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Neurobiology > Eye Movements and Pupillary Control > Flashcards

Eye Movements and Pupillary Control Flashcards

1
Q

What are the 6 extraocular eye muscles and their functions for the primary positions of the eye?

A
  • Lateral rectus: abduction
  • Medial rectus: adduction
  • Superior rectus: elevation and intorsion
  • Inferior rectus: depression and extorsion
  • Superior oblique: intorsion and depression
  • Inferior oblique: extorsion and elevation
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2
Q

What are the functions of recti and oblique extraocular muscles when the eye is in an abducted position?

A
  • Superior rectus: elevation only
  • Inferior rectus: depression only
  • Superior oblique: intorsion only
  • Inferior oblique: extorsion only
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3
Q

What are the functions of recti and oblique extraocular muscles when the eye is in an adducted position?

A
  • Superior rectus: intorsion only
  • Inferior rectus: extorsion only
  • Superior oblique: depression only
  • Inferior oblique: elevation only
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4
Q

What muscles are innervated by cranial nerve 3, oculomotor nerve?

A
  • Medial rectus
  • Superior rectus
  • Inferior rectus
  • Inferior oblique
  • Levator palpebrae superioris
  • Pupil constrictor and ciliary muscles (parasympathetic input)
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5
Q

What muscle is innervated by cranial nerve 4, trochlear nerve?

A

Superior oblique

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6
Q

What muscle is innervated by cranial nerve 6, abducens nerve?

A

Lateral rectus

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7
Q

What nuclei make up the somatic motor column near midline of the brainstem?

A
  • Oculomotor nucleus
  • Trochlear nucleus
  • Abducens nucleus
  • Hypoglossal nucleus
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8
Q

Describe the pathway of the oculomotor nerve

A
  • Arises from oculomotor nucleus and edinger-westphal nucleus and exits midbrain at the intrapeduncular fossa near superior colliculi and red nucleus
  • Travels between posterior cerebral artery and superior cerebellar artery
  • Travels in subarachnoid space where it splits into the superior division to innervate superior rectus and levator palpebrae and the inferior division to innervate medial and inferior recti, inferior oblique, and pupil and ciliary muscles
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9
Q

What are the symptoms of oculomotor nerve palsy?

A
  • Paralysis of all ipsilateral extraocular muscles except superior oblique and lateral rectus: eye rests “down and out” in intorsion, depression, and abduction causing diplopia that worsens when looking up and medially
  • Paralysis of ipsilateral levator palpebrae superioris: complete eye closure if complete lesion, partial eye closure (drooping) if partial lesion
  • Loss of ipsilateral parasympathetic input: pupil remains dilated and unresponsive to light
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10
Q

The oculomotor nucleus consists of 6 subnuclei, what are they and what do they innervate?

A
  • Dorsal subnucleus –> ipsilateral inferior rectus
  • Intermediate subnucleus –> ipsilateral inferior oblique
  • Ventral subnucleus –> ipsilateral medial rectus
  • Edinger-westphal subnucleus –> bilateral pupillary constrictors and ciliary muscles of the lens
  • Central caudal subnucleus –> bilateral levator palpebrae
  • Medial subnucleus –> contralateral superior rectus
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11
Q

Why would a unilateral oculomotor nucleus not results in unilateral ptosis, unilateral dilated unresponsive pupil, and unilateral superior rectus palsy?

A
  • Levator palpebrae and pupillary constrictor muscles are innervated bilaterally by subnuclei (only one central caudal and edinger-westphal subnucleus), so damage to the nucleus would result in bilateral symptoms
  • Unilateral lesions of the oculomotor nucleus affect both contralateral and ipsilateral superior rectus because fibers cross (fibers that innervate contralateral superior rectus) BEFORE they exit the nucleus, so damage to the nucleus would result in bilateral symptoms
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12
Q

Describe the pathway of the trochlear nerve

A
  • Arises from trochlear nucleus in the lower midbrain
  • Exits the brainstem dorsally and immediately crosses over to innervate contralateral superior oblique
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13
Q

What type of damage is the trochlear nerve susceptible to?

A
  • Compression from cerebellar tumors
  • Shear from head trauma
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14
Q

What are the symptoms of trochlear nerve palsy?

A
  • Paralysis of superior leading to hypertropia (upturned eye) and extorsion
  • Vertical diplopia that improves with chin tuck and head tilt away from affected eye and worsens when looking down and toward midline
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15
Q

Describe the pathway of the abducens nerve

A
  • Arises from the abducens nuclei on the floor of the 4th ventricle in the id to lower pons
  • Exits the brainstem ventrally at the pontomedullary junction
  • Takes a long vertical course to reach the lateral rectus
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16
Q

What type of damage is the abducens nerve susceptible to?

A

Downward traction injury caused by elevated ICP

17
Q

What are the symptoms of abducens nerve palsy?

A
  • Paralysis of the lateral rectus muscle causing decreased abduction of and possible esotropia (eye turning in) of the effected eye
  • Horizontal diplopia that is worse with gaze toward impaired side and far vision and better with near vision or with head turn toward the effected side
18
Q

What eye movements do brainstem circuits control?

A
  • Horizontal eye movements
  • Vertical eye movements
  • Vergence eye movements
19
Q

What is the purpose of brainstem circuits controlling eye movements?

