The Motor Unit - Neurological Consideration for Movement (week 7)

Question 1

muscles are responsible for…

Answer 1

muscles are responsible for producing force and absorbing energy during locomotion

Question 2

state 3 introductory facts about the neuromuscular basic for human movement

Answer 2

1. MVMT = combined effort of several muscles under the control of the CNS
2. CNS distributes signals to appropriate motor nerves with specific timing and in the appropriate number
3. to accomplish this, the CNS needs constant feedback from a variety of sensory receptors

Question 3

state the anatomical differences between the CNS PNS

Answer 3

1. CNS - brain + spinal chord

2. PNS - cranial nerves (12 pairs) and spinal nerves (31 pairs)

Question 4

what’s the main function of cranial nerves (12 pairs)

Answer 4

mostly used in relation to human senses. do not relate to the control of movement

Question 5

state how many pairs of nerves are located at each section of the vertebrae

Answer 5

1. cervicle - 8 pairs
2. thoracic - 12 pairs
3. lumbar - 5 pairs
4. sarcal - 5 pairs
5. coccygeal - 1 pair

Question 6

state the function of the cervicle nerves

Answer 6

control head, neck, and upper extremities

Question 7

state the function of the thoracic nerves

Answer 7

control the upper extremities + trunk

Question 8

state the function of the lumbar nerves

Answer 8

control the lower extremities + pelvis

Question 9

state the function of the sarcal nerves

Answer 9

control the lower extremities + pelvis

Question 10

state the function of the coccygeal nerves

Answer 10

control the coccyx

Question 11

state what it is meant by the key term - nerve

Answer 11

a nerve is a bundle of fibres within a connective tissue sheath

Question 12

state 2 facts about nerves

Answer 12

1. nerves may consist of only efferent or afferent neurones

2. however, a typical spinal nerve contains both in the same sheath

Question 13

state what it is meant by the key term - neurone

Answer 13

a neurone is a single nerve cell

Question 14

state the 3 types, and functions, of neurones

Answer 14

1. motor neurones = efferent, signals exit spinal chord (ventral/front)
2. sensory neurones = afferent, signals enter the spinal chord (dorsal/back)
3. interneurones = only within the CNS, can elicit excitatory and inhibitory responses in other neurones

Question 15

state what it is meant by the key term - alpha motor neurones

Answer 15

responsible for initiating the muscle contractions by innervating extrafusal muscle fibres

Question 16

state what it is meant by the key term - gamma motor neurones

Answer 16

innervate intrafusal muscle fibres of the muscle receptors (muscle spindles)

Question 17

state the names of the two types of motor neurones

Answer 17

1. alpha motor neurones

2. gamma motor neurones

Question 18

state the 6 main structures you need to know in motor neurones

Answer 18

1. cell body/soma
2. dendrites
3. axon
4. terminal branches
5. myelin sheath
6. nodes of ranvier

Question 19

state 2 facts about the cell body/soma

Answer 19

1. contains the nucleus
2. usually contained within the grey matter of the spinal chord, or in bundles of cells just outside the spinal body called ganglia

Question 20

state 2 facts about dendrites

Answer 20

1. projections of the cell body

2. receive signals from other neurones

Question 21

state 3 facts about axons

Answer 21

1. the nerve fibre
2. exits spinal chord via ventral (front) root where it’s bundled together with axons from other cells
3. axons of motor neurones are large

Question 22

state 2 facts about terminal branches

Answer 22

1. un-myelinated branches at the end of motor neurones known as the motor end planes
2. form neuromuscular junction with muscle fibres

Question 23

state 2 facts about myelin sheaths

Answer 23

1. axon is insulated to aid with transmission of the signals
2. Schwann cells form the myelin sheaths in sections around the axon

Question 24

state 2 facts about the nodes of ranvier

Answer 24

1. the gaps between the Schwann cells

2. AP jumps between nodes via a process called saltatory conduction

Question 25

state 3 facts about neuromuscular synapses

Answer 25

1. uni-directional
2. influenced by use and disuse
3. all or nothing principle
4. may be thousands of synapses at the end of a neurone
5. no physical union between cells

Question 26

state what it is meant by the key term - motor unit

Answer 26

a motor unit is the motor neurone plus all the muscle fibres it innervates

Question 27

how many muscle fibres can there be within a motor unit, and what is the effect of this?

Answer 27

1. between 10 and 2000 muscle fibres per motor neurone

2. the ratio directly determines the precision of the movement of the muscle

Question 28

muscle fibres innervated by an axon…

Answer 28

muscle fibres innervated by an axon are not necessarily in the same fascicle, they are spread across the belly of the muscle

Question 29

state the metabolism, size, contraction time, conduction velocity, and examples of… type 1 MU’s

Answer 29

1. oxidative
2. small
3. > 70 ms
4. 80 m/s
5. endurance activities

Question 30

state the metabolism, size, contraction time, conduction velocity, and examples of… type 2a MU’s

Answer 30

1. oxidative
2. medium
3. 30-50 ms
4. 80-100 m/s
5. sustained power required

Question 31

state the metabolism, size, contraction time, conduction velocity, and examples of… type 2x MU’s

Answer 31

1. glycolytic
2. large
3. 30-40 ms
4. 100 m/s
5. explosive power required

Question 32

state the 4 steps to the experiment to how they determined what determines motor unit type

Answer 32

1. isolated a type 1 and type 2b motor unit from a cat
2. cut axons in half on each motor neurone sand swapped them over to the other muscle fibre
3. came back in a couple weeks and saw muscle fibres had adapted to the new motor neurone
4. proves motor neurone determines MU type

Question 33

state the 2 ways you can increase the force of a muscle contraction

Answer 33

1. increase the number of MU’s recruited
2. increase the frequency of stimulation (frequency/rate coding)

generally happens in that order

Question 34

state 2 things fibre type influences

Answer 34

1. the contraction force and velocity

2. time to develop force

Question 35

order of MU recruitment (3 points)

Answer 35

1. MU recruitment starts with smallest MU as has lowest threshold
2. followed progressively by larger MU’s if more force is required
3. principle reversed with release of tension (first on = last off)

Question 36

state 3 facts about the frequency of MU stimulation

Answer 36

1. if frequency low, muscle fibres can partially relax
2. at higher frequency stimulation, there is no relaxation - max contraction
3. combination of max MU’s and high frequency stimulation = max strength

Question 37

state the 2 types of electromyography

Answer 37

1. indwelling EMG

2. surface EMG

Question 38

what is EMG used for

Answer 38

EMG can be used to measure muscle activation

Question 39

state the 3 principles that EMG sticks to:

Answer 39

1. brain sends signals via motor neurones
2. motor neurones innervate their associated muscle fibres
3. the AP in the muscle fibres initiates excitation-contraction coupling

Question 40

state the 3 determinants of EMG signal size

Answer 40

1. the number of MU’s activated
2. MU AP firing rate
3. types of MU’s activated

Question 41

state 2 uses of EMG

Answer 41

1. can tell you when a muscle is turned on and off

2. can tell you if a muscle is active or passive during a movement

Question 42

state 1 thing you can’t use EMG for

Answer 42

can’t tell you muscle force (force is determined by activation, fibre length and conduction velocity)