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Second Year - Biomedical Sciences BS22001 > Lecture 7 - Motor Units And Movement > Flashcards

Lecture 7 - Motor Units And Movement Flashcards

1
Q

What does the somatic system consist of

A

Skeletal muscle and all the elements of the nervous system that controls them

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2
Q

What comprises the neural elements of the motor system

A

Upper motor neurones and lower motor neurones

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3
Q

Where are upper motor neurones found

A

In the brain

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4
Q

Where are lower motor neurones found

A

Their soma is in the brain stem and the cell bodies are in the ventral horn of the spinal cord

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5
Q

Function of upper motor neurones

A

Supply output to lower motor neurones and modulate their activity

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6
Q

Other than upper motor neurones, where else do lower motor neurones receive input from

A

Proprioceptors and interneurones

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7
Q

Function of LMNs

A

Command muscle contraction and form the final common pathway

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8
Q

What are LMNs comprised of

A

Alpha motor neurones

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9
Q

Function of the alpha motor neurones in LMNs

A

Innervate the bulk of fibres within a muscle that generate force

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10
Q

What do gamma motor neurones innervate

A

The muscle spindle

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11
Q

Where do axons of LMNs exit the spinal cord

A

In ventral roots

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12
Q

What do the ventral roots join with

A

Dorsal roots

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13
Q

What do joined ventral and dorsal roots form

A

A mixed spinal nerve

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14
Q

What is contained within a mixed spinal nerve

A

Sensory and motor fibres

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15
Q

Where do motor units belong

A

To a spinal segment

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16
Q

What are the spinal segments

A

Cervical (C1-8)
Thoracic (T1-12)
Lumbar (L1-5)
Sacral (S1-5)

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17
Q

Are motor neurones equally distributed through the spinal cord

A

Nope

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18
Q

What areas of the spinal cord are the most motor neurones found

A

The cervical enlargement (C3-T1) and the lumbar enlargement (L1-3)

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19
Q

What does the cervical enlargement supply

A

The upper limb

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20
Q

What does the lumbar enlargement supply

A

The lower limb

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21
Q

Motor neurones that innervate distal and proximal musculature are mainly found

A

In the lumbar-sacral segment

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22
Q

Motor neurones that innervate axial musculature are found

A

At all levels of the spinal cord

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23
Q

An alpha motor unit and all the skeletal muscle it innervates is collectively known as

A

A motor unit

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24
Q

What is the smallest component of the motor system

A

A motor unit

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25
Q

What does muscle contraction result from

A

The individual and combined action of motor units

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26
Q

The collection of alpha motor neurones that innervate a single muscle is known as

A

A muscle pool

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27
Q

What are the two mechanisms that control the force of muscle contraction

A

The frequency of action potential discharge of the motor neurone and the recruitment of additional, synergistic, motor units

28
Q

Where are the cell bodies of alpha motor neurones found

A

The ventral horn

29
Q

What are the three sources of input that regulate an alpha motor neurones activity

A

The central terminals or dorsal root ganglion cells, the upper motor neurones and the spinal interneurones

30
Q

What do the axons of the central terminals/dorsal root ganglion innervate

A

The muscle spindle

31
Q

Small motor units are involved in

A

Fine motor control

32
Q

What are large motor units involved in

A

Large postural muscles

33
Q

What are small motor units innervated by

A

Small alpha motor neurones

34
Q

What are large motor neurones innervated by

A

Large alpha motor neurones

35
Q

What is the fore of contraction dependent on

A

The size of the motor unit

36
Q

What are the two types of motor units

A

Fast and slow

37
Q

Fats and slow motor units contain

A

Muscle fibres of only one type

38
Q

What are they types of muscle fibres involved in fast and slow motor units

A

Rapidly fatiguing or slowly fatiguing

39
Q

Lower motor neurones innervating fast type motor units tend to be

A

Larger and have faster conducting axons than those of slow units

40
Q

Where is each muscle fibre innervated

A

At the end plate (which is usually at the centre of the fibre)

41
Q

Each muscle fibre is innervated by

A

A single motor axon

42
Q

What does muscular strength depend on

A

The neuromuscular activation and the force produced by innervated muscle fibres

43
Q

The neuromuscular activation involves

A

The firing rate of LMNs, the number of LMNs and the coordination of the movement

44
Q

The force produced by innervated muscle fibres is dependent on

A

The fibre size (hypertrophy) and the fibre phenotype (fast or slow contracting muscles)

45
Q

What does the frequency summation of a muscle fibre contraction affect

A

The neuromuscular activation

46
Q

What does a single action potential in an alpha motor neurone cause

A

The muscle fibre to twitch

47
Q

What does a summation of twitches cause

A

A sustained muscular contraction

48
Q

What is an increase in the force due to

A

Temporal summation of individual fibres/motor units and then the recruitment of more motor units

49
Q

The velocity of the contraction is due to

A

The muscle fibre type and the load on the muscle

50
Q

The two main types of skeletal muscle are

A

Fast and slow

51
Q

How do fast and slow skeletal muscle differ

A

In how fast myosin ATPase splits ATP to provide energy

52
Q

How is the difference in fast and slow skeletal muscle reflected

A

In the time taken to reach peak tension

53
Q

Characteristics of slow oxidative (type I) fibres

A

ATP derived, slow contraction/relaxation, fatigue resistant and have a high myoglobin content

54
Q

What are the two types of fast fibres

A

Type IIa and type IIx (type IIb or glycolytic)

55
Q

Characteristics of type IIa

A

ATP derived, fast contraction/relaxation rates, fatigue resistant, highly vascularised and high in myoglobin

56
Q

Characteristics of type IIx

A

ATP derived, fast contraction rates, not fatigue resistant, poorly vascularised and high in glycogen

57
Q

How are type I and type IIa fibres derived of ATP

A

Through oxidative phosphorylation

58
Q

How are type IIx fibres derived of ATP

A

Through glycolysis

59
Q

What are the three types of motor units

A

Slow (S), fatigue resistant (FR) and fast fatiguing (FF)

60
Q

Characteristic of alpha motor neurones of the slow motor units

A

Small and have a low threshold

61
Q

Characteristic of alpha motor neurones of the fast fatiguing motor units

A

Large and have a high threshold

62
Q

Characteristics of a fast fatiguing motor unit

A

Very high tension, large alpha motor unit and type IIx fibres

63
Q

Characteristics of a fatigue resistant motor unit

A

High tension, slow fatiguing, intermediate alpha motor neurone and type IIa fibres

64
Q

Characteristics of a slow motor unit

A

Low tension, fatigue resistant, small alpha motor units and type I fibres

65
Q

What is the Henneman size principle

A

The susceptibility of a motor neurone to discharge action potentials as a function of its size

Second Year - Biomedical Sciences BS22001 (28 decks)

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