Cranial nerve assessment

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Cranial Nerve 1- Olfaction
This CN is tested one nostril at a time by using a nonirritating smell such as tobacco, orange, vanilla, coffee, etc. Detection of the smell is more important than the actual identification.

The common cold is the most frequent cause of dysfunction. Dysfunction can be associated with fractures of the cribriform plate of the ethmoid bone. Frontal lobe tumors may compress the olfactory bulb and/or tracts and cause anosmia, but this is rare occurrence.

Cranial Nerve 2- Visual acuity

The first step in assessing the optic nerve is testing visual acuity. This can be done with a standard Snellen chart or with a pocket chart

The following tests also appropriate:

  • Test Pupillary Reactions to Light

  • Visual fields, by means of confrontation or perimetry if indicated

  • Color, with use of an Ishihara chart or by using common objects, such as a multicolored tie or color accent markers

  • Funduscopy

Lesions of the visual pathways result in blindness and pupillary abnormalities, such as the retinal or optic nerve disease, scotomata and quadrant or hemianopsias (optic tract and radiation)

Oculomotor nerve - CN III

  • Observe for Ptosis

  • Test Extraocular Movements

    1. Stand or sit 3 to 6 feet in front of the patient.

    2. Ask the patient to follow your finger with their eyes without moving their head.

    3. Check gaze in the six cardinal directions using a cross or "H" pattern.

    4. Pause during upward and lateral gaze to check for nystagmus. [6]

    5. Check convergence by moving your finger toward the bridge of the patient's nose.

  • Test Pupillary Reactions to Light

The oculomotor nucleus of the nerve is located in the midbrain and innervates the pupillary constrictors; the levator palpebrae superioris; the superior, inferior, and medial recti; and the inferior oblique muscles. Lesions of CN III result in paralysis of the ipsilateral upper eyelid and pupil, leaving the patient unable to adduct and look up or down. The eye is frequently turned out (exotropia). In subtle cases, patients complain of only diplopia or blurred vision. Lesions at the nucleus of the third nerve cause bilateral ptosis. Paralysis of CN III is the only ocular motor nerve lesion that results in diplopia in more than 1 direction, distinguishing itself from CN IV paralysis (which also can result in exotropia). Pupillary involvement is an additional clue to involvement of CN III. Pupil-sparing CN III paralysis occurs in diabetes mellitus, vasculitides of various etiologies, and certain brainstem lesions such as due to multiple sclerosis.

Trochlear nerve - CN IV

The nucleus of the nerve is located in the midbrain. It innervates the superior oblique muscle, which incycloducts and infraducts the eye. Trochlear nerve typically allows a person to view the tip of his or her nose.Test Extraocular Movements (Inward and Down Movement)

Trigeminal nerve - CN V

The nucleus of the nerve stretches from the midbrain (ie, mesencephalic nerve) through the pons (ie, main sensory nucleus and motor nucleus) to the cervical region (ie, spinal tract of the trigeminal nerve). It provides sensory innervation for the face and supplies the muscles of mastication.

Tests used are

  • Test Temporal and Masseter Muscle Strength

    1. Ask patient to both open their mouth and clench their teeth.

    2. Palpate the temporal and massetter muscles as they do this.

  • Test the Three Divisions for Pain Sensation

    1. Explain what you intend to do.

    2. Use a suitable sharp object to test the forehead, cheeks, and jaw on both sides.

    3. Substitute a blunt object occasionally and ask the patient to report "sharp" or "dull."

  • If you find and abnormality then:

    1. Test the three divisions for temperature sensation with a tuning fork heated or cooled by water.

    2. Test the three divisions for sensation to light touch using a wisp of cotton.

  • Test the Corneal Reflex

    1. Ask the patient to look up and away.

    2. From the other side, touch the cornea lightly with a fine wisp of cotton.

    3. Look for the normal blink reaction of both eyes.

    4. Repeat on the other side.

    5. Use of contact lens may decrease this response.

The nucleus of the nerve stretches from the midbrain (ie, mesencephalic nerve) through the pons (ie, main sensory nucleus and motor nucleus) to the cervical region (ie, spinal tract of the trigeminal nerve). It provides sensory innervation for the face and supplies the muscles of mastication.

Paralysis of the first division (ophthalmic; V1) is usually seen in the superior orbital fissure syndrome and results in sensory loss over the forehead along with paralysis of CN III and CN IV. Paralysis of the second division (maxillary; V2) results in loss of sensation over the cheek and is due to lesions of the cavernous sinus; it also results in additional paralysis of V1, CN III and CN IV. Isolated V2 lesions result from fractures of the maxilla. Complete paralysis of CN V results in sensory loss over the ipsilateral face and weakness of the muscles of mastication. Attempted opening of the mouth results in deviation of the jaw to the paralyzed side.

Abducens nerve - CN VI

The nucleus of the nerve is located in the paramedian pontine region in the floor of the fourth ventricle. It innervates the lateral rectus, which abducts the eye.

Test used

  • Test Extraocular Movements (Lateral Movement)

Isolated paralysis of CN VI results in esotropia and inability to abduct the eye to the side of the lesion. Patients complain of double vision on horizontal gaze only. This finding is referred to as horizontal homonymous diplopia. Paralysis of CN VI may result from increased intra cranial pressure without any lesion in the neuraxis, and it may result in false localization if one is not aware of it.

