Brain control of Movement - Motor control 2

Question 1

Where does directional tuning occur?

Answer 1

Primary motor cortex (area 4)

Question 2

What can be said about the neurons in M1 and the direction of movement they control?

Answer 2

Each neuron has a preferred direction but the responses of all neurons are combined to produce a population vector

Question 3

What kind of loop mechanisms control movement?

Answer 3

Both feedback and feedforward mechanisms control movement

Question 4

What are examples of feedback mechanisms in movement?

Answer 4

Change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurons to correct postural instability

In addition, before movement begins brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustements to stabilise posture

Question 5

In damage to descending motor pathways, what does the injury site determine?

Answer 5

The symptoms

Question 6

In terms of movement, what does cortical damage cause?

Answer 6

Immediate flaccidity of contralateral muscles:

initial hypotonia due to “spinal shock” where spinal circuits are deprived of cortical input

days later spinal motor reflexes re-emerge in a consistent pattern as spared connections strengthen and new connections sprout

Question 7

what does actual change in body position initiate?

Answer 7

initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability

Question 8

what do brainstem reticular formation nuclei do before movements are carried out?

Answer 8

initiate feedforward anticipatory adjustments to stabilize posture in preparation

Question 9

what is evidence for anticipatory maintenance of body posture?

Answer 9

Hear sound - pull on handle - contracts biceps. BUT - gastrocnemius muscle in leg contracts first to ensure stability

Question 10

how can a Cat strike with a front paw and not fall over?

Answer 10

due to anticipatory feedforward adjustments
- Contralateral front & ipsilateral back legs contract, shift weight to diagonal distribution

Question 11

where does major subcortical input to area 6 come from?

Answer 11

ventral lateral nucleus in dorsal thalamus (VLo)

Question 12

where does Input to VLo?

Answer 12

Input to VLo comes from basal ganglia

Question 13

what are basal ganglia?

Answer 13

Basal ganglia are targets of frontal, prefrontal and parietal cortex

Question 14

describe the course for basal ganglia motor loop?

Answer 14

Cortex 🡪 thalamus & basal ganglia🡪
SMA (cortex area 6)

Question 15

what does basal ganglia motor loop initiate?

Answer 15

willed movements

Question 16

what are the major components of the basal ganglia?

Answer 16

Corpus striatum (“striped body”)

Question 17

what does the Corpus striatum (“striped body”) include?

Answer 17

includes two principal nuclei the caudate and the putamen

Question 18

what are the caudate and the putamen of corpus striatum known for?

Answer 18

input zone of the basal ganglia

Question 19

where does corpus striatum receive input from?

Answer 19

corticostriatal pathway - multiple parallel pathways with different functions

Question 20

what is the appearance of neurones in putamen and caudate?

Answer 20

Medium spiny neurones

Question 21

what do Medium spiny neurones in putamen and caudate receive?

Answer 21

receive excitatory (glutamatergic) cortical inputs on dendrites

Question 22

describe neurones & circuits of basal ganglia?

Answer 22

Large dendritic trees and integrate massive somatosensory, premotor and motor cortical inputs

Each cortical axon contacts 1000s of spiny neurones, so integrating influence of 1000s of cortical cells

Question 23

describe the axons of the neurons of basal ganglia?

Answer 23

Axons are inhibitory (GABAergic). Project to globus pallidus and substantia nigra pars reticulata

Question 24

where do axons of the basal ganglia fire to?

Answer 24

Project to globus pallidus and substantia nigra pars reticulata

Question 25

when does putamen fire?

Answer 25

before limb/trunk movements

Question 26

when does caudate fire?

Answer 26

before eye movements

Question 27

what do both putamen and caudate do?

Answer 27

predict movement

Question 28

what is the motor loop?

Answer 28

Cortex → Basal ganglia → Cortex

Question 29

how would you describe the type of pathway between cortex to putamen?

Answer 29

excitatory pathway

Question 30

how would you describe the type of pathway between putamen to globus pallidus?

Answer 30

inhibitory pathway

Question 31

describe the type of pathway between Globus pallidus to VLo neurones?

Answer 31

inhibitory pathway

Question 32

describe the type of pathway between VLo back to SMA?

