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Neuroanatomy > Cranial Nerves - IX, X, XI & XII > Flashcards

Cranial Nerves - IX, X, XI & XII Flashcards

1
Q

Where does the glossopharyngeal nerve leave the brainstem?

Where are its cell bodies located?

A
  • it leaves the brainstem at the level of the cerebellopontine angle
  • it passes lateral to the olive and inferior to the cerebellar peduncle
  • some cell bodies are locard within the superior ganglion of IX and some are located within the inferior ganglion of IX
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2
Q

What are the 5 nuclei associated with IX and what fibre type do they receive?

A

SVA fibres:

  • associated with the rostral solitary nucleus

GVE fibres:

  • associated with the inferior salivatory nucleus

GVA fibres:

  • associated with the caudal solitary nucleus

SVE fibres:

  • associated with the rostral nucleus ambiguus

GSA fibres:

  • associated with the trigeminal sensory nucleus
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3
Q

Where does the vagus nerve leave the brainstem?

Where are the cell bodies found?

A
  • leaves the brainstem just inferiorly to IX and is made up of many different rootlets
  • cell bodies are found in the superior ganglion of X and the inferior ganglion of X
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4
Q

What are the 5 nuclei associated with the vagus nerve and what fibre type do they receive?

A

SVE fibres:

  • associated with the caudal nucleus ambiguus

SVA fibres:

  • associated with the rostral solitary nucleus

GVE fibres:

  • associated with the dorsal motor nucleus of X

GVA fibres:

  • associated with the caudal solitary nucleus

GSA fibres:

  • associated with the trigeminal sensory nucleus
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5
Q

What is the role of the nucleus ambiguus and which nerves is it associated with?

A
  • the nucleus ambiguus has roles in speech and swallowing
  • it is associated with IX and X
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6
Q

Describe the pathway of the UMN and LMNs associated with the nucleus ambiguus

A

UMN:

  • travels from the motor cortex and through the corticobulbar tract of the internal capsule
  • sends bilateral projections to both the superior (rostral) and inferior (caudal) poles of both nuclei ambiguus
  • UMN synapses with LMN within the relevant pole of the nucleus ambiguus

LMN from superior pole of nucleus ambiguus:

  • SVE fibres travel in IX to innervate stylopharyngeus

LMN from inferior pole of nucleus ambiguus:

  • SVE fibres travel in X to innervate the palatine muscles, pharyngeal constrictors and intrinsic muscles of the larynx
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7
Q

What would happen if there was a lesion to the UMN or the nucleus ambiguus involved in speech / swallowing?

A

there would be no significant defect

  • this pathway is served bilaterally, so a neurone from the opposite side of the brain would still send projections to the superior and inferior poles of the nucleus ambiguus on both sides
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8
Q

What would happen if there was a lesion to the vagus nerve (LMN) travelling from the inferior pole of the nucleus ambiguus to the relevant muscles?

A
  • SVE fibres would not be able to reach the muscles that X usually supplies, resulting in:
  1. atrophy & paralysis of the palatine muscles
  2. nasal speech due to paralysis
  3. deviation of the uvula away from the lesion
  4. problems with speech and swallowing
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9
Q

Why does the uvula deviate AWAY from the lesion when there is a vagus nerve lesion?

A
  • usually the palatine arches will elevate symmetrically
  • if there is a lesion on the left side, the left levator veli palatini muscle is not working effectively
  • the left palatine arch is unable to elevate, causing the uvula to deviate towards the right
  • Uvula deviation is a sign of a vagus nerve lesion*

Right uvula deviation suggests left vagus nerve lesion, and vice versa

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10
Q

What is the pathway involved in sending parasympathetic neurones to thoracic and abdominal viscera?

A

UMN:

  • hypothalamus sends an UMN to the dorsal motor nucleus of X
  • the UMN synapses with the pre-ganglionic GVE fibres within the dorsal motor nucleus of X

LMN:

  • preganglionic GVE fibres travel in X to specific ganglia located near the target organ
  • the postganglionic fibres will innervate thoracic and abdominal viscera
  • these GVE fibres are parasympathetic so are associated with “rest and digest” functions
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11
Q

What is the vagal trigone and where can it be found?

A
  • it is a bulge located on the dorsal aspect of the brainstem
  • it is found in the floor of the IVth ventricle
  • it is caused by the presence of cell bodies of the dorsal motor nucleus of X and the nucleus ambiguus
    • the bulge is mainly due to the presence of cell bodies within the dorsal motor nucleus
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12
Q

How is the solitary nucleus divided and what fibre types are received by each division?

A

Caudal solitary nucleus:

  • receives GVA fibres associated with the condition of internal organs (IX, X)

Rostral solitary nucleus:

  • receives SVA fibres associated with taste (VII, IX, X)
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13
Q

Where do IX and X carry GVA fibres from to reach the caudal nucleus solitaris?

