Motor systems Flashcards
What is the role of the motor cortex?
Fine, voluntary movements
What is the role of the basal nuclei?
Used in planning and deciding movements
What is able to generate motor output?
Red nucleus and substantia nigra in midbrain
Where do UMNs take information?
From the brain to lower motor neurons
Where do LMNs take information?
They synapse with muscles via a neuromuscular junction
What is the role of UMNs, what are they required for?
Initiate, regulate, modify and terminate LMN activity
Required for voluntary movement of skeletal muscle
Are UMNs excitatory or inhibitory on LMNs?
Most are inhibitory
Where do UMNs supplying
1) flexor muscles
2) extensor muscles
travel in the spinal cord?
1) lateral funiculi
2) ventral funiculi
Where do LMNs have their cell bosy and axon?
Cell body in CNS
Axons in PNS
Where do LMNs for forelimb and hindlimb come from?
Forelimb = cervical intumescence (C6-T2) Hindlimb = lumbar intumescence (L4-S3)
How do LMNs cause a reflex action?
They can fire an AP without UMN input
What is atrophy?
loss of muscle tone
What is the result of LMNs having a constant sub-threshold depolarisation?
ACh release
Muscle tone and trophic support
What makes up a motor unit?
LMN + NMJ + skeletal muscle fibres
Which group of muscles are dominant in the body as they maintain posture against gravity?
Extensor muscles
What would occur if UMNs weren’t inhibitory on the LMNs that supply extensor muscles?
Spasticity of extensors
What causes a reflex to be exaggerated?
Removal of UMN input, as the temporing effect they possess is lost
What is the result of a LMN injury?
Muscle will lose tone, rapidly lose bulk (atrophy) and have reduced/absent reflexes
What is the result of a UMN injury?
Reflexes will be normal or increased as will tone, and any atrophy will be relatively mild and due to disuse. Coordination will be reduced, but strength will be normal
What is a reflex?
It is an innate reaction to a stimulus and is present from birth
Sensory input leads to motor output without input from higher centres – doesn’t require UMN input
How is a response different to a reflex?
It is learned behaviour
Describe the patella reflex
- Monosynaptic reflex
- Intersegmental reflex, it enables the lower limb to be extended
Describe the flexor withdrawal reflex
- Polysynaptic reflex
- Has a painful sensory input - reflex occurs before this is felt
- Inhibition of extensor muscles, stimulation of flexor muscles to draw limb away
What is the function of the spindle?
Arranged in parallel with the muscle fibres and are stretch receptors.
Body uses them to tell you the position of muscles e.g. how flexed or extended
