*L08 - Motor control - role of the motor cortex and spinal reflexes Flashcards
Which descending motor pathways are voluntary and which are brainstem controlled?
The lateral pathways are voluntary and the ventromedial are brainstem controlled
What are the three main features of a motor system?
- heirarchial organisation - top down arrangement
- feedback loops - essential for control of movements whilst ongoing, recieve sensory input so can modulate movement.
- Somatotrophic representation - different muscles relate to different parts of the brain.
What are the three basic types of movement?
Reflex - protective motor pattern that is automatic
Rhythmic motor patterns - voluntary and reflex movement. e.g. chewing
Voluntary - purposeful goal orientated movement
What are the three main inputs into spinal motor control and what do they do?
Sensory neurones - provide information about the movement via dorsal rootlets
Spinal interneurones - can be inhibitory or excitatory to allow for appropriate movements
Upper motor neurones - initiate movements.
How can coordinated movements still occur when descending motor neurones are severed?
Due to spinal circuits such as the spinal locomotor system - simply require upper motor neurone input to modulate. Proprioceptive information can allow cats with severed spine to walk on treatmill once set off. This is caused by rhythmic activity in the flexors and extensors.
How does descending input from upper motor neurones effect spinal circuits?
It is superimposed on the spinal circuit so it can influence it.
What is the organisation of motor neurones within the spinal cord for distal and proximal muscles?
Proximal muscles (trunk muscles) are innervated by motor neurones that lie medially in the cord. Usually brainstem controlled. Distal muscles (hands and feet) are innervated by muscles that lie laterally in the cord. Usually voluntary control.
What tracts are lateral and what muscles are they concerned with?
The corticospinal tract and the rubrospinal tract. They are concerned with voluntary control of distal muscles.
What is the pathway of the corticospinal tract?
Fibres originate from areas 4 and 6 of the motor cortex in the frontal lobe. Descend through corona radiata and internal capsule before passing through the medullary pyramids. 85% decussate to form the lateral corticospinal tract, 15% are the venteral corticospinal tract and decussate near termination.
Monosynaptic contact with alpha motor neurones on contralateral side.
What is the pathway of the rubrospinal tract?
Originates in the midbrain tegmentum. Decussates in the ventral tegmental decussation and then descend in the lateral spine non pyramidally.
What are the effects of a lesion to both cortico and rubrospinal tracts? What would the effects to just corticospinal be?
When both affected then would have slower voluntary motor control however posture would be unaffected as no loss of ventromedial tracts. Loss of discrete movements.
When only corticospinal affected then can get some back over time from the rubrospinal tract taking over however not fine digit control.
What are the four ventromedial tracts and what are their general role?
All extra-pyramidal
Tectospinal tract, vestibulospinal tract, pontine reticulospinal tract and medullary reticulospinal tract.
They control motor output to proximal and axial muscles to primarily control posture and locomotion.
What are the roles of the vestibulospinal and the tectospinal?
Vestibulospinal uses the vestibular system to control motor function to maintain head and neck position aswell as legs.
Tectospinal uses the retinal and visual stimuli to orientate head and neck to visual and auditory inputs.
What do the pontine and medullary reticulospinal tracts do?
The pontine one does antigravity muscles e.g. leg extensors.
The medullary one releases these muscles.
What are the two main areas of the motor cortex and what do they do?
Area 4 is the primary motor cortex and does contralateral movement with the lowest stimulus threshold for movement.
Area 6 is made up of the pre motor area (preperation) and the supplementary motor area (planning and initiation). Allow complex planned movements to be performed.
