LEC 8 Flashcards
hierarchical organisation of sensorimotor system
Organised parallel, functionally segregated, sensory = afferent, motor = efferent
feedback
for coordination of motor movements (vision, touch, vestibular, proprioception monitoring body responses). movements not requiring feedback are ballistic movement e.g. swatting fly.
when good at skill feedback processes are automatic
posterior parietal cortex
integrate info about the environment and body, directing movement and attention. outputs to frontal cortex, dorsolateral prefrontal cortex, secondary motor cortex, frontal eye field. damage = deficits in deployment of attention and apraxia
apraxia
disorder of voluntary movement, cannot preform specific task when requested but can preform task spontaneously e.g. carpenter cannot mime hammer being nailed but can nail a hammer
Apraxia = damage to left parietal cortex
Neglect = damage to right parietal cortex
dorsolateral prefrontal cortex
output to secondary motor area, primary motor cortex, frontal eye field. neurons respond to certain characteristics and location of objects. neurons fire before and while action is being executed
secondary motor cortex
contains the supplementary motor area, premotor cortex, cingulate motor areas.
inputs from parietal and dorsolateral prefrontal cortex
outputs to primary motor cortex. elicit complex movements to both sides of the body
mirror neurons
mechanism for social cognition. understanding perceptions, ideas, and intentions of other. may be basis for social understanding, cooperation and imitation.
respond to the understanding of the purpose of the action not just a superficial characteristic.
Primary motor cortex
homunculus
certain areas when stimulate may illicit full responses e.g. full feeding responses. primary motor cortex neurons initiate movement towards specific goals rather than coding for one direction of movement.
primary motor cortex lesions
not that bad
may lose certain movement in muscles e.g. one finger disabled, and unable to identify objects strictly from touch
Cerebellum
interacts but is not apart of the descending sensorimotor pathway
contains 50% of brains neurons.
input from primary and secondary motor cortex, input from brain stem motor nuclei, somatosensory and vesitubular systems.
plays role in motor learning involving sequences where timing is a factor. corrects movement deviated from course.
Damage = loss of ability to control direction, force, velocity, and amplitude of movement.
basal ganglia
cluster of interconnected nuclei. input from motor cortexes. involved in motivation and movement. responsible for movement vigour. responsible for inhibiting motor activity
descending motor pathways (ventromedial)
both follow ipsilateral pathways.
direct is projections from primary motor cortex down to spine and innervate and interneuron circuits on both sides of spinal cord. Indirect goes to tectum and then goes down bilaterally to connect to brain stem connecting to tectum (audio), Vestibular nucleus (balance); reticular formation (regulation of behaviours e.g. walking).
similarities and difference between ventromedial and dorsolateral pathways
both have major tracts one descends straight to spinal cord, other has axons that synapse at brain stem on neurons that then descend to spinal cord. ventromedial is more diffuse. dorsolateral tracts terminate on contralateral half of spinal cord
ventromedial neurons project to proximal muscles
dorsolateral projects distal muscles
sensorimotor spinal circuits
motor unit = smallest unit of motor activity, comprised of single motor neuron connected to multiple skeletal muscles. when fire muscle fibres connected to unit contract together. different units have different fibres
descending motor pathways (dorsolateral)
both decussate. direct project from primary motor cortex to medullary pyramid down to spine than distal limbs. indirect goes to cranial nerves and mid brain then goes down to connect to interneurons that then connect to motor neurons.
muscle flexors and extensors
synergistic muscles move joints in the same way, antagonistic is opposite
motor end plate
junction between motor neuron and muscle fibre, acetylcholine released at junction causing muscle to contract
receptor organs of tendons and muscles
golgi tendon organs = embedded in tendons and respond to increase in tension, protect as inhibits muscle contraction if tension is too strong.
muscle spindles = embedded in muscle tissue, signals change muscle length
stretch reflex
ellicited by sudden external stretching force on muscle
spindle receptors are stretched and send signal to spinal cord, that stimulate motor neurons in ventral horn and send action potentials back to spindle muscles
reccurent collateral inhibition
motor neuron branches before it exits spinal cord, one branch synapse onto small inhibitory neuron. Renshaw cell inhibit motor neurons each time it ifres, diverting action to another member of motor pool to prevent fatigue
