Lab Activity 19 & 20

Cranial Nerves

General Senses

Portland Community CollegeBI 232

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Cranial Nerves

• Nerves that originate from the brain rather than the spinal cord

• Part of the peripheral nervous system (not the central nervous system)

• May contain one or more of the following:• Sensory• Somatic Motor (voluntary movement)• Parasympathetic Motor (involuntary “rest and

digest” part of the autonomic nervous system)

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CN I: Olfactory Nerve

• Function: • Sensory for smell

• Test: Have patient identify aromatic substances like vanilla or coffee (avoid irritating substances like smelling-salts, cloves, mint)

• Symptoms of nerve damage: Anosmia: diminished or absent sense of smell

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CN II: Optic Nerve

• Function: • Sensory for vision

• Tests: 1. Eye chart

2. Check peripheral vision

3. Funduscopic exam

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CN II: Optic Nerve

• Optic chiasm: Fibers from the nasal half of each retina cross over to the opposite side of the brain.

• Symptoms of nerve damage:• Loss of vision (peripheral

or central)• Abnormal funduscopic

appearance

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CN II: Optic Nerve PathologyPapilledema. Note swelling of the disc, hemorrhages, and exudates, with preservation of the physiologic cup.

Proliferative Diabetic Retinopathy. Note the multiple hemorrhages throughout the retina.

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Cranial Nerves III, IV & VI(Control Eye Movements)

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CN III: Oculomotor nerve• Function:

• Somatic Motor to extraocular muscles (voluntarily move the eye)

• Parasympathetic (motor) to iris and lens (pupillary constriction)

• Tests: 1. Check pupils for size, shape and equality2. Shine light in each eye and check for pupil constriction 3. Have patient follow an object in all directions to check

for symmetric eye movements

Originates in the midbrain

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CN III: Oculomotor Nerve Injury

• Symptoms of nerve damage:• Double vision (diplopia): The affected eye

turns outward when the unaffected eye looks straight ahead

• The affected eye can move only to the middle when looking inward and cannot look upward and downward.

• Ptosis: eyelid droop• Pupil may be dilated and sometimes fixed

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Oculomotor Nerve Injury Right Eye

Normal side

Injured side

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Pupillary Reflex

Efferent Afferent

Consensual reflex: Both pupils should constrict at the same time

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CN IV: Trochlear Nerve

• Function: • Somatic motor to superior oblique muscle of the eye.

• Test: Check eye movements• Symptoms of nerve damage:

• Outward rotation of the affected eye • Vertical diplopia

Injured sideNormal side

Originates in the midbrain

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CN VI: Abducens Nerve

• Function: • Somatic Motor to lateral rectus

muscle of the eye.• Test: Check eye movements• Symptoms of nerve damage:

• The affected eye will tend to be deviated inward because of the unopposed action of the medial rectus muscle.

• Cannot move eyeball laterally beyond the midpoint Injured

sideNormal

side

Originates in the pons

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CN V: Trigeminal Nerve

3 Branches

1. Ophthalmic

2. Maxillary

3. Mandibular

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CN V: Trigeminal Nerve

• Function: • Somatic Motor (mandibular branch) to

muscles of mastication (chewing)• Sensory (all branches)to face and

cornea.

Originates in the pons

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CN V: Trigeminal NerveTest: Have patient bite down while you palpate the masseter muscle

Test: Touch patient with an open paperclip and ask “sharp or dull”

Test: Touch cornea with a wisp of cotton. Patient should blink

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CN V: Trigeminal Nerve

• Symptoms of nerve damage:• Inability to firmly bite down (mandibular branch

only)• Loss of sensation (each branch can be affected

independently)• Loss of corneal reflex (may indicate brain stem

injury)• Trigeminal Neuralgia (Tic Douloureux):

debilitating intermittent pain on one side of the face

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CN VII: Facial Nerve

5 Branches1. Temporal2. Zygomatic3. Buccal4. Mandibular5. Cervical

• Function: • Somatic Motor to muscles of facial expression• Parasympathetic (motor) to lacrimal and salivary

glands• Sensory taste to anterior 2/3 tongue

Originates in the pons

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CN VII: Facial Nerve

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CN VII: Facial Nerve Testing

