Sensory CN: I, II, V, VII, VIII, IX, and X Flashcards Preview

Neurology Week 2 > Sensory CN: I, II, V, VII, VIII, IX, and X > Flashcards

Flashcards in Sensory CN: I, II, V, VII, VIII, IX, and X Deck (64)
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1
Q

Early in development, the neural tube is separated into a dorsal (posterior) alar plate and a ventral (anterior) basal plate by what?

A

the sulcus limitans; Nuclei dorsal to the sulcus limitans are sensory (afferent) and nuclei ventral to the sulcus limitans (in basal plate) are motor (efferent).

2
Q

This is a cross-section through the neural tube. The red arrows indicate the sulcus limitans. Sensory nuclei (green, blue, purple) are dorsal to the sulcus limitans (in the alar plate). Motor nuclei (shown yellow, gold, red) are located ventral to the sulcus limitans in the basal plate.

A
3
Q

This is a posterior view of the adult brainstem with the cerebellum removed to show the floor of the fourth ventricle (within red square).

In the adult the neural tube has opened dorsally, thus the alar plate is displaced laterally, relative to the basal plate. This is as if you took a hose (neural tube), used a knife to slit the top (dorsal) side along the length of the hose, and then grabbed the cut ends and pulled them laterally (see next slide)

Note the rhomboid shape of the floor of the ventricle. The sulcus limitans can be seen as the outer margin of the floor of the fourth ventricle.

The yellow line indicates the plane of section for the next slide.

A

This is a cross section of the adult rostral medulla taken at about the level of the yellow line in the previous slide. The dotted lines indicate the sulcus limitans (border of the floor of the fourth ventricle) and mark the boundaries between the alar plate (dorsal) and the basal plate (ventral). Sensory nuclei are in the alar plate and motor nuclei in the basal plate.

4
Q

Note that there are three sensory nuclei for the Trigeminal nucleus, namely:

A

chief sensory, spinal, and mesencephalic nuclei of V

5
Q

The chief sensory and mesencephalic nuclei of CN V are typical discrete nuclei in the _____ and _________, respectively.

A

pons and mesencephalon

6
Q

The spinal nucleus of CN V extends as a column from the mesencephalon to the spinal cord, where it is continuous with what?

A

the substantia gelatinosa of the spinal cord (layers I and II). Several cranial nerves (V, VII, IX, X) project to this nucleus.

7
Q

Also in the pons, the vestibular nuclei and cochlear nuclei are concerned with body position and hearing, respectively. They are associated with _____

A

CN VIII.

8
Q

Several cranial nerves project to the solitary nucleus (nucleus solitarius). The rostral part of the nucleus is concerned with what?

A

taste (CNs VII, IX, X) and the caudal part of the nucleus is concerned with cardiorespiratory inputs.

9
Q
A
10
Q

Cranial nerve I is completely sensory. It serves olfaction. The sensory receptors reside where?

A

in the nasal epithelium. These cells send very fine axons (olfactory nerves or filae) through the cribriform plate to synapse in the olfactory bulb.

11
Q

Axons of projection neurons in the olfactory bulb project where?

A

travel as the olfactory tract to synapse in olfactory cortex, amygdala, and related forebrain structures.

12
Q

Cranial nerve II is the Optic Nerve. It is completely sensory - it transmits visual input to the brain. The receptors are located in the retina, at the rear of the eye. The optic nerve is made up of axons of retinal ganglion cells. Describe the route of the optic nerves

A

The optic nerves from each eye converge just outside the mesencephalon. At this point, about 50% of the fibers from each eye cross to the opposite side of the body at the optic chiasm (“cross”). Central to the chiasm, the fibers run as the optic tract.

13
Q

Describe the route of the optic tract

A

The optic tract runs along the outside of the mesencephalon to the lateral geniculate body (the visual thalamus: LGN), which in turn projects to primary visual cortex (banks of calcarine fissure).

NOTE: Some optic nerve fibers bypass the LGN and instead travel in the brachium (“arm”) of the superior colliculus to synapse in the superior colliculus (tectum of mesencephalon). This input is important for visual “startle” reflexes.

14
Q

Cranial Nerve V is the Trigeminal nerve. This system is the primary one for somestheses for the face. Peripherally, there are three main branches to the nerve:

A

V1 = Ophthalmic, V2 = Maxillary, and V3 = Mandibular.

