Week 6 - Motor Control

Question 1

Compare the different type of motor control:

Answer 1

1. Reflex
   a) Most automatic and least controllable
   b) Least adaptable
   c) All-or-nothing
2. Rhythmic
3. Voluntary
   a) Least automatic and most controllable
   b) Most adaptable
4. Autonomic
   a) Movements from ANS
5. Postural
   a) Movements for posture

Question 2

How are movements classified?

Answer 2

1. Reflex movements
   a) Most autoamtic
   b) Least controllable
   c) Least adaptable
   d) All or nothing response
2. Voluntary movements
   a) Least automatic
   b) Most controllable
   c) Most adaptable
3. Autonomic
4. Postural

Question 3

What is involved in skilled movements?

Answer 3

1. Brain develops mathematical model which enables you to change the desired outcome into signals (motor commands)
2. These motor commands are sent to the muscles to end up with actual outcome
3. Efference copy is taken from that initial motor command to create second mathematical model to predict the predicted outcome
4. Brain then compares the predicted outcome with the actual outcome to adjust the mathematical models for better control next time

Question 4

How are movements from brain sent to muscles?

Answer 4

1. Complex planning occurs in the brain using cortical, cerebellar and basal ganglia to generate signal based on memory, somatosensation and other sensory feedback
2. The signal are transmitted from brain to spinal cord via the Upper Motor Neuron (UMN)
3. Signal synapses in spinal reflex circuit in spinal cord which controls the tuning of this signal and provides reflex correction
4. Lower motor neuron synapses with upper motor neuron in the spinal cord and takes signal to muscle
   a) No further modification of signal occurs at this site

Question 5

Describe Lower Motor Neuron:

Answer 5

1. Cell bodies in spinal cord or brainstem
2. Takes input from higher centres as well as from local (spinal) reflex circuits
3. It is an alpha motor neuron and is myelinated (very fast)
4. Muscles innervated by LMN have variety of motor units
   a) Combinations of nerve neurons with muscle fibres
   b) Vary in size
   c) Muscles with finer control have more motor units
   d) There is a size principle - larger units progressively recruited as required force increases

Question 6

How does the spinal reflex circuit work? Diagram 23

Answer 6

1. Muscle is stretched
2. Muscle spindle detects stretch and sends signal via afferent nerve into the spinal cord
3. Afferent nerve excites LMN and as a result the muscle contracts
4. An inhibitory interneuron in spinal cord connects to antagonist muscle and inhibits contraction of this muscle
5. A copy of afferent signal is also sent to the brain to let it know what is happening

Question 7

Describe upper motor neurons:

Answer 7

1. UMNs begin in cortex and synapse with LMNs in brainstem (head or neck) or spinal cord (muscles below neck)

Question 8

Describe the lateral corticospinal tract: Diagram 24

Answer 8

1. Provides direct connection of UPM to LMN

2. Sends signals for fine, fractionated control of peripheral muscles

Question 9

What are the distinctive features of UMN pathology?

Answer 9

1. Hyperflexia (increased reflexes)
2. Hypertonia (increased muscle tone)
3. Spasticity
4. Clonus
5. Disuse atrophy
6. Weakness

Question 10

Describe premotor cortex:

Answer 10

1. Inputs:
   a) Multisensory (somatosensory cortex, parietal lobe)
   b) Motivation and intention (rostral division of frontal lobe - “prefrontal”)
2. Outputs:
   a) Reciprocal connections to primary motor cortex
   b) Some axons project through corticospinal and corticobulbar tracts to LMN
3. Role:
   a) Selects movements appropriate for context and goal
   b) Movements in “extrapersonal: space (primary motor cortex: personal space)

Question 11

Describe the supplementary Motor Area and Broca’s area:

Answer 11

1. SMA:
   a) Active for internally-selected movements (e.g. from memory), rather than from external cues
   b) Active during mental rehearsal
   c) Stimulation can evoke bilateral movements and halt voluntary movements
2. Broca’s Area:
   a) Speech - and particularly its production

Question 12

Describe the functions of the cerebellum:

Answer 12

1. Produces coordinated, smooth, and accurate movements
2. Has a fractured topographic mapping
3. Body is represented ipsilaterally
4. Large amount of sensory inputs including proprioception, vestibular, auditory, and visual

Question 13

What are the 3 main regions of the cerebellum? Diagram 24

Answer 13

1. Spinocerebellum
   a) Takes inputs from spinal cord
   b) Central part is for proximal muscles and outside for distal muscles
2. Cerebrocerebellum:
   a) Inputs from cortex
   b) Planning and execution of complex spatio-temporal movements, including speech
3. Vestibulocerebellum:
   a) Inputs from vestibular system via brainstem
   b) VOR, posture, equilibrium

Question 14

Describe the features of cerebellum pathology:

Answer 14

1. Scanning speech can be affected
2. Nystagmus
3. Dysmetria
4. Braking movements inhibited
5. Dysdiadochokinesia
6. Knee jerk response - leg will keep swinging multiple times due to hypotonia
7. Gait - unbalanced and staggering