Cranial Nerves CN VIII- CNXII

Question 1

what is the cranial nerve CN VIII

Answer 1

VESTIBULOCOCHLEAR NERVE

Question 2

what are the two divisions of vestibulocochler nerve

Answer 2

the cochlear division

the vestibular division

Question 3

what does the cochlear division do

Answer 3

The cochlear division of this nerve carries sound information from the organ of Corti in the cochlea

Question 4

What does the vestibular division do

Answer 4

The vestibular division transfers information about balance and posture from the vestibular organ (the semicircular canals, the utricle and the saccule)
- it is functional associated with the cerebellum and oculomotor nuclei

Question 5

what is the main functions of the vestibular systems on the vestibule nerve

Answer 5

• maintaining balance

- stablising the eye

Question 6

what are the two components of monitoring motion

Answer 6

• must be able to detect rotation

- must also be able to detection motion along a line

Question 7

what is the vestibular system divided into in order to monitor motion

Answer 7

• it is divided into two receptor organs
  1. The semicircular canals detect angular acceleration/deceleration of the head.

2.The utricle and saccule detect linear acceleration and the pull of gravity.

Question 8

how do you monitor eye movements

Answer 8

• there is complex connections between the 3 vestibular nuclei and the cranial nerve nuclei that control eye movement by a pathway called the medial longitudinal fasculus

Question 9

what 2 reflexes does the vesitbular nerve participate in

Answer 9

the oculocephalic reflex (dolls eye manouvre) and the oculovestibular (caloric) reflex.

Question 10

what are the clinical test that you can use in order to assess the vesicular never function

Answer 10

Doll’s eye reflex:This involves conjugate eye movements in response to head movement. This is performed with the patient lying down and the normal response is for the patients eyes to deviate in the opposite direction to head turning i.e. if the head is briskly extended, the eyes go downwards and if to the right, the eyes move to the left.

Caloric reflex:The caloric test involves irrigation of the ears with cold or warm water that set up convection currents in the semicircular canals and induce nystagmus of the eyes. The normal response to irrigation with cool water is for the nystagmus to develop towards the contralateral side and towards the irrigated ear if warm water is used.

Gait and station:Various patterns of gait abnormalities occur with different disorders. The test of gait is probably the most useful motor system test and should be observed in all patients.

1. Gait: The patient walks normally back & forth at a moderate rate; he/she then walks on their heels and toes and tandem along a straight line, touching heel to toe; the patient then hops on each leg.
2. Station - Romberg’s test: Ask the patient to stand with their feet together, initially with their eyes open and then with them shut. There should be little or no sway. Where there is proprioceptive or vestibular damage, balance is impaired only when the eyes are shut and the patient may fall over.

Question 11

what are the similarities between the glossopharyngeal nerves and vagus nerves

Answer 11

• they are mixed nerves that convey somatic and visceral information to and from various brainstem nucleic
• they both contain parasympathetic fibres that innervate the parotid gland (CNIX) and viscera of the neck, thorax and abdomen (CNX)

Question 12

what nerve is CNIX

Answer 12

glossopharyngeal

Question 13

What nerve is CN X

Answer 13

vagus nerve

Question 14

what does CN IX do

Answer 14

• primarily a sensory nerve that mediates taste, salivation and swallowing (together with CN X).
• CN IX also monitors blood pressure and blood CO2/O2 levels (from the carotid sinus and body respectively).

Question 15

what does the CN X do

Answer 15

• they vagus alone innervates the larynx and is primarily involved in phonation

Question 16

where does the sensory input from the posterior pharynx, external ear skin, dura (posterior fossa) and the tympanic membrane terminate in

Answer 16

spinal trigeminal nucleus (CN V)

Question 17

what projection to the solitary nucleus

Answer 17

Taste bud (visceral) fibres of the tongue (CN IX) and epiglottis (CN X) and carotid afferents (CN IX) project to separate regions of the solitary nucleus.

Question 18

where do motor fibres from CN IX and X originate from

Answer 18

nucleus ambiguous

Question 19

what do the motor fibres of CN IX and X supply

Answer 19

• brachial arch muscles that control movements of the soft palate, pharynx and larynx

Question 20

what reflexes are CN IX and X involved in

Answer 20

The gag reflex - constriction and elevation of the pharynx and palate in response to tactile stimulation of the posterior oropharynx and tonsils.

Oculocardiac reflex - pressure on the eyes slows the heart rate.

Carotid reflex - masssaging the neck over the carotid bifurcation causes heart rate to slow.

Question 21

how do you test the glossopharyngeal and vagus nerve

Answer 21

1. Ask Patient to Swallow tests integrity of pharyngeal muscles
2. Ask Patient to Say “Ah” and watch the movements of the soft palate and the pharynx. The ulvula and palate usually lift centrally; unilateral damage causes uvula deviation to the good side and bilateral lesion means no lifting.
3. Test Gag Reflex

Stimulate the back of the throat on each side. It is normal to gag after each stimulus. Absence of a gag reflex could mean damage to the CN IX nerve (afferent limb loss of sensation) or efferent limb (CN X) to the pharyngeal muscles.

4. Assess laryngeal function by asking patient to speak and cough. Is it hoarse or nasal? Is the cough weak?
5. Ask patient to puff out cheeeks – to do this the palate must elevate to close off the nasopharynx. If movement is weak, air will audibly escape through the nose

Question 22

what is cranial nerve CN XI

Answer 22

accessory

Question 23

what type of nerve is the accessory nerve

Answer 23

motor

Question 24

where does the cell bodies of the accessory nerve lie

Answer 24

• lie in the ventral horn C1-C5

Question 25

describe the root of the accessory nerve

Answer 25

• the nerve has a spinal part (cell bodies of the motoneurons lie in the ventral horn of C1-C5) that travels into the skull through the foramen magnum to join the IX and Xth cranial nerves and then exits via the jugular foramen
• The cranial division arises from the nucleus ambiguus in the medulla.

Question 26

what are the clinical tests of the accessory nerves

Answer 26

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


1. Ask patient to shrug shoulders against resistance – tests strength of trapezius muscle.


2. Ask patient to turn their head against resistance– tests strength of sternocleidomastoid muscle (rotates head to opposite).

Test both sides.

Question 27

what does damage to the accessory nerve cause

Answer 27

Damage results in a lower motoneuron lesion that produces drooping of the shoulder and downward lateral rotation of the scapula. Upper motoneuron damage produces spastic paresis of the contralateral muscles

Question 28

what nerve is CN XII

Answer 28

hypoglossal nerve

Question 29

what does the hypoglossal nerve supply

Answer 29

he hypoglossal nerve supplies all the intrinsic and all but one of the extrinsic tongue muscles.

Question 30

describe the root of the hypoglossal nerve

Answer 30

. Its nucleus lies near the midline in the rostral (open) medulla. The nerve exits the brain between the pyramids and the olive. Neurons in the nucleus receive descending control from (contralateral) corticobulbar fibres from the motor cortex.

Question 31

what is the clinical test of the cranial nerve

Answer 31

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 - observe speed

Question 32

what happens if there is damage to the hypoglossal nerve

Answer 32

• there is deviation towards the side of the injury
• there is flaccid paralysis and atrophy of the tongue muscles and fasciculation
• If damage occurs to the corticobulbar tract then the tongue deviates to the opposite side of the lesion
• In some types of brainstem lesions, there may be a combination of the two conditions.
• Bilateral atrophy and fasciculation is usually a sign of motoneuron disease.