motor control

Question 1

describe the structure of muscles?

Answer 1

composed of elastic fibers that can change length and tension

antagonist pairs

Question 2

what are muscles controlled by?

and how?

Answer 2

motor neurons in the spinal cord

action potential in these neurons triggers release of acetylcholine which makes muscle fibres contract

Question 3

what do the 12 cranial nerves do?

Answer 3

control essential reflexes which keep us alive

Question 4

what are extrapyramidal tracts?

and hence what is the function of the brainstem?

Answer 4

direct pathways from brainstem nuclei down spinal cord to control posture, muscle tone and movement speed

so this is the role of the brainstem in motor control

Question 5

what are the brainstem and cerebellum and basal ganglia examples of?

Answer 5

subcortical motor structures

Question 6

describe the structure and function of the cerebellum?

what do lesions lead to?

Answer 6

more neurons than rest of CNS combined

controls balance and coordination

lesions lead to ataxia (loss of fine coordination)

Question 7

what is the structure and function of the basal ganglia?

what do lesions cause?

Answer 7

role in selection and initiation of actions

lesions cause Parkinsons disease

contains 5 nuclei

Question 8

examples of cortical motor regions

Answer 8

primary motor cortex
secondary motor areas
association motor areas

Question 9

describe the function and organisation of the primary motor cortex?

what do lesions produce?

Answer 9

regulates activity of spinal motor neurons

somatotopic organisation - different regions represent different body parts

lesions produce hemiplegia (loss of contralesional (other side of body) voluntary movement)

Question 10

describe the function and structure of secondary motor areas?

what do lesions cause?

Answer 10

contain premotor cortex and supplementary motor area

involved in planning and control of movement (top of hierarchy)

lesions result in apraxia (can’t link simple gestures to create actions)

Question 11

describe association motor areas?

what it contains?
what are the functions of these sections?

Answer 11

parietal - representing space and attention - lesions produce apraxia

and prefrontal cortex - contains Broca’s area and frontal eye fields for eye movement

Question 12

what did Sherrington do?

method?
what he found?
conclusions drawn?

Answer 12

severed spinal cord of cats and placed them on a treadmill

found cats able to produce limb movements to walk despite no commands from cortex or subcortex

so neurons able to hold representation of entire pattern movements required to produce complex motor act

Question 13

what did Bizzi do?

method?

how conclusions generated?

Answer 13

trained monkeys who had severed somatosensory signals to reach target

applied opposing force to arm but monkey’s couldn’t feel it

if brain encodes trajectory, opposing force to arm should result in arm falling short of target as wouldn’t adjust to force
if location encoded then monkey should get target

monkey reached target so neurons represent movement by encoding location of end point

Question 14

what did Georgopoulos do?

and what did they find?

what do these findings suggest about encoding of neurons?

Answer 14

found neurons in primary motor cortex show preferred direction both moving lever in and out (fire most strongly when movement in that direction)

actually preferred multiple directions as neuronal response tuned to broad range of directions

shows neurons also encoded with direction as location different

Question 15

what is a vector?

Answer 15

direction of cell’s preferred direction combined with info about strength of firing

Question 16

what is a population vector?

Answer 16

sum of individual neuron vectors

provide most accurate estimate of planned direction of movement

Question 17

what did Chapin do regarding brain-machine interfaces?

what he did?
what he found?

Answer 17

trained rats to press lever for reward
measured neuron responses in motor cortex

neural networks learnt patterns of neuronal activation predicting different force exerted on lever. led to complex population vector response

changed it so that mice gained reward if displayed cortical signals necessary to move lever without actually moving it

Question 18

how can you study visuomotor adaptation in a lab?

what was found about patients with lesions in motor areas?

Answer 18

hand hidden
mismatch between where subject moves hand and where they see it move
over time adapt movements to this mismatch

see increased activation across many different motor regions during visuomotor adaptation phase

lesions in motor areas performed poorly suggesting motor regions are critical

Question 19

whats are the effects of transcranial direct current stimulation (tDCS) on visuomotor adaptation?

what is tDCS?

cerebellum and motor cortex?

deadaptation?

Answer 19

tDCS - currents applied to scalp which change excitability of neurons

tDCS of cerebellum - faster rate of adaptation
tDCS of motor cortex - increased retention of adaptation (Galea)

deadaptation (no mismatched feedback) occured but hindered if motor cortex stimulated (double dissociation between cerebellum and motor cortex)

Question 20

what have tDCS studies shown about the role of the cerebellum?

Answer 20

• important for learning new mapping by generating forward models (prediction of sensory consequences of motor command) as errors used to correct future predictions

Question 21

what have tDCS studies shown about the role of the primary motor cortex?

Answer 21

important for consolidating newly learnt mapping

Question 22

describe studies into effect of TMS on cerebellum?

Answer 22

hear beep then move arm toward visual target

TMS of cerebellum changed movement trajectory
deactivating cerebellum = deactivating forward model
as provides prediction of where hand will be when movement is initiated and adjusts motor command accordingly

Question 23

what is the role of the basal ganglia in motor control?

Answer 23

movement initiation and inhibition

complex network of inhibitory (indirect pathway) and excitatory (direct pathway) connections within basal ganglia and connecting it to other structures

pathways act in mutual antagonism to balance the system

Question 24

describe Parkinsons disease?

symptoms?

Answer 24

loss of dopamine neurons in the basal ganglia

symptoms:
hypokinesia: reduction in volunatry movement
bradykinesia: slow movement
tremor

Question 25

describe treatment of Parkinsons?

Answer 25

levodopa - dopamine precursor (converted into dopamine after entering CNS)

deep brain stimulation

Question 26

describe cognitive function in parkinsons?

what does this suggest about the role of the basal ganglia?

Answer 26

have impairments in cognitive function

so basal ganglia has a dual role in cognition and action as cognitive and motor control rely on same neuronal circuits

Question 27

what is the explanation for Sherrington’s findings that cortex commands not necessary for movement?

Answer 27

central pattern generators - neurons in spinal cord being able to hold representation of pattern of movements required to produce a complex act

high region of hierarchy sending signal to trigger central pattern commands so no need for high level regions to hold representations

Question 28

what is a central patttern generator?

Answer 28

biological neural circuits that produce rhythmic outputs in the absense of rhythmic input

evolved to enable actions essential for survival

Question 29

what question regarding neurons does Bizzi’s research tackle?

Answer 29

whether neurons encode trajectory (direction, distance and force) of movement or location of the target

found they encode location

Question 30

what are the compoents of the motor control system hierarchy?

Answer 30

premotor and parietal cortex (top)
primary motor cortex
basal ganglia
cerebellum
brainstem
spinal cord

ends in output signals to muscles (bottom)

Question 31

what is the role of the spinal cord in motor control?

Answer 31

the neurons in the spinal cord control muscles

by generating action potentials to make muscles contract/relax