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1019 Neuro > Cranial Nerve Reflexes > Flashcards

Cranial Nerve Reflexes Flashcards

1
Q

What are the protective reflexes in the nervous system?

A

Corneal Blink

Pupillary Light reflex

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2
Q

What reflexes help to coordinate eye movements?

A

Gaze
Vestibulo-ocular reflex
Accommodation

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3
Q

What is the function of the corneal blink reflex?

A

Protective reflex to ensure cornea is lubricated to remove foreign particles from the eye

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4
Q

Outline the corneal blink reflex

A
  1. Ophthalmic Division of Trigeminal Nerve (CN V1) provides sensory innervation to the cornea
  2. Synapse in spinal trigeminal and chief sensory nuclei
  3. Interneurons synapse bilaterally with facial motor nucleus
  4. Axons from facial motor nucleus innervate Orbicularis Oculi for blinking
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5
Q

What is the function of the Pupillary Light Reflex?

A

Limits the amount of light that falls onto the retina.

Pupils constrict in bright light conditions through contraction of constrictor pupillae muscle

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6
Q

Outline the pupillary light reflex

A
  1. Afferent limb begins with photoreceptors of the retina
  2. Sends via optic nerve (CN II) and optic tract through superior colliculus to pretectal area
  3. Projects ipsilaterally and contra laterally via Posterior commissure to Edinger-Westphal Nucleus
  4. Preganglionic parasympathetic fibers travel with E-W nucleus together with oculomotor nerve to orbits and synapse in ciliary ganglia
  5. Innervate constrictor pupillae muscles
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7
Q

What are the cranial nerves that control eye movement?

A

Oculomotor Nerve (CN III), Trochlear Nerve (CN IV), Abducens Nerve (CN VI)

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8
Q

What somatic muscles does the oculomotor nerve (CN III) innervate?

A

Superior, Medial, Inferior Rectus muscles
Inferior oblique
Levator Palpebrae superioris

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9
Q

What visceral muscles does CN III innervate?

A

Intraocular muscles like constrictor pupillae and ciliary muscles

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10
Q

What muscle does the trochlear nerve (CN IV) innervate?

A

Superior oblique muscle

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11
Q

What muscle does the Abducens nerve (CN VI) innervate?

A

Lateral rectus muscle

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12
Q

What is gaze?

A

Coordinated, Synergistic movement of both eyes to focus the image onto the fovea

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13
Q

What structures does gaze involve?

A

Coordinated movement of 2 eyes
6 extrinsic muscles of each eye
3 pairs of cranial nuclei
Medial Longitudinal Fasciculus

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14
Q

What is the function of medial longitudinal fasciculus?

A

Allows coordinated movement of both eyes and adjusts eye position in response to head movement

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15
Q

What is the descending MLF also known as?

A

Medial vestibulospinal tract

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16
Q

What are the 2 general categories of eye movement?

A

Conjugate and Vergence

17
Q

What is the function of saccades?

A

Redirects gaze to an object of interest so that image falls on fovea

18
Q

What cortical and subcortical structures initiate saccades?

A

Frontal eye field
Supplementary eye field
Parietal eye field

19
Q

Where do fibers that initiate saccades project to for horizontal saccades?

A

Contralateral Paramedian Pontine Reticular formation +/- ipsilateral superior colliculus

20
Q

Where do fibers that initiate saccades project to for vertical saccades?

A

Rostral Midbrain reticular formation (RMRF)

21
Q

Outline the coordination of horizontal conjugate eye movement (saccades)

A
  1. Abducens and Oculomotor nerve receives input from PPRF to direct gaze IPSILATERALLY
  2. Cell bodies of somatic motor neurons send projections to ipsilateral lateral rectus
  3. Axons from interneurons cross midline and ascend in MLF to contralateral Oculomotor nerve
  4. Oculomotor neuron innervates ipsilateral medial rectus so eye moves to contralateral side

Results in abduction of left eye by the left lateral rectus and adduction of right eye by right medial rectus

22
Q

What happens to horizontal gaze when there is a lesion in the tegmentum of caudal pons?

A

Loss of conjugate gaze on side of lesion

Eyes deviated away from side of lesion

23
Q

What happens to horizontal gaze when there is cortical lesion?

A

Loss of conjugate gaze away from side of lesion

Eyes deviate to side of lesion

24
Q

What structure provides main input for reflexive saccades?

A

Superior colliculus

25
Q

What is the function of a smooth pursuit?

A

Track a slow moving object to keep object on fovea

26
Q

What is the function of the Vestibulo-ocular reflex?

A

Generates eye movement to counteract head movements to maintain a stable image on the retina

27
Q

Outline the Vestibulo-ocular reflex

A
  1. Head movement detected by vestibular nerve of CN VIII through mechanoreceptor hair cells at pontomedullary junction
  2. Vestibular nuclei in brainstem decussate, project to contralateral abducens nucleus and move lateral rectus
  3. Project ipsilateral to oculomotor nucleus via median longitudinal fasciculus
  4. Oculomotor nerve moves medial rectus.

Response: if head moves to the right, compensatory eye movements to the left; if head moves to the left, compensatory eye movements to the right

28
Q

When does accommodation happen?

A

When we focus on a near object

29
Q

What are the 3 things that must happen for a near image to be projected on the fovea?

A

Eye must converge: Moving towards midline via activation of medial rectus

Increased refractive power by increasing curvature of lens

Pupil constriction: Increases depth of field

30
Q

Outline the accommodation reflex

A
  1. Nasal retinal fibers of CN II decussate at optic chiasm
  2. Optic tract projects to lateral geniculate nucleus (thalamus) -
  3. projection fibres travel to calcerine sulcus occipital lobe via optic radiation
  4. . Oculomotor nerve stimulated to innervate medial rectus muscles
  5. . Project to Edinger-Westphal nuclei for pupillary constriction by stimulating constrictor pupillae muscles
  6. . Stimulation of ciliary muscle leads to relaxation of the lens, increasing curvature

1019 Neuro (9 decks)

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