Lecture 13

Question 1

how are motor neurons slightly different to other neurons

Answer 1

they have a long axon at one end which allows transport of electrochemical signals

Question 2

what is an electrical signal

Answer 2

action potential

Question 3

what are the two types of synapses

Answer 3

between neuron and neuron

between neuron and muscle fibre

Question 4

how does a neuron to neuron synapse work

Answer 4

electrical > chemical > electrical

Question 5

how does a neuron to muscle fibre synapse work

Answer 5

electrical > chemical

Question 6

what is acetylcholine

Answer 6

a neurotransmitter

Question 7

when do muscles contract

Answer 7

when acetylcholine is released by motor nerves

Question 8

what does a muscle fibre contain that are very important to allow muscle contraction

Answer 8

filaments such as actin and myosin

Question 9

1 muscle fibres is innervated by how many motor neurons

Answer 9

1 muscle fibre is innervated by ONLY 1 motor neuron

Question 10

how many muscle fibres can a motor neuron innervate

Answer 10

many muscle fibres

Question 11

what do Alpha (a) motor neurons innervate and what does this cause

Answer 11

skeletal muscle, cause muscle contractions

Question 12

what is a motor unit

Answer 12

a motor neuron and all the muscle fibres it innervates

Question 13

how many muscle fibres would be in a motor unit found in the hand or the eye (why is this important)

Answer 13

< 100 muscle fibres = key for precise movements

Question 14

how many muscle fibres would be found in a motor unit in something like the lower leg

Answer 14

> 1000 muscle fibres

Question 15

what is a characteristic of all fibres within a motor unit

Answer 15

they are all similar

• produce the same type of movement (fast twitch and slow twitch are grouped together)

Question 16

on a nueral signal what all happen to the motor unit

Answer 16

the whole motor unit is activated

Question 17

what is the corticospinal tract

Answer 17

connection between cortex and spine

Question 18

what is the medulla known as

Answer 18

the switch board

Question 19

what % of neurons cross the midline at the medulla

Answer 19

75%

Question 20

what do the neurons that cross the midline at the medulla control

Answer 20

peripheral movement

• distal movements on the contralateral (opposite) side

Question 21

what % of neurons stay on the ipsilateral (same) side of the body

Answer 21

25%

Question 22

what do the neurons that stay on the same side of the body control (also example)

Answer 22

control axial muscles on both sides of the body

• example = core etc

Question 23

what do motor neurons form in the spinal tract

Answer 23

form “pools” or “bundle’s” in the spinal tract

Question 24

how are motor neurons organised into bundles in spinal cord

Answer 24

somatotopically = according to function (similar to motor cortex organisation)

Question 25

what is afferent information

Answer 25

carrying information to the brain

Question 26

what is efferent information

Answer 26

carrying information leaving the brain

Question 27

what type of afferent fibres do muscle spindles have

Answer 27

1a afferent

Question 28

what carries neural impulse from CNS to muscle spindles

Answer 28

gamma motor neurons

Question 29

what fibres do golgi tendon organs have

Answer 29

type 1b afferent fibres

Question 30

how do golgi tendon organs cause muscles relax

Answer 30

when a muscle contracts the golgi tendon is fired

Question 31

what is proprioceptive neuromuscular facilitation stretching

Answer 31

completely maximal contraction before the stretch

Question 32

how does proprioceptive neuromuscular facilitation stretching allow for a deeper stretch

Answer 32

the maximal contraction prior to the stretch causes more intense relaxation of the muscle in the stretch phase which allows for a deeper stretch

Question 33

where do afferent neurons from GTO and muscle spindles project

Answer 33

project to the spinal cord

Question 34

where are short reflex loops in the spinal cord

Answer 34

same spinal level

Question 35

what are examples of short reflex loops

Answer 35

stretch reflex

golgi tendon reflex

gamma reflex

Question 36

where are long reflex loops in the spinal cord and what type of movements are they

Answer 36

across spinal levels

• more complex movements

Question 37

what are examples of long reflex loops

Answer 37

flexion reflex (standing on a pin)

postural control

Question 38

what are the 5 steps to the short reflex loop (stretch reflex with patella tendon hammer)

Answer 38

1. muscle is stretched, muscle spindle fibres activate
2. impulse passed on to afferent neuron (type Ia) to spinal column
3. this synapses onto alpha motor neuron for agonist, also onto inhibitory internueron to antagonist
4. alpha motor neuron of agonist is stimulated so the muscle will contract
5. this relieves the stretch on the muscle so the spindle organ stops firing

Question 39

what are the 4 steps to the short reflex loop (golgi tendon reflex)

Answer 39

1. muscle contracts = tendon is stretched > golgi organ fires
2. afferent (type 1b) neuron synapses onto an inhibitory interneuron (in the spine)
3. inhibitory interneuron synapses onto motor neuron which inhibits the agonist. antagonist is activated by alpha neuron that causes the muscle to contract
4. agonist relaxes = tendon stretch is reduced so golgi stops firing

Question 40

what is the goal of long reflex loops

Answer 40

adjustments in limb and body position

Question 41

what level do long reflex loops act on

Answer 41

subconscious level

Question 42

what does longer reflex loops have influence on

Answer 42

posture and stability

Question 43

in the tuning of spinal reflexes, how does the spinal cord and brain operate

Answer 43

spinal cord works with the brain not independently

Question 44

what does the gamma motor neuron do

Answer 44

prepare the muscle spindle for action

Question 45

in terms of muscle, what can be increased in preparation for movement

Answer 45

muscle tone can be increased in preparation for movement