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A Physiology > 8.7. Motor functions of the spinal cord. Cord reflexes. Spinal cord transection and spinal shock. > Flashcards

8.7. Motor functions of the spinal cord. Cord reflexes. Spinal cord transection and spinal shock. Flashcards

1
Q

I. Spinal cord motor function
1. What is a motor unit?

A

a single motor neuron + the muscle fibers it innervates

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2
Q

I. Spinal cord motor function
2. What is the role of motor unit?

A

Motor neurons can innervate anything from a few to thousands of fibers, depending on how precise the innervation needs to be

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3
Q

I. Spinal cord motor function
3. What is Ocular muscle movement?

A

Ocular muscle movement needs to be extremely precise, therefore, each motor neuron in the orbit innervates only a few muscle fibers

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4
Q

I. Spinal cord motor function
4. What is motor neuron pool?

A

Motor neuron pool: consists of many motor neurons, each of which innervates a motor unit with the muscle

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5
Q

I. Spinal cord motor function
5A. What are the 2 types of motor neurons?

A

Motor neurons: either α or γ

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6
Q

I. Spinal cord motor function
5B. What is the role of Aα motor neurons?

A

Aα motor neurons: innervate extrafusal muscle fibers, or regular skeletal muscle that is used to generate

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7
Q

I. Spinal cord motor function
5B. What is the role of Aγ motor neurons?

A
  • Aγ motor neurons: innervate intrafusal muscle fibers (muscle spindle).
  • These muscle spindles are very small fibers that run parallel to the extrafusal fibers and are very common in muscles used for fine and precise movements
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8
Q

I. Spinal cord motor function
6A. What are the 3 types of skeletal muscle fiber?

A

Type I (slow)
Type IIa (fast)
Type IIb (fast)

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9
Q

I. Spinal cord motor function
6B. What are the features of type I (slow) muscle fiber?

A
  • Red color (high oxidative capacity) -> mitochondrial activity↑
  • Need at least 1 second to give a contraction (maximum force)
  • Not fatigable = fatigue-resistant fibers
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10
Q

I. Spinal cord motor function
6C. What are the features of Type IIa (fast) muscle fiber?

A
  • Red fibers
  • Achieve maximum contractivity within 1 second (fast!)
  • Slow fatigue after a few minutes
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11
Q

I. Spinal cord motor function
6D. What are the features of Type IIb (fast) muscle fiber?

A
  • White color (glycolytic fiber) -> mitochondrial activity + myoglobin↓
  • Very fast
  • Very fatigable
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12
Q

I. Spinal cord motor function
7. Describe achievable contractile force in skeletal muscle fiber types

A
  • Type I: low (twitch) – 1g (standing)
  • Type IIa: higher – 10x (running)
  • Type IIb: highest – 20x (jumping/sprinting)
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13
Q

I. Spinal cord motor function
8. What is the innervation of muscle spindles?

A
  • Innervated by both afferent and efferent nerve fibers and can be different in shape
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14
Q

I. Spinal cord motor function
9. What is the basic function of muscle spindles?

A
  • Their basic function is to correct any change in muscle fiber length after a contraction or stretch via the stimulation of α-motor neurons to oppose the change
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15
Q

I. Spinal cord motor function
10. What is the variation in innervation of muscle spindles?

A
  • The variation in innervation is to regulate the sensitivity of the fiber
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16
Q

I. Spinal cord motor function
12. What are the 2 shapes of muscle spindle?

A

nuclear chain or nuclear bag

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17
Q

I. Spinal cord motor function
13. What are the features of nuclear bag fibers?

A

Nuclear bag fibers: have all their nuclei arranged in the central region.
- They only get sensory innervation from primary (annulospiral) endings (Ia nerve fibers – fast) + motor innervation from dynamic γ motor neurons

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18
Q

I. Spinal cord motor function
14A. What are the features of nuclear bag fibers?

A

Nuclear chain fibers: get sensory innervation from both primary (annulospiral) endings (Ia – fast) and secondary
endings (II nerve – slower) + motor innervation
from static γ motor neurons

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19
Q

I. Spinal cord motor function - Nuclear chain fibers
14C. What are the features of Ia nerve fibers?

A

Ia nerve fibers: centrally located and detect the velocity of change of the fiber length

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20
Q

I. Spinal cord motor function - Nuclear chain fibers
14D. What are the features of II nerve fibers?

A

II nerve fibers: detect the length of the fiber

21
Q

I. Spinal cord motor function - Nuclear chain fibers
14E. What are the features of Dynamic γ motor neurons?

A

Dynamic γ motor neurons: innervation of nuclear bag fibers.
- Have a small synaptic ‘’plate ending’’

22
Q

I. Spinal cord motor function - Nuclear chain fibers
14F. What are the features of Static γ motor neurons?

A

Static γ motor neurons: innervation of nuclear
chain fibers.
- Have a synaptic end plate with a large surface area (‘’trail ending’’)

23
Q

I. Spinal cord motor function - Interneurons
15. Are interneurons motoneurons?

A

There are 30x more interneurons than there are motor neurons!

