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PTH9111 > Lecture 14 - Descending Pathways Part 2 > Flashcards

Lecture 14 - Descending Pathways Part 2 Flashcards

1
Q

Name 2 types of lower motor neurons

A
  1. Alpha motor neuron
  2. Gamma motor neuron
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2
Q

Alpha motor neuron function

A

Innervate muscle fibers (extrafusal fibers) to trigger generation of force by muscle

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3
Q

Gamma motor neuron function

A

Innervate intrafusal fibers in the muscle spindle

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4
Q

Describe the properties of alpha and gamma motor neurons (in terms of size, conduction speed and function)

A
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5
Q

Motor unit

A

One alpha motor neuron and all the muscle fibers it innervates

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6
Q

Motor neuron pool

A

Collection of alpha motor neurons for a single muscle

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7
Q

Axial muscles are

A

postural muscles

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8
Q

Distal muscles are

A

extremities

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9
Q

How do motor neuron pools travel in the spinal together and why

A

As a cluster in rods along the spinal cord for redundancy (muscles are innervated at many areas of the spinal cord 1/2 segments)

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10
Q

How did we visualize the motor neuron pools

A

Used a retrograde tracer to visualize distribution

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11
Q

T or F: A motor unit is a 1:1 relationship

A

F

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12
Q

T or F: An increased rate of innervation of a motor unit means that there is a higher level of precise control

A

T (eg. lateral rectus is 1:5 vs medial gastrocnemius is 1:1800)

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13
Q

Name the 3 types of motor units

A

1) type I (Slow twitch fibers)
2) Type IIA (Fast twitch, slow fatigue)
3) Type IIB (Fast twitch, fast fatigue)

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14
Q

4 characteristics of Type 1 (Slow twitch fibers)

A
  1. Slow to contract
  2. Sustain contraction
    3) Resistant to fatigue
  3. Small motor neurons
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15
Q

4 characteristics of type II A: Fast twitch, slow fatigue

A
  1. Rapid contraction/powerful
  2. Moderately strong and fast
  3. Relatively resistant to fatigue
  4. Intermediate-sized motor neurons
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16
Q

3 characteristics of Type II B: Fast twitch, fast fatigue

A
  1. Strongest and fastest contractions
  2. quickly fatigue
  3. Largest motor neurons
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17
Q

Neuromuscular Matchmaking

A

Match between neuron and the properties of the muscle fiber

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18
Q

Who came up with neuromuscular matching, how, and the result?

A

Who: John Eccles
How: Removed normal innervation of fast muscle fiber and replaced with a nerve that innervated slow muscle fiber
Result: Muscle fiber acquired slow properties (type of contraction and biochemistry of muscle fiber)

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19
Q

What did Terje Lomo and colleagues do

A

Altered the pattern of activity in the motor neuron changed the muscle phenotype, which results in synaptic plasticity of the periphery (input is important for how motor unit behaves)

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20
Q

T or F: Varying activity/exercise will not change muscles

A

F, it will (eg. inactivity causes atrophy and isometric exercise results in hypertrophy)

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21
Q

ALS

A

Degeneration of large alpha motor neurons that causes significant muscle weakness and atrophy (Excitotoxicity)

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22
Q

How does excitotoxicity relate to ALS

A

Release of too much glutamate triggers degeneration of large alpha motor neurons

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23
Q

Graded control of contraction results in

A

Precision of the muscle (eg. how much force were using to pick up a can)

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24
Q

What are 2 mechanisms to control the force of muscle contraction?

A
  1. Rate coding
  2. Recruitment
    -Size Principle
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25
Q

Rate Coding

A

Rate of firing of motor units (impacts force production)

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26
Q

Recruitment

A

Recruits motor unit based on size

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27
Q

T or F: In recruitment largest motor units are recruited first

A

F, smaller motor units are recruited first and largest last

28
Q

Size principle

A

Smaller motor units will be recruited first so specific and appropriate units are matched to the task at hand (only using fatigable motor units when needed)
eg. Stand -> Run -> Jump (muscles involved)

29
Q

Order of motor unit recruitment based on size principle

A
  1. Type 1 - Slow Twitch Fibers
  2. Type IIA - Fast twitch, slow fatigue
  3. Type II B, Fast twitch, fast fatigue
30
Q

What are the 3 main sources of input to the alpha motor neuron

A
  1. Input from UMN in motor cortex and brainstem
  2. Sensory input from muscle spindles
  3. Input from interneurons (largest input**)
31
Q

