Nervous System

1. NERVOUS SYSTEM I
HUMAN ANATOMY II
MR. F.C. UDEH
3/15/2023
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2. Definition and division
 Master controlling system
 Central Nervous System (CNS) - Brain and spinal cord
 Peripheral Nervous System (PNS): 12 pairs of cranial nerves and 31 pairs of
spinal nerves
A. Afferent (Sensory) division- brings signals from receptors to the CNS
 General somatic afferent (GSA) division- skin, joints, skeletal muscles,
bones receptors
 General visceral afferent (GVA) division- visceral organs
Efferent (Motor) division – returns signals from the CNS to effector organs
 General somatic efferent (GSE) division- skeletal muscles
 General visceral efferent (GVE) division- involuntarily controlled
 Involuntary Nervous System or Autonomic Nervous System (ANS) -
Sympathetic and Parasympathetic divisions 3/15/2023
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3.  Excitable, conductive, secretory
 Cell body and cell processes (dendrites and axon)
1. Cell body/soma/perikaryon - central nucleus; large
nucleolus; mitochondria and RER (Nissl bodies),
lysozomes, cytoskeleton/neurofibril, a golgi complex;
inclusions like glycogen granules, lipid droplets,
lipofuscin (“wear and tear” pigment)
Cell bodies form the grey matter of the CNS
2. Dendrites
3. Axon – cylindrical; made of axon hillock, axolemma,
axoplasm, myelin sheath, node of Ranvier, terminal
buttons; axon collateral
Axons form white matter in CNS
Myelinated and unmyelinated
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Neuron

