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BMS1052 > 15 - Motor Units And Excitation-contraction Coupling > Flashcards

15 - Motor Units And Excitation-contraction Coupling Flashcards

1
Q

Pathway from stimulus to response

A

Stimulus -> sensory neurons -> interneurons interneurons -> motor neurons -> effectors -> response

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2
Q

T/F — stimulus can be internal/external and response can be detected internally/externally

A

True

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3
Q

T/F - spinal cord arranged same as cortex w/ grey matter outside and white matter on inside

A

FALSE — arranged inside out to cortex

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4
Q

What is white matter of spinal cord?

A

Myelinated axons

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5
Q

Descending axons head…

A

Away from brain (ascending head towards)

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6
Q

Does ventral or dorsal root carry sensory info into spinal cord?

A

Dorsal (ventral carries motor info out)

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7
Q

Lower motor neurons

A
  • involved in all movements
  • directly innervate muscle
  • cell bodies in spinal cord
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8
Q

Mixed spinal nerve

A

Combines axons of motor and sensory fibres and synapses into single muscle fibre

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9
Q

What neurotransmitter is involved in muscle contraction?

A

Acetylcholine (ACh)

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10
Q

How many muscle fibres does individual motor neuron innervate?

A

One or more

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11
Q

Motor unit

A

1 alpha motor neuron + muscle fibres it innervates

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12
Q

Small motor units involve….

A

<10 muscle fibres

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13
Q

Large motor units involve…

A

> 1000 muscle fibres

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14
Q

Motor neuron pool

A

Collection of alpha motor neurons that innervates a single muscle

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15
Q

Following each successive AP, there’s an increase in…

A

Force within muscle fibres

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16
Q

As freq of APs increases ________ occurs

A

Force summation

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17
Q

Unfused tetanus

A

Oscillations in summed force generation

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18
Q

Fused tetanus

A

Smooth force summation

19
Q

Small motor unit

A

Motor neuron w/ small cell body that innervates few muscle fibres

20
Q

Large motor unit

A

Motor neuron with large cell body that innervates many muscle fibres

21
Q

To generate graded forces…

A

Small motor units (small forces) recruited 1st, followed by progressively larger motor units (larger forces)

22
Q

What takes care of grading motor recruitment automatically?

A

Cell body size

23
Q

Small motor neurons have a ___________ membrane resistance and reach threshold _______ easily

A

Higher, more easily

24
Q

An incoming spike causes a ________ change in mempot in a smaller neuron

A

Larger (because V = IR, so when R⬆️, V⬆️)

25
Q

T/F larger motor neurons reach spiking threshold more easily

A

False - smaller

26
Q

Inverse relationship between no. Motor units in a muscle and …

A

Their force generating capacity

27
Q

Many small motor units needed to generate small amount of force whereas

A

Fewer larger motor units needed to generate large amount of force

28
Q

Types of muscle

A

Cardiac, skeletal and smooth

29
Q

Skeletal muscle

A
  • striated and under voluntary control
  • each cell has multiple peripheral nuclei
  • orderly structure -> contractions in one direction
30
Q

Cardiac muscle

A
  • striated and under involuntary control
  • single central nucleus per cell
  • branching and unordered striations -> contraction in many directions
31
Q

Smooth muscle

A
  • no striations and under involuntary control

- single nucleus per cell

32
Q

Functional structure of skeletal muscle (hierarchy)

A

Whole muscle -> muscle fibre (single muscle cell) -> myofibril -> myofilaments

33
Q

Excitation

A
  • AP depolarises axon terminal of motor neuron
  • Ca2+ influx in pre-synaptic neuron through Cav channels
  • ACh release, which binds to post-synaptic ACh receptors
  • Na+ entry through ion channels post-synaptically
  • Nav channels open
  • AP propagates along post-synaptic plasma membrane
34
Q

NMJ has probability of vesicle release of…

A

1, so AP leads to guaranteed neurotransmitter release

35
Q

AP propagates along muscle fibre plasma membrane and down…

A

Transverse tubules

36
Q

T-tubules are…

A

Electrically continuous w/ surface of plasma membrane

37
Q

Dihydropyridine receptor

A

Voltage-gated Ca2+ channel that opens in response to AP

38
Q

Both dihydropyridine and ryanodine receptors are

A

Physically coupled ca2+ channels

39
Q

AP ________cytosolic Ca2+ levels because…

A

Increases, because Ca2+ released from SR

40
Q

Contraction — cross-bridge cycling steps

A
  1. Myosin head initially unbound but energised
  2. Actin binding site blocked by tropomyosin
  3. Ca2+ binds to troponin, moving tropomyosin
  4. Myosin cross-bridges bind to actin
  5. Power stroke -> myosin head rotates (+ release of ADP and Pi)
  6. ATP binding to myosin breaks actin-myosin linkage
  7. Bound ATP split, re-energising myosin head
41
Q

Hydrolysis of ATP by myosin energises cross-bridges by providing energy for

A

Force generation

42
Q

ATP binding to myosin dissociates…

A

Cross-bridges bound to actin, allowing repeated cycling

43
Q

What’s the role of the Ca2+-ATPase?

A

Hydrolyses ATP and actively transports Ca2+ back into SR

44
Q

Relaxation

A
  1. Ca2+-ATPase actively sequesters Ca2+ back into SR

2. Ca2+ removal leads to covering of myosin binding sites by troponin, ceasing cross-bridge cycle

BMS1052 (10 decks)

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