15
Q

In addition to motor innervation of muscles of mastication (and a few other muscles), the trigeminal nerves carry fine touch, proprioception, and pain and temperature afferents from the skin of the face region.

Note that the back of the head is mostly innervated by spinal nerves from C2. Also note the complicated arrangement for innervation of the external ear (pinna) by multiple cranial nerves.

A
16
Q

There are three sensory nuclei associated with the trigeminal nerve, namely:

A

The chief sensory nucleus of V, the mesencephalic nucleus of V, and the spinal nucleus of V.

17
Q

Where is the chief sensory nucleus found? What does it relay?

A

The chief sensory nucleus is located in the rostral pons and receives epicritic inputs from afferents for fine touch and vibration sense from the face.

It is thus analogous to the posterior column nuclei (chief sensory nucleus of V is to fine touch for the face as posterior columns are for fine touch from the body).

18
Q

Epicritic afferents in the trigeminal nerve have their cell bodies where?

A

in the trigeminal (or Gasserian) ganglion. This ganglion is located outside of the brainstem and is analogous to the dorsal root ganglia associated with the spinal cord.

The central process of these cells synapse in the chief sensory nucleus.

19
Q

It is important to note that fine touch afferents that run in other cranial nerves (VII, IX, X) have cell bodies in different peripheral ganglia but also synapse in the chief sensory nucleus of V. The chief sensory nucleus is thus the first integration center for all fine touch and vibration inputs for the face region.

A
20
Q

The mesencephalic nucleus of V contains the cell bodies of what?

A

proprioceptive afferents (spindle organs, Golgi tendon organs, etc.) from the muscles of mastication (and probably extraocular muscles and muscles of the tongue). It is essentially a displaced peripheral ganglion in the tegmentum of the mesencephalon. The peripheral processes of these cells form the mesencephalic tract of V.

21
Q

The spinal nucleus of V extends from the mesencephalon to the spinal cord, where it becomes continuous with what?

A

the substantia gelatinosa (layers I and II of dorsal horn).

22
Q

The spinal tract of CN V receives inputs from what sensations?

A

pain and temperature afferents for the face that run in cranial nerve V, as well as cranial nerves VII, IX, and X.

23
Q

Pain and temperature afferents in branches of V have their cell bodies in the _______ ganglion.

A

trigeminal.

The central processes of these cells project into and synapse in the spinal nucleus of V. These axons, as well as second order axons from the spinal nucleus of V, run in the associated spinal tract of V.

24
Q

What is the trigeminal lemniscus?

A

Path that runs from the chief sensory nucleus of V to the ventroposteromedial nucleus (VPM) of thalamus. It is analogous to the medial lemniscus for spinal pathways.

25
Q

What is the trigeminothalamic tract?

A

Tract that runs from the spinal nucleus of V to the VPM. It is analogous to the spinothalamic tract for spinal pathways.

26
Q

Summary of chief nucleus of CN V

A

Input: from discriminative touch, vibraiton, conscious proprioception.

Output: Second order neurons travel in the contralateral trigeminal lemniscus and terminate in the VPM of the thalamus; Second-order neurons from affarents from inside the mouth travel in the ipsilateral posterior trigminothalamic tract

27
Q

Summary of spinal nucleus of CN V

A

Input: pain and temp

Output: Second-order neurons travel in the contralateral trigeminothalamic tract, collaterals to pain-modulating systems terminate in the VPM of the thalamus

28
Q

Summary of mesencephalic nucleus of CN V

A

Input: Nonconscious proprioception from the muscles of mastication

Output: Central processes travel to the reticular formation, cerebellar, and motor nucelus of CN V

29
Q

Afferents from the different cranial nerves and nerve branches remain segregated within the spinal tract and nucleus of V (somatotopic organization). This is indicated in the figure by the color coding.

A

Afferents from CNs VII, IX and X are located most dorsal.

Afferents from the mandibular branch of V (V3) are next most dorsal (posterior), followed by afferents from V2 (maxillary), with ophthalmic (V1) afferents the most ventral (anterior).

This pattern can be useful for localizing brain stem lesions.

30
Q

The cell bodies of proprioceptive afferents from muscles of mastication (also extraocular muscles and tongue) are located where?

A

in the mesencephalic nucleus of V. These cells project bilaterally to the trigeminal motor nucleus (TrMNu) to mediate monosynaptic stretch reflexes.

