Motor Control Basics Flashcards
Voluntary brain control of muscles is via what?
Alpha motor neurones in the spinal cord
Descending inputs from which two tracts regulate trunk and limb muscle movements?
Vestibulospinal tract
Reticulospinal tract
The brainstem receives control inputs about voluntary movements from higher centres. Name these higher centres.
Cerebral cortex
Basal ganglia
Cerebellum
Which muscles do motor neurons supply?
Skeletal muscles
What coordinates the output from the brainstem down into the lower motor neurons?
Cerebellum
Which four systems control movement?
- Descending control pathways
- Basal ganglia
- Cerebellum
- Local spinal cord/brainstem circuits
In the spinal cord, what does the lateral white matter contain?
Axons from the motor cortex
In the spinal cord, what does the medial white matter contain?
Axons from the brainstem
Which muscles do the more medial motor neurons in the ventral horn supply?
Proximal muscles e.g. muscles of trunk
Which muscles do the more lateral motor neurons in the ventral horn supply?
Distal muscles e.g. muscles in legs, toes, hands, etc.
Higher brain centres are functionally interdependent. What does this mean?
They integrate information to work out what they should/shouldn’t do.
They control different aspects of voluntary movements.
How does the spinal cord receive descending input?
Via the brainstem AND directed cortical input via corticospinal (pyramidal) tract
Which types of information come from the spinal cord?
Proprioceptors
Touch
Pain
Where does the brainstem get inputs from?
Vestibular system informs about balance
The cortex produces movements in response to which types of cues?
Visual, olfactory, auditory, emotional, intellectual, etc.
What happens if there is damage to the sensory inputs?
Paralysis
What causes sensory neuropathy?
Loss of large myelinated fibres
Can sensory neurons regernate?
No
Which type of reflex is present in all muscles?
Stretch reflex
Give a common example of the stretch reflex.
Patellar tendon- knee jerk reflex
In the knee jerk reflex, a sharp tap is given to the patellar tendon, which is an inelastic tendon. How does this provoke a stretch reflex?
Tendon transmits force to the muscle fibres as they are more elastic and able to stretch.
Which type of sensory nerve terminals are activated in the muscle spindles in response to stretch?
1a afferent sensory nerve terminals
What happens when there is activation in the 1a afferent sensory nerve terminals due to stretch?
Increases the number of action potentials
Spindle sensory afferent projections make three connections. What are these connections with?
Two with the spinal cord
One with the brain
What happens as a result of the direct contact to the A-motorneurons in the stretched muscle?
Rapid contraction of agonist muscle.
Muscles are arranged as agonists and antagonists in order to move joints.
Therefore, what happens when the spindle branch is in direct contact with the A-motorneurons and cause the agonist muscle to contract?
Another spindle branch connects with the antagonist muscle and stretches it.
Therefore, as agonists are contracted, antagonists stretch.
Just to double check that it’s gone in- what happens when the agonist muscle contracts?
Antagonist muscle stretches
What is meant by reciprocal inhibition in terms of agonist and antagonist muscles?
Simultaneous activation of agonist motorneuron and inhibition of antagonist muscle.
The third branch of afferent spindle fibres travels up to the brain via the dorsal column. To which part of the brain does it travel to?
Thalamus and somatosensory cortex
What is the final common pathway for movements?
Alpha motorneurons
If you picked up a weight, your muscle would stretch initially. Then, there would be reflex muscle contraction. What happens in this?
Muscle shortens back to previous length
What is the inverse stretch reflex mediated by?
Golgi tendon organs
Which nerves cause the inverse stretch reflex?
1b afferent nerves
What do Golgi-tendon organs monitor?
Tension
What causes the 1b afferent nerves from the GTOs to increase their frequency of action potentials?
The contraction and shortening of a muscle
RECAP-
Spindles are innervated by??
GTO’s are innervated by??
- Spindles innervated by 1a afferent neurons
- GTO’s innervated by 1b afferent neurons
The firing of 1b afferent neurons leads to a decrease in contraction strength. Why is this?
There is activation of inhibitory interneurons to the agonist muscle
->girl i know this is not making sense but these lectures are not it
What else happens when there is increased firing of 1b afferent neurons, as well as the activation of inhibitory interneurons in the agonist muscle?
Activation of excitory interneurons to antagonist muscles
How does information about the muscle tension get to the somatosensory cortex?
Ascends up spinal dorsal column
The inverse stretch reflex can also be called the clasp-knife reflex. Why is this?
There is greatly increasing tension in the tendon which leads to a collapse of resistance.
So, like a spring-loaded knife opening up, the joint extends
Why is the knife clasp/ inverse stretch reflex important>
Protective mechanism which prevents muscle damage
Okay read this to try and simplify it.
Inverse stretch reflex/knife-clasp reflex:
If too heavy, the muscle gives in and you drop something to protect the muscle from becoming badly damaged
Describe what would happen in weightlifting if the weight is too heavy.
Firstly, the agonist quadriceps would be contracted, pulling hard on the tendon.
There would be increased GTO afferent firing. These will synapse with inhibitory interneuron which reduces motoneuron firing. Therefore, the agonist muscle is inhibited so it is forced to relax.
Wordy but read through, this one makes more sense
GTO afferents also synapse with excitory interneurons at the same time as synapsing with inhibitory ones.
What does this do?
Increased activation of antagonist motor neurons meaning the antagonist contracts rapidly.
Okay just to break this down a bit.
What happens to agonist and antagonist muscles in the:
1. stretch reflex e.g. knee jerk
2. GTO reflex aka inverse stretch reflex/knife-clasp reflex.
- Agonist contracts, antagonists stretches
- Agonist relaxes/stretches, antagonist contracts
Which reflex is monosynaptic?
Stretch reflex
Which reflex is polysynaptic?
Inverse stretch reflex
Which reflexes will occur in response to a painful stimuli?
Flexor/Withdrawal Reflex
Crossed Extension Reflex
Where does the flexor/withdrawal reflexes get information from?
Nociceptors in skin, muscles and joints
What happens when there is increased action potentials in the nociceptors.?
- Increased activity in flexor muscles
- Antagonistic extensors are inhibited
What is involved in the flexor/withdrawal reflex?
The flexor withdrawal reflex involves flexing the affected part towards the body, withdrawing it from painful stimuli.
Which fibres carry the signals which provoke withdrawal in the flexor reflex?
A delta nociceptive axons
How does the flexor reflex differ compared to others in terms of number of muscles controlled?
Most reflexes control one muscle acting on a joint but the flexor reflex controls all the muscles of the affected limb.
To prevent falling over, what happens to the contralateral limb when the affected limb withdraws?
Contralateral limb extends via crossed extensor reflex
In the crossed extensor reflex, what role do excitatory interneurons have?
They cross the spinal cord and excite contralateral extensors
What happens at the same time as the excitation of the contralateral extensors?
Simultaneous inhibition of contralateral flexors
Just to clarify-
what happens to flexor and extensor muscle on both legs if stepping on something sharp.
Affected leg- interneurons excite flexors and inhibit extensors.
Contralateral leg- interneurons excite extensors and inhibit flexor muscles.
Give an example of a time where the GTO reflex may be overridden.
If you were carrying something you didn’t want to drop, even if it was heavier than expected, like a child.
This can be over-ridden by voluntary input from the CNS.
