Motor CNs- V, VII, IX, X, XI, and XII Flashcards Preview

Neurology Week 2 > Motor CNs- V, VII, IX, X, XI, and XII > Flashcards

Flashcards in Motor CNs- V, VII, IX, X, XI, and XII Deck (61)
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1
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2
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This slide is presented simply as an overview of the brainstem motor nuclei and their cranial nerves. These are highlighted by the red and purple boxed legends. This slide presents Netter’s rendition of the brainstem with the location of the motor nuclei and nerves in red and the parasympathetic nuclei and nerves in purple.

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3
Q

I will be showing you a repeated sequence of slides for each of the cranial nerves. The sequence begins with a slide of the location of the motor nuclei in the brain stem, then a slide showing the emergence of the cranial nerves from the brain stem, next a slide of the skull base showing the foramina through which the cranial nerves pass, then an anatomical slide showing the target organs for each cranial nerve, and finally the clinically relevant features for each cranial nerve.

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4
Q

Describe cranial nerve V, the trigeminal nerve.

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This is a mixed motor and sensory nerve.

5
Q

The motor nucleus of the trigeminal nuclei lies where?

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at the mid pontine level.

6
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Where do the motor fibers of CN V travel?

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Along the floor of Meckel’s cave to join to the mandibular or V3 division of the nerve, as shown by the red arrow, and exits the calvarium via the foramen ovale.

7
Q

What does Motor V innervate?

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the muscles of mastication including the masseter, temporalis, and pterygoid muscles. The first two muscles clench the jaw and the pterygoid muscles grind the teeth and open the jaw.

also innervates the tensor tympani (that dampens sound), the tensor veli palatini (that opens the eustachian tube),

8
Q

CN V exits the brainstem at the mid pontine level. Note that unlike the picture on the right, the actual specimen shows the motor fascicle, labeled 7, to be considerably smaller in caliber when compared to the sensory nerve labeled 1.

Below: ventral brainstem

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The numbers on the left identify 1 the sensory root of trigeminal nerve, 2 Pons, 3 Vestibulocochlear nerve, 4 Facial nerve, 5 Abducent nerve, 6 Medulla oblongata, 7 Motor root of trigeminal nerve, 8 Basilar sulcus.

9
Q

Motor CN V travels with the V3 or mandibular branch of the trigeminal nerve and exits the calvarium via ________

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the foramen ovale.

10
Q

What is the jaw reflex, also known as the jaw jerk?

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Tapping gently on the lower jaw triggers muscle spindles in the masseter muscle to send an impulse through the sensory fibers of cranial nerve V whose cell bodies lie in the mesencephalic nucleus; the mesencephalic nucleus projects to the nearby motor nucleus of V which sends an impulse to the masseter muscle to contract.

11
Q

How can you test motor CN V?

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by palpating the masseter and temporalis muscles when the patient bites down on a tongue blade. The muscles closing the jaw, however, are powerful and mild or moderate weakness will be difficult to detect.

The muscles opening the jaw are much weaker. Thus, jaw opening against resistance provided by the examiner is a more sensitive test. The strong lateral pterygoid will cause the jaw to deviate toward the side of the weakened pterygoid muscle (analogous to a tongue deviating toward the weaker side on protrusion).

The masseter muscle has muscle spindles and can be tested via a muscle stretch reflex known as the jaw jerk

12
Q

T or F. The upper motor neuron input to the trigeminal motor nuclei is largely bilateral,

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thus unilateral lesions to motor cortex or corticobulbar fibers do not produce unilateral weakness of jaw opening or closing but the jaw jerk may be increased.

13
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Lesions of motor CN V or its nuclei will cause what?

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unilateral weakness of jaw closure, reduced jaw jerk, and atrophy of the temporalis and masseter muscles.

14
Q

The rules of UMN and LMN change apply here as well as in the spinal cord. The jaw jerk is especially valuable at the bedside when there is concern of cord compression in the neck, typically by cervical spondylosis. Why?

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Because the leg fibers descending in the corticospinal tract lie in the periphery, they are squeezed first and hence the patient develops weakness in the legs and problems with gait. The muscle stretch reflexes in the legs increase. The upper extremities may have combined UMN and LMN picture as explained in another session.

