how is the sensorimotor system organised
hierarchically
functional segregation (each level comprised of different units)
motor input is guided by sensory input (sensory feedback)
ballistic movements
only response not mediated by sensory feedback
learning
changes the nature and locus of sensorimotor control
hierarchy
association cortex (top) secondary motor cortex primary motor cortex brain stem and motor nuclei spinal motor circuits (bottom)
sensorimotor association cortex
receives input from 3 somatosensory systems:
visual system
auditory system
somatosensory system
has different segments that control different sections of the body
before movement is initiated, what is needed?
original muscle location
external objects location
damage to the association cortex
apraxia - disorder of voluntary movement
contralateral neglect - struggle to respond to stimuli on on opposite side of body to image
dorsolateral prefrontal association cortex
initiates voluntary movement - interacts with prefrontal association cortex and frontal areas
where does the secondary motor cortex receive input from?
association cortex
where does the secondary motor cortex send information?
primary motor cortex and secondary motor areas
divisions of the secondary motor cortex
8 areas with own subdivisions:
3) different supplementary motor areas (SMA, preSMA & supplementary eye field)
2) premotor areas (dorsal and ventral)
3) small areas (cingulate motor areas)
frontal eye field
controls eye movement
mirror neurons
fire when a particular goal directed hand movement is done, or when it is observed
- mechanism for social cognition?
primary motor cortex
organised somatotopically - body parts map onto it
-> motor homunculous
two different hand areas in PMC - one for stereognosis
complex species specific movements which involve several parts of the body
neurons initiate movement
primary motor cortex lesions
astereognosia - deficits in stereognosis
- speed, accuracy and force of patients movements
cerebellum
interact with different levels of the hierarchy
used for motor learning (sequences)
correcting ongoing movement
cerebellum information in
primary and secondary motor cortex
descending motor signals
feedback
damage to the cerebellum
no precise movements force velocity amplitude posture balance gait
basal ganglia
collection of interconnected nuclei
what does the basal ganglia do?
modulatory function - adjustment of movement
habit learning
how does the basal ganglia work?
carries information in loops from motor cortex via the thalamus
dorsolateral corticospinal tract
direct - straight to spinal cord synapses on interneurons of spinal grey matter (distal muscles) - hands - wrists - fingers
betz cells
large pyramidal neurons of the primary motor cortex
dorsolateral corticorubrospinal tract
indirect - brain stem then spinal cord
synapses in red nucleus controlling cranial nerves (face) and on motor neurons (arms and legs)
