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neuro 3050 > 9/30 - Brainstem Nuclei in the Medulla-Pons > Flashcards

9/30 - Brainstem Nuclei in the Medulla-Pons Flashcards

1
Q

Is the spinal tract of V an ascending or Descending tract?

Does it get larger or smaller as you go up rostrally?

A

Due to fact that Spinal Tract of V is a descending fiber tract, is larger at more rostral levels.

The Spinal Tract of V is getting larger as we go rostrally due to the fact that it enters the brainstem at the level of the pons and descends to the medulla. Thus as we move, rostrally, we will encounter more and more of these axons.

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2
Q

Are the Fasciculus gracilis and the Fasciculus cuneatus ascending or descending tracts?

A

they are both ascending tracts

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3
Q

BRAINSTEM “FUNCTIONS”

A

Cranial Nerves
Integrative
Conduit

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4
Q

Caudal Medulla

A

Closed medulla

Related to Central Canal

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5
Q

Rostral Medulla

A

Open Medulla

Dorsal Surface Opens To 4th Ventricle

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6
Q

The pyramids are formed by ____ .

A

a large group of axons coursing between the cerebral cortex and the spinal cord called the Cortiocspinal Tract.

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7
Q

At the pyramids’ most caudal end, just above the spinal cord, the midline groove that separates the right and left pyramidal tract (the Anterior Median Fissure) seems to blur and become less distinct on the cross section. Why?

A

That is because the axons in this fiber tract cross the midline at this level forming the pyramidal decussation.

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8
Q

Are the pyramids on the ventral or dorsal surface of the brain?
Are they Motor or Sensory?

A

The pyramids are Ventral and motor.

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9
Q

Above the obex, the medulla is called “_____”.

A

Above the obex, the medulla is called “open”.

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10
Q

Fasciculus Gracilis

A

Fiber tract carrying input to Nucleus Gracilis

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11
Q

Fasciculus Cuneatus

A

Fiber tract carrying input to Nucleus Cuneatus

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12
Q

SpV

A

Fiber tract carrying input to Spinal Nucleus of V

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13
Q

Do nucleus gracilis and cuneatus relay the same kind of sensory information the Spinal V does?

A

No, they carry different kinds of sensory information

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14
Q

The olivary tubercle is over what nucleus?

A

the Inferior olive

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15
Q

Are the inferior olives on the ventral or dorsal surface of the brain?
Are they Motor or Sensory?

A

The inferior olives are Ventral and motor.

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16
Q

What changes do you see dorsally between section at transition from spinal cord to medulla and caudal medulla?

A
  1. Fasciculus gracilis gets much smaller (almost gone) and nucleus gracilis enlarges suggesting fiber tract is ending.
  2. Fasciculus cuneatus is getting smaller and nucleus cuneatus is emerging.
  3. Spinal tract of V is getting larger. Nucleus still prominent. Due to fact that this is descending fiber tract that is larger at more rostral levels.
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17
Q

Chaacteristics of a Rostral Medulla Cross Section

A

A wide, large V-shaped depression on the dorsal (top) part of the cross section, representing the 4th ventricle. This depression is much more profound than that of the narrow Posterior Median Fissure, which is visible at more caudal levels.

The inferior olivary nucleus is expanded and it forms a large, obvious, squiggly-shaped protuberance on the ventral surface of the medulla.

Long/Deep Incision on the ventral (bottom) half of the cross section, representing the Anterior Median Fissure.
This incision gets much shorter as you descend past the pyramidal decussation towards the spinal cord.

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18
Q

ROSTRAL MEDULLA - DORSAL

Cross Section and Gross Brain

A

4th ventricle is evident.

Begin to see cranial nerve nuclei for the first time.

Nucleus gracilis and nucleus cuneatus are no longer present.

Spinal tract of V very prominent; Spinal nucleus of V is obscured by large fiber tract but still present.

.On the gross brainstem, 2 new elevations are in the floor of the 4th ventricle. The medial one is the hypoglossal trigone and the lateral bump is the vagal trigone. The names tell you that these bumps are related to cranial nerves X, the vagus, and cranial nerve XII, the hypoglossal.

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19
Q

How does the position of structures change from the Spinal Cord through the Brainstem

A

As the brainstem develops, the 4th ventricle “opens” the brainstem. Structures that were located dorsally in the spinal cord are moved laterally whereas structures that were ventral move dorsal and medial. Visceral structures remain between somatic motor and somatic sensory nuclei.