4. Classification of neurons
1. Functional classification:
1. Sensory/afferent neurons - light, hearing, taste, balance, pain, temperature, etc
2. Interneurons
3. Motor/efferent neurons - from the CNS to effector organs (muscles and gland
cells)
2. Structural classification:-
1. Anaxonic neurons: in the brain, retina, adrenal medulla
2. Unipolar or Pseudounipolar neurons: mostly in ganglia in the PNS
3. Bipolar neurons: found in olfactory cells, the retina, inner ear (spiral ganglia of the
cochlear, vestibular ganglion
4. Multipolar neurons: most common
3. Length of axon: Golgi type I – long axon; Golgi type II – short or no axon
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5. Neuron
types
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6. NEUROGLIA CELLS –supportive or glial cells
1. Microglial cells - small macrophages; dense; elongated; wander throughout the
CNS
2. Astrocytes – star-shaped; most abundant; supportive framework in the CNS;
maintain blood-brain barrier formation
3. Oligodendrocytes - Octopus-like in shape; about fifteen processes; form
myelin sheath in the CNS
 Ependymal cells - line the ventricles and their cilia assist in CSF flow, modified
ependymal cells produce little CSF.
 5. Schwann cells - form myelin sheath in the PNS
 6. Satellite cells - surround the cell body of neurons in the PNS, provide
electrical insulation around the cell body.
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7. ALZHEIMER DISEASE
Aging disease – old age
Caused by loss of neurons and synapses
mainly within the cerebral cortex followed by
atrophy of the individual cerebral lobes.
Hippocampus is one of the first damaged
region of the brain
Causes dementia (impaired memory, thinking
and social abilities)
Available neurons develop β-amyloid plaques
and neurofibrillary tangles (from
degenerated neurofilaments) that render the
neurons nonfunctional
CLINICAL CORRELATE
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8. CLINICAL CORRELATE
MULTIPLE SCLEROSIS
Autoimmune disease, antibodies demyelinate the neurons in CNS and optic
nerve.
Causing chronic and progressive dysfunction of the nervous system.
Primary sign: Scanning speech, Intention tremor, Nystagmus (rapid involuntary
eye movement)– SIN gets worse with increased temp.
Higher degree of damage will cause thinking and learning problem.
Female to male ratio is 2:1; females in their 20s -40s
Diagnosed by increased IgG level (oligoclonal bands) and myelin basic protein in
CSF and periventricular plaques in MRI.
Immunosuppressor (corticosteroids) and GABAB receptor agonists.
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9. CLINICAL CORRELATE
PERIPHERAL NEUROPATHIES e.g.,
Acute idiopathic polyneuritis (Guillain-Barré syndrome)
Rare autoimmune disease caused mostly by infection (gastroenteritis and
respiratory tract infections)
Antibodies destroy Schwann cells causing segmental demyelination and
inflammation of peripheral nerves.
Results in muscle weakness or paralysis that begins from the lower limbs
upwards, facial paralysis (bilateral facia n. palsy), sensory irregularities
(numbness, tingling and pain).
In acute cases whereby respiratory muscles are affected, it can be life-
threatening as such mechanical respiration is recommended.
Treatment includes plasmapheresis and intravenous immunoglobulins3/15/2023
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10. SYNAPSE  Made of presynaptic terminal; synaptic cleft; postsynaptic
membrane
1. Action potential reaches axon terminal, influx of Ca2+
2. Ca2+ facilitate the release of neurotransmitter into the
synaptic cleft
3. The neurotransmitter bind to specific receptors on the
postsynaptic membrane
4. Chemically-gated channels to open to allow NA+ influx.
 Excitatory or inhibitory of action potential depending on
neurotransmitter – glutamate, acetylcholine,
norepinephrine, aspartate, dopamine, γ-aminobutyric acid,
glycine, serotonin, enkephalins, and endorphins.
 Neurotransmitters are broken down, removed so rapidly
and re-used
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11. PARKINSON DISEASE
Progressive neurodegenerative disease
Loss of dopaminergic neurons from the substantia
nigra; cause of loss is yet unknown
Dopaminergic neurons produce dopamine and
transmit it to other neurons; participate in
pleasure, movement, motivation, intelligence, and
cognition.
Causes – Parkinson TRAPS your body. Tremor,
muscular rigidity, akinesia (no movement), postural
instability, and shuffling movement, and masklike
facial expression
Industrial toxins (manganese miners) and
poisonous MTPT (methylphenyl-
tetrahydropyridine) heroin
Levodopa, which gives some relief, although cells
still die
CLINICAL CORRELATE
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12. CLINICAL CORRELATE HUNTINGTON CHOREA
Autosomal dominant disease due to error
in the repeat of trinucleotide (CAG)n in
chromosome 4.
Atrophy of the caudate nucleus and
putamen leads to loss of neurons that
produce γ-aminobutyric acid (GABA), low
GABA
Evident at 20 – 50 years
Symptoms: presents as painful joints first
then uncontrolled flicking of joints, motor
dysfunction, aggression, depression,
dementia, and death.
Dementia is thought to be associated
with loss of the cells secreting
acetylcholine.
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13. NERVE FIBERS AND NERVE
Nerve fiber
Individual axon enveloped by a
myelin sheath
Nerve
Cordlike bundle of nerve fibers
wrapped by sheaths of connective
tissue.
Visible to the unaided eye
Usually appear whitish because of
the presence of myelin. 3/15/2023
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14. MENINGES, MENINGEAL SPACES
DURA MATER (from mesoderm); is made of dense
connective tissue and is double-layered around the
brain and single-layered around the spinal cord. Falx
cerebri, falx cerebelli and tentorium cerebelli 3/15/2023
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ARACHNOID (from neural crest cells). Middle meninx
& is a net-like membrane. Arachnoid villi project into
the venous dural sinus. Arachnoid fuses with the dura
matter at S2 level
PIA MATER (from neural crest cells): Thin; made of
highly vascularized loose connective tissue; tightly
fused to the brain & spinal cord. Continues as filum
terminale that attaches to the coccyx