Muscle spindles

A

Stretch receptors that are specialized for detecting change in muscle length (proprioceptor)

32
Q

Ia sensory axons wrap around

A

muscle fibers of the spindle

33
Q

Ia sensory axons

A

Provide information of muscle length (thickest and myelinated so very fast) and is necessary for sensory info input to LMN

34
Q

Another name for the stretch reflex

A

Myotatic Reflex

35
Q

Stretch/Myotatic reflex

A

When a muscle is pulled on it contracts in response

36
Q

Monosynaptic stretch reflex arc is composed of: (2)

A
  1. Ia axon
  2. Alpha motor neuron its synapses on
37
Q

T or F: Motor neurons receive continual input from muscles

A

T

38
Q

Discharge of Ia sensory axons is closely related to

A

the length of the muscle

39
Q

Reciprocal Inhibition of stretch reflex

A

Contraction of agonist requires relaxation of antagonist

40
Q

What is an example of a stretch reflex

A

Knee-jerk reflex

41
Q

Muscle spindles contain

A

intrafusal fibers

42
Q

Muscle spindles are innervated by

A

Gamma motor neurons at its two poles and has sensory info medially

43
Q

Gamma and alpha motor neurons are a [positive/negative] feedback loop

A

Positive

44
Q

Extrafusal fibers are innervated by

A

Alpha motor neurons

45
Q

When muscle is stretched what is firing

A

The muscle spindle

46
Q

When a muscle is contracting/shortening

A

the muscle spindle relaxes and it cannot provide us with information

47
Q

How do we get information during contraction from muscle if muscle spindle is turned off

A

The alpha and gamma motor neurons cause contraction in intrafusal fibers to activate muscle spindle and provide proprioception

48
Q

Without the gamma motor neuron what would happen to sensory information of muscle spindle?

A

We would lose the sensory information (proprioception) but the muscle would still contract

49
Q

Golgi tendon organs is located

A

at the junction of the muscle and tendon

50
Q

Function of the golgi tendon organs

A

Monitors muscle tension/force contraction (protective mechanism against damage)

51
Q

The golgi tendon organs is innervated by

A

Ib sensory axons

52
Q

Golgi tendon organs are a [negative/positive] feedback

A

Negative

53
Q

Autogenic inhibition of the golgi tendon organs

A

Ib axons synapse on ib inhibitory neurons in ventral horn to form inhibitory connection with the alpha motor neuron on the same muscle (decreases contraction for protection by monitoring force)

54
Q

Name 5 differences/characteristics between the muscle spindle and golgi tendon organ

A
55
Q

Do we only receive proprioception information from muscle spindle and golgi tendon organ?

A

No also joint capsules and ligaments

56
Q

What are 3 strategies the body uses to control the motor system?

A
  1. Feedback Systems
  2. Feedforward Systems
  3. Adaptive Systems
57
Q

Feedback system function, its advantage, disadvantages and an example

A

Function: Closed loop of continuous control
Advantages: Simple and compensates for disturbances
Disadvantages: Not perfect and slow
Example: Stretch reflex

58
Q

Feedforward system function, its advantage, disadvantages and an example

A

Function: Moment-to-moment control via an open loop
Advantages: Increases speed of response and is anticipatory
Disadvantages: None
Example: Exercise, thermoreceptors of skin and pelvic floor activation

59
Q

Adaptive Systems Functions, advantages, disadvantages

A

Function: Elements of the system are modified rather than the output (work in adjunct to feedforward control)
Advantages: Useful and effective
Disadvantages: Slow and complex

60
Q

Causes of LMN disease

A

Infections (polio), injury (prolapsed disc), and disease (spinal muscular atrophy)

61
Q

What are 5 characteristics of LMN disease

A
  1. Interruption of final common pathway
  2. Hypotonia
  3. Flaccid paralysis
  4. Muscle wasting
  5. Segmental loss
62
Q

Causes of UMN disease

A

Stroke, infections, trauma, or demyelinating diseases

63
Q

3 effects of UMN disease

A
  1. Hyperreflexia
  2. Hypertonia (spasticity)
  3. Loss of regulatory influence from descending inputs
64
Q

How to eliminate spasticity of UMN disease

A

Cut dorsal roots (sensory input)

65
Q

Compare LMN and UMN disease in terms of tone, reflexes, babinski, muscle bulk and description

A

PTH9111 (15 decks)

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