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20
Q

Nuclei concerned with somatic motor function are generally located ______ .

A

Nuclei concerned with somatic motor function are generally located on the Midline (few exceptions) in the brainstem.

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21
Q

Nuclei concerned with somatic sensory function will generally be located ____.

A

Nuclei concerned with somatic sensory function will generally be located laterally in the brainstem.

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22
Q

Nuclei related to visceral functions (motor or sensory) are located _____.

A

Nuclei related to visceral functions (motor or sensory) are intermediate.

Visceral structures remain between somatic motor and somatic sensory nuclei.

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23
Q

Motor –> Medial

A

Sensory –> Lateral

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24
Q

Which Cranial Nerves are associated with the Nucleus Ambiguous?

A

IX, Glossopharyngeal
X, Vagus
XI, Spinal Accessory

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25
Q

What KIND of Cranial Nerves are associated with the Nucleus Ambiguous?

A

Branchial Motor

This nucleus that contains motor neurons related to cranial nerves IX, X and XI. These neurons innervate branchial musculature in the larynx, pharynx, the neck (sternocleidomastoid & trapezius).

Also, the preganglionic parasympathetic neurons that innervate the heart are located in this nucleus. Remember, cardiac muscle is neither smooth or skeletal. It is its own special type of muscle.

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26
Q

What trigone in just lateral of the Hypoglossal trigone (CN XII) in the gross brainstem?

A

The Vagal trigone (CN X)

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27
Q

The Vagal trigone (CN X) corresponds with what nucleus that is just lateral to the Hypoglossal nucleus in the brainstem cross section?

A

the dorsal motor nucleus of X

This is the nucleus that contains the neurons that give rise to axons in the vagus nerve that innervate smooth muscle; that is these are the preganglionic parasympathetic neurons.

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28
Q

the dorsal motor nucleus of X

A

of the Vagus cranial nerve.

This is the nucleus that contains the neurons that give rise to axons in the vagus nerve that innervate smooth muscle.
Thus, these are preganglionic parasympathetic neurons. The one exception are the neurons that innervate the heart. These are located in another nucleus

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29
Q

nucleus solitarius:

Cross Section Identification

A

On the cross section, it is located just lateral to the dorsal motor nucleus of X. It has a very characteristic dark, roundish appearance that allows it to be easily recognized.

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30
Q

In the medulla, there are 6 cranial nerves, one of which is somatic motor functioning. Which one is that? Where would it be seen in a cross section?

A

The Hypoglossal (XII) Cranial Nerve.

Midline of the dorsal, rostral midbrain, in the light-colored “V” of the 4th Ventricle.

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31
Q

nucleus solitarius

A

The principal visceral sensory nucleus of the brainstem

The site of termination of the visceral primary afferents in the solitary tract.

Located near the floor of the fourth ventricle in the rostral medulla and caudal pons, just lateral to the sulcus limitans and surrounding the solitary tract.

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32
Q

vestibular nuclear complex

A

Cranial Nerve VII

hearing

It is very long and is sensory

It extends from the medulla to the pons.

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33
Q

vestibular nuclear complex:

Cross Section

A

More lateral and dorsal from the Solitarius Nucleus, which is more lateral than the Hypoglossal Nucleus

34
Q

The “rest” of the tegmentum is called the ______.

A

reticular formation.

‘the rest’: the part of the tegmentum that is not cranial nerves or other major nuclei or tracts.

35
Q

Cochlear Nucleus

A

The nuclei in which the primary auditory afferents of the vestibulocochlear nerve terminate. The dorsal and ventral cochlear nuclei form a continuous band of gray matter draped over the inferior cerebellar peduncle near the pontomedullary junction, and project bilaterally to the superior olivary nucleus and into the lateral lemniscus.

Looks like a dog ear on the cross section of the PontoMedullary Junction

36
Q

What structures are visible at the PontoMedullary Junction?

A

The cross section of the PontoMedullary Junction looks a lot like a butterfly.

Cochlear Nucleus (dorsal and very lateral, looks like a dog ear)

Inferior Cerebellar Peduncle (dorsal and lateral)

The 4th Ventricle (dorsal, looks like long thin wings at this level)

Vestibulocochlear Nuclei, Nucleus Solitarius, Spinal V, Pyramids, Inferior Olive

37
Q

List the vessels that Supply Blood to the Medulla

A

Anterior Spinal Artery

Posterior Spinal Artery

Posterior inferior cerebellar Artery (PICA)

AICA

38
Q

BLOOD SUPPLY TO THE MEDULLA

A

The ventral medulla is supplied directly by branches of the vertebral artery. This includes the pyramids and the inferior olive.