31
Q

The cell bodies of afferents for fine touch and vibration sense of the face are located where?

A

in ganglia outside of the brainstem (especially the trigeminal ganglion (V), but also geniculate for VII, for inferior and superior glossopharyngeal for IX, inferior and superior vagal for X).

The central processes of these cells project to the chief (principal) sensory nucleus of V. Second order projections from this nucleus cross the midline and travel in the trigeminal meniscus to the VPM (thalamus).

32
Q

The cell bodies of pain and temperature afferents are located where?

A

in various ganglia (Trigeminal for V, geniculate for VII, inferior and superior glossopharyngeal for IX, inferior and superior vagal for X).

Thus several cranial nerves contribute to this nucleus (V, VII, IX, X). Their central processes project into the spinal tract of V and synapse in the spinal nucleus of V. The second order projections cross the midline and travel in the trigeminothalamic tract (also shown in red).

33
Q

In addition to its motor functions, Cranial nerve VII (facial) has two sensory components:

A

taste sensation for the anterior 2/3 of the tongue and somesthetic afferents (fine touch, vibration, pain and temperature) for a small area around the external auditory meatus.

34
Q

Cell bodies for the somesthetic afferents of CN VII are located where?

A

in the geniculate ganglion. The central processes project to the chief sensory nucleus of V (epicritic) or spinal nucleus of V (pain and temperature).

35
Q

GSA (general somatic afferents) (i.e. for discriminative touch, pain, and temp from the outer ear) for CN VII go where?

A

chief sensory trigeminal nucleus

spinal trigeminal nucleus

second order neurons then travel in the contralateral lemniscus and terminate in the VPM of the thalamus

36
Q

SVA (special visceral afferents) (i.e. taste from the anterior 2/3rds of the tongue) for CN VII go where?

A

to the nucleus of the solitary tract, and then output to the ipsilateral insula

37
Q

SVE (special visceral efferents) (i.e. motor innervation to the muscles of facial expression) for CN VII go where?

A

from the facial nucleus in the braimstem to motor neurons through contralateral innervation from the primary motor cortex via the corticobulbar tract to the lower face

bilateral innervation from the cingulate gyrus via the corticobulbar tract to the upper face

38
Q

GVE (general visceral efferents) (i.e. parasympathetics innervation to lacrimal, submandibular, and sublingual glands) for CN VII go where?

A

from the superior salivatory nucleus via the hypothalamus

39
Q

The nucleus solitarius runs as a column through the pons and medulla. The rostral portions of this nucleus are also called _______

A

the gustatory nucleus and are concerned with taste sensation. The gustatory nucleus receives inputs from CNs VII, IX, and X.

40
Q

The rostral part of nucleus solitarius is the gustatory nucleus. It receives taste input (indicated in red) from CNs VII (anterior 2/3 of tongue), IX (posterior 1/3 of tongue), and X (pharynx and epiglottis).

The caudal part of the solitary nucleus is known as what?

A

the cardiorespiratory nucleus. It receives visceral sensory input (glands, chemoreceptors, baroreceptors: shown in blue) carried by CNs VII, IX, and X.

41
Q

The vestibulocochlear nerve (cranial Nerve VIII) has one functional component (sensory) with 2 divisions:

A
  1. vestibular (balance and acceleration)
  2. auditory (hearing)
42
Q

The sensory afferents for audition (hearing) and vestibular sense (body position in space) are located where?

A

in the inner ear- Auditory receptors (hair cells) are located in the organ of Corti in the cochlea. These receptors are sensitive to airborne pressure waves, as transduced into fluid waves in the cochlea. Depending on location in the cochlea, these receptors are tuned to different frequencies of sound (tonotopic organization). Auditory afferents travel in CN VIII.

43
Q

Vestibular receptors are also hair cells. The vestibular hair cells are located where?

A

in the saccule, utricle, and three semicircular canals. Vestibular afferents also travel in CN VIII.

44
Q

The cell bodies of auditory afferents are located where?

A

in the spiral ganglion. These cells send axons in CN VIII (cochlear division) to synapse in the dorsal and ventral cochlear nuclei.

45
Q

Hair cells and supporting cells comprise the organ of Corti, located in the cochlea. Hair cells synapse on cells in the spiral ganglion. Spiral ganglion cells send their axons in the cochlear division of the vestibulocochlear nerve.

