, which relays
visual information to the
cortex.
Function - vision
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Cranial Nerve III: Oculomotor Nerve
Cranial Nerve III: Oculomotor Nerve
 Functions - Supply extrinsic mm of the eye (Motor to
Medial rectus, superior rectus, inferior rectus, inferior
oblique & levator palpebrae superioris muscle ),constrictor
pupillae and ciliary mm
 Location of Cell Bodies – Within midbrain
(occulomotor nucleus) &
(Edinger-Westphal nucleus).
 Functions - Supply extrinsic mm of the eye (Motor to
Medial rectus, superior rectus, inferior rectus, inferior
oblique & levator palpebrae superioris muscle ),constrictor
pupillae and ciliary mm
 Location of Cell Bodies – Within midbrain
(occulomotor nucleus) &
(Edinger-Westphal nucleus).
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Cranial Nerve IV:Trochlear Nerve
Cranial Nerve IV:Trochlear Nerve
 Functions- Motor to Superior oblique muscle
 Location of Cell Bodies –Within Brain Stem –Trochlear
nucleus
 Functions- Motor to Superior oblique muscle
 Location of Cell Bodies –Within Brain Stem –Trochlear
nucleus
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Cranial nerveV :TRIGEMINAL NERVE
Cranial nerveV :TRIGEMINAL NERVE
 Largest , mixed ( have
both motor & sensory
part)
 Has 3 divisions: -
Ophthalmic, Maxillary,
& Mandibular.
Motor component of the
Trigeminal N
Motor nucleus supplies:
1.Muscles of
mastication
2.Anterior belly of the
digastrics
3.Tensor tympani
4.Tensor veli palatine
5.Mylohyoid
 Largest , mixed ( have
both motor & sensory
part)
 Has 3 divisions: -
Ophthalmic, Maxillary,
& Mandibular.
Motor component of the
Trigeminal N
Motor nucleus supplies:
1.Muscles of
mastication
2.Anterior belly of the
digastrics
3.Tensor tympani
4.Tensor veli palatine
5.Mylohyoid
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Sensory fibers supplies the face and parts of the scalp
Sensory fibers supplies the face and parts of the scalp
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 Purely motor
 Emerges from the anterior surface of the brain, in the groove
between the lower border of the pons and the medullaoblogata.
 Finally, it runs forward and supplies the lateral rectus muscle.
 Purely motor
 Emerges from the anterior surface of the brain, in the groove
between the lower border of the pons and the medullaoblogata.
 Finally, it runs forward and supplies the lateral rectus muscle.
Cranial NerveVI : Abducent Nerve
Cranial NerveVI : Abducent Nerve
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The facial nerve
consists of a
motor and a
sensory part
The two parts
emerge at the
lower border of
the pons in the
recess between
the olive and
the inferior
peduncle
The facial nerve
consists of a
motor and a
sensory part
The two parts
emerge at the
lower border of
the pons in the
recess between
the olive and
the inferior
peduncle
Facial nerve: CNVII
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Vestibular Nerve
 Transmits information about position and movement of the
head
 Its nerve fiber are Central processes of nerve cell located in
vestibular ganglion situated in internal acoustic meatus
Vestibular Nerve
 Transmits information about position and movement of the
head
 Its nerve fiber are Central processes of nerve cell located in
vestibular ganglion situated in internal acoustic meatus
CNVIII:Vestibulocochlear Nerve
CNVIII:Vestibulocochlear Nerve
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Its nerve fiber are Central processes of nerve cell located in
spiral ganglion of the cochlea
 On reaching the mid brain the fiber terminate on inf.
Colliculus or medial geniculate body.
 Leave posterior cranial fossa via internal acoustic meatus
to inner ear.
Its nerve fiber are Central processes of nerve cell located in
spiral ganglion of the cochlea
 On reaching the mid brain the fiber terminate on inf.
Colliculus or medial geniculate body.
 Leave posterior cranial fossa via internal acoustic meatus
to inner ear.
Cochlear Nerve :- conduct impulse concerned with sound
Cochlear Nerve :- conduct impulse concerned with sound
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 Mixed
 Has 3 nuclei:- two motor &
one sensory
 Main motor supply
stylopharyngus msc.
