Task 1 - Voluntary Motor Control

Question 1

CNS

Answer 1

Cerebrum
Cerebellum: movement control center
Brain Stem: vital functions + relay station from cerebrum to spinal cord
Spinal cord: communication between brain & skin, joints, muscles
-> dorsal root: afferent, ventral root: efferent

Question 2

PNS

Answer 2

Somatic PNS: all spinal nerves innervating skin, joints muscles under voluntary motor control

• motor axons
• sensory axons
• ANS/Visceral PNS: neurons innervating internal organs, blood vessels, glands

Question 3

Motor System levels

Answer 3

High: association areas of neocortex & basal ganglia
-> Strategy
Middle: motor cortex & cerebellum
-> tactics
Low: brain stem & spinal cord
-> execution
all relies on sensory information except for ballistic movements

Question 4

Ballistic movements

Answer 4

Brief all-or-none high speed movements

-> don’t rely/ are not influenced by sensory feedback

Question 5

High level motor systems

Answer 5

Association areas of neocortex & basal ganglia

• > strategy: fiture out goal of movement and best strategy
• sensory info from cortex about spatial information and alternatives are filtered through basal ganglia

Question 6

Middle level momtor systems

Answer 6

Motor cortex & cerebellum

• > tactics: sequences of muscle contractions to smoothly and accurately achieve goal
• basd on memory of sensory info fom past movements
• translation of action goals into movement instructions for lower level

Question 7

Low level motor systems

Answer 7

Brain stem & spinal cord

• > Execution: activate neurons generating the goal directed movements & necessary adjustments of posture
• motor neurons + interneurons
• sensory feedback used to maintain posture, muscle lenght + tension before & after each voluntary movement

Question 8

Posterior Parietal Cortex

Answer 8

Directs behavior by providing spatial information,
Area 5: input from primary somatosesnroy cortical areas
Area 7: input from higher order visual areas
-largely connected to PFC
-> damage produces deficits in perception and memory of spatial relationships (Apraxia, Contralateral negleect)

Question 9

Apraxia

Answer 9

• loss of skilled action
• Difficulty of performing movements when asked about it out of context, can readily perform movement in natural situations
• > results from parietal cortex lesions

Question 10

Contralateral Neglect

Answer 10

inability of a person to process and perceive stimuli on the opposite side of the brain damage even though they can be subconsiously perceived

Question 11

Prefrontal Cortex

Answer 11

Makes decisions about what actions to take & their likely outcome

• > evaluation of external stimuli perceived by parietal cortex
• > Posterior parietal + PFC together encode what actions are desired and send axon to area 6

Question 12

Planning (secondary motor areas)

Answer 12

Supplementary Motor Area (SMA)
Premotor Area (PMA)
-convert info about what action is desired into how the action will be carried out
-> programming specific patterns of movment after receiving instructions from PFC,
-output to primary motor cortex
-each has own somatotopic map
-> lesions lead to apraxia

Question 13

Supplementary Motor Area (SMA)

Answer 13

• sends axons directly to innervate distal motor units
• interconnected with M1/area 4
• strong connections with PFC
• fires about a second before action

Question 14

Premotor Area (PMA)

Answer 14

Primarily connects with reticulospinal neurons innervating proximal motor neurons

Question 15

Ideomotor Apraxia

Answer 15

still have rough sense of desirec action but problems with proper execution

Question 16

Ideational Apraxia

Answer 16

Don’t know how to perform actions anymore

Question 17

Ready-set-go principle

Answer 17

Ready: depends on parietal & PFC activity
Set: depends on SMA & PMA
Go: depends on M1

Question 18

Initiation Primary Motor Cortex

Answer 18

M1

• only fires when doing, not when imagining (like secondary areas)
• precentral gyrus (motor strip)
• strongest connections with motor neurons
• input: cortical areas (6), cerebellum through thalamus
• output: to spinal cord
• rostral neurons: terminate on spinal interneurons
• caudal neurons: terminate on alpha neurons

Question 19

Hemiplegia

Answer 19

Loss of voluntary movement on contralateral side due to lesion to primary motor cortex

Question 20

Motor Action Coding

Answer 20

Cells encode force & direction of movement by population coding

• > each cell has tuning curve + activity of cell represents direction vector
• > direction of movement depends on average of direction vectors of cells: population vector
• the larger the population the finer the possible control