15.  Inflammation of the pia mater and arachnoid
 Viral (aseptic)meningitis caused by HSV, HIV, mumps virus, & enteroviruses.
 Bacterial (pyogenic) meningitis is contagious via coughing and sneezing. Children
˂5 yrs account for ˃ 70% of total cases. This form is dangerous, it may cause
palsies of CRN III, IV, VI, & VIII, and hydrocephalus. May lead to learning
impairment, brain damage, and death sometimes within 24 hours if untreated.
 S. agalactiae & E. coli (˂1 mo.); Hemophilus influenza (1 mo. -9 yrs); S. pneumoniae
& Neisseria meningitidis (10-60 yrs); S. pneumoniae (˃60 yrs).
 Symptoms are fever, headache, stiff neck (nuchal rigidity), Kernig sign, and
alteration of consciousness
 Specific antibiotic for treatment after spinal tap to confirm the bacteria. Other CSF
findings are numerous neutrophils, ↓ glucose level, ↑ protein level
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MENINGITIS

16. MENINGIOMA
 Benign and slow-growing tumour that arises from
meningotheal arachnoid cells.
 Most common type of brain tumour (20% of primary
intracranial tumours), and 25% of spinal tumours.
 Mostly in the anterior cranial fossa (parasagittal 25%,
convexity 20%, and basal 40%).
 Micrograph shows a characteristic ‘whorling pattern and
calcified psammoma bodies’. Grown meningiomas can
create a cavity in the adjacent brain.
 Occurs within 20 and 60 years of age, most often in
women.
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17. SUBARACHNOID HEMORRHAGE
Bleeding in the subarachnoid space
Caused by rupture of cerebral
arteries and veins that cross the
subarachnoid space, or
rupture of an aneurysm on the circle
of Willis (mostly on the anterior part
of the circle) or,
less commonly, by a hemangioma -
proliferation of blood vessels
therefore forming a mass of tissue
This causes onset of severe headache
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CLINICAL CORRELATE

18. 3/15/2023
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CLINICAL CORRELATES SUBDURAL HEMATOMA
• Blood clot in the subdural space
• Caused by rupture of bridging cerebral veins
(Mostly resulting from a blow on the front or
the back of the head)
EPIDURAL HEMATOMA
• Blood clot in the subdural space caused by
the rupture of the middle meningeal arteries
or veins
• Resulting from injury near the pterion,
fracture of the greater wing of the sphenoid
bone, or a torn dural venous sinus.
• This forms a classic biconvex pattern on CT
scan or MRI

19.  Cavities inside the brain; contain cerebrospinal fluid
 Two lateral ventricles - within the cerebral hemispheres, below the corpus callosum,
and they communicate with the 3rd ventricle via interventricular foramina (of Monro).
Frontal horn, body, temporal horn, trigone, & occipital horn.
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VENTRICLES
 Third ventricle - inferior to the lateral
ventricles and superior to the thalamus;
cerebral aqueduct (of Sylvius)links the 3rd
ventricle to the 4th ventricle
 Fourth ventricle - diamond-shaped; behind
pons and medulla. Communicates with the
subarachnoid space via 2 lateral apertures
(of Luschka)and 1 median aperture (of
Magendie).
 It continues with the central canal of the
spinal cord.

20. CEREBROSPINAL FLUID (CSF)
Colourless, clear and acellular fluid of the CNS
≈500mL/day is produced, although 140-200ml bath the CNS at any given
period.
Composition: ≤5 lymphocytes/mm3 (usually sterile); pH, 7.35; specific gravity:
1.007; glucose: >45mg/dL (66% of plasma glucose; 70-100mg/dL or 3.9-5.6
mmol/L); total protein: <45 mg/dl in the lumbar cistern
Production sites: choroid plexus in the ventricles (major), and some modified
ependymal cells lining the lateral ventricles
Functions: cushions and protects the CNS from mechanical injury; floats the
CNS; keeps the CNS moist; provides nutrients to the CNS; it helps remove
metabolic wastes from nervous tissue.
Normal pressure: 80-180 mmH2O / 8-18 cmH2O
Cloudy, >100mg/dL protein level, >1000PML, ↓ glucose level (bacterial
meningitis) 3/15/2023
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21. 3/15/2023
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 CSF circulation:
CSF flows from the lateral ventricles →
interventricular foramina → 3rd ventricle
→ cerebral aqueduct → 4th ventricle → 2
lateral and a median aperture →
subarachnoid space to bath the CNS →
reabsorbed into the blood in the superior
sagittal sinus via the arachnoid villi

