Structure, function and assessments of cranial nerves ... · Cranial Nerves • Exchange...

Structure, function and

assessments of cranial nerves:

Part 1 (CN 1-7)

MSTN121 - Neurophysiology

Session 12

Department of Myotherapy

Session Overview

• The four functions of the cranial nerves (CNs).

• Understanding each CNs 1-7 by number, name, function(s), reflex

activity (if any), and connection to the brain.

Cranial Nerves

• Exchange information

between the peripheral

nervous system (PNS) and

the central nervous system

(CNS).

• Serve sensory, motor, and

autonomic functions.

• Differ from spinal nerves in

specialization; some are only

motor, others are only

sensory, and some are both

sensory and motor.

www.endeavour.edu.au© Endeavour College of Natural Health

(Lundy-Ekman, 2018, p. 386)Image: (Lundy-Ekman, 2018, p. 387)

Cranial Nerves (CNs) have four functions:

1. Supply motor innervation to the muscles of the face, eyes, tongue, jaw,

and two neck muscles

2. Transmit somatosensory information from the skin and muscles of the

face and from the temporomandibular joint (TMJ)

3. Transmit special sensory information related to visual, auditory,

vestibular, gustatory, olfactory, and visceral sensations

4. Provide parasympathetic regulation of pupil size, curvature of the lens of

the eye, heart rate, blood pressure, breathing, and digestion


Cranial Nerves Function

(Lundy-Ekman, 2018, p. 386)

© Endeavour College of Natural Health

Cranial

Nerves

Image: (Lundy-Ekman, 2013, p. 388)


Cranial Nerve 1: Olfactory

• Olfactory nerve is sensory.

• Sense of smell is dependent on

olfactory nerve function.

• Connection to the brain: inferior

frontal lobe.

• Much of the information attributed

to taste is olfactory in origin

because the information from taste

buds is limited to chemoreceptors

for salty, sweet, sour, umami (i.e.,

“savory”), and bitter.


Cranial Nerve II: Optic Nerve


• Optic nerve is sensory.

• Connection to the brain: diencephalon

• Retina is the inner layer of the posterior eye; light striking the retina is

converted into neural signals by the photosensitive cells.

• Visual signals sent to the midbrain are involved in reflexive responses of the

pupil, awareness of light and dark, and orienting the head and eyes.


Cranial Nerves 3, 4, and 6:

Oculomotor, Trochlear & Abducens


• Oculomotor, Trochlear, and Abducens

nerves are primarily motor.

A. Oculomotor: moves the eyes up,

down, medially and raises the

upper eyelid. Also constricts the

pupil and adjusts the shape of the

lens.

B. Trochlear: moves eyes down,

particularly when eye is adducted.

C. Abducens: Abducts the eye

(Lundy-Ekman, 2018, p. 389 & 427)Image: (Lundy-Ekman, 2018, p. 434)

Cranial Nerves 3, 4, and 6: Oculomotor,

Trochlear & Abducens (Cont.)


• Contain motor neuron axons innervating the six

extraocular muscles that move the eye and

control reflexive constriction of the pupil

• Connection to brain:

– Oculomotor: anterior midbrain

– Trochlear : posterior midbrain

– Abducens: between pons and medulla

(Lundy-Ekman, 2018, p. 389 & 427)Image: (Lundy-Ekman, 2018, p. 434)


Cranial Nerve 5: Trigeminal

• Trigeminal nerve is a mixed nerve containing both sensory and motor fibers

• Sensory fibers transmit information from the face and TMJ.

• Trigeminal nerve named for its three branches

– Ophthalmic

– Maxillary

– Mandibular

• The motor axons are contained in the mandibular branch. Carry signal to muscles of

mastication and tensor tympani.

• Sensory neurons transmit information from the face and the TMJ. All 3 branches

convey somatosensory signals.

• Reflex: afferent limb corneal reflex

• Connection to the brain: pons (lateral)



Cranial Nerve 5: Trigeminal

Image: (Lundy-Ekman, 2018, pp. 390-391)


Cranial Nerve 7: Facial

• Innervates muscles of facial expression

and most glands in the head (tears,

salivation etc.); also conveys sensory

information from the posterior ear canal

and taste from the anterior tongue

• Signals to and from CN VII are

processed in the nuclei located in the

pons, medulla, and upper spinal cord

• Reflex: Efferent limb corneal reflex.

