Huntington's Disease –
A. Cause: Hereditary (too much dopamine)
B. Prognosis: Progressive, fatal (Usually w/in 15 years of onset of symptoms)
C. Signs: Large amts. of huntingtin protein builds up in the basal nuclei & eventually the cerebral
cortex, causing tissue degeneration & death
D. Symptoms: Chorea - Continual, involuntary movement. Hyperkinesis Eventually marked mental
deterioration
E. Treatment: No cure
1. Medications that block the effect of dopamine in the basal nuclei
2. +/- stem cell research to provide fetal tissue implantation of basal nuclei
II. Parkinson's Disease –
A. Cause: Unknown (too little dopamine)
B. Signs: Degeneration of dopamine-releasing neurons in the substantia nigra, causing over-activity of
the basal nuclei
C. Symptoms: Persistent tremor, awkward posture, shuffling gait, slow initiation of movement, stiff
facial expression
D. Treatment: No cure
1. L-dopa can alleviate symptoms but has bad SEs, & eventually becomes ineffective
2. Deprenyl is safer with fewer SEs
3. +/- stem cell research to explore intra-brain transplants of dopamine-producing cells
III. Alzheimer's Disease –
A. Cause: Unknown (Genetics plays a role)
B. Prognosis: Progressive, eventually fatal
C. Signs: ACh shortage, & structural changes in brain areas involved with memory & cognition
1. Neuronal degeneration. Plaques of beta amyloid peptide & tangles of tau
2. Increased Ca++ influx into neurons
D. Symptoms: Memory loss, decreased attention span, language loss, personality changes,
hallucinations, mental deterioration
E. Treatment: No cure
1. Medications inhibiting ACh breakdown help alleviate symptoms
I.
I.
Peripheral nervous system: Provide brain with link to environment
A. Sensory receptors (Afferents)
B. Peripheral nerves - Cranial & spinal nerves (& associated ganglia)
C. Efferent motor endings
D. Cranial nerves: (emanate from ventral surface of brain & extend out foramen magnum)
12 pair –
a. 1st 2 - Optic (II) & Olfactory (I) originate from forebrain
b. All others extend from brain stem
c. Vagus (X) extends into abdomen
d. All others innervate only the head & neck.
1. Olfactory (I) –
a. Sensory (smell)
b. From nasal mucosa to olfactory bulbs
c. Olfactory bulbs & tracts are really brain structures
d. Terminates in frontal lobe of cortex
2. Optic (II) –
a. Sensory (vision)
b. Actually part of the optic tract (brain structure) to optic chiasma to....
c. terminate in occipital lobe of cortex
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3. Oculomotor (III) –
a. Motor (mostly)
b. Extrinsic eyeball muscles, lens accommodation,
pupil constriction
c. Has some parasympathetic fibers
 Motor PS to iris constrictors & lens shapers
from midbrain
d. From midbrain to eyeball muscles
4. Trochlear (IV) –
a. Motor (mostly)
b. Extrinsic eyeball muscles
c. From midbrain to eyeball muscles
5. Trigeminal (V) –
a. Sensory & motor
b. Largest
c. Three branches:
 Sensory to face (Touch, pain, temp.)
 From face to pons
 Motor to muscles of mastication
 To muscles of mastication from pons
6. Abducens (VI) –
a. Motor (mostly)
b. Abduction (Lateral movement) of eyeball
c. From Pons to orbital muscles
7. Facial (VII) –
a. Sensory & motor
b. Motor to facial muscles (facial expression)
 From pons to facial skeletal muscles
c. Sensory to tongue (taste)
 From taste buds to pons
d. Has some parasympathetic fibers
 Motor PS impulses to tear & salivary glands
8. Vestibulocochlear (auditory or acoustic) (VIII) –
a. Sensory
b. Hearing & balance
c. From Inner ear to brain stem
9. Glossopharyngeal (IX) –
a. Sensory & motor
b. Sensory to tongue (taste)
 Sensory fibers from pharyngeal muscles & posterior tongue to medulla
 From Chemoreceptors in carotid sinus (to monitor CO2 & O2 levels) to medulla
c. Motor to pharynx
 From medulla to pharyngeal muscles
d. Swallowing, gag reflex, salivary glands
e. Has some parasympathetic fibers
 Motor PS fibers to parotid salivary gland from medulla
10. Vagus (X) –
a. Sensory & motor
b. Extends to thorax & abdomen
c. Sensory (taste)
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 From posterior tongue & pharynx to medulla.
d. Motor (swallowing)
 To skeletal muscles of pharynx & larynx from medulla.