22. HYDROCEPHALUS
Excessive accumulation of CSF in the ventricles or subarachnoid space.
Causes are variable. Common in infants and adults ≥60 years
Communicating H.- blockage within the subarachnoid space due to
adhesions after meningitis. This causes ↑ ICP, papilledema
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Non-communicating H. – blockage of the CSF flow either
by stenosis of cerebral aqueduct (congenital aqueductal
stenosis), colloid cyst blocking interventricular foramen, or
tumour.
Hydrocephalus ex vacuo: occurs when there is a loss of
cells in the caudate nucleus, as seen in patients with
Huntington’s disease.

23. HYDROCEPHALUS cont.
Normal pressure H.- low CSF absorption, maybe due to post-traumatic
meningeal haemorrhage. CSF pressure is normal but the ventricles are dilated
distorting the thalamic adhesion (corona radiata). 3 clinical characteristics;
urinary incontinence (wet), ataxia (poor gait, wobbly), and dementia (wacky).
Pseudotumor cerebri (benign intracranial hypertension): ↑ resistance to CSF
outflow at the arachnoid villi → ↑ CSF pressure and papilledema that can
worsen vision. Occurs in obese young women
Symptoms include unusual big head, downward deviation of the eyes,
headache, nausea and vomiting, seizure, poor gait, and urinary incontinence.
Shunt is mostly used to divert the intracranial pressure to another body cavity
like the peritoneal cavity.
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24. BRAIN – (divisions)
FOREBRAIN
Telencephalon (cerebrum [805 of the 1.5kg of brain]and basal ganglia)
Cerebrum - lobes (frontal, parietal, occipital, temporal, insular, and
limbic lobes), gyri, sulci, ventricles, white matter (cerebral commissures
that interconnect the hemispheres, and internal capsule)
Basal ganglia (caudate nucleus, globus pallidus, putamen, amygdala)
Diencephalon - epithalamus, thalamus [ant. tubercle; med. and lat.
geniculate bodies; pulvinar; interthalamic adhesion, relay center]
hypothalamus (reg. pituitary gland, temp. food satiety, water balance,
sexual response, and response to emotion), subthalamus
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25. 3/15/2023
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26. BRAIN – (divisions cont.)
MIDBRAIN (Mesencephalon)
Ventral surface - cerebral peduncles [cerebral crura, substantia nigra,
tegmentum], post. perforated substances, CN III),
Dorsal surface - tectum (quadrigeminal plates [ superior colliculus, inferior
colliculus), CN IV)
HINDBRAIN
Pons ( anteriorly -CNs V, VI, VII, VIII; Posteriorly – rhomboid fossa)- control
breathing
Medulla oblongata (anteriorly – pyramids, olives, CNs IX, X, XI, XII;
posteriorly – cuneate tubercle, gracile tubercle, rhomboid fossa) - control
breathing, contracts/relaxes arterioles
Cerebellum [hemispheres, vermis, lobes, folia, fissures, tonsil, peduncles)-
precise movement coordination and time keeping
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27. 3/15/2023
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28. The inferior surface of the brain
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29. BRODMANN MAP
 Korbinian Brodmann; German;
1908
Map of the cerebral cortex that
shows about 50 distinct areas
called the Brodmann’s area
These areas are marked based
on their histological
differences
The numbers on the map are
important in identifying or
referring to a particular portion
of the cortex
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30. BRODMANN MAP Areas 3,1 & 2 - postcentral gyrus & post. part
of paracentral lobule. All sensory stimuli
terminate here
Areas 5 & 7 - interpret deeper meaning of the
sensory information
Area 4- precentral gyrus & ant. part of
paracentral lobule. Initiates contralateral
movements of voluntary muscles, especially in
the limbs.
Area 6- plays a role in the control of proximal
and axial muscles (programs complex motor
