Voluntary Movements

Question 1

Describe the somatotopic organisation of M1

Answer 1

controls movement via innervation of populations of spinal motor neurons (selectively activated depending on movement)

in pre-central gyrus (Brodmann’s A4) to produce motor response

organisation not for life (altered with age/growth/learning)

Question 2

Describe the direct descending motor pathways

Answer 2

pyramidal (corticospinal) tract; no synapses between M1/motor neurons in ventral SC

regulates fast movement for precision/skill

lateral: proximal limb movement
ventral (ant.) proximal muscles (balance)

Question 3

Describe the descending motor pathways

Answer 3

extrapyramidal system projects from brainstem to SC MNs

Tectospinal (head rotation/eye movement)
Vestibulospinal (balance)
Rubrospinal (distal limb coordination)
Reticulospinal (visceral motor functions/unskilled movement)

Question 4

Describe cortical ‘upper’ motor neurons

Answer 4

project to spinal motor neurons/motor nuclei in brainstem

Phase (activity bursts initiate movement)
Tonic (steady firing rate/force when movement achieved)

Question 5

What are some differences between cortical upper vs spinal lower motor neurons?

Answer 5

Upper: active for precision movements, unlinked to contraction, firing rate inversely proportional to muscle force

Lower: active for many movements, leads to muscle contraction, firing rate directly proportional to muscle force

Question 6

Describe spike triggered averaging

Answer 6

recording action potentials from neuron and simultaneously record EMG of muscle

Question 7

Describe population coding

Answer 7

extracting reliable info from population rather than single neuron which is noisy/unprecise

could be used to control brain-machine interfaces

Question 8

Describe premotor cortices

Answer 8

Premotor areas (Brodmann’s A6)

F4/F5: PMv Ventral (lateral external trigger, direction specific)
F2: PMd
F7: PrePMd
dorsal: external trigger (non-spatial, semantic cues)

F3: SMA (internal generated/sequence specific)
F6: PreSMA

Question 9

Define affordance

Answer 9

visual properties of object regarding information provided to interact with it detected by dorsal visual system

project to ventral premotor cortex

Question 10

Describe canonical neurons

Answer 10

AIP in dorsal visual stream reciprocally connected to F5 in PMv

F5; 20% neurons respond to 3D objects (affordances)

Each tuned for specific grasp, inhibitory control via prefrontal cortex

Question 11

Describe mirror neurons

Answer 11

neurons of F5 in PMv fire

monkey see monkey do

problems could underlie Autism Spectrum Condition