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Physiology > lecture 22 - nervous system 2: movement & motor control > Flashcards

lecture 22 - nervous system 2: movement & motor control Flashcards

1
Q

what does movement depend on?

A

coordinated muscle contraction and relaxation

muscles contract to operate around a joint to bring about flexion and extension

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2
Q

what muscles does flexion require?

A

flexor muscles
• bicep brachi
• branchialis

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3
Q

what muscles does extension require?

A

extensor muscles
• tricep branchi
• anconeus

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4
Q

what happens in flexion?

A

contract flexors

relax extensors

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5
Q

when happens in extension?

A

contract extensors

relax flexors

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6
Q

what are synergists?

A

muscles that pull in the same direction

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7
Q

what are antagonists?

A

muscles that pull in opposite directions

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8
Q

what nerves control the muscles?

A

neurons that innervate muscle
• alpha motor neurons
• located in the ventral horn of the spinal cord
• responsible for making muscle fibres contract

muscle units
• motor neurones and the muscle fibres they innervate

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9
Q

what is a large motor neurone?

A

neurone innervating many muscle fibres

provides strong forces but less precision

e.g. antigravity muscles (legs)

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10
Q

what is a small motor neurone?

A

neurone innervating few fibres

fine control, more precision

eg. finger

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11
Q

types of muscle contraction

A

twitch

summation

unfused tetanus

fused tetanus

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12
Q

twitch

A

individual brief contraction

muscle shortens and relaxes quickly

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13
Q

summation

A

increased frequency of APs

2nd twitch begins before 1st relaxes

building 1 twitch on top of another

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14
Q

unfused tetanus

A

no full relaxation

increasing APs

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15
Q

fused tetanus

A

remains contracted

no ripple in contraction

eg. lifting something heavy

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16
Q

what are the 3 sources of input to motor neurones?

A

upper motor neurones

interneurons in spinal cord (local circuits, largest input)

receptors: muscle spindles and Golgi tendon organs

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17
Q

upper motor neurones

A

found in the cerebral motor cortex and brainstem

basis of voluntary control of movement

provide input to alpha/lower motor neurone

pathway activated when movement needs to be initiated

18
Q

interneurons in spinal cord

A

excitatory and inhibitory

spinal movement programs

19
Q

receptors: muscle spindles and Golgi tendon organs

A

sensory receptors in muscles and tendons

feedback to alpha motor neurones

important in the control of movement

20
Q

muscle spindles

A

intrafusal muscle fibres in parallel with extrafusal

innervated by 1a afferents that go to the spinal cord

activated by muscle stretch

muscle contraction unloads spindle

gamma motor neurons contract intrafusal fibres - keep spindle in operating range

21
Q

Golgi tendon organs

A

activated by muscle tension

innervated by 1b nerve afferents that go to the spinal cord

22
Q

muscle receptor structure

A

extrafusal muscle fibres do the work of contraction

intrafusal muscle fibres run parallel to them

at the base of the muscle there are Golgi tendon organs

tendon attaches muscle to bone extrafusal fibres surround the intramural fibres which are sensory terminals for the 1a afferent

muscle spindles have their own motor neurone

23
Q

what motor neurones do muscle spindles have?

A

gamma motor neurones

send their information to the intramural muscle fibres from the CNS

can stretch the central region of the myofibrils

24
Q

what does the 1a afferent do?

A

sends signals about stretching (increase in APs) to the spinal cord

25
Q

what happens to the spindle when it contracts?

A

spindle is unloaded so ceases to fire

26
Q

role of gamma motor neurones in controlling muscle spindles

A

motor centres predict force required for task

firing of alpha and gamma motor neurones together keeps spindle firing constant even though muscle contracts

but if the force required is more than predicted, spindle is stretched and 1a fibres from spindle activated leading to greater force of contraction

27
Q

whats it called when the alpha and gamma neurones fire together?

A

alpha-gamma co-activation

28
Q

what are the 3 types of movement?

A

reflex

voluntary

rhythmic

29
Q

reflex movement

A

involuntary

simple movement limited to 1 or 2 muscles

initiated by external stimuli via receptors

30
Q

voluntary movement

A

under conscious control

complex

may be learned

can become unconscious - muscle memory

31
Q

rhythmic movement

A

initiated and terminated by conscious control

activates an autonomic pattern generated within spinal cord

intermediate complexity

32
Q

what are reflexes?

A

simplest unit of movement

reflex arc involving at least 1 sensory and 1 motor neurone

involuntary

33
Q

what are the origins of reflexes?

A

spinal

cranial

34
Q

what are monosynaptic reflexes?

A

only 1 synapse (2 neurones) in the arc

35
Q

what are polysynaptic reflexes?

A

several neurones in the arc

36
Q

what happens in the stretch reflex?

A

maintains contraction with increased load - monosynaptic

1) contraction applied isn’t enough
2) arm dips and muscle stretches
3) muscle spindle stretches
4) 1a muscle fibres activated
5) muscle contracts more slowly
6) can hold a heavier load

37
Q

what is the Golgi tendon reflex?

A

protection against excessive load

also important for control of posture

it detects tension

38
Q

what happens in the Golgi tendon reflex when too much load is added?

A

1) too much for muscle to support
2) when we stretch the muscle, tension goes up and signals back to the spinal cord
3) 1b afferent goes back to the spinal cord but contacts interneurone (not motor neurone)
4) it is an inhibitor neurone that switches off the motor neurone reducing firing of the muscle
5) muscle relaxes and drops load

39
Q

what is the knee jerk reflex?

A

example of a stretch reflex

lower leg jerks forward after striking tension below the knee cap (patella)

40
Q

what is the flexion and cross extensor reflex?

A

polysynaptic refelx - involves multiple interneurons in the spinal cord

painful stimulus to foot - withdrawal of the limb and extension of opposite limb

helps support body on 1 leg

41
Q

what happens in the flexion and cross extension reflex after stimulus to the foot?

A

1) activates nocireceptors in the sole which signal back to spinal cord
2) input from the sensory neurone will go via a chain of interneurons to drive the alpha motor neurones
3) for the limb that made contact: inhibit extensors and excite flexors - this lifts the foot away from painful stimulus
4) opposite for the other leg - strengthens contraction as leg has to support whole body
5) basic pattern of walking - alternate contraction and relaxation

42
Q

what areas in the brain are involved in planning and organising voluntary movement?

A

cerebral cortex
• planning, coordinating and initiating

basal ganglia
• planning and selection of movements

cerebellum
• fine tunes movement bases on experience and sensory feedback

brainstem
• control of posture

Physiology (29 decks)

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