cranial nerve testing.ppt 2012

PREPARED BY: JENNIFER C.ACEBEDO

Examination of the cranial nerves allows one to "view" the brainstem all the way from its rostral to caudal extent.

The brainstem can be divided into three levels, the midbrain, the pons and the medulla.

The cranial nerves for each of these are: 2 for the midbrain (CN 3 & 4), 4 for the pons (CN 5-8), and 4 for the medulla (CN 9-12).

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.

• Visual acuity• SNELLEN CHART• POCKET CHART (Rosenbaun)Visual fields IF PT. CAN SEE BOTH

HANDS SYMMETRIC GRID CARD COTTON TIP APPLICATOROPTHALMOSCOPIC EXAM

The afferent or sensory limb of the pupillary light reflex is CN2 while the efferent or motor limb is the parasympathetics of CN3. Shine a flashlight into each eye noting the direct as well as the consensual constriction of the pupils.

Before checking ocular movements it is important to inspect the eyes. Look for ptosis. Note the appearance of the eyes and check for ocular alignment (the reflection of your light source should fall on the same location of each eyeball).

Testing extraocular range of motion with both eyes open and following the target (conjugate gaze) is called versions. The patient is asked to follow a target through the six principle positions of gaze. Note any misalignment of the eyes or complaint of diplopia (double vision).

If there is any misalignment of the eyes or diplopia on versions it is important to then examine each eye with the other covered (this is called ductions). The patient should follow an object through the six principle positions of gaze so each extraocular muscle's function is tested.

Test for both light touch (cotton tip applicator) and pain (sharp object) in the 3 sensory divisions (forehead, cheek, and jaw) of CN 5.

The ophthalmic division (V1) of the 5th nerve is the sensory or afferent limb and a branch of the 7th nerve to the orbicular is oculi muscle is the motor or efferent limb of the corneal reflex.

The limbal junction of the cornea is lightly touched with a strand of cotton.

The patient is asked if they feel the touch as well as the examiner observing the reflex blink.

The motor division of CN 5 supplies the muscles of mastication (temporalis, masseters, and pterygoids).

Palpate the temporalis and masseter muscles as the patient bites down hard. Then have the patient open their mouth and resist the examiner's attempt to close the mouth. 

Motor-The motor division of CN 7 supplies the muscles of facial expression. Start from the top and work down. Have the patient wrinkle forehead (frontalis muscle), close eyes tight (orbicularis oculi) show their teeth (buccinator), and purse lips or blow a kiss (orbicularis oris).

Taste is the sensory modality tested for the sensory division of CN 7. The examiner can use a cotton tip applicator dipped in a solution that is sweet, salty, sour, or bitter. Apply to one side then the other side of the extended tongue and have the patient decide on the taste before they pull their tongue back in to tell you their answer.

The cochlear division of CN 8 is tested by screening for auditory acuity .This can be done by the examiner lightly rubbing their fingers by each ear or by using a ticking watch. Compare right versus left.

Weber test consists of placing a vibrating tuning fork on the middle of the head and asking if the patient feels or hears it best on one side or the other. The normal patient will say it is the same in both ears. 

The Rinne test consists of comparing bone conduction (placing the tuning fork on the mastoid process) versus air conduction (placing the tuning fork in front of the pinna). Normally, air conduction is greater than bone conduction. For neurosensory hearing loss air conduction is still greater than bone conduction but for conduction hearing loss bone conduction will be greater than air conduction.

The motor division of CN 9 & 10 is tested by having the patient say "ah" or "kah". The palate should rise symmetrically and there should be little nasal air escape

With bilateral weakness neither side of the palate will elevate and there will be marked nasal air escape.

The gag reflex tests both the sensory and motor components of CN 9 & 10. This involuntary reflex is obtained by touching the back of the pharynx with the tongue depressor and watching the elevation of the palate.

CN 11 is tested by asking the patient to shrug their shoulders (trapezius muscles) and turn their head (sternocleidomastoid muscles) against resistance.

The 12th CN is tested by having the patient stick out their tongue and move it side to side. Further strength testing can be done by having the patient push the tongue against a tongue blade. Inspect the tongue for atrophy and fasciculations. 

If there is unilateral weakness, the protruded tongue will deviate towards the weak side.