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Neuroscience and Head and Neck Anatomy > Brainstem 3 > Flashcards

Brainstem 3 Flashcards

1
Q

Describe the action and innervation of the following muscles:

  • Superior rectus
  • Inferior rectus
  • Lateral rectus
  • Medial rectus
A
  • A: Superiorly; CN 3
  • A: Inferiorly; CN 3
  • A: Laterallyl; CN 6
  • A: Medially; CN 3
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2
Q

What motion does the superior oblique muscle produce for the eyeball?

What nerve innervates this muscle?

A
  • Intorsion, meaning movement of the upper pole of the eye inward
  • Trochlear
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3
Q

What motion does the inferior oblique muscle produce for the eyeball?

What nerve innervates this muscle?

A

Extorsion, meaning movement of the upper pole of the eye outward.

Oculomotor

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4
Q

Describe the origin and insertion points of the rectus muscles.

A

These muscles originate in a common tendinous ring at the orbital apex and insert onto the sclera

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5
Q

Describe the origin and insertion of the superior and inferior obliques.

A
  • Superior: originates on the sphenoid bone in the posterior medial orbit and passes anteriorly through the trochlea, a pulley-like fibrous loop on the medial superior orbital rim. It then inserts on the superior surface of the eye
  • Inferior: originates along the anterior medial orbital wall and inserts on the inferior surface of the eye
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6
Q

Although the rectus muscles tend to produce horizontal and vertical movements and the obliques tend to produce torsional movements, there are times when the opposite can be true. Describe why this is the case.

A

The movement produced by an extraocular muscle depends on the direction in which the muscle pulls relative to the main axis of the eye. Therefore, as the eyes move by rotating in the orbit, the extraocular muscles can have different actions. Thus, depending on eye position, the rectus muscles can also produce torsional eye movements, and the oblique muscles can make important contributions to vertical eye movements

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7
Q

What is the action and innervation of the following muscles?

  • Levator Palpebrae Superior
  • Pupillary constrictor
  • Pupillary Dilator
  • Ciliary Muscle
A
  • A: Elevates the eyelid; I: CN 3
  • A: Causes pupil to beome smaller; I: CN3
  • Causes pupil to become larger
  • A: Adjusts the thickness of the lens in response to viewing distance; I: CN 3
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8
Q

What nerves enter through the superior orbital fissure?

A

CN 3, 4 and 6

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9
Q
A
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10
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A
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11
Q

What would right CN 3 palsy present?

A
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12
Q

How would left CN 4 palsy present?

A

Head tilt away from affected eye

Vertical diplopia

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13
Q

How would left CN 6 palsy present?

A

Horizonal diplopia

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14
Q

Describe the path taken by the oculomotor nerve as it runs through the brain.

A

Oculomotor nucleus –> oculomotor nerve –> subarachnoid space –> cavernous sinus –> superior orbital fissure –> orbit

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15
Q

The parasympathetic fibers in CN 3 are susceptible to compression from aneurysms from what artery?

A

Posterior communicating artery

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16
Q

Where is the trochlear nuclei located?

A

The trochlear nuclei are located in the lower midbrain at the level of the inferior colliculi.

Ventral to the periaqueductal gray matter and are bounded ventrally by the fibers of the medial longitudinal fasciculus

17
Q

What types of injuries is the trochlear nerve particularly susceptible to?

A
  • Compression from cerebellar tumors
  • Very thin and are relatively easily damaged by shear injury from head trauma
18
Q

Describe the path taken by the trochlear nerve as it runs through the brain.

A

Subarachnoid space –> cavernous sinus –> superior orbital fissure –> orbit –> superior oblique muscles

19
Q

Where is the abducens nuclei?

A

The abducens nuclei lie on the floor of the fourth ventricle under the facial colliculi in the mid-to-lower pons

20
Q

Describe the path taken by the abducens nerve as it runs through the brain.