Question 21

Spinal Tracts

Answer 21

Corticospinal tract
Rubrospinal tract
Vestibulospinal trac
Tectospinal tract
Pontine & medullary Reticulospinal tracts

Question 22

Lateral Pathways

Answer 22

Corticospinal trct
Rubrospinal tract
-> voluntary movement of distal muscles (direct cortical control

Question 23

Ventral Pathways

Answer 23

Vestibulospinal tract
Tectospinal tract
Pontine & Medullary Reticulospinal tracts
-> control, maintenance, of posture & locomotion
-> proximal muscles (brainstem control)

Question 24

Corticospinal tract

Answer 24

-longest & largest in CNS
-direct
-2/3 originate in motor cortex (areas 4,6), 1/3 in somatosensory areas
Trajectory:
cortex -> internal capsule -> cerebral peduncle -> pons -> medulla -> forms medullary pyramid (pyramidal tract) where it decussates at junction to spinal cord -> runs down lateral column of spinal cord
-> terminates in dorsolateral region of ventral horns & intermediate grey matter
-> controlls distal muscles

Question 25

Rubrospinal Tract

Answer 25

- indirect - originates in red nucleus of midbrain - decussates in pons and joins corticospinal tract - no major role - compensates when corticospinal tract is lesioned

Question 26

Vestibulospinal tract

Answer 26

keeps head balanced and turns in response to stimuli - originate in vestibular nuclei of medulla - bilateral tract: controls neck & back muscles -> head movement - ipsilateral tract: runs down lumbar spinal cord to maintain posture (up to motor neurons of legs)

Question 27

Tectospinal tract

Answer 27

- originates in superior colliculus (input from retina) | - colliculus creates map of environment: stimulation of one point on map leads to orienting response

Question 28

Pontine & Medullary Reticulospinal tracts

Answer 28

Origin: reticular formation - pontine: enhances antigravity reflexes of spinal cord (standing posture, maintains muscle length) - medullary: frees antigravity muscles from reflex control (opposite of pontine)

Question 29

Effector

Answer 29

Part of body that can move as result of muscle contraction e.g. finger, neck,

Question 30

Alpha motor neurons

Answer 30

Innervate muscle fibers & provide physical basis for translating nerve signals into mechanical action -spinal cord -> ventral root -> muscles fibers -> ACh -> contraction

Question 31

Spinal interneurons

Answer 31

integrate sensory feedback with motor commands resulting in voluntary movement - input from descending motor fibers - output to motor neurons

Question 32

Brain Machine Interface (BMS)

Answer 32

Microelectrode implanted, spike patterns analyzed to see how they encode movement - > decoded activity used to move e.g. a cursor on a screen - > video game can be played only using neural signals from M1, bypassing usual pathway involving muscles - works with cells in M1, PMA, SMA, parietal cortex

Question 33

Amyotrophic Lateral Sclerosis (ALS)

Answer 33

Muscle weakness & atrophy - > degenration of large alpha motor neurons & neurons innervaing them - cognitive functions and intelligence unchanged - possible causes: genetic mutation affecting enzyme superoxide dismutate (normally reduced toxic superoxide radicals; Excitotoxicity: elevated levels of glutamate lead to overstimulation (cell death) - Treatment: Roluzole: blocks glutamate release, can only slow progress of disease

Question 34

Duchenne Muscular Dystrophy

Answer 34

Progressive weakness & deterioration of muscle in boys (passed on from mothers) -defective region on X chromosome encoding dystrophin contributing to cytoskeleton under muscles -> lack mRNA Treatment: gene therapy; replacing defective gene by sending virus or transplanting stem cells

Question 35

Myasthenia Gravis

Answer 35

Weakness & fatigability of voluntary muscles (typically facial expression) - severity fluctuates a lot - fatal when respiration compromised - causes: autoimmune disease: system generates antibodies against own receptors; less effective ACh release at neuromuscular junction - Treatment: drugs reinhibiting reuptake (leads to desensitization - suppression of immune system (drugs, removal of thymus gland)

Question 36

Premotor - primary motor area order

Answer 36

Info influencing movement must first be processed by association and higher order sensory cortices - > then info must be communicated to non-primary motor areas - > premotor areas coordinate output lvel of M1 & spinal cord (primary motor areas)