• Connection to brain: between pons and

medulla.


Introduction to

Cranial Nerve Examination

MSTN121 - Neurophysiology

Session 12

Department of Myotherapy



Cranial Nerve

Name Composition

I Olfactory Sensory only

II Optic Sensory only

III Oculomotor Motor & sensory

IV Trochlear Motor & sensory

V Trigeminal Motor & sensory

VI Abducens Motor & sensory

VII Facial Motor & sensory

VIII Vestibulocochlear Sensory only

IX Glossopharyngeal Motor & sensory

X Vagus Motor & sensory

XI Spinal Accessory Motor & sensory

XII Hypoglossal Motor & sensory

We do not

routinely

test cranial

nerve I –

olfactory

nerve.

Routinely

tested as a

group

Routinely

tested as a

group

(Jarvis, 2016, pp. 644-647)

© Endeavour College of Natural Health


Cranial Nerve II – Optic Nerve

Test – Visual Acuity Abnormal Findings

This can be tested by asking the patient to read signs and describe pictures about 6 metres distance away. Test both eyes, asking her to cover one eye at a time.

(Butler, 2000)

Image: (Jarvis, 2016, p. 318)



Cranial Nerve III, IV & VI – Oculomotor, Trochlear &

Abducens Nerves

Test – Check Pupil Size Abnormal Findings

This reflects the balance in tone between parasympathetic and sympathetic nervous system.

Best examined in a dark room.

Pupils should appear round, regular and equal in size.

In adults the resting size is 3-5mm.

Larger than normal pupil size suggests high sympathetic tone. If in both suggests systemic increase in tone, on one side suggests unilateral overactivity or under activity in the parasympathetic nervous system on the same side.

Size variation from right to left must be noted – may indicate lesion on either side.

(Jarvis, 2016)


Cranial Nerve Examination Cranial Nerve III, IV & VI – Oculomotor, Trochlear &

Abducens Nerves

Test – Pupillary Light Reflex Abnormal Findings

In a dim room, shine the pen light into one of the clients eyes. Test both sides.

Normal response: both pupils constricting at the same time and with equal velocity and size of constriction.

• Direct reflex is demonstrated when the light on one side = pupil constriction on same side

• Consensual reflex is demonstrated when the light on one side = pupil constriction on the opposite side.

When a slow or absent response occurs it suggests a lesion of the

pathway.

(Jarvis, 2016)




Abducens Nerves

Test – Visual Fields Abnormal Findings

Get the client to cover their left eye. Using the tip of a pen, move the pen from behind their ear (at a distance of 25cm from their head) into their vidual field. Get the client to say when they see the tip of the pen. Test the opposite side getting them to swap eyes covered.

Normal response: demonstrated by the observation of the pen tip just after it passes the ear.

If the client has lost vision on one side of their visual field it is called homonymous hemianopia normally due to visual pathway lesion. Left visual field loss suggests right side optic tract or occipital lobe lesion.

(Jarvis, 2016)




Abducens Nerves

Test – Resting Eye Position Abnormal Findings

Ask the client to look straight ahead, examine the height of the space between the upper and lower eyelids and the position of the eyelids relative to the iris and pupil. Then ask the client to look upwards without moving their head.

Normal response: The position of the eyelids is symmetric with the upper eyelid covering the upper iris. The eyelid retracts with upwards gaze.

Asymmetric space between the eyelids and iris –the eyelid that is lower does not retract with upwards gaze. Suggest lesion of the oculomotor nerve. CNIII lesions normally will also include dilated pupil, lateral and downwards deviation of the eye when attempting to look forward and diplopia.

(Jarvis, 2016)


Cranial Nerve Examination Cranial Nerve III, IV & VI – Oculomotor, Trochlear &

Abducens Nerves

Test – Accommodation Reflex Abnormal Findings

Get the client to look straight ahead at the tip of the pen, slowly move the pen towards the bridge of their nose and watch their eyes.