Facial nerve - CN VII

Although CN VII is considered a pure motor nerve, it also innervates a small strip of skin of the posteromedial aspect of the pinna and around the external auditory canal

Tests used are

  • Observe for Any Facial Droop or Asymmetry

  • Ask Patient to do the following, note any lag, weakness, or asymmetry:

    1. Raise eyebrows

    2. Close both eyes to resistance

    3. Smile

    4. Frown

    5. Show teeth

    6. Puff out cheeks

  • Test the Corneal Reflex

Vestibulocochlear nerve - CN VIII

The vestibulocochlear nerve enters the brainstem at the pontomedullary junction and contains the incoming fibers from the cochlea and the vestibular apparatus, forming the eighth CN and serves hearing and vestibular functions.

  • Screen Hearing

    1. Face the patient and hold out your arms with your fingers near each ear.

    2. Rub your fingers together on one side while moving the fingers noiselessly on the other.

    3. Ask the patient to tell you when and on which side they hear the rubbing.

    4. Increase intensity as needed and note any asymmetry.

    5. If abnormal, proceed with the Weber and Rinne tests.

  • Test for Lateralization (Weber)

    1. Use a 512 Hz or 1024 Hz tuning fork.

    2. Start the fork vibrating by tapping it on your opposite hand.

    3. Place the base of the tuning fork firmly on top of the patient's head.

    4. Ask the patient where the sound appears to be coming from (normally in the midline).

  • Compare Air and Bone Conduction (Rinne)

    1. Use a 512 Hz or 1024 Hz tuning fork.

    2. Start the fork vibrating by tapping it on your opposite hand.

    3. Place the base of the tuning fork against the mastoid bone behind the ear.

    4. When the patient no longer hears the sound, hold the end of the fork near the patient's ear (air conduction is normally greater than bone conduction).

  • The Schwabach test

1. Use a 512 Hz or 1024 Hz tuning fork.

2.Start the fork vibrating by tapping it on your opposite hand.

3. place the vibrating tuning fork against the patient's mastoid bone.

4. when the patient no longer here the sound; place the vibrating fork against the examiner.

5. . If the examiner can hear the sound after the patient has stopped hearing it, then hearing loss is suspected

  • The vestibular division of CN 8 can be tested for by using the vestibulo-ocular reflex (The vestibulo-ocular reflex is obtained by having the patient visually fixate on an object straight ahead, then rapidly turning the patient's head form side to side and up and down. The eyes should stay fixed on the object and turn in the opposite direction of the head movement.) or by using ice water calorics to test vestibular function. The later test is usually reserved for patients who have vertigo or balance problems.

Glossopharyngeal nerve - CN IX

The nucleus of the nerve lies in the medulla and is anatomically indistinguishable from the CN X and CN XI nuclei (nucleus ambiguous). Its main function is sensory innervation of the posterior third of the tongue and the pharynx. It also innervates the pharyngeal musculature, particularly the stylopharyngeus, in concert with the vagus nerve.

Lesions affecting the glossopharyngeal nerve result in loss of taste in the posterior third of the tongue and loss of pain and touch sensations in the same area, soft palate, and pharyngeal walls. CN IX and CN X travel together, and their clinical testing is not entirely separable. Therefore, examination of CN IX is discussed with that of the vagus nerve

Vagus nerve - CN X

Starting in the nucleus ambiguous, the vagus nerve has a long and tortuous course providing motor supply to the pharyngeal muscles (except the stylopharyngeus and the tensor veli palati), palatoglossus, and larynx. Somatic sensation is carried from the back of the ear, the external auditory canal, and parts of the tympanic membrane, pharynx, larynx, and the dura of the posterior fossa. It innervates the smooth muscles of the tracheobronchial tree, esophagus, and GI tract up to the junction between the middle and distal third of the transverse colon.

The vagus provides secretomotor fibers to the glands in the same region and inhibits the sphincters of the upper GI tract. Along with visceral sensation from the same region, the nerve participates in vasomotor regulation of blood pressure by carrying the fibers of the stretch receptors and chemoreceptors (ie, aortic bodies) of the aorta and providing parasympathetic innervation to the heart.

The pharyngeal gag reflex (ie, tongue retraction and elevation and constriction of the pharyngeal musculature in response to touching the posterior wall of the pharynx, tonsillar area, or base of the tongue) and the palatal reflex (ie, elevation of the soft palate and ipsilateral deviation of the uvula on stimulation of the soft palate) are decreased in paralysis of CN IX and CN X.

Tests used are

  • Listen to the patient's voice, is it hoarse or nasal?

  • Ask Patient to Swallow

  • Ask Patient to Say "Ah"

    • Watch the movements of the soft palate and the pharynx.

  • Test Gag Reflex (Unconscious/Uncooperative Patient)

    1. Stimulate the back of the throat on each side.

    2. It is normal to gag after each stimulus.

Spinal accessory nerve - CN XI

From the nucleus ambiguous, the spinal accessory nerve joins the vagus nerve in forming the recurrent laryngeal nerve to innervate the intrinsic muscles of the larynx.

Tests used are

  • From behind, look for atrophy or assymetry of the trapezius muscles.

  • Ask patient to shrug shoulders against resistance.

  • Ask patient to turn their head against resistance. Watch and palpate the sternomastoid muscle on the opposite side.

Hypoglossal nerve - CN XII

The nucleus of this nerve lies in the lower medulla, and the nerve itself leaves the cranial cavity through the hypoglossal canal (anterior condylar foramen). It provides motor innervation for all the extrinsic and intrinsic muscles of the tongue except the palatoglossus

  • Listen to the articulation of the patient's words.

  • Observe the tongue as it lies in the mouth

  • Ask patient to:

Protrude tongue

Move tongue from side to side

Category: Medicine Notes



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