If the jaw jerk is normal or low under these conditions, then the lesion is likely to be in the neck and you would order a cervical MRI to rule out cord compression there. If the jaw jerk is increased as well, then the lesion is not in the neck but above that level, for example a parasagittal meningioma You would order MRI of the head rather than of the neck.

An MRI study costs about $1000, and as a physician, you will be monitored by insurance companies for cost effectiveness in ordering expensive studies.

15
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16
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Cranial nerve VII, the facial nerve, is a mixed motor, parasympathetic, and sensory nerve. The motor component is served by the _____ nucleus (shown in the red box) that lies at the mid pontine level and innervates the muscles of facial expression and several smaller muscles such as the stapedius muscle.

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facial

17
Q

The _______ _______ nucleus is seen just below the facial motor nucleus.

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superior salivatory

18
Q

What does the superior salivary nucleus do?

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This efferent nucleus sends preganglionic, parasympathetic fibers through the intermediate nerve of CN VII. These fibers synapse in parasympathetic ganglia serving the lacrimal and salivary glands.

19
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CN VII and its adjoining intermediate nerve exit the brainstem where?

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at the pontomedullary junction in a region called the cerebellopontine angle.

NOTE: the intermediate nerve lies lateral to the facial nerve as it emerges from this important area.

20
Q

What does this MRI show?

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The MRI shows a right cerebellopontine angle mass found to be an acoustic neuroma, as is the case about 80% of the time. The pathology shows this tumor to be a Schwannoma and it usually arises from the vestibular and not the acoustic nerve, so the purists call it a vestibular Schwannoma while everyone else is used to acoustic neuroma.

21
Q

This slide depicts a cross section of the brainstem at the level of the facial nucleus shown in orange.

Note how the axons initially pass dorsal medially and loop over the abducens nucleus shown in red before turning ventrally to exit the brainstem at the pontomedullary junction.

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22
Q

Note that the facial nucleus axons create a bulge on the floor of the fourth ventricle called the ____ ______

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facial colliculus.

23
Q

The facial nerve and the nervus intermedius (intermediate nerve) that accompanies it exit the calvarium via what?

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Motor VII exits brainstem at pontomedullary junction. It traverses the cerebellopontine angle to enter the internal auditory meatus to travel in the auditory canal of the petrous bone. It bends ventrally to enter the facial canal and exits the cranium via the stylomastoid foramen.

24
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How do the fibers (nervus intermedius) of the superior salivatory nucleus run?

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They exit the brainstem as a small root adjacent to motor VII. These fibers travel with motor VII to synapse in the sphenopalatine and submandibular ganglia with secondary neurons innervating the salivary glands.

25
Q

How is motor CN VII tested?

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•Test motor CN VII by asking patient to wrinkle their forehead, close their eyes tightly, and to show you their teeth. Look for symmetric furrowing of the forehead, the ability to symmetrically close eyes, and symmetric retraction of the corners of the mouth. Also note the width of the palpebral fissure since weakness of the orbicularis oculi muscle will cause widening of eye opening at rest

26
Q

T or F. Upper motor neuron input to motor CN VII is largely bilateral for the forehead muscles but unilateral for the muscles of the lower face.

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T. Thus, unilateral lesions to motor cortex or corticobulbar fibers causes unilateral weakness of the contralateral lower facial muscles but spares the forehead muscles. A common cause is stroke.

27
Q

Unilateral lower motor neuron lesions of motor CN VIII cause what?

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ipsilateral weakness of the lower face and forehead muscles. Ipsilateral hyperacusis and dry eye may also occur. A common cause is Bell’s palsy.

28
Q

What else does motor CN VII do?

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Motor VII and its nerve mediate the efferent arm of the corneal reflex elicited by gently stroking the cornea and observing eye closure

29
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This slide presents an artist’s idea of an upper motor neuron lesion (Lesion A or B) and a lower motor neuron lesion (Lesion C) involving CN VII. Note sparing of the forehead muscles with an upper motor neuron lesion because of bilateral innervation of CN VII nuclei.

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Two examples of LMN lesions due to Bell’s palsy are shown on the right and one example of an UMN lesion, a patient recovering from a right cortical stroke, is shown on the left.

