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anatomy 3 > Motor System > Flashcards

Motor System Flashcards

1
Q

What are lower motor neurons?

A
  • Neurons within the spinal cord or brainstem that innervate skeletal muscle
  • hardwired within the spinal cord
  • use acetylcholine onto nicotine receptors
  • In the spinal cord, are spatially arranged:
    medial - trunk muscles
    laterally - distal limbs
    dorsal - flexors
    ventral - extensors
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2
Q

Explain what is meant by the “size principle”:

A

Increasing contraction requires the recruitment of more motor units. LMN are recruited in a specific pattern according to size and force:
S units first, then FR then FF.

  • allows us to increase force almost directly proportional to the amount of units we are recruiting
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3
Q

What is a motor unit?

A

All the muscle fibers innervated by 1 LMN.

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4
Q

S-units:

A 
Type I muscle fibers, Red
Slow twitch
Small force
Fatigue resistant 
Hi mitochondria
Hi capillaries 
Small motor neuron
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5
Q

FR-units:

A 
Type IIa muscle fibers, white 
Fast twitch
Moderate force
Fatigue resistant 
Moderate mitochondria
Moderate capillaries
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6
Q

FF-units:

A 
Type IIb muscle fibers, white
Fast twitch 
Large force
Fatiguable 
Lo mitochondria
Lo capillaries
Large motor neuron
  • less mitochondria/capillaries means its more dependent on glycogen storage.
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7
Q

What is an upper motor neuron?

A

anything with influence above the LMN.

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8
Q

What are the 4 levesl of control on LMN?

A
  1. Reflex and pattern generators in the spinal cord
  2. Descending pathways
  3. Higher cortical centers
  4. Basal ganglia and cerebellum
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9
Q

Describe the 5 descending pathways that control the LMN:

A
  1. corticospinal tract- excitatory using glutamate; fine motor movements
  2. vestbulospinal tract- postural adjustments/head movements
  3. reticulospinal tract- locomotion and postural control
  4. tectospinal tract - reflex turing head to visual/auditory stimuli
  5. rubrospinal tract- significance in humans??
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10
Q

Where in the internal capsule do Corticospinal tract lies?

A

Posterior limb of the internal capsule.

Corticospinal tract is all excitatory (glutamate is the transmitter)

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11
Q

Lesion in the basal ganglia, cerebellum or cerebral cortex will have what effect?

A

No muscle weakness, issues with coordination.

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12
Q

Lesion in lower motor neurons will have what effect?

A

Muscle weakness, flaccid paralysis, atrophy of muscle, fasciculations

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13
Q

What is one test you can use to determine an UMN lesion?

A

Babinksi:

Positive = fanning of the toes,

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14
Q

Describe the corticobulbar tract:

A 
- Cortex to motor nuclei 
(except CN III, IV, and VI).
- sensory relay nuclei 
- reticular formation
- most end on interneurons of the reticular formation, may end on motor neurons
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15
Q

What cranial nerves receive no direct corticobulbar innervation?

A

CN 3, 4 and 6

- controlled by other innervations of the brainstem

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16
Q

Where in the internal capsule do the corticobulbar tract lies?

A

Genu of internal capsule

17
Q

What and how do the descending pathways control spinal cord LMNs?

A
  • Lateral Corticospinal Tract: all excitatory, using glutamate
  • Vestibulospinal Tract: postural adjustments/head movements
  • Reticulospinal Tract: locomotion and postural control
  • Tectospinal tract: reflex turning of head to visual/auditory stimuli
  • Rubrospinal tract: more significant for quad-peds?
18
Q

What and how do the higher cortical centers control LMNs?

A
  • Associated cortex: “decide” that a movement is needed
  • Supplementary motor area: planning/learning complex movements
  • Premotor cortex: devises a “plan” for the movement
  • Motor cortex: issues “commands” to motor neurons
19
Q

What and how do the basal ganglia and cerebellum control LMNs?

A

Planning/monitoring movements.

NO direct control of LMN; control by controlling the other areas that control LMNs.

20
Q

What is unique about CN VII and its innervation of the face?

A

CN VII, has bilateral innervation of the upper face but uni-lateral innervation of the lower face.

  • This is how we can is if its a LMN lesion: if both the brows and lower face is affected.
21
Q

What is unique about CN IX and X, for example, and their innervations?

A

Almost bilateral innervation, due to the function they perform requiring both sides to do the fxn at the same time. (CN 9 = speaking, CN 10 = swallowing)

22
Q

Which nucleus receives INDIRECT innervation from the corticobulbar tract:

A

CN nuclei 3,4,6

CBT –> reticular formation –> 3,4,6

23
Q

What two CN have predominantly innervations contralaterally..

A

CN V and VII

anatomy 3 (16 decks)

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