1. Peripheral Nervous System
Chapter 13 –
Cranial Nerves
Chapter 14 –
Spinal Nerves
Somatic Reflexes

2. The Cranial Nerves
12 pair of nerves that arise from brain & exit through foramina leading to muscles, glands & sense organs in head & neck
Input & output remains ipsilateral except CN II & IV

3. Photograph of Cranial Nerves

4. Olfactory Nerve Provides sense of smell
Damage causes impaired sense of smell

5. Optic Nerve
Provides vision
Damage causes blindness in visual field

6. Oculomotor Nerve
Provides some eye movement, opening of eyelid, constriction of pupil, focusing
Damage causes drooping eyelid, dilated pupil, double vision, difficulty focusing & inability to move eye in certain directions

7. Trochlear Nerve Provides eye movement
Damage causes double vision & inability to rotate eye inferolaterally

8. Trigeminal Nerve
Main sensory nerve to face (touch, pain and temperature) and muscles of mastication
Damage produces loss of sensation & impaired chewing

9. Abducens Nerve Provides eye movement
Damage results in inability to rotate eye laterally & at rest eye rotates medially

10. Facial Nerve
Provides facial expressions, sense of taste on anterior 2/3’s of tongue, salivary glands and tear, nasal & palatine glands
Damage produces sagging facial muscles & disturbed sense of taste (missing sweet & salty)

11. Branches of Facial Nerve
Clinical test: Test anterior 2/3’s of tongue with substances such as
sugar, salt, vinegar, and quinine; test response of tear glands to
ammonia fumes; test motor functions by asking subject to close eyes,
smile, whistle, frown, raise eyebrows, etc.

12. Vestibulocochlear Nerve
Provides hearing & sense of balance
Damage produces deafness, dizziness, nausea, loss of balance & nystagmus

13. Glossopharyngeal Nerve
Provides control over swallowing, salivation, gagging, sensations from posterior 1/3 of tongue, control of BP and respiration
Damage results in loss of bitter & sour taste & impaired swallowing

14. Vagus Nerve Provides swallowing, speech, regulation of viscera
Damage causes hoarseness or loss of voice, impaired swallowing & fatal if both are cut

15. Accessory Nerve Provides swallowing, head, neck & shoulder movement
Damage causes impaired head, neck & shoulder movement, head turns towards injured side

16. Hypoglossal Nerve
Provides tongue movements of speech, food manipulation & swallowing
Damage results in inability to protrude tongue if both are damaged or deviation towards injured side & ipsilateral atrophy if one side is damaged

17. Cranial Nerve Disorders
Trigeminal neuralgia (tic douloureux)
recurring episodes of intense stabbing pain in trigeminal nerve area (near mouth or nose)
pain triggered by touch, drinking, washing face
treatment is cutting of nerve
Bell palsy
degenerative disorder of facial nerve
paralysis of facial muscles on one side
may appear abruptly & disappear within 3-5 weeks

18. PET Scans during a Language Task

19. Anatomy of a Nerve A nerve is a bundle of nerve fibers (axons)
Epineurium covers nerves, perineurium surrounds a fascicle & endoneurium separates individual nerve fibers
Blood vessels penetrate only to the perineurium

20. Anatomy of Ganglia in the PNS
Cluster of neuron cell bodies in nerve in PNS
Dorsal root ganglion is sensory cell bodies
fibers pass through without synapsing

21. Branches of a Spinal Nerve
Spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
Each has dorsal and ventral ramus.

22. Shingles Skin eruptions along path of nerve
Varicella-zoster virus (chicken pox) remains for life in dorsal root ganglia
Occurs after age 50 if immune system is compromised
No special treatment

23. Nerve Plexuses
Ventral rami branch & anastomose repeatedly to form 5 nerve plexuses
cervical in the neck, C1 to C5
supplies neck and phrenic nerve to the diaphragm
brachial in the armpit, C5 to T1
supplies upper limb and some of shoulder & neck
lumbar in the low back, L1 to L4
supplies abdominal wall, anterior thigh & genitalia
sacral in the pelvis, L4, L5 & S1 to S4
supplies remainder of butt & lower limb
coccygeal, S4, S5 and C0

24. Cutaneous Innervation & Dermatomes
Each spinal nerve receive sensory input from a specific area of skin called dermatome
Overlap at edges by 50%
a total loss of sensation requires anesthesia of 3 successive spinal nerves

25. Nature of Somatic Reflexes
Quick, involuntary, stereotyped reactions of glands or muscle to sensory stimulation
automatic responses to sensory input that occur without our intent or often even our awareness
Functions by means of a somatic reflex arc
stimulation of somatic receptors
afferent fibers carry signal to dorsal horn of spinal cord
interneurons integrate the information
efferent fibers carry impulses to skeletal muscles
skeletal muscles respond

26. The Muscle Spindle
Sense organs that monitor the length of skeletal muscles (proprioceptors) = stretch receptors
respond to onset of stretch or prolonged stretch
4 to 10 mm long modified skeletal muscle cells
intrafusal fibers that respond to gamma motor neurons & are wrapped with afferent fibers that respond to stretch

27. The Stretch (Myotatic) Reflex
When a muscle is stretched, it contracts & maintains increased tonus (stretch reflex)
helps maintain equilibrium & posture
head starts to tip forward as you fall asleep
muscles contract to raise the head
stabilize joints by balancing tension in extensors & flexors smoothing muscle actions
Very sudden muscle stretch causes tendon reflex
knee-jerk (patellar) reflex is monosynaptic reflex
testing somatic reflexes helps diagnose many diseases
Reciprocal inhibition prevents muscles from working against each other

28. The Patellar Tendon Reflex Arc

29. Flexor Withdrawal Reflexes
Flexor(withdrawal) reflex occurs during withdrawal of foot from pain
polysynaptic reflex arc
neural circuitry in spinal cord controls sequence and duration of muscle contractions

30. Crossed Extensor Reflexes
Crossed extensor reflex maintains balance by extending other leg
intersegmental reflex extends up and down the spinal cord
contralateral reflex arcs explained by pain at one foot causes muscle contraction in other leg

31. Golgi Tendon Reflex
Proprioceptors in a tendon near its junction with a muscle -- 1mm long, encapsulated nerve bundle
Excessive tension on tendon inhibits motor neuron
muscle contraction decreased
Also functions when muscle contracts unevenly

32. Spinal Cord Trauma 10-12,000 people/ year are paralyzed
55% occur in traffic accidents
This damage poses risk of respiratory failure
Early symptoms are called spinal shock
Tissue damage at time of injury is followed by post-traumatic infarction