 Parasympathetic supply –
parotid gland
 Sensory – common & taste
sensation
 Mixed
 Has 3 nuclei:- two motor &
one sensory
 Main motor supply
stylopharyngus msc.
 Parasympathetic supply –
parotid gland
 Sensory – common & taste
sensation
CN IX: Glossopharyngeal Nerve
CN IX: Glossopharyngeal Nerve
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CN X:VAGUS NERVE
CN X:VAGUS NERVE
 Is mixed
Has three nucleus
 Main motor nucleus -
Efferent fibers supply
constrictor muscles of
pharynx and intrinsic
mm of larynx.
 Parasympathetic nucleus
- Efferent fibers to
abdominal viscera
 Sensory nucleus-
common sensation &
taste sensation.
 Is mixed
Has three nucleus
 Main motor nucleus -
Efferent fibers supply
constrictor muscles of
pharynx and intrinsic
mm of larynx.
 Parasympathetic nucleus
- Efferent fibers to
abdominal viscera
 Sensory nucleus-
common sensation &
taste sensation. 9/7/2021
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CN XI:Accessory Nerve
CN XI:Accessory Nerve
 Is Purely Motor
 Has spinal and cranial
root.
 The 2 roots exit via
jugular foramen
 Join vagus and
distribute in its
pharyngeal and
recurrent laryngeal
branch to mm of soft
palate, pharynx &
larynx.
 Spinal root Supply
trapezius and SCM
mm
 Is Purely Motor
 Has spinal and cranial
root.
 The 2 roots exit via
jugular foramen
 Join vagus and
distribute in its
pharyngeal and
recurrent laryngeal
branch to mm of soft
palate, pharynx &
larynx.
 Spinal root Supply
trapezius and SCM
mm
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Hypoglossal nerve : CN XII
Origin and distribution
Is purely motor
Arise from medulla oblongata
Supply mm of the tongue
Origin and distribution
Is purely motor
Arise from medulla oblongata
Supply mm of the tongue
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Spinal Cord
 Begin at foramen magnum and ends at L1(adult), L3(child)
 Surrounded by
 Meninges
 CSF
 Bones
 Stabilized in position
Filum terminale
Denticulate ligament
Spinal nerve roots
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Spinal Cord
 The spinal cord is divided
into 31 segments
 The distal end of the spinal
cord (the conus
medullaris) is cone
shaped.
 A fine filament of
connective tissue (the pial
part of the filum
terminale) continues
inferiorly from the apex of
the conus medullaris
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111
External structure of spinal cord
 In cross-section,the shape
of spinal cord in different
regions varies.
It has two major swellings or
enlargements
 A cervical enlargement C3-T2
 A Lumbosacral enlargement
L1-S3
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External structure of spinal cord
is marked by a number
of fissures and sulci
 The anterior median
fissure
 The posterior median
sulcus
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Internal structure of spinal cord
 Has a small central canal
surrounded by gray and
white matter
 Gray Matter
 On cross section it is H
shaped
 It posses Columns
 The ventral (or anterior)
gray column
 The intermidiolateral
gray column
 The dorsal gray column
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Structure of Gray Matter
 Consists of :
 Mixture of multipolar nerve cells arranged in groups
 Process of nerve cells
 Blood vessels
 Neuroglia
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Internal structure of spinal cord
White Matter
Columns
 dorsal (also termed
posterior), lateral, and
ventral (also termed
anterior)
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Structure of white matter
Consist of:
Nerve fibers
Neuroglia
Blood vessels
 Arrangement of Nerve
Fiber in Spinal Cord is
termed asTracts
Ascending (sensory,
posterior)
Descending (motor,
anterior)
Intersegmental
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The spinal cord cont…
The spinal cord has two main functions
 Serving as a conduction pathway for impulses going to
and from the brain.
 Serving as a reflex center
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Spinal nerves
There are 31 pairs spinal nerves
 All of the spinal nerves are "mixed
 Formation
 The anterior root
 The posterior root
 Those fromT1 to L2 sympathetic fibers; while S2 to S4 contain
parasympathetic fibers.