e. Autonomic NS functions (has parasympathetic fibers)
 Motor PS fibers from medulla to heart, lungs, abdominal viscera
 Sensory PS from abdominal & thoracic viscera to medulla
 Sensory PS from pressoreceptors in carotid sinus (blood pressure regulation) &
chemoreceptors in carotid & aortic bodies (respiratory regulation)
f. Innervates visceral muscles (see above)
11. Accessory (spinal accessory) (XI) –
a. Motor (mostly)
b. Joins with a spinal nerve, which innervates large neck muscles from medulla
c. Motor (swallowing)
 Joins with Vagal branches to larynx, pharynx, & soft palate from medulla
12. Hypoglossal (XII) –
a. Motor (mostly)
b. Muscles of tongue (speech & swallowing)
 From medulla to tongue muscles
E. Spinal Nerves - From SC to supply all body parts except head & neck
1. 31 pair
2. All are mixed nerves (sensory & motor)
3. Named according to where they originate in the SC
a. Cervical-Spinal - (C1-C8) - 8 pair
b. Thoracic - (T1-T12) - 12 pair
c. Lumbar - (L1-L5) - 5 pair
d. Sacral - (S1-S5) - 5 pair
e. Coccygeal - (C0) - 1 pair
4. Connect to the SC by a ventral root (motor) & dorsal root (sensory)
a. Ventral root fibers - (also contain some ANS efferent fibers)
 From anterior horn neurons
 Innervate skeletal muscles
b. Dorsal root fibers –
 From sensory neurons in dorsal root ganglia
 Conduct impulses from peripheral sensory receptors to SC
c. Both roots join prior to emerging from the vertebral column
5. Divide into (small) dorsal ramus, (large) ventral ramus, & tiny meningeal branch
a. Each ramus is mixed (sensory/motor)
b. Dorsal rami supply voluntary muscles & skin of the back
c. Ventral rami supply rest of trunk & limbs
 Most ventral rami join into complex nerve plexuses in the cervical, brachial, lumbar, &
sacral regions & serve the limbs
 Advantage - When one segment is damaged, an entire limb is not paralyzed
 Ventral rami of T1-T12 form the intercostal nerves
 Give off cutaneous branches to the skin
6. Cervical Plexus - (1st 4 cervical nerves) –
a. Most cutaneous sensory (superficial) to neck, ear, back of head, & shoulder
b. Some motor (deep) to anterior aspect of neck
 Phrenic nerve - Motor & sensory to diaphragm
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7. Brachial Plexus – Very large, complex. Formed by the 5 ventral rami of C5-T1
Upper, middle, & lower trunks
(small nerve fibers branch off continually
Anterior & posterior divisions of each
along the way to supply muscles/skin of shoulder & thorax)
Lateral, medial, posterior cords
Ends in the axilla to give rise to
the main 5 limb nerves
a. Axillary - Shoulder muscles (deltoid, teres minor), joint capsule, skin
b. Musculocutaneous – Biceps, brachialis, & cutaneous to lateral forearm
c. Median – Flexors, skilled wrist/finger movements, & cutaneous to anterior forearm
d. Ulnar – Medial hand/wrist muscles & skin
e. Radial – Upper limb extensors, among others
8. Lumbar plexus – (lumbosacral plexus) – Overlapping fibers of spinal nerves L1-L4 & L4-S4
a. Parts of abdominal wall
b. Anterior & medial thigh –
 Femoral nerve - Thigh flexors & knee extensors
 Opturator nerve – Adductor muscles
9. Sacral plexus – (L4-S4 immediately caudal to the lumbar plexus)
a. Pelvic structures & perineum
 Gluteal nerves (superior & inferior) – Pelvic area
 Pudendal nerve – Perineum
b. Buttocks & lower limb
 Sciatic nerve (Tibial & Common Fibular – Diverge just proximal to the knee) – Thigh
extensors, knee flexors, & adductor
 Tibial nerve – Posterior lower leg
 Common Fibular nerve – (Superficial & deep) – Knee joint & anteriolateral leg
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10. Dermatome – The area of skin innervated by a single spinal nerve
a. Every spinal nerve but C1 innervates a dermatome
b. Uniform, almost horizontal, in-line w/spinal nerve
 Ventral rami of C5-T1-2 – Skin of upper limbs
 Lumbar nerves – Anterior thighs & legs
 Sacral nerves – Posterior surfaces of lower limbs
11. Joint Innervation –
a. Hilton’s law – Any nerve serving a muscle causing movement at a joint also innervates that
joint & the skin covering it
b. Peripheral Motor Endings - (neurotransmitters) - Descending efferent circuits
c. Neuromuscular junction - The area of innervation of somatic skeletal muscle (effectors)
d. Axon terminals - Contain synaptic vesicles with ACh (Acetylcholine)
 Remember transmission of nerve impulses via neurotramsmitters!
e. Autonomic nerve junctions - Between ANS (motor endings) & visceral effectors
 Visceral effectors = Smooth & cardiac muscle + visceral glands
 Varicosities - Knob-like swellings w/ synaptic vesicles & mitochondria
 Contain ACh or norepinephrine
 Synaptic cleft is wider, so visceral motor responses usually slower
12. Motor integration –
a. Cerebral cortex - Conscious motor pathways
b. Cerebellum + basal nuclei = Ultimate planner & coordinator of complex motor activity
 Fixed action patterns - Stereotyped, sequential motor actions triggered internally, or by
appropriate environmental $
c. Segmental - Lowest circuit
 Spinal cord circuits - Anterior horn neurons within a single SC segment, which $ a
specific group of muscle fibers
 Central Pattern Generators (CPGs) - Circuits controlling locomotion & frequently
repeated motor activities
d. Projection - Upper motor neurons of the motor cortex which initiate the direct (pyramidal)
system + brain stem motor areas over-seeing the indirect (multi-neuronal) system
 Project to the SC & help control reflex & fixed-action motor activity + discrete,
voluntary skeletal muscle movement
 Send information about what's happening to the higher command centers
e. Pre-command - Highest level (Cerebellum & basal nuclei) - Control outputs of the cortex &
brain stem motor centers. Cortex says " I wanna move my toe", then pre-command areas
take over to lay the groundwork for the movement (Provide proper timing/pattern) Then, the
cortex decides whether to go through with it. (carry out the command)
 Precisely start/stop movements
 Coordinate movement w/ posture
 Block unwanted movement
 Monitor muscle tone
 Cerebellum is the key center for sensorimotor integration & control
 Basal nuclei - Involved in more complex actions
 Inputs from all cortical areas, sending output to premotor & prefrontal areas
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