• Tests:1. Check taste on anterior 2/3 of

tongue by having patient taste sugar, salt, sour and bitter

2. Check symmetry of facial muscles:• Close eyes, smile, whistle, puff

out cheeks (make funny faces)3. Check tearing with ammonia

fumes

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CN VII: Facial Nerve

• Symptoms of nerve damage:• Mild weakness to total paralysis of facial

muscles (may include twitching),• Drooping eyelid• Drooping corner of the mouth• Drooling or dry mouth• Impairment of taste• Excessive tearing in the eye or dry eye

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CN VII: Facial Nerve Injury (Bell’s Palsy)

Paralyzed facial muscles

Patients can still feel their face because sensory is supplied by the trigeminal nerve

Injured side

Normal side

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CN VIII: Vestibulocochlear

• Function: Sensory • Vestibular system for balance & equilibrium• Cochlea for hearing

• Tests:• Auditory component of the nerve:

• Hearing test• Vestibular control of balance and movement:

• Romberg test (tests equilibrium)

Originates in the medulla

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CN VIII: Vestibulocochlear Tests

• Simple hearing test:• Rub fingers together near the ear

and ask “right or left” If there is lateralization (hearing louder on one side) there is a problem

• Other hearing tests:• Performed by an audiologist with special

equipment to determine tones, frequencies and degree of hearing loss

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CN VIII: Vestibulocochlear TestsRomberg Test

• Have patient stand with arms at side and feet together

• Have patient stand with their eyes closed

• Stand close to prevent falls• Normally, they should maintain

position for 20 seconds with only minimal swaying• If they loose their balance, they have

failed the equilibrium test.

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CN IX: Glossopharyngeal

• Function: • Somatic Motor to muscles of pharynx• Parasympathetic (motor) to salivary glands• Sensory to pharynx and taste to posterior tongue

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CN IX: Glossopharyngeal

• Tests: • Gag reflex: Touch each side of the throat with

the tongue depressor• Evaluate swallowing movements • Say AHH, and watch the palate

and uvula elevate. • Evaluate taste on posterior 1/3 of tongue

• Symptoms of nerve damage: • Loss of gag reflex• Difficulty swallowing• Loss of taste

Originates in the medulla

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CN X: Vagus Nerve

• Function: • Somatic Motor to

muscles of pharynxand larynx

• Parasympathetic (motor) fibers of the heart and other viscera

• Sensory to pharynx and larynx

Originates in the medulla

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CN X: Vagus Nerve

• Test:• Inspect palate• Test gag reflex

• Symptoms of nerve damage: • Loss of gag reflex• Difficulty swallowing• Hoarse voice

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CN XI: Accessory Nerve

• Function: Somatic Motor to sternocleidomastoid and trapezius muscles

Originates in the medulla

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CN XI: Accessory Nerve

• Test:• Shrug shoulders against

resistance• Turn head against

resistance.

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CN XI: Accessory Nerve

• Symptoms of nerve damage:• Weakness• Uneven

shoulders• Winged

scapula

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CN XII: Hypoglossal Nerve

• Function: Somatic Motor to tongue

Originates in the medulla

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Hypoglossal Nerve Injury

• Test:• Ask patient to stick out

tongue• Symptoms of nerve

damage: • When paralyzed, the tongue

will point to the damaged side

Normal side

Injured side

Lab Activity 20

General Senses

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General Senses: Receptors

• Nociceptors: Pain receptors• Thermoreceptors: Temperature receptors (free

nerve endings)• Chemoreceptors: Detect small changes in the

concentration of specific chemicals or compounds• Mechanoreceptors: Sensitive to stimuli that distort

their cell membranes (contain mechanically gated ion channels)• Tactile receptors• Baroreceptors• Proprioceptors

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Classes of Mechanoreceptors• Tactile receptors: sensations of touch, pressure and vibration

• Free nerve endings• Root hair plexus• Tactile discs (Merkel’s discs)• Tactile corpuscles (Meissner’s corpuscles)• Lamellated corpuscles (Pancinian corpuscles)

• Baroreceptors: Detect pressure changes in the walls of blood vessels and portions of the digestive, reproductive and urinary tracts

• Proprioceptors: Monitor the positions of joints and muscles.

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Pancinian Corpuscle (aka: Lamellated Corpuscle)

• Lie deep in the dermis• Respond only when deep pressure is first applied• Monitor high frequency vibrations

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Meissner’s Corpuscle (aka: Tactile Corpuscle)

• Lie in the dermal papillae of the skin• Respond to light touch

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The End