Cranial Nerve Examination

Question 1

What are each of the cranial nerves responsible for (recap)? When is each nerve function examination taught?

Answer 1

• Cranial nerve one (I). Olfactory nerve. Sense of smell (sensory).
  o This is taught in year 2.
• Cranial nerve two (II). Optic tracts (actually tracts of the brain). Vision (sensory).
  o The visual fields by confrontation is taught in year 1 (see below).
  o Visual acuity by reading, Snelling chart etc. is taught in year 2.
• The pupillary reflexes (to light and accommodation) is taught in year 2.
• Cranial nerve three (III). Occulomotor nerve.
  o Motor to four extrinsic muscles of eye: inferior oblique (turns the eye up), medial rectus (adducts eyeball), inferior rectus (turns eye down), superior rectus (turns eyeball up).
  o Motor to levator palpebrae superioris (elevates eyelid, opens eye)
  o Parasympathetic to pupil (constriction) and to controlling muscle of lens.
• Cranial nerve four (IV). Trochlear nerve. Motor to one extrinsic muscle of eye: superior oblique. Turns eyeball down.
• Cranial nerve six (VI): Abducens nerve
  o Motor to the lateral rectus muscle of the eyeball.
• Examination of the eye movements is taught in year 1 (see below).
• The pupillary reflexes (which examine the optic nerve (sensory input) plus oculomotor parasympathetic to pupil and ciliary body) are taught in year 2
• Cranial nerve five (V): Trigeminal nerve.
  o Sensory nerve to face including touch, pain etc from inside mouth, nasal mucosae, mucosae of the sinuses and part of the pharynx.
  o Motor nerve to muscles of mastication (masseter, temporalis, pterygoids etc. (Also tensor veli palatini, mylohyoid, anterior belly digastric, tensor tympani).
  o Various autonomic and special sensory (taste) fibres travel in branches of the trigeminal nerves, but they originate in other cranial nerves, joining parts of the trigeminal via communicating branches.
• The motor part of this (muscles of mastication) is taught in year 1 (see below). The sensory examination is taught in year 2.
• Cranial nerve seven (VII): The Facial nerve
  o Motor to muscles of facial expression, (also stapedius, stylohyoid, and posterior belly of digastric).
  o Sensation from the outer ear, and oro-pharyngeal mucosae.
  o Special sensory (taste) from anterior two thirds of the tongue.
  o Parasympathetic, including efferents controlling lacrimation (tears) from the lacrimal glands, and salivation from submandibular and sublingual salivary glands.
• Only the motor part of this is routinely examined, and this is taught in year 1 (see below). The sensory part is not routinely examined, though the outer ear can easily be if special situation (e.g. Bell’s palsy). Taste, lacrimation and salivation are not routinely examined.
• Cranial nerve eight (VIII): vestibulo-cochlear.
  o Sensory nerve carrying balance and orientation information from semi-circular canals, and acoustic information from the cochlea.
• Examination of the auditory part is taught in year 2. The vestibular function is not routinely examined, though dysfunction may be indicated by nystagmus of the gaze.
• Cranial nerve nine (IX): Glosso-pharyngeal nerve.
  o Motor to stylopharangeus muscle (involved in swallowing and speech)
  o Parasympathetic efferent to the parotid salivary gland
  o Visceral afferent from the carotid body and sinus.
  o General sensory (touch, pain, temperature) from upper pharynx and posterior third of tongue, and inner surface of tympanic membrane.
  o Special sensory information (taste) from posterior surface of tongue.
• Cranial nerve ten (X): vagus
  o Motor to various pharyngeal and laryngeal muscles.
  o Afferent and efferent parasympathetic to organs of body: heart, bowels, bronchial tree, sweat glands.
• Between them, and together with the hypoglossal, the glosso-pharyngeal and vagus are responsible for swallowing and speech functions. Examination of their function is learned in the second year.
• Cranial nerve eleven (XI): Accessory nerve.
  o Motor to trapezius and sterno-cleido-mastoid muscles.
  o Examination is taught in the second year.
• Cranial nerve twelve (XII): Hypoglossal.
  o Motor to tongue. It is responsible for tongue movements. Together with Glosso-pharyngeal and vagus, the hypoglossal nerve is responsible for swallowing and speech.