The vesitbulocochlear nerve fibers synapse where?

A

in the ipsilateral dorsal and ventral cochlear nuclei (at the pontomedullary junction). From this point, auditory pathways ascend bilaterally to the inferior colliculus. Inferior colliculus neurons project in turn to the medial geniculate body (auditory thalamus). The medial geniculate projects to auditory cortex (Heschel’s gyrus: transverse gyri in superior temporal lobe).

46
Q

The other division of CN VIII is vestibular. This system is important for what?

A

adjustment of posture, regulating muscle tone, and for coordination of eye movements. The hair cells are located in the semicircular canals, saccule and vestibule.

47
Q

Vestibular hair cells synapse where?

A

on cells in the vestibular ganglion (Scarpa’s ganglion). These cells send their axons in the vestibular division of the vestibulocochlear nerve (VIII).

48
Q

Where do axons from the vestibular ganglion go?

A

The axons of cells from the vestibular ganglion synapse in the vestibular nuclei (located in the pons and rostral medulla, near floor of fourth ventricle).

49
Q

NOTE: There are four vestibular nuclei (superior, lateral, medial, inferior).

The lateral vestibular nucleus gives rise to what?

A

the lateral vestibulospinal tract, a descending motor pathway (balance and extensor tone).

50
Q

The medial vestibulospinal tract arises from what vestibular nuclei?

A

the medial and inferior vestibular nuclei.

51
Q

What does the medial vestbulospinal tract do?

A

It only extends to cervical levels of the cord and helps control neck and head position.

52
Q

The medial and superior vestibular nuclei contribute to what?

A

the medial longitudinal fasciculus (MLF), which is important for coordinating eye movements.

53
Q

In addition to motor functions, CN IX mediates what?

A

taste from the posterior 1/3 of the tongue,

somatic sensation from the pharynx and posterior 1/3 of the tongue,

chemo- and baroreception from the carotid sinus and carotid bodies,

and fine touch and pain and temperature from the middle ear and a portion of the external ear.

54
Q

CN IX is associated with several nuclei in the brainstem. This nerve sub serves taste from the posterior 1/3 of the tongue. These afferents terminate where?

A

in the rostral solitary tract (gustatory nucleus).

55
Q

Afferents from Baroreceptors (carotid sinus) and chemoreceptors (carotid body) are carried by IX and project where?

A

to the caudal part of the solitary nucleus and tract.

56
Q

The ______ ________ is a motor nucleus containing neurons that project with CNs IX and X efferents.

A

Nucleus Ambiguous

57
Q

Pain and temperature afferents from the posterior 1/3 of the tongue, pharynx, tonsils, tympanum, and a small area around the external ear travel in CN IX afferents and project where?

A

into the spinal tract and nucleus of V.

58
Q

Afferents for Epicritic touch from the posterior 1/3 of the tongue, pharynx, tonsils, tympanum, and a small area around the external ear travel in IX and project where?

A

to the Chief Sensory Nucleus of V.

59
Q

Afferents from Baroreceptors (carotid sinus) and chemoreceptors (carotid body) are carried by IX and project where?

A

to the caudal part of the solitary nucleus and tract.

60
Q

The sensory components of the vagus nerve include what?

A

taste from the pharynx and epiglottis, visceral information from aortic arch baro- and chemoreceptors, somatic information from pharynx and larynx, and touch and pain and temperature from a small portion of the external ear.

61
Q

The sensory components of the vagus nerve include taste from the pharynx and epiglottis. These afferents project where?

A

to the rostral solitary tract and nucleus.

62
Q

Afferents carrying visceral information from aortic arch baro- and chemoreceptors (CN X) project where?

A

to the caudal solitary tract and nucleus.

63
Q

Afferents carrying somatic information from pharynx, posterior meninges, and larynx, and touch and pain and temperature from a small portion of the external ear (all CN X) project where?

A

into the spinal tract and nucleus of V.

64
Q

The gag reflex is for protecting and clearing the airway in response to an irritant to the palate, pharynx, and associated areas. Describe its afferent and efferent limbs.

A

1) The afferent limb of this reflex is carried by afferents of CN IX projecting to the caudal solitary nucleus.
2) An interneuron is interposed between the afferent and efferent located in the Nucleus Ambiguous.
3) The efferent response is mediated by motoneurons in N. Ambiguous whose axons travel with CN X.