24
Q

I. Spinal cord motor function - Interneurons
16A. What are the main 4 types of interneurons?

A
  1. Ia
  2. Renshaw
  3. Ib
  4. Excitatory
25
Q

I. Spinal cord motor function - Interneurons
16B. What are the features of type Ia interneuron?

A

inhibitors of antagonist muscles depending on the situation

26
Q

I. Spinal cord motor function - Interneurons
16C. What are the features of Renshaw interneuron?

A

modulate the strength and firing rate of α motor neurons

27
Q

I. Spinal cord motor function - Interneurons
16D. What are the features of type Ib interneuron?

A

the interneuron of the Golgi Tendon Organ (GTO) reflex

28
Q

I. Spinal cord motor function - Interneurons
16E. What are the features of Excitatory interneuron?

A

used in the flexor-withdrawal reflex

29
Q

II. Spinal cord reflexes
1. What does a reflex arc consist of?

A

A reflex arc consists of
- A receptor (inside/outside of body)
- Afferent neuron (sensory neuron)
- Center (spinal cord mostly
- efferent neuron (motor neuron)
- effector (skeletal muscle fibers).
** In some cases they also have interneurons (ventral horn).

30
Q

II. Spinal cord reflexes
2. What are the 3 main spinal cord reflexes?

A

The main reflexes are the stretch reflex, Golgi tendon reflex and flexor-withdrawal reflex

31
Q

II. Spinal cord reflexes
3A. Fill in the table

A
32
Q

II. Spinal cord reflexes
3B. Fill in the table

A
33
Q

II. Spinal cord reflexes
3C. Fill in the table

A
34
Q

II. Spinal cord reflexes
4A. What is stretch reflex?

A
  • Monosynaptic reflex triggered by stretching a muscle and finishes with contraction of that muscle
  • proprioceptive – receptor located inside effector organs
35
Q

II. Spinal cord reflexes
4B. What is the pathway of stretch reflex?

A
36
Q

II. Spinal cord reflexes
5A. What are the features of Golgi tendon reflex?

A
  • inverse myotatic/stretch reflex
  • This reflex arc contains 1 inhibitor interneuron that is triggered by muscle contraction and finishes with muscle relaxation
37
Q

II. Spinal cord reflexes
5B. What is the pathway of Golgi tendon reflex?

A
38
Q

II. Spinal cord reflexes
6A. What are the features of Flexor-withdrawal reflex?

A
  • Exteroceptive reflex – receptors not in the muscle
  • This polysynaptic reflex is stimulated with pain/temperature sensation (nociception) and triggers ipsilateral muscle flexion and contralateral muscle extension to ‘’jump away’’ from the stimuli
39
Q

II. Spinal cord reflexes
6B. What is the pathway of Flexor-withdrawal reflex?

A
40
Q

III. Spinal cord transection and spinal cord shock
1A. What is spinal shock (spinalization)?

A

It is the loss of muscle tone and spinal reflexes after an injury to the spinal cord

41
Q

III. Spinal cord transection and spinal cord shock
1B. What is the molecular mechanism of spinal shock?

A
42
Q

III. Spinal cord transection and spinal cord shock
1C. Give an example of spinal shock?

A

The patellar tendon will not initiate the patellar reflex, because motor neurons are so hyperpolarized that excitation from the spindles is not enough to depolarize the neurons to initiate an AP

43
Q

III. Spinal cord transection and spinal cord shock
2A. What is the spinal cord transection?

A

Spinal cord transection is the partial or complete tear of the spinal cord which leads to loss of all neurological activity below the level of injury.
- This is, as mentioned above, due to the discontinuation of the tracts and thus the inability to cause depolarization of the motor function

44
Q

III. Spinal cord transection and spinal cord shock
2B. What are the effects caused by spinal cord transection?

A
45
Q

III. Spinal cord transection and spinal cord shock
3A. What does recovery of functions mean?

A
46
Q

III. Spinal cord transection and spinal cord shock
3B. What is the autonomic reflex?

A
  • Autonomic reflexes (mass reflex): stimulation below the level of lesion can result in flexor muscle spasms
  • Example: hit the leg of a person in a wheelchair very hard -> can excite some spinal cord segments -> autonomic reflexes initiated (urination, defecation)
47
Q

III. Spinal cord transection and spinal cord shock
3C. What is the role of Positive + negative support reflexes?

A

anti-gravity body actions (standing)
=> activation of antigravity muscles. Extensors or flexor muscles, respectively.

48
Q

III. Spinal cord transection and spinal cord shock
3D. What is Fictive locomotion?

A
  • Walking-like rhythmic activity recorded in ventral roots or
    peripheral nerves in paralyzed animals.
  • Imagine your spinal cord activating the walking reflex but of course there is no actual walking.

A Physiology (88 decks)

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