Question 2

How do the sympathetic nerves differ from the cranial nerves? How are they examined?

Answer 2

• The sympathetic nerves are initially separate from the cranial nerves: they originate in the thoracic sympathetic trunk, and accompany arteries to the face. They may join branches of cranial nerves. Mostly examined via effect on pupillary dilation and levator palpebrae, which is taught in the second year.

Question 3

How do you begin an examination?

Answer 3

• Professionalism!
• Wash hands
• Introduce yourself, and get patient’s name
• Ask permission, with a short explanation of what you are going to do.
• In the second year, we will draw attention to general inspection, and assessing the patient’s demeanour, but we will skip over this in first year.

Question 4

How do you test visual fields by direct confrontation?

Answer 4

• There are various ways of doing this, this is the basic way we teach.
• “Examiner” and “patient” sit opposite each other, fairly close. They close corresponding eyes, if “patient” closes left eye, “examiner” closes right eye, and vice versa. It is usual for each person to keep the eye closed with the fingers of one hand, without encroaching on the nasal visual field of the eye that is open.
• Examiner asks patient to keep looking at her (open) eye.
• If the examiner is covering her R eye with her R hand, the patient will be covering his L eye with his L hand. The examiner positions her L hand at the periphery of her temporal visual field, initially in the upper quadrant. She wiggles her finger, askes the patient if they can see it, says “tell me when it stops”, stops, and hopefully the patient says “stopped”. If the patient cannot see the finger, the examiner slowly moves her finger in until the patient can see it.
• She then moves to the lower quadrant, the nasal quadrants (she may need to change hands), and then the four quadrants of the other eye.
• She is directly comparing her visual fields with those of the patient.

Question 5

How do you test eye movements?

Answer 5

• Patient has both eyes open!
• The examiner sits in front of “patient”, and holds up her finger about half a meter in front of patient. She hasks him to follow her finger with his eyes, while keeping head still. She asks him to report any double vision.
• At the beginning, before moving it, and when moving it, she looks for nystagmus (one eye moving off laterally before flicking back to correct position).
• She moves her finger in an “H” shape, laterally, up and down, back to centre and laterally out to the other side, up and down, back to centre.
• She is watching for deviations of gaze in either eye, (squint, or strabismus) and for nystagmus.
• At the end of this, she could look for lid lag, but this is really part of second year examination.

Question 6

How do you test muscles of mastication?

Answer 6

• Examiner tells patient she is going to touch him lightly.
• She touches him on both sides on the masseter muscle, below the zygomatic arch. She asks him to clench his jaw and relax again, and feels for the muscle tensing bilaterally.
• She touches him on both sides on the temporalis muscle, above the zygomatic arch. She asks him to clench his jaw, and relax again and feels for the muscle tensing bilaterally (less obvious than the masseter!)
• She puts one hand under his jaw, and the other on top of his head, and asks him to open his jaw against light resistance.

Question 7

How do you test the facial nerve/muscles of facial expression?

Answer 7

• Ask patient to raise eyebrows, in expression of surprise.
• Ask patient to screw eyes up tight shut. You can test the strength of this by gently trying to open them with your fingers, after warning him
• Ask the patient to give a wide toothy grin.
• Ask the patient to blow out cheeks. You can test the strength of this by gently pushing on each cheek, one side then the other, after warning the patient.
• In an upper motor neurone unilateral lesion, the upper part of the face (forehead) will be spared because not all the upper motor neurones cross.

Question 8

How do you finish an examination?

Answer 8

• Wash hands
• Thank the patient,
• Make sure he or she is comfortable.
• Answer any questions.