Motor units

Question 1

What does the somatic motor system consist of?

Answer 1

the skeletal muscles and elements of the nervous system that control them

Question 2

What is the function of UMNs?

Answer 2

supply input to LMNs to mosulate their activity

Question 3

What is the function of alpha motor neurones?

Answer 3

innervate the bulk of fibres within a muscle that generate force

Question 4

What is the function of gamma motor neuones?

Answer 4

innervate muscle spindles

Question 5

What is the function of axial muscles?

Answer 5

control movements of the trunk- maintaining posture

Question 6

What is a motor unit?

Answer 6

an alpha motor neurone and allof the SK muscle fibres it innervates

Question 7

What is a motor neurone pool?

Answer 7

a collection of alpha motor neurones that innervate a single muscle

Question 8

What are the factors that decide the force of muscle contraction?

Answer 8

frequency of AP discharge of the alpha-motor neurone and the recruitment of additional, synergisitc motor units

Question 9

where are LMNs supplying axial muscles found in relation to distal muscles in the ventral horn?

Answer 9

foudn medial

Question 10

Where are the LMNs innervating flexors compared to extensors found in the ventral horn?

Answer 10

dorsal

Question 11

What are the 3 input sources that regulate alpha motor neurone activity?

Answer 11

dorsal root ganglion cells whose axons innervate the muscle spindles; UMNs in the motor cortex and brain stem; spinal interneurones

Question 12

What are the features of type 1/slow-oxidative fibres?

Answer 12

ATP derived from oxidative phosphorylation- slow contraction and relaxation; fatigue resistant

Question 13

What is the gross difference between type 2a and type 2b muscle fibres?

Answer 13

type 2a are red whereas type 2b are white

Question 14

What is the difference between type 2a and type 2 b fibres?

Answer 14

2a- ATP derived from oxidative phosphorylation; fast contraction and relaxation; fatigue resistance; well vascularised; 2b- ATP dervied from glycolysis; fast contraction but not fatigue resistant; poorly vascularised

Question 15

What is the difference in activation of slowm otor units vs fast motor units?

Answer 15

slow motor units (smaller a-MNs) are more easily activated

Question 16

What is the myotatic reflex?

Answer 16

when an SK muscle is pulled, it pulls back

Question 17

What are the parts of a muscle spindle?

Answer 17

fibrous capsule; intrafusal muscle fibres; sensory afferents; gamma motor neurone

Question 18

What does stimulation of gamma MNs cause?

Answer 18

the spindle to contract so that intrafusal muscle fibres contract in parallel with extrafusal maintaining the sensitivity of the spindle

Question 19

What are the 2 regions of an intrafusal muscle fibre?

Answer 19

non-contractile equatorial region innervated by 1a sensory neurones; contractile polar ends that are innervated by gamma MNs

Question 20

What are the 2 main types of intrafusal fibres?

Answer 20

nuclear bag fibres; chain fibres

Question 21

What is the difference between the 2 types of nuclear bag fibres?

Answer 21

bag 1- very sensitive to the rate of change of muscle length; bag 2- more senstiive to the absolute length of the muscle

Question 22

What is the function of chain fibres?

Answer 22

snesitive to the absolute length of the muscle

Question 23

What are the 2 types of afferent fibre that innervate intrafusal fibres?

Answer 23

1a afferents and 2 fibres

Question 24

What is the appearane adn function of 1a afferents with intrafusal fibres?

Answer 24

form a primary annulospiral nerve ending winding around the centre of all intrafusal fibres

Question 25

What is the funciton of 2 fibres with intrafusal fibres?

Answer 25

more slowly conudctin form flower spray endings on all intrafusal fibres except the bag 1 dynamic type

Question 26

What is the difference etbween the sensitivity of 1a and 2 fibres?

Answer 26

1a are more sensitive to rate of change whereas 2 are more sensitive to the absolute length of the intrafusal fibres

Question 27

When are dynamic gamma MNs active?

Answer 27

during behaviours in which muscle length changes rapidly and unpredicatbly

Question 28

When are only static gamma MNs active?

Answer 28

in which muscle length changes slowly and predictably

Question 29

Where a golgi tendon organs found?

Answer 29

at the junction of muscle and tendon

Question 30

What is the difference between golgi tendon organs vs intrafusal fibres?

Answer 30

monitor changes in muscle tension in series with rather than parallel to extrafusal fibres

Question 31

How are golgi tendon organs innervated?

Answer 31

group 1b sensory afferents

Question 32

What is the function of golgi tendon organs?

Answer 32

to regulate muscle tendion to protect muscle rom overload and keep in optimal range

Question 33

Where do group 1b afferents from the golgi tendon organs synpase?

Answer 33

upon inhibitory interneurones to form the reverse myotatic reflex

Question 34

What type of fibres give proprioception from joints?

Answer 34

free nerve endings; golgi-type endings; paciniform endings; ruffini endings

Question 35

What is the function of paciniform endings?

Answer 35

acceleration detectors

Question 36

What is the function of ruffini endings?

Answer 36

static position and speed and movments