Cranial Nerve Testing

What type of sensory information does CN I carry?

Smell — SVA (special visceral afferent)

How do you test CN I?

Visually inspect nostrils.

Have the patient occlude one nostril.

Present a non-noxious odor.

Ask the patient to identify the smell.

Repeat on the opposite side.

What is the primary symptom of an olfactory lesion?

Anosmia — loss of smell

What type of nerve is CN II?

Sensory

What 3 major things are tested for CN II?

Visual acuity

Afferent pupillary light reflex

Visual fields

How is visual acuity tested?

Snellen chart

What is tested during the pupillary light reflex?

Direct and consensual pupil responses to light

What is the direct pupillary response?

Constriction of the pupil in the eye receiving the light

What is the consensual pupillary response?

Constriction of the opposite pupil when light is shined into one eye

Loss of consensual pupillary light reflex affects which cranial nerve?

CN III

Loss of direct pupillary light reflex affects which cranial nerve?

CN II

What does an oculomotor nerve lesion do to the pupillary light reflex?

Both direct and consensual responses are lost on the lesion side

What happens with an optic tract lesion according to the slides?

No change may be detectable with a small lesion; a large lesion can produce bilateral diminished responses

How do you test CN III, IV, and VI?

Have the patient keep their head still and follow the examiner's finger through the 6 cardinal positions of gaze

What movements are impaired with an oculomotor nerve lesion?

The affected eye cannot turn up, down, or medially

What movement is impaired with a trochlear nerve lesion?

The eye cannot turn downward and internally

What movement is impaired with an abducens nerve lesion?

The eye cannot turn laterally

What is the accommodation reflex?

The eyes shift from distant gaze to near gaze, with the eyes moving temporally initially and then focusing near

What happens during convergence?

Both eyes move nasally and both pupils constrict

What are the two major functions of CN V?

Sensory: face

Motor: muscles of mastication

How do you test CN V sensory function?

Test bilateral pain and temperature over each CN V division.

How do you test CN V motor function?

Ask the patient to bite down while palpating the masseter muscle

What are the major functions of CN VII?

Motor: facial expression

Sensory: anterior 2/3 of tongue/taste

Parasympathetic: salivation and tears

How do you test the upper division of CN VII?

Resist eye closing

Ask patient to raise eyebrows

Look for asymmetry

How do you test the lower division of CN VII?

Ask patient to smile and show all teeth and look for asymmetry

What does an UMN facial lesion cause?

Contralateral weakness/paralysis of the lower face, while forehead movement is preserved

What does an LMN facial lesion cause?

Ipsilateral paralysis/weakness of the entire face, including the forehead

What happens to taste with a peripheral facial nerve lesion?

Loss of taste in the anterior portion of the tongue.

What are the two major functions of CN VIII?

Hearing and balance

How can hearing be tested?

Whispered word test or finger-rub test

What is CN IX associated with during clinical testing?

Gag reflex

What type of nerve is CN X?

Mixed nerve with motor, sensory, and autonomic/parasympathetic functions

How do you test CN X?

Observe palate elevation while asking the patient to say "AH."

What happens with a vagus LMN lesion?

The palate droops on the affected side and the uvula deviates toward the intact side

In a vagus LMN lesion, which way does the uvula deviate?

Away from the lesion → toward the intact side

What muscles does CN XI primarily innervate?

Upper trapezius and sternocleidomastoid (SCM)

How do you test the SCM component of CN XI?

Ask the patient to turn their head and perform MMT

How do you test the trapezius component of CN XI?

Ask the patient to elevate their shoulders and perform MMT

What does CN XII innervate?

Intrinsic and extrinsic tongue muscles

What happens to the tongue with an UMN lesion of CN XII?

The tongue deviates away from the lesion

What happens to the tongue with an LMN lesion of CN XII?

The tongue deviates toward the side of the lesion