Neurological Exam

Although taste is not typically assessed during a routine neurological examination, the 7th nerve does supply taste to the anterior two-thirds of the tongue and hard and soft palates. This can be tested using salty, bitter, sour or sweet solutions.

Examination Technique

• the tongue is protruded and held gently by the examiner.
• a small sample of solution is applied to one side of the anterior two-thirds of the tongue using a cotton tipped applicator saturated with the solution.
• with the tongue still protruded, the patient should be asked to point to a sign displaying one of the four possible tastes.
• the patient is then given a small sip of water and the test is repeated using an alternate stimulus.
• the reason the tongue is maintained protruded is because if the patient were allowed to put their tongue back in their mouth in order to verbalize their response, they could masticate and transfer the stimulus to the opposite side which could be affected if there was a lesion of the 7th nerve.

The major role of the facial nerve is to innervate the muscles of facial expression. These can be observed while taking the history and then more formally assessed during the neurological examination.

Examination Technique:

• observe for asymmetry – widening of the palpebral fissure or flattening of the nasolabial fold.
• observe for involuntary facial movements (e.g. hemifacial spasm, orofacial dyskinesia, myokymia, or synkinesis).
• ask the patient to wrinkle their forehead by raising their eyebrows and close their eyes tightly. Observe for asymmetry of ability to burry the eyelashes and palpate for differences of ability to resist eye opening. Ask the patient to show their teeth, puff out their cheeks and appose their lips.
• recall that the efferent limb of the corneal reflex (see trigeminal nerve) is through the 7th cranial nerve.

Normal Response:
although patients may have an asymmetric face, there should be no facial weakness.

Abnormal Response:

• lower motor neuron weakness causes weakness of the entire side of the face with equal involvement of upper and lower facial muscles.
• an upper motor neuron lesion of the contralateral supranuclear pathway results in weakness primarily of lower muscles of facial expression. The upper muscles of facial expression (frontalis and orbicularis oculi) are much less affected because the facial nucleus that innervates them receives partial input from the ipsilateral hemisphere.