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SP17: Anatomy Test 1 > Descending Motor Systems > Flashcards

Descending Motor Systems Flashcards

1
Q

What is a lower motor neuron?

A

Directly innervates striated muscle

Last neuron in chain

Only way movement can be initiated

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2
Q

What results from a lower motor neuron injury?

A
  1. Atonia: loss of muscle tone
  2. Loss of myotatic reflex
  3. Flaccid paralysis
  4. Spontaneous contractions
  5. Atrophy: loss of tissue
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3
Q

What is an upper motor neuron?

A

Axons descend from cortex and end on or near LMN

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4
Q

What results from an upper motor neuron lesion?

A

Hypertonia: tense while resting

Less atrophy then LMN lesion

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5
Q

How are motor neurons arranged in the anterior horn?

A

Flexors are posterior while extensors are anterior

Medial muscles are medial while distal muscles are distal

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6
Q

What is a motor unit?

A

Consist of one motor neuron and all the myofibers it innervates

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7
Q

What is the difference between a type 1 and type 2 muscle fiber?

A

Type 1: one slow fat (lipid-rich) red ox (oxidative, lots of mitochondria)

Type 2: fast, glycogen rich, few mitochondria

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8
Q

What is the influence of the basal ganglia, cerebellum, and association cortex on the motor system?

A

They affect the output of the upper motor neurons but have no direct impact on LMNs.

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9
Q

What effect do injuries to the basal ganglia, cerebellum, and association cortex have on muscles?

A

No weakness.

Involuntary movements and incoordination

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10
Q

What are the several origins of the corticospinal tract?

A
  1. Primary motor area (precentral gyrus)
  2. Somatic sensory area (postcentral gyrus)
  3. Premotor area (lateral surface)
  4. Supplementary motor area (medial surface)
  5. Superior parietal lobe
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11
Q

What is the function of the fibers in the corticospinal tract from the primary motor area? Result of lesion?

A

Contralateral voluntary movement and control of fine digital movement

Paralysis of contralateral muscles

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12
Q

What is the function of CST fibers from the premotor area? Lesion result?

A
  1. Plans movements in response to instructions
  2. controls proximal and axial musculature
  3. empathetic facial movements

Loss of ability to associate learned hand movements to verbal or visual cues

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13
Q

What is the function of CST fibers from the supplementary motor area?

A

Plans movement while thinking (ex. Play new music)

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14
Q

T/F: It is unlikely the CST has one simple function.

A

TRUE

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15
Q

Is it likely that cutting the corticospinal tract will result in total paralysis?

A

No. Not all movements are completely dependent on the CST

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16
Q

Describe the path of the corticospinal tract?

A

Descends thru cerebral peduncle -> basis Pontus -> medullary pyramid -> pyramidal decussation -> skeletal muscles

17
Q

Do all fibers in the CST cross in the pyramidal decussation?

A

No. The Anterior CST fibers do not cross and are associated with axial muscle activity

18
Q

What is the somatotopic organization of the CST?

A

Lateral: Leg
Medial: Arm

19
Q

What is the function of the rubrospinal tract?

A

Control of shoulder and proximal arm

20
Q

What is the function of the reticulospinal tract?

A

Control axial musculature for walking

21
Q

What is the function of the vestibulospinal tract?

A

Control of axial musculature for balance

22
Q

What is the function of the tectospinal tract?

A

Head turning reflexes in response to visual stimuli

23
Q

T/F: Most neurons in the corticobulbar tract end directly on lower motor neurons.

A

FALSE

Most end on interneurons in the RF

24
Q

What cranial nerves receive bilateral input from the corticobulbar tract?

A

CN V, CN VII, CN XII, nucleus ambiguus, and CN XI

25
Q

Where does the corticobulbar tract originate?

A

In the face/mouth portion of the motor cortex

26
Q

Describe how the corticobulbar pathway descends.

A

It descends with the CST and does not decussate

27
Q

What is special about the way the corticobulbar pathway interacts with CN VII?

A

Upper facial muscles innervated bilaterally

Lower facial muscles only contralateral

28
Q

Where is the corticospinal tract found throughout the medulla and pons? Where does it migrate to in the midbrain?

A

Anterior; anterolateral

29
Q

Where is the spinothalmic tract throughout the medulla and pons? Where does it migrate to in the midbrain?

A

Lateral (to the ML); posterolateral (posterior to ML)

30
Q

Where is the medial lemniscus throughout the brainstem?

A

Always found fairly medial

SP17: Anatomy Test 1 (19 decks)

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