Branches of the anterior spinal artery supply midline structures in the ventral medulla and the adjacent tegmentum.

The posterior inferior cerebellar artery (PICA) supply the dorsal and lateral medulla, in addition to the cerebellum. This would include the vestibular nuclei, the cochlear nucleus, nucleus solitarius, and the dorsal motor nucleus of the vagus.

39
Q

Vertebral artery supplies ____ .

A

Vertebral artery supplies ventral and lateral medulla

40
Q

Anterior spinal artery supplies ____ in medulla and ______ .

A

Anterior spinal artery supplies midline structures in medulla and medial tegmentum

41
Q

Posterior inferior cerebellar a. (PICA) supplies ____ medulla and ____

A

Posterior inferior cerebellar a. (PICA) supplies dorsal and lateral medulla and cerebellum

42
Q

BASILAR PONS

A

Extends from exit of cranial nerve VI (abducens: caudal) to exit of cranial nerve III (occulomotor: rostral)

Characterized by transverse oriented bands that coalesce to form middle cerebellar peduncle laterally

Landmarks to demarcate the pons include cranial nerve VI caudally and cranial nerve III rostrally. On the ventral surface it is easily distinguished as it is greatly expanded compared to the medulla. It has the appearance of planks running transversely across the ventral surface giving it a bridge like appearance, hence the name pons which is latin for bridge (think pontoon bridge). This large expanded portion of the pons is the basilar pons.

43
Q

Structures of the Caudal Pons,

From Rostral to Caudal

A

Abducens Nucleus

Basal pons

Facial Motor Nucleus

Spinal Trigeminal (V) tract & nucleus

Vestibular Nuclei

44
Q

Structures of the MidPons,

From Rostral to Caudal

A

Basal Pons

Main Sensory of V –> Medial Lemniscus

Trigeminal Main Sensory Nulcleus

Trigeminal Motor Nucleus

45
Q

Structures of the Rostral Pons,

From Rostral to Caudal

A

Basal Pons

Locus Ceruleus

Superior Cerebellar Peduncle

46
Q

pontine nuclei.

A

Neurons in basilar pons form the pontine nuclei. They give rise to axons that cross the midline and project to the cerebellum as pontocerebellar projections.

47
Q

The ventral, or motor portion of the pons, is called the basilar pons and it appears to protrude from the brain.

A

The dorsal portion is called the tegmentum, and contains several important nuclei and tracts.

48
Q

On the gross brain, the basilar or ventral, pons has the characteristic appearance of bands oriented in the transverse plane.

As on the surface, the basilar pons is characterized by bands of myelinated axons oriented in the transverse plane.

A

These axons converge laterally to form a very large fiber tract that connects the basilar pons to the cerebellum; this large fiber bundle is the middle cerebellar peduncle which is clearly seen in the cross section, as well as on the gross brain.

49
Q

The axons traversing the basilar pons to form the middle cerebellar peduncle are called ____ .

A

pontocerebellar axons.

50
Q

In between the transversely oriented axons are clear spaces indicating the presence of neurons. This collection of neurons in the basilar pons are called pontine nuclei.

A

Neurons in these nuclei give rise to the pontocerebellar axons.

51
Q

A feature of the caudal pons is the presence of axons that appear to be cross cut rather than being oriented in the transverse plane.

A

These distinct axons are the corticospinal tract. They began in the cerebral cortex and will extend to the spinal cord. It is these axons that continue in the medulla as the pyramid.

52
Q

What is the Ventral portion of the Pons?

Is it Motor or Sensory in Function?

A

basilar pons

motor

53
Q

What is the Dorsal portion of the Pons?

A

Tegmentum

54
Q

Tegmentum

A

A general anatomical term for the area anterior to the ventricular spaces of the medulla, pons, and midbrain.

“Tegmentum” is a useful umbrella term (Latin for “covering”) for all structures covering the basal components of the brainstem (pyramids, basal pons, cerebral peduncles) and includes the reticular formation, nuclei of cranial nerves, most ascending and descending tracts (except the corticospinal tract), the red nuclei, and substantia nigra.

