Motor units and muscle spindles Flashcards Preview

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Flashcards in Motor units and muscle spindles Deck (74)
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1

Where can upper motor neurones be found?

Brain

2

Where can lower motor neurones be found?

Soma of brain stem and ventral horn of spinal cord

3

What is the relationship between upper and lower motor neurones?

UMN supply input to LMN to modulate their activity

4

From which sources do LMNs receive input?

UMN
Proprioception
Interneurons

5

What are the different types of LMNs?

Alpha motor neurones that innervate the bulk of fibres within a muscle that generate force
Gamma motor neurones that innervate a sensory organ within the muscle known as the muscle spindle

6

Where are the spinal cord enlargements?

Cervical (C3-T1)
Lumbar (L1-S3)

7

What is a motor unit?

An alpha motor unit and all of the skeletal muscle it innervates

8

What is a motor neurone pool?

The collection of alpha motor neurones that innervate a single named muscle

9

What determines the force of muscle contraction?

Frequency of action potential discharge of the alpha motor neurone
Recruitment of additional, synergistic motor units

10

Where can the cell bodies of LMNs be found?

Ventral horn

11

Where can LMNs that innervate axial muscles be found?

Medial to those innervating distal muscles

12

Where can MNs supplying flexors be found?

Dorsal to those supplying extensors

13

What are the sources of input to an alpha motor neurone?

Central terminals of dorsal root ganglion cells whose axons innervate the muscle spindles
UMNs in motor cortex and brain stem
Spinal interneurones

14

What does muscle strength depend on?

Activation of muscle fibres
Force production by innervated muscle fibres

15

What does activation of muscle fibres depend on?

Firing rate of LMNs (force of motor unit increases to a max as a function of LMN firing frequency)
Number of LMNs that are simultaneously active
Co-ordination of movement

16

What does the force production of innervated fibres depend on?

Fibre size - hypertrophy
Fibre phenotype - fast or slow contracting muscle

17

What does a single action potential in an alpha motor neurone result in?

Twitch in muscle fibre

18

What does a sustained twitching of muscles result in?

Tetany

19

Describe the variable sizes of motor units

Small - extraocular eye muscles
Large - postural antigravity muscles

20

Describe the relationship between the size of a cell body of an alpha motor neurone and excitability

Smaller cell bodies are more excitable

21

What is each muscle fibre innervated by?

Single motor axon at endplate (neuromuscular junction) which is usually at the centre of the fibre

22

What is the difference between fast and slow muscle fibres?

Alpha motor neurones innervating fast type tend to be larger and have faster conductive axons than those of slow units

23

What determines a slow and fast twitch muscle?

Differs in how quickly myosin ATPase splits ATP to provide energy for the cross bridge formation
Expression of different myosin heavy chains

24

Describe a slow oxidative type 1 muscle fibre

ATP derived from oxidative phosphorylation
Slow contraction and relaxation
Fatigue resistant
Red fibres due to high myoglobin content

25

Describe a fast type 2a muscle fibre

ATP derived from oxidative phosphorylation
Fast contraction and relaxation
Fatigue resistant
Red and well vascularised

26

Describe a fast type 2b muscle fibre

ATP derived from glycolysis
Fast contraction but not fatigue resistant
Pale in colour and poorly vascularised
White

27

What are the 3 types of motor units?

Fast fatiguing
Fatigue resistant
Slow

28

Describe a fast fatiguing motor unit

High tension
Large alpha motor neurone
High threshold
Type 2b fibres
Utilised in burst power

29

Describe a fatigue resistant motor unit

High tension
Slow fatiguing
Intermediate alpha motor neurone
Intermediate threshold
Type 2a fibres
Utilised in sustained locomotion

30

Describe a slow motor unit

Low tension
Fatigue resistant
Small alpha motor neurone
Low threshold
Type 1 fibres
Utilised in antigravity and sustained movement