The motor system

Question 1

What are the types of motor control?

Answer 1

Voluntary - running , talking, playing music

Goal-directed - conscious, explicit, controlled

Habit - unconscious, implicit, automatic

Involuntary - eye movements, facial expressions, cardiac, diaphragm

Question 2

What is the difference in the role of the upper motor neurons and the lower motor neurons?

Answer 2

Upper - originate in higher centres and project down to meet lower motor neurons
Lower - begins in brainstem or spinal cord and projects to muscles

Question 3

What do the basal ganglia and cerebellum play a part in the sensorimotor system?

Answer 3

WHAT to do - basal ganglia (inhibitory)
HOW to do it - cerebellum (excitatory)
Kinda outside the system

Answer 4

Descending control system
With lots of ascending feedback along the way

Question 5

How is muscle force controlled?

Answer 5

Not about how much a muscle fibre is activated - all or nothing - contracted or relaxed
Its about how many muscle fibres are activated
And what type of muscle fibres are activated
Antagonistic arrangement
Size of motor units

Question 6

What does antagonistic arrangement mean?

Answer 6

Allows for much better precision of positioning of different body parts e.g. eye, arm

Question 7

How does muscle fibre number differ across different people?

Answer 7

Doesn’t necessarily have more fibres when muscles are bigger
Just means fibres diameter are wider
Genetically determined, changed slightly by training

Question 8

What is the build up of a skeletal muscle?

Answer 8

Muscle fasciculus - several muscle fibres
Muscle fibre - several myofibrils
Myofibrils - protein filaments actin and myosin

Question 9

What does a motor unit consist of?

Answer 9

single alpha motor neuron and all the muscle fibres it innervates
Different motor neurons - different numbers of motor fibres

Question 9

When do motor units have fewer fibres?

Answer 9

Greater movement resolution - fine motor control e.g. those innervating lips and tongue

Question 10

What dictates the average number of muscle fibres innervated by a single motor neuron?

Answer 10

functional requirements of the muscle
- Level of control
- strength

Question 11

What is the size principle

Question 12

How are the intrafusal fibres innervated?

Answer 12

Gamma neurons
Detects muscle stretch
Important for running on uneven surfaces - adjust when limbs aren’t where you expect them to be

Question 13

Withdrawal reflex?

Answer 13

One leg tenses in preparation for taking the weight of the other

Question 14

Powerpoint 2

Question 15

Why is the sensorimotor system so complex?

Answer 15

There can be simple reflex circuits
But a complex array ascending sensory feedback affecting the descending control system

Question 16

What sort of movements are controlled by the brainstem?

Answer 16

Balance
Posture control
Orienting
Gross loimb movement
Affecting occulomotor control
Roles in speech
Respiration

Question 17

How can simple movements be controlled by motor cortex?

Answer 17

Pimary cortex exerts quite direct, top down control over muscular activity
With as few as one synapse (in the spine) between a cortical neurone and innervation of muscle cells.

Question 18

How do projections descend from the motor cortex?

Answer 18

Originate in layers 5-6 grey matter
Pyramidal cells here are upper motor neurones
Axons project directly OR indirectly to spinal cord, where they synapse with lower motor neurons
There descending axons form the pyramidal tract
Most cortical projections innervate contralateral motor units

Question 19

How do basal ganglia and cerebellum affect cortical motor control?

Answer 19

Cerebellum - excitatory
Basal ganglia - inhibitory

Question 20

What do the dorsolateral tracts do?

Answer 20

Control distal limb muscles (contralateral)
Cross over in the pyramids

Question 21

What do the ventromedial tracts do?

Answer 21

Control trunk and proximal limb muscles
Cross over at synapse with lower motor neuron

Question 22

Compare the paths that the dorsolateral and ventromedial tracts take?

Question 23

What path does the dorsolateral corticospinal tract take?

Question 24

Ventro

Question 25

How do pathways in the basal ganglia work?

Answer 25

Substantia nigra can inhibit the inhibitory effect of basal ganglia
Excitatory input received through Glutamate

Question 25

What are the basal ganglia?

Answer 25

Group of nuclei lying deep within cerebral hemispheres
Role in motor control not fully understood
Affects the thalamus and so affects the cortex
Mainly inhibitory

Question 25

Where are 50% CNS neurons?

Answer 25

Cerebellum

Question 26

Where does the cerebellum receive input from?

Answer 26

Cortex -PONS- motor cortex mostly(copies of muscle commoands), also somatosensory and visual areas of parietal cortex
Spinal cord - info about limb position and movement
Vestibular system - rotational and acceleratory head movement

Question 27

What is the gross function of the cerebellum?

Answer 27

Computes motor error and adjusts cortical moto commands accordingly
Provides precise control, fine adjustment and coordination of muscle activity based on continual sensory feedback