30
Q

Cranial nerve IX, the glossopharyngeal nerve, is a mixed motor, parasympathetic, and sensory nerve. Its motor component is served by what nucleus?

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the nucleus ambiguus (shown by the red box) that lies near the junction of the pons and medulla and innervates the stylopharyngeus muscle.

31
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What does the stylopharyngeus do?

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It’s a thin, long slender muscle that helps to elevate the larynx, pharynx and dilate the pharynx to facilitate swallowing.

32
Q

What does the inferior salivatory nucleus (shown in the purple box) do?

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lies near the midline of the medulla and sends preganglionic, parasympathetic fibers through CN IX to the otic ganglion with secondary innervation of the parotid gland.

Note that a small yellow box was placed in the figure to block out the line going to the superior salivatory nucleus because it is a component of CN VII. The red arrow points to CN IX.

33
Q

CN IX exits the brainstem at the junction between the pons and the medulla.

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34
Q

The glossopharyngeal nerve exits the calvarium via what?

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the jugular foramen.

35
Q

What does the nucleus ambiguus do again?

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Nucleus ambiguus fibers exit the calvarium via the jugular foramen and innervate the stylo- pharyngeal muscle to raise the pharynx during talking and swallowing.

36
Q

Describe the route of axons of the inferior salivatory nucleus

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Efferent fibers from the inferior salivatory nucleus travel with the 9th nerve and split off as the lesser petrosal nerve before synapsing in the otic ganglion. Secondary neurons then innervate the parotid gland

37
Q

How is CN IX tested?

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CN IX integrity is routinely tested for its sensory or afferent function by inducing a gag reflex. The motor or efferent component of the gag reflex is shared by both CN IX and X but more so by CN X. The reflex is tested by gently touching the posterior pharynx on the left and right separately and watching for the motor, or gag response, and elevation of the soft palate.

The motor fibers of the glossopharyngeal nerve elevate the pharynx during talking and swallowing. Motor IX also participates with the CN X in the motor (efferent) component of the gag reflex so testing the motor function of CN IX in isolation is difficult clinically

38
Q

Upper motor and lower motor neurons lesions may produce what?

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some dysphagia (difficulty swallowing)

39
Q

Cranial nerve X, the vagus nerve, is a mixed motor, parasympathetic, and sensory nerve. Its motor component is served by what nucleus?

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nucleus ambiguus (red box) that lies near the lateral medulla and innervates muscles of the soft palate, pharynx, and larynx.

40
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What does the dorsal motor nucleus of the vagus (purple box) do?

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lies near the midline of the medulla and sends preganglionic, parasympathetic fibers to the intramural ganglia associated with the heart, lung, and digestive tract. The red arrow points to the nerve.

41
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CN X exits the brainstem as a series of rootlets between what structures?

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between the inferior olive and the inferior cerebellar peduncle.

42
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Where does CN X exit the skull?

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CN X exits the calvarium via the jugular foramen along with CN IX and XI.

43
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Anatomy of motor CN X

The nucleus ambiguus fibers travel in CN X to innervate the pharyngeal laryngeal, and palate muscles.

Preganglionic fibers of the dorsal motor nucleus travel with CN X to synapse in intramural ganglia in the walls of the heart, lungs, and gut

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44
Q

The motor fibers of the vagus nerve elevate the pharynx during talking and swallowing

Motor X also participates along with the motor IX in the efferent arm (motor component) of the gag reflex

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The dorsal motor nucleus of the vagus and its parasympathetic fibers influence many autonomic functions including heart rate, respiration, and digestion

45
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Unilateral lesions involving the nucleus ambiguus or CN X will cause what?

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hoarseness, dysphagia, and inability to elevate the palate on the ipsilateral side

46
Q

Unilateral upper motor neuron lesions of CN X tend to cause less prominent symptoms. Why?

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since there is substantial bilateral upper motor neuron innervation of CN X nuclei

47
Q

Cranial nerve XI (shown by the red arrow) is called the spinal accessory nerve. It is a purely motor nerve that controls head turning through innervation of the sternocleidomastoid muscles and shoulder elevation through innervation of the upper trapezius muscles. It receives motor axons from where?

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both the caudal portion of the nucleus ambiguus and the spinal accessory nucleus.

