Lecture 7 - Motor Units And Movement

Question 1

What does the somatic system consist of

Answer 1

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

Question 2

What comprises the neural elements of the motor system

Answer 2

Upper motor neurones and lower motor neurones

Question 3

Where are upper motor neurones found

Answer 3

In the brain

Question 4

Where are lower motor neurones found

Answer 4

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

Question 5

Function of upper motor neurones

Answer 5

Supply output to lower motor neurones and modulate their activity

Question 6

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

Answer 6

Proprioceptors and interneurones

Question 7

Function of LMNs

Answer 7

Command muscle contraction and form the final common pathway

Question 8

What are LMNs comprised of

Answer 8

Alpha motor neurones

Question 9

Function of the alpha motor neurones in LMNs

Answer 9

Innervate the bulk of fibres within a muscle that generate force

Question 10

What do gamma motor neurones innervate

Answer 10

The muscle spindle

Question 11

Where do axons of LMNs exit the spinal cord

Answer 11

In ventral roots

Question 12

What do the ventral roots join with

Answer 12

Dorsal roots

Question 13

What do joined ventral and dorsal roots form

Answer 13

A mixed spinal nerve

Question 14

What is contained within a mixed spinal nerve

Answer 14

Sensory and motor fibres

Question 15

Where do motor units belong

Answer 15

To a spinal segment

Question 16

What are the spinal segments

Answer 16

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

Question 17

Are motor neurones equally distributed through the spinal cord

Answer 17

Nope

Question 18

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

Answer 18

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

Question 19

What does the cervical enlargement supply

Answer 19

The upper limb

Question 20

What does the lumbar enlargement supply

Answer 20

The lower limb

Question 21

Motor neurones that innervate distal and proximal musculature are mainly found

Answer 21

In the lumbar-sacral segment

Question 22

Motor neurones that innervate axial musculature are found

Answer 22

At all levels of the spinal cord

Question 23

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

Answer 23

A motor unit

Question 24

What is the smallest component of the motor system

Answer 24

A motor unit

Question 25

What does muscle contraction result from

Answer 25

The individual and combined action of motor units

Question 26

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

Answer 26

A muscle pool

Question 27

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

Answer 27

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

Question 28

Where are the cell bodies of alpha motor neurones found

Answer 28

The ventral horn

Question 29

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

Answer 29

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

Question 30

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

Answer 30

The muscle spindle

Question 31

Small motor units are involved in

Answer 31

Fine motor control

Question 32

What are large motor units involved in

Answer 32

Large postural muscles

Question 33

What are small motor units innervated by

Answer 33

Small alpha motor neurones

Question 34

What are large motor neurones innervated by

Answer 34

Large alpha motor neurones

Question 35

What is the fore of contraction dependent on

Answer 35

The size of the motor unit

Question 36

What are the two types of motor units

Answer 36

Fast and slow

Question 37

Fats and slow motor units contain

Answer 37

Muscle fibres of only one type

Question 38

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

Answer 38

Rapidly fatiguing or slowly fatiguing

Question 39

Lower motor neurones innervating fast type motor units tend to be

Answer 39

Larger and have faster conducting axons than those of slow units

Question 40

Where is each muscle fibre innervated

Answer 40

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

Question 41

Each muscle fibre is innervated by

Answer 41

A single motor axon

Question 42

What does muscular strength depend on

Answer 42

The neuromuscular activation and the force produced by innervated muscle fibres

Question 43

The neuromuscular activation involves

Answer 43

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

Question 44

The force produced by innervated muscle fibres is dependent on

Answer 44

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

Question 45

What does the frequency summation of a muscle fibre contraction affect

Answer 45

The neuromuscular activation

Question 46

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

Answer 46

The muscle fibre to twitch

Question 47

What does a summation of twitches cause

Answer 47

A sustained muscular contraction

Question 48

What is an increase in the force due to

Answer 48

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

Question 49

The velocity of the contraction is due to

Answer 49

The muscle fibre type and the load on the muscle

Question 50

The two main types of skeletal muscle are

Answer 50

Fast and slow

Question 51

How do fast and slow skeletal muscle differ

Answer 51

In how fast myosin ATPase splits ATP to provide energy

Question 52

How is the difference in fast and slow skeletal muscle reflected

Answer 52

In the time taken to reach peak tension

Question 53

Characteristics of slow oxidative (type I) fibres

Answer 53

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

Question 54

What are the two types of fast fibres

Answer 54

Type IIa and type IIx (type IIb or glycolytic)

Question 55

Characteristics of type IIa

Answer 55

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

Question 56

Characteristics of type IIx

Answer 56

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

Question 57

How are type I and type IIa fibres derived of ATP

Answer 57

Through oxidative phosphorylation

Question 58

How are type IIx fibres derived of ATP

Answer 58

Through glycolysis

Question 59

What are the three types of motor units

Answer 59

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

Question 60

Characteristic of alpha motor neurones of the slow motor units

Answer 60

Small and have a low threshold

Question 61

Characteristic of alpha motor neurones of the fast fatiguing motor units

Answer 61

Large and have a high threshold

Question 62

Characteristics of a fast fatiguing motor unit

Answer 62

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

Question 63

Characteristics of a fatigue resistant motor unit

Answer 63

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

Question 64

Characteristics of a slow motor unit

Answer 64

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

Question 65

What is the Henneman size principle

Answer 65

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