1. The Peripheral Nervous System and Reflex Activity: Part B13
The Peripheral Nervous System and Reflex Activity: Part B

2. “On occasion, our trusty truck acts funny—very good vehicle anyhow”
Cranial Nerves
Twelve pairs of nerves associated with the brain
Most are mixed in function; two pairs are purely sensory
Each nerve is identified by a number (I through XII) and a name
“On occasion, our trusty truck acts funny—very good vehicle anyhow”

3. Hypoglossal nerve (XII)
Filaments of
olfactory
nerve (I)
Frontal lobe
Olfactory bulb
Olfactory tract
Optic nerve
(II)
Temporal lobe
Optic chiasma
Infundibulum
Optic tract
Facial
nerve (VII)
Oculomotor
nerve (III)
Vestibulo-
cochlear
nerve (VIII)
Trochlear
nerve (IV)
Trigeminal
nerve (V)
Glossopharyngeal
nerve (IX)
Abducens
nerve (VI)
Vagus nerve (X)
Cerebellum
Accessory nerve (XI)
Medulla
oblongata
Hypoglossal nerve (XII)
(a)
Figure 13.5 (a)

4. Yes (hearing and balance)
Cranial nerves
I – VI
Sensory
function
Motor
function
PS*
fibers I
Olfactory
Yes (smell) No No II
Optic
Yes (vision) No No
III
Oculomotor No
Yes
Yes IV
Trochlear No
Yes No V
Trigeminal
Yes (general
sensation)
Yes No VI
Abducens No
Yes No
Cranial nerves
VII – XII
Sensory
function
Motor
function
PS*
fibers
VII
Facial
Yes (taste)
Yes
Yes
VIII
Vestibulocochlear
Yes (hearing
and balance)
Some No IX
Glossopharyngeal
Yes (taste)
Yes
Yes X
Vagus
Yes (taste)
Yes
Yes XI
Accessory No
Yes No
XII
Hypoglossal No
Yes No
*PS = parasympathetic
(b)
Figure 13.5 (b)

5. I: The Olfactory Nerves
Arise from the olfactory receptor cells of nasal cavity
Pass through the cribriform plate of the ethmoid bone
Fibers synapse in the olfactory bulbs
Pathway terminates in the primary olfactory cortex
Purely sensory (olfactory) function

6. Table 13.2

7. II: The Optic Nerves
Arise from the retinas
Pass through the optic canals, converge and partially cross over at the optic chiasma
Optic tracts continue to the thalamus, where they synapse
Optic radiation fibers run to the occipital (visual) cortex
Purely sensory (visual) function

8. Table 13.2

9. III: The Oculomotor Nerves
Fibers extend from the ventral midbrain through the superior orbital fissures to the extrinsic eye muscles
Functions in raising the eyelid, directing the eyeball, constricting the iris (parasympathetic), and controlling lens shape

10. Table 13.2

11. IV: The Trochlear Nerves
Fibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle
Primarily a motor nerve that directs the eyeball

12. Table 13.2

13. V: The Trigeminal Nerves
Largest cranial nerves; fibers extend from pons to face
Three divisions
Ophthalmic (V1) passes through the superior orbital fissure
Maxillary (V2) passes through the foramen rotundum
Mandibular (V3) passes through the foramen ovale
Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

14. Table 13.2

15. Table 13.2

16. VI: The Abducens Nerves
Fibers from the inferior pons enter the orbits via the superior orbital fissures
Primarily a motor, innervating the lateral rectus muscle

17. Table 13.2

18. VII: The Facial Nerves
Fibers from the pons travel through the internal acoustic meatuses, and emerge through the stylomastoid foramina to the lateral aspect of the face
Chief motor nerves of the face with 5 major branches
Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands
Sensory function (taste) from the anterior two-thirds of the tongue

19. Table 13.2

20. Table 13.2

21. VIII: The Vestibulocochlear Nerves
Afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla border
Mostly sensory function; small motor component for adjustment of sensitivity of receptors

22. Table 13.2

23. IX: The Glossopharyngeal Nerves
Fibers from the medulla leave the skull via the jugular foramen and run to the throat
Motor functions: innervate part of the tongue and pharynx for swallowing, and provide parasympathetic fibers to the parotid salivary glands
Sensory functions: fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors

24. Table 13.2

25. X: The Vagus Nerves
The only cranial nerves that extend beyond the head and neck region
Fibers from the medulla exit the skull via the jugular foramen
Most motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal viscera
Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx

26. Table 13.2

27. XI: The Accessory Nerves
Formed from ventral rootlets from the C1–C5 region of the spinal cord (not the brain)
Rootlets pass into the cranium via each foramen magnum
Accessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid muscles

28. Table 13.2

29. XII: The Hypoglossal Nerves
Fibers from the medulla exit the skull via the hypoglossal canal
Innervate extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speech

30. Table 13.2