Upper Motor Neurones, Spinal Reflexes and Control of Movement Flashcards
What are the 4 sources from which an interneurone can receive input?
1) Primary sensory axons (Ia and Ib)
2) Descending axons from the brain
3) Collateral branches of LMNs
4) Other interneurones
Input may be inhibitory or excitatory. The interneurone itself may be excitatory or inhibitory.
What is an interneurone?
A neuron which transmits impulses between other neurons, especially as part of a reflex arc
What is Reciprocal Inhibition?
The process of muscles on one side of a joint relaxing to accommodate contraction on the other side of that joint.
What is the flexor reflex?
A noxious stimulus (e.g stepping on a pin) causes contraction of flexor muscles (excitation) and relaxation of extensor muscles (inhibition) to withdraw from the noxious agent.
What is the crossed extensor reflex?
A noxious stimulus causes contraction of extensor muscles (excitation) on opposite side and relaxation of flexor muscles (inhibition) to stabilise the body as the other limb withdraws.
What is the lateral pathway?
It is involved with voluntary control of distal musculature (discrete, skilled movements) and is under control of the cerebral cortex.
What is the ventromedial pathway?
It is involved with control of posture and locomotion and is under control of the brainstem
Which is the major lateral pathway?
Corticospinal tract
Which is the more minor lateral pathway?
Rubrospinal tract
What is the result of damage to the corticospinal tract? (direct)
The rubrospinal tract (indirect) offers a degree of compensation.
How can the ventromedial pathways be further classified?
Vestibulospinal tract, Tectospinal tract & Reticulospinal tracts (Pontine & Medullary)
How does the vestibulospinal tract divide?
The lateral vestibulospinal tract (descends to lumbar spine) and the medial vestibulospinal tract (descends to the cervical spine).
What does the lateral vestibulospinal tract do?
Helps to maintain upright posture by triggering extensor MNs of anti-gravity muscles.
What does the medial vestibulospinal tract do?
Activates the circuits which control neck and back muscles guiding head movement.
What does the tectospinal tract do?
Receives direct input forms eh retina, visual cortex and afferents conveying somatosensory and auditory information.