A

IX carries GVA fibres from:

  • baroreceptors in the carotid sinus
  • chemoreceptors in the carotid body

X carries GVA fibres from:

  • mucosa of the pharynx, larynx, soft palate & thoracic / abdominal viscera
  • baroreceptors in the aortic arch
  • chemoreceptors in the aortic arch
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14
Q

How does viscerosensory information carried by IX reach the brain?

Where does this information come from?

A
  • baroreceptors in the carotid sinus monitor changes in blood pressure
  • chemoreceptors in the carotid body monitor blood composition (including levels of O2 and CO2
  • baroreceptors and chemoreceptors send GVA fibres via IX
  • cell bodies are located in the inferior ganglion of IX
  • the central processes of IX reach the brainstem and descend to reach the caudal solitary nucleus via the solitary tract
  • from the caudal solitary nucleus, a second order neurone projects to the hypothalamus
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15
Q

How does viscerosensory information carried by X reach the brain?

Where does this information come from?

A
  • X carries GVA fibres carrying sensory information from:
  1. pharynx / larynx
  2. thoracic / abdominal viscera
  3. information about blood pressure / chemistry at the level of the aortic arch
  • cell bodies are located in the inferior ganglion of X
  • central process of X reaches the brainstem and descends within the solitary tract to reach the caudal solitary nucleus
  • ascending projections travel from the caudal solitary nucleus to the hypothalamus to inform it about the current state of the viscera
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16
Q

Which spinal roots contribute to the spinal accessory nerve?

What path does this take into and out of the skull?

A
  • spinal rootlets from C1-C5 merge to form one large spinal root
  • this travels up into the skull via the foramen magnum
  • the spinal root is joined by the cranial root of XI (part of X) after it passes through foramen magnum
  • both X and XI leave the skull via the jugular foramen
17
Q

What type of fibres are found in XI?

What do they innervate?

A
  • XI is a purely motor nerve that contains SVE fibres only
  • fibres of XI innervate sternocleidomastoid and trapezius muscles bilaterally
  • bilateral innervation means that an UMN lesion does not lead to significant paralysis of these muscles
18
Q

What is the result of a lesion to XI (LMN)?

A
  • it will affect both trapezius and sternocleidomastoid on the SAME side as the lesion
  • paralysis of trapezius leads to drooping of the shoulder towards the affected side
    • fibres of trapezius are unable to assist in elevating the shoulder
  • paralysis of SCM leads to difficulty turning the head to the side opposite the lesion against resistance
19
Q

Where does XII leave the brainstem and skull?

A
  • it leaves the brainstem at the level of the medulla between the pyramids and inferior olives
  • it leaves the skull via the hypoglossal canal
20
Q

Where is the hypoglossal nucleus located?

What fibre type is it associated with?

A
  • the hypoglossal nucleus is associated with GSE fibres
  • it is located dorsally and medially within the open medulla
  • fibres travel from the hypoglossal nucleus to leave the medulla between the olives and the pyramids
21
Q

What is the hypoglossal trigone?

A
  • the cell bodies within the hypoglossal nucleus form a bulge in the floor of the IVth ventricle at the level of the open medulla
  • the hypoglossal nucleus is located dorsally and medially within the open medulla
22
Q

Describe the pathway involved in innervating the extrinsic muscles of the tongue

A

UMN:

  • projects from the precentral gyrus and travels through the corticobulbar tract at the level of the internal capsule
  • UMN projects to the CONTRALATERAL hypoglossal nucleus at the level of the open medulla
  • UMN synapses with LMN within the contralateral hypoglossal nucleus

LMN:

  • LMN carries GSE fibres via CN XII from the hypoglossal nucleus
  • LMN will innervate ALL of the extrinsic muscles of the tongue
23
Q

What is strange about the innervation of the hypoglossal nucleus compared to other cranial nerve nuclei?

A
  • most cranial nerve nuclei receive bilateral projections from the UMN travelling via the corticobulbar tract
  • the hypoglossal nucleus (and lower facial nucleus) receive contralateral projections only
24
Q

What is the normal action of genioglossus?

A
  • usually contraction of genioglossus causes protrusion of the tongue
  • the muscles of the tongue on both sides work simultaneously to cause protrusion of the tongue
25
Q

What happens if there is a lesion to XII (LMN)?

A
  • there is deviation of the tongue towards the side of the lesion (ipsilateral side)
26
Q

What happens if there is a lesion to the UMN travelling to the hypoglossal nucleus?

A
  • there is deviation of the tongue away from the lesion (contralateral side)
  • UMN lesion means that there is no stimulus travelling to the contralateral hypoglossal nucleus
  • there are no GVE fibres travelling to the muscles of the tongue on the contralateral side
  • paralysis of tongue muscles on the contralateral side allows the non-paralysed muscles to “take over” and cause the tongue to deviate towards the paralysed side
27
Q

Identify the trigones / tubercles

A
  • hypoglossal trigone and vagal trigone are present on the floor of the IVth ventricle at the level of the open medulla
    • hypoglossal trigone is more medial than the vagal trigone
  • the gracile nucleus and cuneate nucleus are located at the level of the closed medulla
  • the trigeminal tubercle is located more laterally and in the caudal medulla

Neuroanatomy (16 decks)

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