control of movement Flashcards
what are the 3 key levels to movement control
- spinal chord;
- motor cortex;
- cerebellum + BG;
3 classifications of movement
- simple reflexes;
- rhythmic motor patterns (initiation/termination are voluntary but actual action is reflexive);
- volunatry;
4 key players in simple reflexes
- golgi tendon organs;
- muscle spindles;
- afferent/efferent neurons;
- interneurons
interneuron role
provide basic level processing through selective excitation/inhibition of motor neurons e.g. coordination of flexors and extensors within same limb
what does the patella reflex aid with
walking -> selectively excites hamstrings but inhibits quadriceps
what are central pattern generators
self-organizing biological neural circuits that produce rhythmic outputs in the absence of rhythmic input -> movements can be sustained indefinitely at SC level after initial initiation e.g. walking, breathing
what neurons are key in central pattern generation
inter neurons -> selective excitation/inhibition of muscles
how do central pattern generator neurons work (2)
- pacemaker/follower
- reciprocal inhibition
CPGs may be a combination of both
explain the pacemaker/follower mechanism (central pattern generation)
certain neurons act as core oscillators where they create their own intrinsic APs (leaky channels), these cells are coupled to others and cause depol in them when they themselves depol
explain reciprocal inhibition (central pattern generation)
one neuron fires which also causes inhibition in another neuron to which it is coupled => it cannot fire -> the inhibition eventual wears off and the second nerve can now fire -> causes inhibition of the first neuron -> leads to rhythmic pattern of firing
what are the 2 major motor pathways in the motor cortex
- corticospinal (goes to SC to cause movement of body);
- corticobulbar (movement of head, neck and face);
what is the function of the pre motor cortex
motor planning, works alongside the BG
what is the function of the supplemenatry motor area
complex sequence planning; skill learning; movement based on sensation; bilateral movement
corticospinal tract pthaway (M1 -> SC)
motor cortex -> midbrain -> cerebral peduncles -> pons -> pyramids (brainstem) -> decussation (in oyramids) for 90% -> lateral corticalspinal tract (distal msucles)
for those that dont dessucate: pyramids -> ventral/anterior corticospinal tract (proximal muscle) -> decussate in DH -> sunampse to LMN
4 symptoms of UMN lesions
- weakness in muscles;
- hyperactive reflexes;
- decreased motor control -> loss of fine muscle movements;
- abnormal muscle tone
what is the role of the BG in movement
smooths out movement (tremor), movement motivation
role of cerebellum in movement (3)
- error correction -> distinction between desired/planned movement and the actual movement;
- maintain muscle tone;
- balance/stability
what is the BG direct pathway (draw out!)
motor cortex → glutaminergic activation of dorsal striatum (caudate nucleus and putamen) → D1 route activation (this is also activated by dopamine release from the SNc, this is the largest dopamine pathway and is known as the nigrostriatal pathway) → substance P/ GABA release causes inhibition of GPi and SNr → decreases GABAergic inhibition of thalamus (aka excitation) → execution of the action can occur
BG indirect pathway (draw out!)
motor cortex → glutaminergic activation of the dorsal striatum (corticospinal tract) → D2 route activation → enkephalin release causes inhibition of GPe → inhibition of STN → excitation of GPi → inhibition of thalamus → inhibition of movement
what is the role of the substantia nigra
releases DA
role of the BG indirect pathway
smooths movement (downregulated unwanted movements)
what are the 3 peduncles of the cerebellum and what do they do
Superior peduncle: this connects the cerebellum to the midbrain (colliculi, tegmentum etc.) and allows for deep cerebellar nuclei to communicate with the motor cortex (via the thalamus)
Middle peduncle: connects cerebellum to the pons and receives input from the cerebral cortex
Inferior peduncle: connects cerebellum to medulla, input from proprioceptors and vestibular receptors, outputs to upper motor neurons (non-sc neurons)
what structures does the BG comprise of (3)
- striatum (caudate nucleus, nucleus Accumbens and the putamen)
- the globus pallidus
- some also include the substantia nigra and subthalamic nuclei
what separates the cerebellum from the occipital lobe
the cerebellar tentori