48
Q

The fibers of CN XI originating from the nucleus ambiguus travel for only a short distance with CN XI before joining with what?

A

CN X, the vagus nerve, to innervate the pharynx and larynx; these fibers are more appropriately considered a part of the vagus nerve.

49
Q

The spinal accessory nucleus is comprised of neurons that lie where?

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in the intermediolateral gray area between the dorsal and ventral horns of the first four to five segments of the cervical spinal cord.

50
Q

How do fibers from the spina accessory nucleus run?

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Fibers from the spinal accessory nucleus exit the cord between the dorsal and ventral roots and ascend alongside the spinal cord, enter the calvarium through the foramen magnum and then exit the calvarium through the jugular foramen.

51
Q

This slide shows CN XI axons exiting the lower medulla and upper spinal cord and joining together to form the spinal accessory nerve.

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52
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Motor anatomy of CN XI

The caudal end of nucleus ambiguus sends fibers through the proximal portion of CN XI before joining CN X.

Fibers from the spinal accessory neurons in the C1-C5 cervical cord ascend through the foramen magnum and exit through the jugular foramen to innervate the sternocleidomastoid and the trapezius muscles.

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53
Q

To begin with the simpler presentation of lower motor neuron lesions, i.e. to CN XI or its nuclei, you should understand that a unilateral lesion of CN XI or its nuclei will cause what?

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weakness of the ipsilateral trapezius muscle resulting in difficulty elevating the shoulder ipsilateral to the lesion side. Likewise, the ipsilateral SCM will be weak and there will be difficulty turning the head away from the lesion side since the SCM turns the head to the side opposite its location.

You would also expect to see atrophy of both muscles if the lesion existed for at least several weeks

54
Q

Now for the more complex upper motor neuron lesions of CN XI. Unilateral upper motor neuron lesions will cause what?

A

weakness of the contralateral trapezius muscle in the typical crossed-control pattern for most cranial nerve and appendicular muscles.

However, CN XI nuclei controlling the SCM muscle receive ipsilateral rather than contralateral innervation from the motor cortex via the ventral corticospinal tract. The latter innervation assures that the head turns in the direction of the active arm and hand, e.g. when you reach out to catch a ball with your right hand (under control of left motor cortex) you want your head and eyes turned toward the right looking at the hand catching the ball. Since the left SCM turns the head to the right the left upper motor neurons innervates the left SCM instead of the right.

55
Q

Unilateral upper motor neuron lesions will cause weakness of contralateral shoulder elevation and weakness of the ipsilateral SCM muscle. Thus a left upper motor neuron lesion will produce weakness of elevating the right shoulder and turning the head to the right (left SCM)

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56
Q

Cranial nerve XII is called the hypoglossal nerve and it is a pure motor nerve that controls tongue movement. It is served by what nucleus?

A

the hypoglossal nucleus that lies near the midline in the mid to posterior portion of the medulla.

57
Q

CN XII axons exit the brainstem ventrally between what structures?

A

the inferior olives and the pyramids.

58
Q

This slide shows CN XII axons as a group of nerve fibers exiting the brainstem between the inferior olives and pyramids and then joining together to form the hypoglossal nerve.Note the location of the nerve lying at the junction of the medulla and spinal cord.

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59
Q

CN XII exits the calvarium through its own foramen called ______

A

the hypoglossal foramen that lies along the posterior aspect of the petrous temporal bone.

60
Q

The hypoglossal nerve innervates all intrinsic and extrinsic tongue muscles. The tongue protrudes from the mouth in the midline in normal individuals. Contraction of the tongue muscles on the left pushes the tongue out the mouth towards the right and vice versa. Thus unilateral lesions of CN XII or its nuclei (lower motor neuron) will produce what?

A

tongue protrusion towards the side of the lesion, unilateral atrophy and fasciculations

61
Q

Note also that lower motor neuron lesions of CN XII will result in unilateral tongue atrophy and fasciculations of the tongue muscle. In contrast, upper motor neuron lesions, i.e. those of the motor cortex or corticobulbar fibers, will cause the tongue to protrude away from the lesion since the corticobulbar fibers cross over to the opposite side to innervate the hypoglossal nuclei

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