Normal response: both eyes adduct equally and can maintain position. The client reports diplopia only when the pen is close to the nose.Pupils should constrict as eyes focus and as you take the pen away the eyes should dilate.

One eye does not adduct as much as the opposite side and has early diplopia. Suggests an ipsilateral CNIII lesion.

(Jarvis, 2016)

Image: (Jarvis, 2016, p. 296)




Abducens Nerves

Tests – Visual Pursuits Abnormal Findings

Get the client to follow the tip of a pen in each plane of eye motion –side to side, up and down from corner to corner (oblique axis).

Normal response: eyes move symmetrically and smoothly.

Abnormal response: nystagmus/weakness in adduction, depression or elevation of the eye. May be due to single CNIII or VI lesion or an upper motor neuron lesion or medial longitudinal fasciculus lesion.

Abducens nerve abnormal response: unable to move eyes laterally and may have nystagmus during the pursuit.

(Jarvis, 2016)





Abducens Nerves





Abducens Nerves

Tests – Inferior Oblique Muscle Test Abnormal Findings

The examiner gets the client to follow the tip of the pen to 50 degrees adduction and then lifts the pen up so the eye goes inwards and up.

Normal response: eyes follows the pen tip.

Eye is unable adduct and elevate. May be due to oculomotor nerve lesion or UMN/medial longitudinal fasciculus lesion.

(Jarvis, 2016)




Abducens Nerves

Tests – Trochlear Nerve Test Abnormal Findings

The examiner gets the client to follow the tip of the pen to 50 degrees adduction and then drops the pen so the eyes look down and inwards.

Normal response: eyes follow the pen tip.

Difficulty looking inferomedially and may present with diplopia, difficulty reading and/or difficulty descending stairs. May be due to trochlear nerve lesion or UMN lesion.

(Jarvis, 2016)



Cranial Nerves V– Trigeminal Nerve

Test – Trigeminal NerveMotor Testing

Abnormal Findings

Active resisted testing of jaw opening and closing then palpating the masseters muscles on both sides while the client clenches their teeth, feeling for tone. Normal response: 5/5 in strength and normal resting tone compared with clenching.

4/5 or less in strength and high or low tone in masseter/temporalis. Low tone suggests a LMN lesion like trigeminal neuralgia, high tone suggests UMN lesion.

(Jarvis, 2016) (Image: Jarvis, 2016, p. 645)


Cranial Nerves V– Trigeminal Nerve

Test – Trigeminal Nerves Sensory Testing

Abnormal Findings

Pin prick, soft touch, vibration and cold testing for the face over the forehead, under the eyes, over the nose, over the cheeks, over the chin and lips. Ask the client to localise, describe and rate the stimulus from one side of the face compared to the other.

Normal response: symmetry in sensation and localisation.

Anesthesia over the face, hyperesthesia over the face, hyperalgesia in pin prick, allodynia in cold, vibration or soft touch.

(Jarvis, 2016) (Image: Jarvis, 2016, p. 645)

Cranial Nerve Examination Cranial Nerves V– Trigeminal Nerve

Test – Corneal Reflex Abnormal Findings

Using a wisp of cotton touch the outer cornea.

Normal response: client blinks both eyes.(afferent = trigeminal, efferent = facial)

Opposite side and/ or same side does not blink, suggesting a lesion in the CNV or CNVII (indicated if other tests are positive).

Test – Jaw Jerk Reflex Abnormal Findings

Place your thumb on the clients jaw in a pistol grip fashion. Whilst your thumb is in this position tape on the clients chin with a reflex hammer.

Normal response: masseter contraction and mandible elevation.

Lost/ decreased reflex suggesting CNV lesion or if hypperreflexive suggesting UMN lesion.

(Lundy-Ekman, 2013)


Cranial Nerves VII – Facial Nerve

Test – Facial Expressions Abnormal Findings

Get the client to lift their eye brows, close and open eyes, smile and puff up cheeks.

Normal response: symmetry and able to do all movements.

Asymmetry and paresis/paralysis. If upper and lower face affected this may suggest Bell’s palsy.Corticobrainstem/UMN lesion results in paresis/paralysis of lower face.

