The Motor System

Question 1

What does motor control involve

Answer 1

Motor control involves a dynamically changing mix of conscious and unconscious regulation of muscle force, informed by continuous and complex sensory feedback, operating in a framework sculpted by evolutionary pressures

Question 2

Examples of voluntary motor control

Answer 2

Running
Walking
Talking

Question 3

Examples of goal directed motor control

Answer 3

Conscious
Controlled

Question 4

Examples of involuntary motor control

Answer 4

Eye movement
Facial expressions
Postural muscles

Question 5

How is motor control governed

Answer 5

By upper and lower neurons

Question 6

Where are Lower motor neuron cell bodies found

Answer 6

In the brain stem or spinal cord

Question 7

Where do lower motor neurons project to

Answer 7

Muscles

Question 8

Where do upper motor neurons originate

Answer 8

In higher centres in the cerebral cortex

Question 9

Where do upper motor neurons project to

Answer 9

They project to the lower motor neurons

Question 10

Describe a basic descending control system

Answer 10

Association cortex
Motor cortex
Brainstem circuits
Spinal circuits
Motor unit
Effect

Question 11

What is control of muscle force depend on

Answer 11

Individual muscle fibres act in an all or one manner and so the control of muscle force depends on the way in which lower motor neurons activate different types of muscle fibre

Question 12

What are the 3 types of muscle

Answer 12

Skeletal
Smooth
Cardiac

Question 13

What percentage of muscle makes up or body weight

Answer 13

40%

Question 14

What is an example of antagonistic arrangement of muscles

Answer 14

Bicep/tricep/eye

Question 15

What is an antagonistic arrangement of muscles

Answer 15

Combined co-ordinated actions

Question 16

What is recruitment of muscle fibres

Answer 16

Fast/slow twitch

Question 17

What is a fasciculi

Answer 17

A group of muscle fibres

Question 18

What is a muscle fasciculus

Answer 18

Several muscle fibres which make up a muscle cell

Question 19

What makes a muscle fibre

Answer 19

Several myofibrils

Question 20

What do myofibrils contain

Answer 20

Actin and myosin myofilaments

Question 21

What is a motor unit

Answer 21

A single alpha motor neuron + all the muscle fibres it innervates

Question 22

If a motor neuron innervates a fewer number of fibres causes what

Answer 22

A greater movement resolution eg-finger tips

Question 23

What does activation of the alpha motor neuron cause

Answer 23

The alpha motor neuron depolarises and causes contraction of all the muscle fibres in that unit going along with the all or none theory

Question 24

How do we increase the power of the muscle

Answer 24

More motor units are activated

Question 25

The number of muscle fibres innervated by a single motor neuron depends on

Answer 25

The functional requirements of that muscle - level of control - strength

Question 26

What are lower motor neurons

Answer 26

They originate in the grey matter of the spinal. Cord or in the brain stem

Question 27

What is includes in the unit of control of muscle force

Answer 27

The lower motor neuron and the muscle fibres it connects with

Question 28

What do all lower motor neurons innervate

Answer 28

They all innervate a single muscle

Question 29

What does the motor pool contain

Answer 29

Alpha and gamma motor neurons

Question 30

How are motor pools arranged

Answer 30

Motor pools are arranged in a rod like shape within the ventral horn of the spinal cord

Question 31

How are cell bodies in the ventral horn activated

Answer 31

They are activated by sensory information from the muscle and descending information from the brain

Question 32

How much tension is on the muscle is sensed by what

Answer 32

Golgi tendon organs sense tension

Question 33

What senses stretch of muscle fibres

Answer 33

Muscle spindles

Question 34

Where is the Golgi tendon organs found

Answer 34

They are found within the tendon where the muscle joins to the bone

Question 35

What is the function of the Golgi tendon organ

Answer 35

It sends ascending sensory information to the brain via the spinal cord about how much force there is in the muscle

