lecture 22 - nervous system 2: movement & motor control

Question 1

what does movement depend on?

Answer 1

coordinated muscle contraction and relaxation

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

Question 2

what muscles does flexion require?

Answer 2

flexor muscles
• bicep brachi
• branchialis

Question 3

what muscles does extension require?

Answer 3

extensor muscles
• tricep branchi
• anconeus

Question 4

what happens in flexion?

Answer 4

contract flexors

relax extensors

Question 5

when happens in extension?

Answer 5

contract extensors

relax flexors

Question 6

what are synergists?

Answer 6

muscles that pull in the same direction

Question 7

what are antagonists?

Answer 7

muscles that pull in opposite directions

Question 8

what nerves control the muscles?

Answer 8

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

Question 9

what is a large motor neurone?

Answer 9

neurone innervating many muscle fibres

provides strong forces but less precision

e.g. antigravity muscles (legs)

Question 10

what is a small motor neurone?

Answer 10

neurone innervating few fibres

fine control, more precision

eg. finger

Question 11

types of muscle contraction

Answer 11

twitch

summation

unfused tetanus

fused tetanus

Question 12

twitch

Answer 12

individual brief contraction

muscle shortens and relaxes quickly

Question 13

summation

Answer 13

increased frequency of APs

2nd twitch begins before 1st relaxes

building 1 twitch on top of another

Question 14

unfused tetanus

Answer 14

no full relaxation

increasing APs

Question 15

fused tetanus

Answer 15

remains contracted

no ripple in contraction

eg. lifting something heavy

Question 16

what are the 3 sources of input to motor neurones?

Answer 16

upper motor neurones

interneurons in spinal cord (local circuits, largest input)

receptors: muscle spindles and Golgi tendon organs

Question 17

upper motor neurones

Answer 17

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

Question 18

interneurons in spinal cord

Answer 18

excitatory and inhibitory

spinal movement programs

Question 19

receptors: muscle spindles and Golgi tendon organs

Answer 19

sensory receptors in muscles and tendons

feedback to alpha motor neurones

important in the control of movement

Question 20

muscle spindles

Answer 20

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

Question 21

Golgi tendon organs

Answer 21

activated by muscle tension

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

Question 22

muscle receptor structure

Answer 22

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

Question 23

what motor neurones do muscle spindles have?

Answer 23

gamma motor neurones

send their information to the intramural muscle fibres from the CNS

can stretch the central region of the myofibrils

Question 24

what does the 1a afferent do?

Answer 24

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

Question 25

what happens to the spindle when it contracts?

Answer 25

spindle is unloaded so ceases to fire

Question 26

role of gamma motor neurones in controlling muscle spindles

Answer 26

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

Question 27

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

Answer 27

alpha-gamma co-activation

Question 28

what are the 3 types of movement?

Answer 28

reflex voluntary rhythmic

Question 29

reflex movement

Answer 29

involuntary simple movement limited to 1 or 2 muscles initiated by external stimuli via receptors

Question 30

voluntary movement

Answer 30

under conscious control complex may be learned can become unconscious - muscle memory

Question 31

rhythmic movement

Answer 31

initiated and terminated by conscious control activates an autonomic pattern generated within spinal cord intermediate complexity

Question 32

what are reflexes?

Answer 32

simplest unit of movement reflex arc involving at least 1 sensory and 1 motor neurone involuntary

Question 33

what are the origins of reflexes?

Answer 33

spinal cranial

Question 34

what are monosynaptic reflexes?

Answer 34

only 1 synapse (2 neurones) in the arc

Question 35

what are polysynaptic reflexes?

Answer 35

several neurones in the arc

Question 36

what happens in the stretch reflex?

Answer 36

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

Question 37

what is the Golgi tendon reflex?

Answer 37

protection against excessive load also important for control of posture it detects tension

Question 38

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

Answer 38

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

Question 39

what is the knee jerk reflex?

Answer 39

example of a stretch reflex lower leg jerks forward after striking tension below the knee cap (patella)

Question 40

what is the flexion and cross extensor reflex?

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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