sequences & coordinates bilateral
movements
Areas 41, 42- posterior part of the superior
temporal (Heschl’s) gyrus - audition 3/15/2023
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31. BRODMANN MAP Areas 9 -12 – prefrontal cortex (social
behaviour)
Area 17 - calcarine sulcus, vision
Areas 18, 19 – visual hallucination if damaged
Area 8 – contralateral horizontal gaze
Area 34 – prepiriform and periamygdaloid
cortices, olfaction
Speech centers: Wernicke area 22 - angular
gyrus – language reception (speaks faster than
normal); Broca area (44,45) – post. part of
inferior frontal gyrus, language output
(nonfluent slow speaking)
Area 43 - parietal operculum and parainsular
cortex; taste.
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32. BLOOD SUPLY TO THE BRAIN
Arterial supply
 Left and Right Internal carotid arteries
Ant. and mid. cerebral arteries
 Left and right vertebral arteries
Post. cerebral arteries
Arteries to the cerebellum
 Circle of Willis
Venous drainage
 Superficial (bridging) veins drain into
superior sagittal sinus
 Deep veins: Great cerebral vein (of
Galen), Basal cerebral of (of Rosenthal), Int.
cerebral vein
 Venous dural sinuses receive blood from
the superficial and deep cerebral veins into
the internal jugular vein 3/15/2023
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33. CAVERNOUS SINUS
THROMBOSIS
 Formation of a thrombus in the cavernous sinus
 Ophthalmic veins  Cavernous sinus  sup. and inf.
petrosal vein  sigmoid vein
 Cause: bacterial infection (Staphylococcus).
Squeezing pimples or boil around the nose and
upper lip.
 Headache, fever, papilledema (edema of the blind
spot or nerve due to ↑ intracranial pressure),
exophthalmos, double vision, vision loss,
ophthalmoplegia (paralysis of the extrinsic muscles -
LR mostly), chemosis (fluid accumulation in the
conjunctivae), slow pupillary responses, ptosis, and
meningitis.
 CNs III, IV, V1, V2, and VI
 High dose of antibiotics, surgery may be needed to
drain the sinus.
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34. CLINICAL CORRELATE
 Cerebral concussion is an abrupt, brief loss of consciousness immediately after
a severe head injury. Recovery <6 hours is excellent but >6 hours → brain tissue
damage.
 Chronic traumatic encephalopathy (punch drunk syndrome) – unsteady gait,
weakened leg muscles, tremors in the hand, and delay in speaking.
 Shaking baby syndrome and car accident (sudden stop from high acceleration)
can cause diffuse axonal injury
 Cerebral laceration – a depressed fracture that tears blood vessels in the brain
causing hemorrhage into the subarachnoid space, ↑ICP and causing cerebral
compression
 Cisternal puncture through atlanto-occipital membrane into the
Cerebellomedullary (magna) cistern for the collection of CSF in infants and
children. Lumbar puncture (spinal tap) for adults 3/15/2023
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35. CLINICAL CORRELATE
 CSF leakage into the nose (CSF rhinorrhea) or the ears (CSF otorrhea) if the floor
of the anterior and middle cranial fossae are fractured respectively
 Transient ischemic attacks (TIAs): a neurologic symptom due to obstruction in the
blood supply to the brain. It lasts mostly for a few minutes but may persist for up
to an hour. Symptoms may be staggering, dizziness, light-headedness, fainting,
and paresthesia. Persons with TIAs are at increased risk for myocardial infarction
and ischemic stroke
 Ischemic stroke – caused by embolism or occlusion of cerebral arteries
 Hemorrhagic stroke – caused by rupture of an artery or aneurysm
 Exogenous substances (herpesvirus, polio virpoliovirus, and tetanus toxin) move
by retrograde transport (movement from the axon terminal to soma) to affect
the cell body. The opposite is antegrade axonal transport for proteins and
vesicles. 3/15/2023
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