Question 36

What is the Golgi tendon organ critical for

Answer 36

Pro-perception

Question 37

When a muscle is under extreme tension what does the Golgi tendon organ do

Answer 37

During extreme tension it is possible that the Golgi tendon organ can act to inhibit muscel fibres via the circuit in the spinal cord to prevent damage

Question 38

What are reflexes

Answer 38

Reflexes can be quite simple or quite complex They can operate without engaging with the brain and are critical for the avoidance of injury and effective motor control

Question 39

What is the most simple reflex

Answer 39

Monosynaptic

Question 40

What is an example of a monosynaptic reflex

Answer 40

The patellar tendon reflex

Question 41

What are intrafusal fibres innervated by

Answer 41

They are innervated separately by gamma motor neurons

Question 42

What is needed for an efficient motor control system

Answer 42

An efficient motor control system needs to know how much each muscle is stretching which is provided by the muscle spindles

Question 43

Where are muscle sensory receptors found

Answer 43

In the muscle spindles

Question 44

What are coiled around the intrafusal fibres

Answer 44

Sensory fibres

Question 45

What does reciprocal innervation explain

Answer 45

Reciprocal innervation of antagonistic muscles explains why the contraction of one muscle induces the relaxation of the other

Question 46

What does reciprocal innervation allow

Answer 46

Execution of smooth movements

Question 47

Where do motor commands originate

Answer 47

In the motor cortex pyramidal cells in layers 5-6 of the grey matter

Question 48

What type of motor neurons are found in the motor pyramidal cells

Answer 48

Upper motor neurons

Question 49

Where do axons from the pyramidal cells project to

Answer 49

Directly or indirectly via the brainstem to the spinal cord

Question 50

In the spinal cord upper motor neurons synapse with what

Answer 50

Lower motor neurons

Question 51

What do axons of the upper motor neurons make

Answer 51

The pyramidal tracts

Question 52

What is the motor homunculus

Answer 52

The homunculus is a reasonable representation of what areas of the motor cortex control what in the body

Question 53

What do both dorsolateral tracts and ventromedial tracts both contain

Answer 53

They both contain a direct corticospinal route They both contain an indirect route via brainstem nuclei

Question 54

What is the brain stem nuclei that the dorsolateral tract travel by

Answer 54

The red nucleus

Question 55

What are the brainstem nuclei that the ventromedial tracts travel through

Answer 55

They travel through the tectum, vestibular nuclei, reticular formation and cranial nuclei

Question 56

What do the dorsolateral tracts innervate

Answer 56

They innervate the contralateral side of one segment of the spinal cord

Question 57

What does the ventromedial tracts innervate

Answer 57

The ventromedial tracts diffuse there innervation which projects to both sides and multiple segments of the spinal cord

Question 58

Where do the dorsolateral tract projections go to

Answer 58

They sometimes project directly to alpha motor neurons Project to the distal muscles eg— fingers

Question 59

Where do the projections of the ventromedial tracts go to

Answer 59

Proximal muscles muscles of trunk and limbs

Question 60

What is the basal ganglia

Answer 60

A group of structures beneath the cortex that act as a gate keeper for control of the motor system

Question 61

What is the cerebellum

Answer 61

The cerebellum is a large brain structure that acts as a parallel processor enabling smooth coordinated movements and important in a range of cognitive tasks

Question 62

What does the cerebellum do in relation to motor neurons

Answer 62

The cerebellum has no direct projections to lower motor neurons but does modulate activity of upper motor neurons

Question 63

What inputs does the cerebellum get from the cortical tract

Answer 63

Mostly from the motor cortex which are copies of the motor commands and somatosensory and visual areas of parietal cortex

Question 64

What inputs does the cerebellum get from to spinal tract

Answer 64

Proprioceptive information about limb position and movement

Question 65

What inputs do the cerebellum get from the vestibular tract

Answer 65

Rotational and acceleratory head movements

Question 66

What are the function of the cerebellum

Answer 66

It knows what the current motor command is It knows about actual body positions It projects back to the motor cortex Computes motor error and adjusts cortical commands accordingly