w3+w4 Motor systems Flashcards
motor plan
we don’t think about individual muscle contractions, we think about motor plans: I want to move my finger, not every muscle in it in a particular way
can be stimulated electrically (done on monkeys) in the primary motor cortex (so not a single muscle stimulated, but a complex movement)
areas in the brain that do initiation, stopping and planning of motor actions/sequences
pre-motor cortex (PMC) and supplementary motor area (SMA)
part of the CNS responsible for reflexes
spinal cord
executing motor programs
motor cortex
gating and control over action based on motivation, affective state
basal ganglia
adjusting ongoing behavior, timing
cerebellum
Sylvian fissure
the same as the lateral fissure
transverse fissure
hierarchies in the motor system
lateral cortical spinal tract
it’s the hierarchy of the motor system, but represented as anatomy
primary motor neurons
more common: upper motor neurons
travel from motor cortex or brain stem down the spinal cord to synapse onto local circuits
Lateral cortico-spinal tract
Cross over to contralateral side
lower motor neurons
directly control muscles
local circuits
after/down the spinal cord
can operate with a level of (reflex) autonomy. e. g. Pain reflexes
central pattern generators
neuronal circuits that can produce rhythmic motor patterns in the absence of sensory inputs: walking, breathing, flying, and swimming
topology of the motor system in the spinal cord
medial to lateral
we can electrically stimulate a complex movement - so what?
“course/broad tuning”
problem: we cannot predict direction/intensity from a single M1 neuron
means that movements are specified by populations of neurons. Combined output determines actual movement
planning sequences of action: SMA
Sequences, more than repeated movements (Example: only active for “Pull, Push, Turn”, Activity aligned to “Push”, Not “Pull, Turn, Push”, Some neurons active for given position in sequence, irrespective of particular action required)
Self-generated more than cued motor sequences or action plans
Relatively abstract representations
planning sequences of action: PMC
PMC involved in the initiation and termination of cued sequences
Action / motor unit linked representations
“Working memory for action”
function of the basal ganglia
exert control over action selection
cortico-striato-thalamic loop
basal ganglia: direct vs indirect pathways
when are the basal ganglia the most active?
when learning new motor skills
: blocks of new learning vs. normal execution: joystick mapping rotated 90 degrees
anatomy of the cerebellum
functions of the cerebellum
Error correction: To produce smooth movement, Compare motor output to actual produced movement, Dentate Nucleus (deep structure) outputs back to motor cortex
Motor learning: When acquiring new motor skills, large activations of cerebellum ▪ Like Basal Ganglia ▪ Could be related to large “errors” to be processed
Non-motor learning: Also involved in cognitive tasks. Huge input from prefrontal regions. Hypothesis: efficient circuit for error correction
damage to the cerebellum
Midline: truncal ataxia
- Unsteady gait
- Seems drunk
Lateral cerebellar cortex: appendicular ataxis
- Non-smooth movement
- Intention Tremor during voluntary movement
motor system vs motivation
Value information or cueing from perception can bias motor preparation
PPC: spatial goals with higher value more active
SC: population action vectors can be manipulated
damage to cortical motor areas
M1: paralysis (often due to stroke)
PMC: deficiency in cue-based sequencing behavior ▪ Need to maintain e.g. visual cues to keep plan active
SMA: deficiency in self-generated sequences
Subcortical motor disease leads to
changes in the goal-directedness or smoothness of motor behavior
Parkinson’s disease
Up to 60% of substancia nigra is destroyed: Trauma, tumors, Encephalitis Lethargica, MPTP, Frozen addicts
Up to 80% of DA is lost: Brain tries desperately to compensate, Reducing degradation, Increasing receptors
the anatomy behind Parkinson’s disease
DA in the brain
so dopamine
DA: role in learning
Parkinson’s: treatment
Huntington’s disease
anatomy behind Huntington’s disease
Tourette’s syndrome
Heritable disease, sex-chromosome linked, expressed mostly in males
Link with OCD
Treatment:
DA-receptor antagonists
Haloperidol and others (Antipsychotic medication)
Strong side effects
Tardive dyskinesia