55
Q

MIDDLE CEREBELLAR PEDUNCLE

A

The largest of the cerebellar peduncles, containing fibers from contralateral pontine nuclei that end as mossy fibers in almost all areas of cerebellar cortex. Sometimes referred to as the brachium pontis (“arm of the pons”).

The axons traversing the basilar pons to form the middle cerebellar peduncle are called pontocerebellar axons.

56
Q

pontine nuclei

A

A collective term for the many small nuclei in the basal pons that receive afferents from cerebral cortex (via the internal capsule and cerebral peduncle) and project to contralateral cerebellar cortex (via the middle cerebellar peduncle).

57
Q

corticospinal tract

A

They began in the cerebral cortex and will extend to the spinal cord. It is these axons that continue in the medulla as the pyramid.

58
Q

Axons of the facial nerve course dorsally and medially, bend at the abducens nucleus at the genu (G) and then course ventrally and laterally to exit the brainstem.

A

….

59
Q

CAUDAL PONS - DORSAL

Cranial Nerves

A

the location of several nuclei related to cranial nerves IV, V, VI and VII.

At this caudal level, only motor nuclei related to VI & VII are apparent. On the sensory side, we still see the spinal nucleus of cranial nerve V.

The abducens nucleus is located on the dorsal aspect of the caudal pons, immediately adjacent to the midline. Remember: cranial nerve nuclei with a somatic motor component are usually located on the dorsal surface of the brainstem, immediately adjacent to the midline.

The axons of neurons in the abducens nucleus give rise to axons that leave the brainstem at the junction of the pons and medulla and innervate the lateral rectus muscle of the eye.

Another motor nucleus seen at this level is the facial nucleus. Neurons in this nucleus give rise to the facial nerve. You might ask why it isn’t located dorsally and medially since this is a motor component of the facial nerve. However, remember, the facial nerve innervates those Branchiomeric muscles that have a unique embryological origin. Nuclei giving rise to these axons, migrated a bit deeper into the brainstem and occupy a ventral and lateral position.

The axons of the facial nerve have a very interesting course. They do not just exit the brainstem laterally. Rather, the axons leave the nucleus and course dorsally and medially toward the abducens nucleus. On reaching the dorsal surface of the pons, the axons curve around the abducens nucleus forming an internal genu. Then then go back laterally and ventrally to exit from the lateral side of the brainstem at the junction of the pons and medulla.

We still see some of the nuclei described previously, including the Nucleus Solitarius, the Vestibular Nuclei, and the ever present Spinal Nucleus of V.

60
Q

MID PONS - DORSAL Trigeminal Complex

A

Cross sesction through the mid pons.

This section is at the level of the exiting fibers of cranial nerve V the trigeminal nerve.  At this level, finally, we no longer see the spinal nucleus of V.  

However, we are now at a level where we do see other nuclei related to cranial nerve V:  

Motor nucleus of V contains neurons that give rise to axons that innervate the muscles of mastication. 

Main sensory nucleus of V processes information on general touch sensation from the face.

Mesencephalic nucleus of V: this is actually a sensory nucleus that stayed within the CNS, as opposed to migrating to a peripheral sensory ganglion.  These neurons process proprioceptive information from the jaw.

The remainder of the dorsal pons is called the reticular formation.

61
Q

Motor nucleus of V

A

contains neurons that give rise to axons that innervate the muscles of mastication.

62
Q

Main sensory nucleus of V

A

processes information on general touch sensation from the face

63
Q

Mesencephalic nucleus of V

A

this is actually a sensory nucleus that stayed within the CNS, as opposed to migrating to a peripheral sensory ganglion. These neurons process proprioceptive information from the jaw.

64
Q

What composes the main part of V

A

general sensory from face

65
Q

SUMMARY OF TRIGEMINAL NUCLEAR COMPLEX

A

SPINAL TRIGEMINAL NUCLEUS V: Pain & temperature

MAIN SENSORY NUCLEUS V: Touch, pressure

MESENCEPHALIC V: Proprioception from muscles of mastication

MOTOR V: Motor to muscles of mastication

NOTE: The axons of the trigeminal nerve separate the main sensory from the motor trigeminal nucleus in the Cross Section.

66
Q

What is the highest level that the Spinal V is present?

A

the Caudal Pons

67
Q

MESENCEPHALIC V

A

Proprioception from muscles of mastication

Pressure

Is this object in my hand a marshmallow or a walnut?

