peripheral nervous system & reflex activity part b: cranial nerves prepared by janice meeking...

Peripheral Nervous System & Reflex Activity

Part B: Cranial Nerves

Prepared by Janice Meeking & W. Rose.

Figures from Marieb & Hoehn 8th, 9th ed.

Portions copyright Pearson Education

Copyright © 2010 Pearson Education, Inc.

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”

Copyright © 2010 Pearson Education, Inc. Figure 13.5 (a)

Frontal lobe

Temporal lobe

InfundibulumFacialnerve (VII)Vestibulo-cochlearnerve (VIII)Glossopharyngealnerve (IX)Vagus nerve (X)Accessory nerve (XI)

Hypoglossal nerve (XII)

(a)

Filaments ofolfactory nerve (I)

Olfactory bulb

Olfactory tract

Optic chiasma

Optic nerve(II)

Optic tractOculomotornerve (III)Trochlearnerve (IV) Trigeminalnerve (V) Abducensnerve (VI)CerebellumMedullaoblongata

Copyright © 2010 Pearson Education, Inc. Figure 13.5 (b)

*PS = parasympathetic(b)

Cranial nervesI – VI

I

II

III

IV

V

VI

Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

Yes (smell)

Yes (vision)

No

No

Yes (generalsensation)

No

No

No

Yes

Yes

Yes

Yes

No

No

Yes

No

No

No

Cranial nervesVII – XII

Sensoryfunction

Motorfunction

PS*fibers

Sensoryfunction

Motorfunction

PS*fibers

VII

VIII

IX

X

XI

XII

Facial

Vestibulocochlear

Glossopharyngeal

Vagus

Accessory

Hypoglossal

Yes (taste)

Yes (hearingand balance)

Yes (taste)

Yes (taste)

No

No

Yes

Some

Yes

Yes

Yes

Yes

Yes

No

Yes

Yes

No

No


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


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


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


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


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


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


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


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


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


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


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


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

Cranial Nerve Testinghttp://library.med.utah.edu/neurologicexam/html/cranialnerve_normal.html http://library.med.utah.edu/neurologicexam/html/cranialnerve_abnormal.html

Abnormal: “Cranial nerves 3, 4, and 6 versions” 1

Normal: “Vestibulo-ocular” (this tests III and VIII)

Abnormal: “Cranial Nerve 12- Motor” 3

If time allows: Abnormal: “Cranial nerves 3, 4, and 6 ductions” 2

If time allows: Normal: “Cranial Nerve 12- Motor”

1. Versions: binocular tests, part of a regular exam. Pt. 1 can’t abduct L, i.e. n.6 (L) palsy. Pt.2 limited adduct, elevate, depress L eye, also shows ptosis-+ & dilated pupil, i.e. n.3 (L) palsy.

2. Duction (monocular) tests done iff version results abnormal. Pt can’t medially rotate either eye. Observe nystagmus upon abduction of each eye. This & other results (not shown) suggest bilateral internuclear ophthalmoplegia, often caused by demyelinating lesion affecting medial longitudinal fasciculus (MLF) bilaterally. Adduction defect occurs due to disruption of MLF connections between the abducens nucleus and the lower motor neurons in the oculomotor nucleus that innervate the medial rectus muscle.

3. Atrophy, weakness, r. deviation of tongue due to lesion of r. cranial nerve 12.

Movies from the Neurologic Exam and PediNeurologic Exam websites by Paul D. Larsen, M.D., University of Nebraska Medical Center and Suzanne S. Stensaas, Ph.D., University of Utah School of Medicine. Additional materials for Neurologic Exam are drawn from resources provided by Alejandro Stern, Stern Foundation, Buenos Aires, Argentina; Kathleen Digre, M.D., University of Utah; and Daniel Jacobson, M.D., Marshfield Clinic, Wisconsin.

http://library.med.utah.edu/neurologicexam/html/cranialnerve_abnormal.html

http://library.med.utah.edu/neurologicexam/html/cranialnerve_abnormal.html

peripheral nervous system & reflex activity part b: cranial nerves prepared by janice meeking...

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