Answer 32

excitatory pathway

Question 33

what is the functional consequence of cortical activation of putamen?

Answer 33

excitation

Question 34

what do globus pallidus neurones do at rest?

Answer 34

At rest globus pallidus neurones are spontaneously active and inhibit VLo

Question 35

describe cortical excitation?

Answer 35

Excites putamen, which Inhibits (inhibitory) globus pallidus, which therefore Reduces inhibition of VLo cells, so Activity in VLo boosts SMA activity Positive feedback loop for focussing or funnelling activation of widespread cortical areas back onto cortical SMA

Question 36

what does ‘Gating’ by basal ganglia depend on?

Answer 36

disinhibitory arrangement

Question 37

describe the direct pathway through basal ganglia?

Answer 37

positive feedback loop, a “GO” signal to the SMA in cortex Enhances initiation of movements by the SMA Globus pallidus neurones are spontaneously active at rest, so tonically inhibit (restrain) VL thalamus input from the cortex releases this inhibition

Question 38

describe the indirect pathway through basal ganglia?

Answer 38

Striatum inhibits GPe (globus pallidus, external) which then inhibits both GPi (GP, internal) & STN (subthalamic nuclei) Cortex excites STN; this excites Gpi; which inhibits thalamus

Question 39

action of direct pathway?

Answer 39

Direct pathway - selects specific motor actions

Question 40

action indirect pathway?

Answer 40

Indirect pathway - suppresses other/inappropriate action

Question 41

what are some disorders of the basal ganglia?

Answer 41

Parkinson’s disease

Question 42

who does parkinsons disease affect?

Answer 42

affects 1% over 60 years

Question 43

what is hypokinesia?

Answer 43

slowness, difficult to make voluntary movements, increased muscle tone (rigidity), tremors of hand and jaw.

Question 44

what is the cause of parkinsons disease?

Answer 44

degeneration of neurones in substantia nigra (SN), so loss of their dopaminergic (excitatory) inputs to the striatum

Question 45

what is the function of dopamine?

Answer 45

(normally) enhances cortical inputs through the “direct” pathway and suppress inputs through “indirect” pathway

Question 46

what results from depletion of dopamine?

Answer 46

(Parkinson’s) closes down focussed motor activities that funnel through thalamus to SMA

Question 47

what is huntingtons disease?

Answer 47

Hyperkinesia with dementia and personality disorders

Question 48

is huntingtons disease hereditary?

Answer 48

rare (5-10/100,000) progressive and fatal

Question 49

what is a characteristic symptoms of huntingtons disease?

Answer 49

Characteristic chorea – spontaneous, uncontrolled, rapid flicks and major movements with no purpose

Question 50

what is the cause of huntingtons disease?

Answer 50

Cause - profound loss of caudate, putamen and globus pallidus i.e. loss of ongoing (tonic) inhibition by basal ganglia

Question 51

how much of brain volume does the cerebellum take up?

Answer 51

only 10% of brain volume, but - 50% of total CNS neurones

Question 52

what is the involvement of cerebellum in movement?

Answer 52

‘Commanding’ a contraction is not enough - skilled movements need detailed sequence of timed contractions of varied intensity and duration

Question 53

what do lesions in cerebellum result in?

Answer 53

uncoordinated, inaccurate movements = ataxia: - e.g. fail to touch nose with eyes shut (similar to alcohol which depresses cerebellar circuits)

Question 54

what are M1 Layer 5, areas 4 & 6, somatosensory cortex all are part of?

Answer 54

HUGE cortico-ponto-cerebellar projection (connects cortex, pontine nuclei & cerebellum) - 20 mill axons (20x more than CST)

Question 55

what does cerebellum instruct?

Answer 55

cerebellum instructs direction, timing and force

Question 56

describe the motor loop through lateral cerebellum?

Answer 56

Question 57

what are Brain-machine interfaces (BMI)?

Answer 57

BMI - allow patients to voluntarily control prosthetic limbs and walk again following spinal cord injuries Sensory properties are being built into prosthetic limbs, so patients can get sensory feedback when their prosthetic limb makes contact with objects or people.

Question 58

what are brain-brain interfaces (BBI)?

Answer 58

BBI - use brain signals from one animal to teach another animal a task it has never seen.