68
Q

MAIN SENSORY NUCLEUS V

A

Touch, pressure

69
Q

MOTOR V

A

Motor to muscles of mastication

70
Q

SPINAL TRIGEMINAL NUCLEUS V

A

Pain & temperature

71
Q

TRIGEMINAL COMPLEX

A

Dorsal and lateral part of the mid pons, viewing the trigeminal complex of nuclei. The myelinated axons make up the trigeminal nerve.

Some of these axons are carrying sensory information into the brain and some are leaving the CNS to innervate the muscles of mastication.

The axons of the trigeminal nerve separate the main sensory nucleus of V, located laterally, from the motor nucleus, located medially.

The mesencephalic nucleus of V is a small, indisctinct group of neurons that extend from the mid pons into the midbrain. These are sensory neurons that failed to migrate to the periphery. They carry proprioceptive information from the muscles of mastication and the jaw.

72
Q

Trigeminal Neuralgia

Tic Douloureux

A

Trigeminal neuralgia (also called tic douloureux) is a condition characterized by brief attacks of excruciating pain, usually less than a minute in duration, in the distribution of one (or sometimes more than one) division of the trigeminal nerve. Between attacks, there are no significant sensory abnormalities.

Most cases appear to be caused by compression of the trigeminal nerve by a blood vessel or tumor, resulting in demyelination and aberrant activity in trigeminal nerve fibers; subsequent changes in the sensory nuclei where these fibers terminate are likely to be involved as well.

RECENT STUDY: 92% OF PATIENTS WITH PAIN WERE FOUND TO HAVE NEUROVASCULAR COMPRESSION. MOST COMMON VESSEL IS SUPERIOR CEREBELLAR ARTERY.

73
Q

What blood vessel is most commonly the culprit in Trigeminal Neuralgia (Tic Douloureux)?

A

SUPERIOR CEREBELLAR ARTERY

74
Q

RELATIONSHIP BETWEEN SUPERIOR CEREBELLAR A. AND TRIGEMINAL NERVE

A

They are very close to each other, almost touching.

75
Q

Treatment of Trigeminal Neuralgia

A

Trigeminal neuralgia usually can be treated pharmacologically, but a number of surgical treatments are available if necessary. These include:

  1. Expose the lateral brainstem, move the artery away from the nerve and insert a block to prevent contact. This causes no disruption in nerve function.
  2. Lesioning the involved nerve root and/or the trigeminal ganglion (e.g., transction, radio frequency disruption). The destructive procedures have a serious disadvantage, in that the patient loses all tactile sensibility, in addition to pain, in the area. Also lose corneal blink reflex.
  3. Section the spinal trigeminal tract slightly caudal to the obex, thus removing the afferent input to the caudal nucleus. Tactile sensibility remains intact, and the corneal blink reflex is usually preserved.

NOTE: The fact that this operation abolishes pain sensation over one entire half of the face is a major piece of evidence that the caudal part of the spinal trigeminal nucleus deals with pain and that afferents from all 3 divisions of the trigeminal nerve extend at least into the caudal medulla.

76
Q

VASCULAR SUPPLY TO THE PONS

A

Pontine Including: Paramedian, Short Circumferential, Long Circumferential

Superior Cerebellar Artery:
Supplies Dorsal and Lateral Area of Pons.

77
Q

basilar artery

A

The basilar artery is the primary vascular supply to the pons. This is formed by the fusion of the right and left vertebral arteries ascending from the medulla.

78
Q

Long circumferential

A

supply dorsal lateral area of basilar pons

79
Q

Superior Cerebellar Artery supplies ______; there is some overlap with ____ circumferential.

A

Superior Cerebellar A. supplies tegmental area of pons; there is some overlap with long circumferential.

80
Q

Pons’ Blood Supply

A

Various branches of the basilar artery and the territory they supply.

Paramedian branches supply the midline region of the basilar pons and tegmentum.

Short circumferential, which travel a bit more laterally, supply more lateral regions of the basilar pons.

Long circumferential course dorsally to supply the ventral portion of the tegmentum. Dorsally, there is overlap between the long circumferentials and branches arising from the superior cerebellar artery. This would include the area of the trigeminal complex.

81
Q

Pain is carried by thin unmyelinated fibers that are more easily stimulated than myelinated fibers

A

this is relavant to Trigeminal Neuralgia

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