Motor Control Basics

Question 1

Voluntary brain control of muscles is via what?

Answer 1

Alpha motor neurones in the spinal cord

Question 2

Descending inputs from which two tracts regulate trunk and limb muscle movements?

Answer 2

Vestibulospinal tract
Reticulospinal tract

Question 3

The brainstem receives control inputs about voluntary movements from higher centres. Name these higher centres.

Answer 3

Cerebral cortex
Basal ganglia
Cerebellum

Question 4

Which muscles do motor neurons supply?

Answer 4

Skeletal muscles

Question 5

What coordinates the output from the brainstem down into the lower motor neurons?

Answer 5

Cerebellum

Question 6

Which four systems control movement?

Answer 6

1. Descending control pathways
2. Basal ganglia
3. Cerebellum
4. Local spinal cord/brainstem circuits

Question 7

In the spinal cord, what does the lateral white matter contain?

Answer 7

Axons from the motor cortex

Question 8

In the spinal cord, what does the medial white matter contain?

Answer 8

Axons from the brainstem

Question 9

Which muscles do the more medial motor neurons in the ventral horn supply?

Answer 9

Proximal muscles e.g. muscles of trunk

Question 10

Which muscles do the more lateral motor neurons in the ventral horn supply?

Answer 10

Distal muscles e.g. muscles in legs, toes, hands, etc.

Question 11

Higher brain centres are functionally interdependent. What does this mean?

Answer 11

They integrate information to work out what they should/shouldn’t do.
They control different aspects of voluntary movements.

Question 12

How does the spinal cord receive descending input?

Answer 12

Via the brainstem AND directed cortical input via corticospinal (pyramidal) tract

Question 13

Which types of information come from the spinal cord?

Answer 13

Proprioceptors
Touch
Pain

Question 14

Where does the brainstem get inputs from?

Answer 14

Vestibular system informs about balance

Question 15

The cortex produces movements in response to which types of cues?

Answer 15

Visual, olfactory, auditory, emotional, intellectual, etc.

Question 16

What happens if there is damage to the sensory inputs?

Answer 16

Paralysis

Question 17

What causes sensory neuropathy?

Answer 17

Loss of large myelinated fibres

Question 18

Can sensory neurons regernate?

Answer 18

No

Question 19

Which type of reflex is present in all muscles?

Answer 19

Stretch reflex

Question 20

Give a common example of the stretch reflex.

Answer 20

Patellar tendon- knee jerk reflex

Question 21

In the knee jerk reflex, a sharp tap is given to the patellar tendon, which is an inelastic tendon. How does this provoke a stretch reflex?

Answer 21

Tendon transmits force to the muscle fibres as they are more elastic and able to stretch.

Question 22

Which type of sensory nerve terminals are activated in the muscle spindles in response to stretch?

Answer 22

1a afferent sensory nerve terminals

Question 23

What happens when there is activation in the 1a afferent sensory nerve terminals due to stretch?

Answer 23

Increases the number of action potentials

Question 24

Spindle sensory afferent projections make three connections. What are these connections with?

Answer 24

Two with the spinal cord
One with the brain

Question 25

What happens as a result of the direct contact to the A-motorneurons in the stretched muscle?

Answer 25

Rapid contraction of agonist muscle.

Question 26

Muscles are arranged as agonists and antagonists in order to move joints. Therefore, what happens when the spindle branch is in direct contact with the A-motorneurons and cause the agonist muscle to contract?

Answer 26

Another spindle branch connects with the antagonist muscle and stretches it. Therefore, as agonists are contracted, antagonists stretch.

Question 27

Just to double check that it's gone in- what happens when the agonist muscle contracts?

Answer 27

Antagonist muscle stretches

Question 28

What is meant by reciprocal inhibition in terms of agonist and antagonist muscles?

Answer 28

Simultaneous activation of agonist motorneuron and inhibition of antagonist muscle.

Question 29

The third branch of afferent spindle fibres travels up to the brain via the dorsal column. To which part of the brain does it travel to?

Answer 29

Thalamus and somatosensory cortex

Question 30

What is the final common pathway for movements?

Answer 30

Alpha motorneurons

Question 31

If you picked up a weight, your muscle would stretch initially. Then, there would be reflex muscle contraction. What happens in this?

Answer 31

Muscle shortens back to previous length

Question 32

What is the inverse stretch reflex mediated by?

Answer 32

Golgi tendon organs

Question 33

Which nerves cause the inverse stretch reflex?