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Peripheral nervous system
o Nervous structures outside the brain and spinal cord
o Nerves allow the CNS to receive information and take
action.
o Functional components of the PNS
 Sensory inputs and motor outputs
 Motor -Categorized as somatic or visceral
 Sensory inputs -also classified as general or special
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21
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Basic structural components of PNS
 Sensory receptors
Motor endings
Nerves and ganglia
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Spinal Nerves
31 pairs of spinal
nerves
 8 cervical
 12 thoracic
 5 lumbar
 5 sacral
 1 coccygeal
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 A spinal nerve is a mixed nerve attached to the spinal cord by a
posterior root, composed of sensory fibers, and an anterior
root, composed of motor fibers
 A spinal nerve is formed as the fibers from the posterior and anterior
roots converge and emerge through an intervertebral foramen.
 A spinal nerve divides into several branches
 Posterior ramus, innervates the muscles, joints, and skin of
the back along the vertebral column
 Anterior ramus of a spinal nerve innervates the muscles and
skin on the lateral and anterior side of the trunk
 Except in thoracic nervesT2 throughT12, the anterior rami of the
spinal nerves combine and then split again as networks of nerve fibers
referred to as nerve plexuses
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Innervation of the skin: Dermatomes
 Dermatome – an area of
skin innervated by
cutaneous branches of a
single spinal nerve.
 Upper limb – skin is
supplied by nerves of the
brachial plexus.
 Lower limb
 Lumbar nerves –
anterior surface
 Sacral nerves – posterior
surface
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Branches of spinal Nerves
 Ventral Ramus -what they innervate depends upon which
part of the spinal cord is considered.
 Thoracic region: form intercostal nerves that innervate the
intercostal muscles and the skin over the thorax
 Remaining spinal nerve ventral rami form five plexuses.
 Ventral rami of C1-C4= cervical plexus
 Ventral rami of C5-T1= brachial plexus
 Ventral rami of L1-L4= lumbar plexus
 Ventral rami of L4-S4= sacral plexus
 Ventral rami of S4 and S5= coccygeal plexus
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Cervical plexus
 Formed by ventral rami of
spinal nerves C1-C4
 Motor: Innervates muscles of
the neck (SCM, trapezius),
laryngeal muscles
 Sensory: Skin of upper chest,
shoulder, neck, and ear
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Brachial plexus
 Formed by ventral rami of
spinal nerves C5-T1
 Five ventral rami form three
trunks that separate into six
divisions then form cords
that give rise to:
 Branches/nerves
 Axillary
 Radial
 Musculocutaneous
 Ulnar
 Median
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Lumbosacral plexus
 Lumbar plexus: formed by
ventral rami of spinal
nerves L1-L4
 Sacral plexus: formed by
ventral rami of L4-S4
 Usually considered
together because of their
close relationship
 Four major nerves exit and
enter lower limb
 Obturator
 Femoral
 Tibial
 Common fibular (peroneal)
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Autonomic nervous system
Monitor internal environment of the body
Innervates smooth muscle, cardiac muscle, and glands
 Regulates visceral functions
 Heart rate, blood pressure, digestion, urination
Has afferent, connector and efferent neurons
Afferent neurons originate from visceral receptors
Efferent pathway comprise – preganglionic and
postganglionic neurons
Cell bodies of preganglionic neurons are situated in the lateral
grey column of sc and motor nuclei of III,VII,IX,& X CN
Division – sympathetic
-parasympathetic
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Sympathetic division
Innervate viscera and glands
Activated during exercise, excitement, and emergencies
Prepare the body for emergency condition< fight or
flight>
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Sympathetic division
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The Parasympathetic Division
 Cranial outflow
 Comes from the brain
 Innervates organs of the head,
neck, thorax, and abdomen
 Sacral outflow
 Supplies remaining abdominal
and pelvic organs
Concerned with conserving
energy “rest and digest”
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135
COMPARISON B/N TWO ANS DIVISION
Characteristics Sympathetic Parasympathetic
Action Fight or flight Rest & digest
Outflow T1-L2/3 CN III, VII, IX,X, S2-S4
Preganglionic fiber Myelinated Myelinated
Ganglia Para & Prevertebral Small ganglia
Neurotransmitter in
ganglia
Ach Ach
Postganglionic fiber Long non myelinated Short non myelinated
Ratio of pre to
postganglionic fiber
1:10 1:3 or fewer
Neurotransmitter in
post ganglionic
endings
Norepinephrine- most
Ach- some, sweat g.
Ach
Higher control Hypothalamus Hypothalamus 9/7/2021
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Effect of ANS on organs of the body
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138

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