Lecture 15: Control of movement

Question 1

What three things is the spinal cord involved in?

Answer 1

• processing commands in the brain
• reflexes
• rhythmic motor patterns from central pattern generators

Question 2

What two reflexes is the spinal cord involved in?

Answer 2

stretch reflex and tension reflex

Question 3

How does the brain control muscles?

Answer 3

by interacting with interneurons in the spinal cord

Question 4

Describe the rhythmic pattens of the spinal cord

Answer 4

these come from central pattern generators
the rhythmic patterns are neural circuits that can be arranged such that they will, if activated and given an excitatory input, design a neuronal circuit to connect excitatory and inhibitory neurons that will run a repetitive cycle of activity
you don’t have to think about each action, it just occurs as a flow; a sequence of events that flows due to rhythmic action

Question 5

Spinal cord and brainstem circuits generate basic patterns of rhythmic muscle activity for what?

Answer 5

walking, running
breathing
chewing
swallowing

Question 6

Central pattern generators can be

Answer 6

started and stopped, have their speed regulated, have their force regulated and direction altered via commands from the brain

Question 7

Which part of the brain maps our motor control?

Answer 7

the primary motor cortex

Question 8

The secondary motor cortex is subdivided into which two regions. What are these regions called and what are they for?

Answer 8

They are called the supplementary motor cortex and premotor cortex and this is for the preplanning of movement

Question 9

Output from the primary motor unit goes where?

Answer 9

through the corticospinal tract

Question 10

How is the musculature laid out in the primary motor cortex?

Answer 10

the body parts are represented sequentially across the cortex

Question 11

The area in the primary motor cortex devoted to each part of the body is dependent on what?

Answer 11

the level of fine control

the extent of use

Question 12

What does a motor unit consist of?

Answer 12

a motor axon and muscle fibres

Question 13

Why is it that areas of the body that are under finer control need larger mapping in the brain?

Answer 13

because there are more motor axons going to that region of the body because each one of them controls a relatively small number of fibres

Question 14

What does damage of the primary motor cortex do?

Answer 14

it causes problems with movement, particularly with fine voluntary control in specific parts of the body

Question 15

Is the primary motor cortex fixed?

Answer 15

no, it is modifiable

Question 16

What are the two special roles of the primary motor cortex?

Answer 16

• controlling force of muscle contractions

- controlling the direction of movements

Question 17

Describe the primary motor cortex’s special role in controlling the force of muscle contractions

Answer 17

The greater the rate of neuronal activity, the more input to motor units and the greater the force.
More motor units means that there is a more forceful contraction as there is more output from the primary motor cortex. This means that there is a higher rate of action potentials down a greater number of motor neurons to activate more more motor units

Question 18

What are the two different pathways that take information out of the primary motor cortex?

Answer 18

• the corticospinal pathway

- the brainstem pathway

Question 19

Describe the corticospinal pathway which takes information out of the primary motor cortex

Answer 19

This is for the deliberate direct control of dexterous movement
Outputs from the motor cortex controls spinal neurons for fine, isolated movements. It crosses over to the other side (most input is to interneurons)

Question 20

Describe the brainstem pathway which takes information out of the primary motor cortex

Answer 20

This is for the coordinated activity in large muscle groups, for posture, locomotion and routine activities. This involves both crossed and uncrossed to the other side

Question 21

Describe the primary motor cortex’s special role in controlling the direction of movements

Answer 21

Direction of movement is controlled by the relative activity of many cortical neurons controlling muscles each side of a joint to control the direction of the movement

Question 22

Where do most axons from the motor cortex synapse onto?

Answer 22

interneurons, not α motor neurons

Question 23

Despite most axons from the motor cortex synapsing onto interneurons, some synapse directly onto α motor neurons. What is the special role for these?

Answer 23

• they have a particularly direct, fast and powerful effect
• mostly for control of distal limbs (hands and fingers)
• they are most developed in higher primates

Question 24

Describe how the bionic arm is operated

Answer 24

The nerves that innervated the arm were surgically redirected to the muscles in her breast so on the outside of the body there were all these electrodes to measure the action potentials in the muscle fibres that were happening in her chest because motor units were being activated. The motor output normally controlling the arm is activating motor units in muscles in her chest. The EMG electrodes pick up the action potential activity and that is relayed to the computer in her arm. This is used to activate motor units in the arm to control movement of the bionic arm so the brain controls what it thinks is the arm

Question 25

Describe the role of the basal ganglia during the hierarchical organisation of neural systems controlling movement

Answer 25

The basal ganglia relays sensory information to the right position in the cortex. You want to do something the information is compared to previous actions then the information goes to the motor cortex and it goes around the basal ganglia, thalamus and cortex until the substantia nigra releases dopamine

Question 26

Describe the role of dopamine released by the substantia nigra in hierarchical organisation of neural systems controlling movement

Answer 26

Dopamine is a reward system molecule so there is a positive feedback system that confirms proposed activity is successful so inhibition is removed from the output of motor cortex and motor neurons send information to the corticospinal pathway to motor neurons to control muscles

Question 27

List the thousands of roles of the basal ganglia

Answer 27

• monitors and helps plan cortical activity involved in movement
• helps the cortex select combinations of muscle activation
• there is a loop between the cortex and basal ganglia which occurs several times in preparation for movement
• the positive feedback (withdrawal of inhibition) to cortex for selected motor output pathways
• needed for the initiation of movements
• dopamine input (from substantia nigra) is vital to allow proper functioning

Question 28

What does the death of dopamine neurons produce?

Answer 28

Parkinson’s disease

Question 29

Dopamine is required for us to make the initiation step. True or false?

Answer 29

true - this is so that we don’t have to “think” about doing stuff

Question 30

What are some of the symptoms of Parkinson’s disease?

Answer 30

difficulty beginning movements, there are very slowed movements and people tremor

Question 31

Why do people tremor when they have Parkinson’s disease?

Answer 31

because the basal ganglia system to regulate motor output from the motor

Question 32

What are some treatments of Parkinson’s disease?

Answer 32

• dopamine replacing drugs (the precursors for dopamine are taken up and released by the surviving substantia nigra cells)
• deep brain stimulation
• possibly transplantation of dopamine cells

Question 33

What is the main role of the cerebellum?

Answer 33

it incorporates sensory information at the planning stage and incorporates sensory feedback into the delivery of information

Question 34

What is the role of the purkinje cells in the cerebellum?

Answer 34

to compare what we think we are going to do to what is actually happening

Question 35

What are the 5 roles of the cerebellum?

Answer 35

1. helps plan, execute and learn motor programs
2. integrates sensory information with planned motor programs
3. organises the timing of individual muscle contractions around the joints to control direction
4. compares the intended result of a planned movement with the actual result, and modifies the ongoing activity, for smooth and accurate motor control
5. may also be used by other brain systems (cognition, episodic memory, reading, emotion)

Question 36

What would injury to the cerebellum result in?

Answer 36

Movements that are slow and uncoordinated - individuals with cerebellular lesions tend to sway and stagger when walking

Question 37

Damage to the cerebellum can lead to?

Answer 37

• loss of coordination of motor movement
• the inability to judge distance and when to stop
• the inability to perform rapid alternating movements
• movement tremors
• staggering, wide based walking
• tendency toward falling
• weak muscles
• slurred speech
• abnormal eye movements