The motor system lecture 19 Flashcards
(23 cards)
Movement of which body part has high area of motor cortex associatiated with it?
Fingers, hands and face
An inverse model…
calculates muscle activity from desired trajectories
Parametric feedback…
adjusts a forward model based on errors from the last movement
Where is the motor cortex?
In front of the central sulcus
Which Brodmann’s area is the motor cortex?
4
What stimulation technique did Penfield use when mapping the cortex?
Small electrodes
What was thought happened because of Penfield’s technique?
Overlapping areas were thought to occur just because of current spread, not because the area was responsible for movement in multiple body areas
What technique did Anderson use which proved there is overlap in the motor cortex?
Intracortical microstimulation
What is the corticospinal tract pathway?
From M1, through the midbrain internal capsule and cerebral peduncle, to the medulla where there is pyramidal decussation then to spinal cord
Where does the corticospinal tract cross over?
In the medulla
As we go through phylogenetic species, what changes about the termination of the corticospinal tract?
There is termination in the dorsal horn of the spinal cord in ‘lower’ species, but termination in the ventral horn in mammals
What does the change in termination of the corticospinal tract correlate to?
Ventral termination correlates to improved fine motor skills like independent finger movement
When terminations are in the ventral horn, what neurones are terminations directly on to?
Motor neurones
Experiments by Armand et al 1997 showed what?
That new born monkeys have no corticospinal terminations around motor neurones. These appear around 11 months, when babies begin grooming their mothers with fine motor skills
What are the two pathways in rats?
From cortex to spinal cord interneurons, or from reticular spinal neurones in the brainstem
What are rats motor skills like?
Not very fine
What extra pathway do cats have?
Propriospinal neurones in C3-C4
What extra pathway gives the Masque monkey fine motor skills?
The direct connections onto motor neurones from the cortex
Experiments by Evarts 1968 showed that motor cortex cells encode force. How?
He got monkeys to make a wrist flex movement and recorded from M1 corticospinal cells. There was activity before the movement. Then added a weight which opposes the movement so monkey had to use more force to produce the movement. The cells showed an increased firing rate. When weight helps movement, very little activity. So these cells are encoding force needed to produce a movement.
Experiments by Georgopoulos in 1982 showed some corticospinal cells in M1 encode direction. How?
Got monkeys to make reaching movements in multiple directions. Showed that some cells fire more in particular directions.
How did these experiments show that direction encoding was ambiguous?
The curve is sinusoidal, so there is two directions which cause the same firing of that cell
How is direction encoded?
As a combination of multiple cells firing rate- population vector