A

Exit at the pontomedullary junction –> long course in the subarachnoid space –> exits the dura to enter Dorello’s canal, running between the dura and skull –> passes over the petrous tip of the temporal bone –> cavernous sinus –> superior orbital fissure –> orbit –> lateral rectus

21
Q

What type of injury is the abducens nerve susceptible to and why?

A

Downward traction injury produced by elevated intracranial pressure due to long vertical course in skull

22
Q

What is diplopia?

A

Double vision

23
Q

What are some common causes of CN 3 palsy?

A
  • Diabetic neuropathy
  • Microvascular neuropathy associated with hypertension or hyperlipidemia
  • Head trauma (shearing forces damage nerve)
  • Compression of the nerve by intracranial aneurysms (Posterior communicating artery)
24
Q

How can you differentiate between CN 3 palsy caused by aneurysm and CN 3 palsy caused by diabetic or microvascular neuropathy?

A
  • There should be a high index of suspicion for aneurysms in patients presenting with CN 3 palsy. Aneurysms classically cause a painful oculomotor palsy that involves the pupil.
  • A painless and complete oculomotor palsy that spares the pupil usually caused by diabetes or other microvascular neuropathy
25
Q

How can you test for CN 4 palsy?

A

Hold pen horizontally. Ask patient to tell you what they see. Patient with CN 4 palsy will see 2 pens forming 2 horizontal lines, where one is angled and intersects the normal horizontal line forming an arrow head. The point of the arrow head is toward the affected side.

26
Q
  • Discharge frequency of an oculomotor neuron is directly proportional to the […]
  • Discharge associated with a saccadic eye movement is characterized as […] — overcomes the […] of the eye in the orbit
  • Eyes maintain their new position by a […] that produces a steady contraction of the extraocular muscles.
A
  • position and velocity of the eye
  • pulse-step; viscous drag
  • persistent step in activity
27
Q

Why do people move their eyes (3)?

A
28
Q

What is the fovea?

What does it do?

What aspect of vision would a person lose if they had a problem with their fovea?

A

Responsible for visual acuity

Would have lower acuity (snellen eye chart) if damaged

29
Q
  • What is saccades?
  • What is its relationship to the fovea?
  • What is its purpose as an eye movement?
  • These movements are very fast. Why doesn’t vision appear blurry?
  • What areas of the brain control this movement?
A
30
Q

Horizonal saccades are generated by what area of the brain?

Vertical saccades are generated by what area of the brain?

A
31
Q

What is smooth pursuit?

How does this differ from the vestibular ocular reflex?

Is this movement fast or slow?

A
  • Smooth tracking of moving objects
  • VOR occurs when the head is moved and its purpose is to stablize gaze on a stationary object. In this case, the object is moving.
  • slow
32
Q

What is vergence?

How do the eyes move to focus on an object that moves closer vs. farther away?

Speed?

A
  • Brings an object into focus on the fovea
  • Closer = convergance (rotate toward one another); farther away = divergence (rotate away from one another)
  • Slow
33
Q

What is the vestibular ocular reflex?

What controls this reflex?

Speed? Accuracy?

A
  • Keeps the eyes fixated on a particular object despite movement of the head
  • Vestibular system of inner ear
  • Extremely fast and accurate
34
Q

What is physiological nystagmus?

A

Small normal movements of the eye that prevent adaptation to an image

35
Q

What is pathological nystagmus?

A

Biphasic ocular oscillation alternating between a slow eye movement in one direction with a fast eye movement in the other direction. It can occur spontaneously or from damage to components of the vestibular system.

36
Q

Of the following eye movements, which are controlled by the vestibular system and which are controlled by the extraocular nuclei?

  • Saccades
  • Smooth pursuit
  • Vestibular ocular reflex
  • Nystagmus
  • Vergence
A
37
Q

What changes in extraocular eye movements are obsersved in schizophrenics?

A

Significant and revealing saccadic and smooth pursuit eye movement phenotypes

Neuroscience and Head and Neck Anatomy (40 decks)

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