Lecture 15: Control of movement Flashcards
What three things is the spinal cord involved in?
- processing commands in the brain
- reflexes
- rhythmic motor patterns from central pattern generators
What two reflexes is the spinal cord involved in?
stretch reflex and tension reflex
How does the brain control muscles?
by interacting with interneurons in the spinal cord
Describe the rhythmic pattens of the spinal cord
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
Spinal cord and brainstem circuits generate basic patterns of rhythmic muscle activity for what?
walking, running
breathing
chewing
swallowing
Central pattern generators can be
started and stopped, have their speed regulated, have their force regulated and direction altered via commands from the brain
Which part of the brain maps our motor control?
the primary motor cortex
The secondary motor cortex is subdivided into which two regions. What are these regions called and what are they for?
They are called the supplementary motor cortex and premotor cortex and this is for the preplanning of movement
Output from the primary motor unit goes where?
through the corticospinal tract
How is the musculature laid out in the primary motor cortex?
the body parts are represented sequentially across the cortex
The area in the primary motor cortex devoted to each part of the body is dependent on what?
the level of fine control
the extent of use
What does a motor unit consist of?
a motor axon and muscle fibres
Why is it that areas of the body that are under finer control need larger mapping in the brain?
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
What does damage of the primary motor cortex do?
it causes problems with movement, particularly with fine voluntary control in specific parts of the body
Is the primary motor cortex fixed?
no, it is modifiable
What are the two special roles of the primary motor cortex?
- controlling force of muscle contractions
- controlling the direction of movements
Describe the primary motor cortex’s special role in controlling the force of muscle contractions
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
What are the two different pathways that take information out of the primary motor cortex?
- the corticospinal pathway
- the brainstem pathway
Describe the corticospinal pathway which takes information out of the primary motor cortex
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)
Describe the brainstem pathway which takes information out of the primary motor cortex
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
Describe the primary motor cortex’s special role in controlling the direction of movements
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
Where do most axons from the motor cortex synapse onto?
interneurons, not α motor neurons
Despite most axons from the motor cortex synapsing onto interneurons, some synapse directly onto α motor neurons. What is the special role for these?
- 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
Describe how the bionic arm is operated
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