Answer 33

1b afferent nerves

Question 34

What do Golgi-tendon organs monitor?

Answer 34

Tension

Question 35

What causes the 1b afferent nerves from the GTOs to increase their frequency of action potentials?

Answer 35

The contraction and shortening of a muscle

Question 36

RECAP- Spindles are innervated by?? GTO's are innervated by??

Answer 36

1. Spindles innervated by 1a afferent neurons 2. GTO's innervated by 1b afferent neurons

Question 37

The firing of 1b afferent neurons leads to a decrease in contraction strength. Why is this?

Answer 37

There is activation of inhibitory interneurons to the agonist muscle ->girl i know this is not making sense but these lectures are not it

Question 38

What else happens when there is increased firing of 1b afferent neurons, as well as the activation of inhibitory interneurons in the agonist muscle?

Answer 38

Activation of excitory interneurons to antagonist muscles

Question 39

How does information about the muscle tension get to the somatosensory cortex?

Answer 39

Ascends up spinal dorsal column

Question 40

The inverse stretch reflex can also be called the clasp-knife reflex. Why is this?

Answer 40

There is greatly increasing tension in the tendon which leads to a collapse of resistance. So, like a spring-loaded knife opening up, the joint extends

Question 41

Why is the knife clasp/ inverse stretch reflex important>

Answer 41

Protective mechanism which prevents muscle damage

Question 42

Okay read this to try and simplify it.

Answer 42

Inverse stretch reflex/knife-clasp reflex: If too heavy, the muscle gives in and you drop something to protect the muscle from becoming badly damaged

Question 43

Describe what would happen in weightlifting if the weight is too heavy.

Answer 43

Firstly, the agonist quadriceps would be contracted, pulling hard on the tendon. There would be increased GTO afferent firing. These will synapse with inhibitory interneuron which reduces motoneuron firing. Therefore, the agonist muscle is inhibited so it is forced to relax. Wordy but read through, this one makes more sense

Question 44

GTO afferents also synapse with excitory interneurons at the same time as synapsing with inhibitory ones. What does this do?

Answer 44

Increased activation of antagonist motor neurons meaning the antagonist contracts rapidly.

Question 45

Okay just to break this down a bit. What happens to agonist and antagonist muscles in the: 1. stretch reflex e.g. knee jerk 2. GTO reflex aka inverse stretch reflex/knife-clasp reflex.

Answer 45

1. Agonist contracts, antagonists stretches 2. Agonist relaxes/stretches, antagonist contracts

Question 46

Which reflex is monosynaptic?

Answer 46

Stretch reflex

Question 47

Which reflex is polysynaptic?

Answer 47

Inverse stretch reflex

Question 48

Which reflexes will occur in response to a painful stimuli?

Answer 48

Flexor/Withdrawal Reflex Crossed Extension Reflex

Question 49

Where does the flexor/withdrawal reflexes get information from?

Answer 49

Nociceptors in skin, muscles and joints

Question 50

What happens when there is increased action potentials in the nociceptors.?

Answer 50

1. Increased activity in flexor muscles 2. Antagonistic extensors are inhibited

Question 51

What is involved in the flexor/withdrawal reflex?

Answer 51

The flexor withdrawal reflex involves flexing the affected part towards the body, withdrawing it from painful stimuli.

Question 52

Which fibres carry the signals which provoke withdrawal in the flexor reflex?

Answer 52

A delta nociceptive axons

Question 53

How does the flexor reflex differ compared to others in terms of number of muscles controlled?

Answer 53

Most reflexes control one muscle acting on a joint but the flexor reflex controls all the muscles of the affected limb.

Question 54

To prevent falling over, what happens to the contralateral limb when the affected limb withdraws?

Answer 54

Contralateral limb extends via crossed extensor reflex

Question 55

In the crossed extensor reflex, what role do excitatory interneurons have?

Answer 55

They cross the spinal cord and excite contralateral extensors

Question 56

What happens at the same time as the excitation of the contralateral extensors?

Answer 56

Simultaneous inhibition of contralateral flexors

Question 57

Just to clarify- what happens to flexor and extensor muscle on both legs if stepping on something sharp.

Answer 57

Affected leg- interneurons excite flexors and inhibit extensors. Contralateral leg- interneurons excite extensors and inhibit flexor muscles.

Question 58

Give an example of a time where the GTO reflex may be overridden.

Answer 58

If you were carrying something you didn't want to drop, even if it was heavier than expected, like a child. This can be over-ridden by voluntary input from the CNS.