(Jarvis, 2016, p) (Image: Jarvis, 2016, p. 646)


Cranial Nerves VIII – Vestibulocochlear

Test – Hearing Test Abnormal Findings

Rub your fingers together near the client’s ear, then slowly move away from their ears. Ask when they can no longer hear it. Compare both sides.

Normal response: Client hears both sides equally.

Difference in acuity, may suggest reduce function of the same side cochlear nerve or UMN lesion.

(Butler, 2000)

Cranial Nerve Examination Cranial Nerves VIII – Vestibulocochlear

Test – Weber Test Abnormal Findings

Using a tuning form, place it in the middle of the client’s head. Ask the client if the sound is heard better in one ear or both (must be stated while the tuning fork is in the midline of their head).

Normal response: sound is symmetrical with no lateralisation.

- With conductive hearing loss, the sound will localise towards the affected side.

- With sensorineural hearing loss, the sound will localise towards the unaffected side.

(Butler, 2000)


Cranial Nerves IX – Glossopharyngeal

Test – Gag Reflex Abnormal Findings

Touch the soft palate with a cotton swab.

Normal response: gagging and symmetrical elevation of the soft palate.

(afferent = CNIX, efferent = CNX).

Lack of gag reflex or asymmetrical elevation of soft palate suggesting either CNIX or CNX lesion.

(Jarvis, 2016)


Cranial Nerves X –Vagus Nerve

Test - Uvula Elevation Abnormal Findings

Depress the tongue and ask the client to say “ah” andobserve the soft palate with your pen light.

Normal response: Elevation of the soft palate symmetrically.

Asymmetry of soft palate elevation and they may be present with voice hoarseness.

Hoarse of brassy voice occurs with vocal cord dysfunction, nasal twang occur with weakness of soft palate.

(Jarvis, 2016)


Cranial Nerves XI – Spinal Accessory Nerve

Test – Muscle Strength Abnormal Findings

Check equal strength of the SCM and trapezius muscles. Ask the client to resist cervical rotation,with resistance applied to the side of the chin (see Fig 23-13). Then ask the client to shrug against resistance (see Fig 23-14).

Normal response: These movements should feel equally strong on both sides.5/5 strength.

Atrophy. Muscle weakness or paralysisoccurs with a stroke or following injury to the peripheral nerves.

(Jarvis, 2016, pp. 644-647) (Image: Jarvis, 2016, p. 646)


Cranial Nerves XII – Hypoglossal Nerve

Test – Tongue Deviation Abnormal Findings

Ask the client to protrude their tongue out. Inspect the tongue but also it’s positioning. No wasting or tremors should be present. Not the tongue is forward in the midline.

Normal response: tongue stays on the midline.

Protruded tongue deviates to the side of the lesion. Ipsilateral tongue atrophy may also be observed.

(Jarvis, 2016)


Cranial Nerves XII – Hypoglossal Nerve

Test – Tongue Strength Abnormal Findings

Ask the client to push their tongue to the left and right side of the mouth/cheek. Whilst the client is doing so push their tongue inwards while asking them to resist.

Normal response: tongue able to resist moderate force.

Tongue’s force easily overcome, may suggest CNXII lesion.

(Butler, 2000)

Review Questions

• What do cranial nerves do?

• How do cranial nerves differ from spinal nerves?

• List the four functions of the cranial nerves.

• Identify each CN mentioned in this lecturer by number,

name, function(s), reflex activity (if any), and connection to

the brain.

Image References

• Jarvis, C. (2016). Physical Examination & Health

Assessment (7th ed.). Elsevier: Missouri.

• Lundy-Ekman, L.(2013). Neuroscience : Fundamentals for

Rehabilitation (4th ed.). Missouri: Elsevier.


References

• Butler, D.S. (2000). The Sensitive Nervous System.

Noigroup Publications: Adelaide: City West.

• Jarvis, C. (2016). Physical Examination & Health

Assessment (7th ed.). Elsevier: Missouri.

• Lundy-Ekman, L.(2013). Neuroscience : Fundamentals for

Rehabilitation (4th ed.). Missouri: Elsevier.


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