A
  • Eye movements of the left and right are yoked together for conjugate gaze in all directions
  • Eyes can maintain fused fixation as targets move towards or away from you
20
Q

What is the brainstem circuit to control for horizontal eye movements?

A
  • Paramedian pontine reticular formation sends signals from cortex and other brain regions to the ipsilateral abducens nucleus
  • The abducens nucleus sends innervation to ipsilateral lateral rectus via CN 6 and also sends fibers to the contralateral oculomotor nucleus via medial longitudinal fasciculus
  • The oculomotor nucleus sends innervation to the medial rectus (contralateral to originating PPRF) via CN 3
  • Results in abduction of one eye and adduction of the other to direct gaze toward the same side
21
Q

Lesions to what brainstem structures will cause an issue with horizontal gaze?

A
  • Lesion to abducens nucleus or PPRF (ipsilateral lateral gaze palsy): unable to look towards side of lesion with either eye
  • Lesion to MLF (internuclear ophthalmoplegia INO): ipsilateral eye does not adduct during horizontal gaze, convergence not affected, nystagmus is triggered in the opposite eye
  • Lesion to MLF and abducens or PPRF on the same side (one and a half syndrome, INO + lateral gaze palsy): ipsilateral eye has no horizontal movement with eye to either side, contralateral eye has preserved abduction but with nystagmus
  • Lesion to pons (locked in syndrome): impair horizontal eye movements, preserve vertical eye movements
22
Q

How does the brainstem circuit control for vertical eye movements?

A
  • Structures located in the midbrain –> rostral midbrain reticular formation and pretectal area
  • Ventral portion mediates downward gaze
  • Dorsal portion mediates upward gaze
  • Vertical eye movements are closely coordinated with movement of the upper eyelids in the same direction
23
Q

How will brainstem lesions affect vertical gaze?

A
  • Ventral lesions will impair downward gaze
  • Dorsal lesions will impair upward gaze
  • Progressive supranuclear palsy: caused by midbrain atrophy
24
Q

How does the brainstem circuit control for convergence of the eyes?

A
  • Convergence is performed with contraction of bilateral medial recti
  • Divergence is performed with contraction of bilateral lateral recti
  • Mediated by separate neuron pools in the midbrain reticular formation
  • Influenced by descending inputs
25
Q

Describe cortical control of eye movements

A
  • Frontal eye fields generate saccades in the contralateral direction via connection to contralateral paramedian pontine reticular formation
  • Parieto-occipito-temporal cortex controls smooth pursuit movements in the ipsilateral direction via connection to vestibular nuclei, cerebellum, and paramedian pontine reticular formation
  • Influenced by primary visual cortex, visual associated cortex, and basal ganglia
26
Q

What are right-way eyes?

A
  • Eyes that look away from the side of weakness
  • Occurs with lesions to the cerebral hemispheres
  • Impaired eye movement toward side of weakness
27
Q

What are wrong-way eyes?

A
  • Eyes look toward the side of weakness
  • Occurs with seizures to the frontal eye field or motor association cortex
  • Occurs with thalamic hemorrhage
  • Occurs with lesions to the pons affecting PPRF or abducens nucleus
28
Q

What is the parasympathetic pathway for pupillary constriction?

A
  • Light enters one eye and projects to bilateral optic tracts as some fibers cross in the optic chiasm
  • Signals synapse in the pretectal area in the extrageniculate pathway where some axons cross and others remain ipsilateral
  • Axons synapse on preganglionic parasympathetic fibers in bilateral edinger-westphal nuclei, from here some axons will cross and some will remain ipsilateral to travel bilaterally in oculomotor nerves
  • Nerves will synapse on postganglionic parasympathetic nerves in the ciliary ganglia to innervate pupillary constrictor muscles
29
Q

How can an oculomotor nerve lesion impact the pupillary light response?

A
  • Ipsilateral pupil may appear dilated relative to the opposite eye (this will be more apparent in a bright room)
  • Ipsilateral pupil shows a decreased or absent response to light shown in either eye
  • Contralateral pupil responds appropriately
30
Q

How can damage to the afferent pathway before the optic chiasm impact pupillary light response?

A
  • Neither eye responds to light shone in the ipsilateral eye
  • Both eyes respond appropriately to light shone in the contralateral eye
31
Q

What is the parasympathetic pathway for accommodation response?

A

When a visual object moves from far to near, input from the visual cortex to the parasympathetic pathways in the midbrain result in pupillary constriction, accommodation of lens via ciliary muscle, and convergence of the eyes

32
Q

What is the sympathetic pathways for pupillary dilation?

A
  • Descending sympathetic pathway travels from hypothalamic nuclei to T1-T2
  • Synapses on preganglionic sympathetic neurons in the intermediolateral cell column of the upper thoracic spine
  • Signals exit T1 and T2 nerve roots and travel around the apex of the lung to ascend in the paravertebral sympathetic chain
  • Signals synapse on postganglionic sympathetic neurons in the superior cervical ganglion to ascend in the cervical plexus alongside the internal carotid artery
  • Activated pupillary dilator muscle, superior tarsal muscle, and cutaneous arteries/sweat glands
33
Q
A

Neurobiology (15 decks)

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