Motor systems

Question 1

What is the Moravec’s paradox ?

Answer 1

“Moravec’s paradox is the discovery by artificial
intelligence and robotics researchers that, contrary to
traditional assumptions, high-level reasoning requires very
little computation, but low-level sensorimotor skills require
enormous computational resources.” (Wikipedia)

1997 Deep Blue versus Garri Kasparow (AI beat chess master)

Question 2

what is electromygraphy?

Answer 2

measurement of muscle activity, measuring action potentials (by electrodes), that lower motoneurons elicit on musclefibers

Question 3

how are upper and lower motor neurons connected and what is that good for?

Answer 3

upper motor neuron origins in neocotex, travels down spinal cord and there synapses with lower motor neuron, which then innervates the muscle.
in case of danger, rapid reflexive movement is possible without loop over neocortex but initiated in the spinal cord

Question 4

what s a motor unit?

Answer 4

every muscle fiber is innervated by only one alpha motor neuron, but one motor neuron innervates several muscle fibers.
all muscle fibers innervated by the same motor neuron, including this motor neuron, is a motor unit.
the higher the degree of divergence (many fibers activated by 1 neuron), the lesser the fine control

neurotransmitter: ACTH

Question 5

how does the patellar reflex work?

Answer 5

muscle spindle below the patellar is stretched, sensory signal goes to dorsal spinal cord, synapses with a motor neuron in the ventral spinal cord (without interneuron). this motorneuron innervates the quadriceps femoris muscle and elicits the reflex.

Question 6

cats with disconnected spinal apparatus from cortex and subcortex.
were they still able to move and if so, how?

Answer 6

stretch reflexes remained intact, and could even alternate between hind limbs and thus create walking like movements.
neurons in spinal cord could produce entire movement sequence without feedback
these neurons are called central pattern generators
- lower level mechanism
- most likely to trigger movement patterns essential for survival

Prashanti: entire sequence of actions can be completed without any descending commands or external feedback signals

Question 7

contralaterality.
where do efferent nerve fibers on the way from cerebral cortex through the spinal cord (cortico spinal tract) change sides?

Answer 7

80 % of CST cross at the medullary pyramid (junction of medulla oblongata and spinal cord, and also the reason why it’s called pyramidal tracts)

Question 8

what are population vectors in M1?

Answer 8

neurons in M1 involved in coding for direction are not precisely tuned for one single direction, but also fire for similar directions (the less similar the direction is to their prefered direction, the lesser they fire , approximately like a gaussian tuning curve).
movement in a certain direction is then coded by a firing pattern of several neurons with different firing rates. they all together contribute to the population vector, the contribution of each neuron depends on its firing rate.
(thus direction movement can be much finer adjusted than if each direction would be coded by one single neuron)
georgopolus: single cell recordings of rhesus monkeys
population vector = excellent predictor of movement direction (when there is a delay between initiation and actual movement)
(but: card 9)

Question 9

M1: direction or muscle coding?

Answer 9

32% of neurons in M1 predominately code for muscles , 50 % for direction
(comparison of neuronal activity for movements in the same direction, but with different hand position/ different muscles. if coded for direction all movements show similar activation, if coded for muscles both movements would have to correspond with different neurons.)

Question 10

does input to pyramidal tracts / efferences only stem from M1?

Answer 10

noo.
M1 only codes for simple aspects of movement like direction.
PMA / SMA (movement sequences)
and the more complicated it gets, the more other regions are involved..
S1 (somatosensory feedback),
posterior parietal cortex (sensory motor integration)
area 8
PFC

Question 11

what is open loop control in movement?

Answer 11

ballistic movement without sensory feedback (fixed trajectory), no adjustments

• patient with sensory neuropathy can draw figures in the dark - no visual feedback either : sequence of events can be generated in an open loop
• eye movements (saccades are preplanned)

Question 12

independence of realization in movement schema

Answer 12

hand writing signature can be identified when written with different hands, mouth etc (multiple realizers) apparently existence of pattern generators for sequences

pattern generators are evidence for a hierarchical control of movement

Question 13

how can the somatotopic organization in M1 be mapped non invasively?

Answer 13

transcranial magnetic stimulation

-maps not as well defined as in sensory cortices

Question 14

what is hemiplagia?

Answer 14

loss of voluntary movements on body side contralateral to lesion in M1

Question 15

which is right?

a) most afferent fibers to the basal ganglia terminate in the striatum (caudate and putamen), output from basal ganglia originates in globus pallidus, pars reticularis of substantia nigra
b) most afferent fibers to the basal ganglia terminate in globus pallidus, pars reticularis of substantia nigra, output from basal ganglia originates in the striatum (caudate and putamen)

Answer 15

a

Question 16

describe the direct and indirect pathway ini the substantia nigra..
(maybe rather relevant for neuroanatomy and physiology)

Answer 16

The direct pathway involves fast, direct, inhibitory connections from the striatum to the GPi and SNr. The indirect pathway takes a slower, roundabout route to the GPi and SNr. Striatal axons inhibit the external segment of the globus pallidus (GPe), which in turn inhibits the subthalamic nucleus and GPi. The output from the basal ganglia via the GPi and SNr is also inhibitory
(copy paste from gazzaniga p.375)

Question 17

describe the degrees of freedom problem

Answer 17

veeery large number (they say infinite) of possible motor solutions for a task, due to different possible combinations of angles of the joints and their trajectories
but, likely physical and cognitive constraints
and most probably some generalized motor programs which can simplify computation

Question 18

what is sensory motor transformation?

Answer 18

integration of sensory information and information regarding the position of the receptors in space.
(you only know where exactly in space the object on your retina is, when you know your head and eye position as well)

Question 19

where is voluntary movement of the eyes generated?

Answer 19

in frontal eye field, guided mostly by external senses rather than proprioceptive info

Question 20

role of PFC and premotor regions?

Answer 20

PFC: planning, action control, action selection, goal maintenance
PMR: preparing actions

dorsolateral PFC: most probably involved in freely chosen movements, intention

Question 21

again, what was going on in the Libet experiment?

Answer 21

EEG from M1 und SMA.
subjects pressed a key whenever they wanted,
reported at which time they were aware of wanting to move.
‘readiness potential’ observed 350 ms before report of intention and 550 my before actual response

discussion of free will

later experiment included the choice which hand participants used for their response, observation of lateralized readiness potential showed that awareness of intention is related rather to specific movement than generalized intention

Question 22

what Prashanti says about Penfields somatotopy..

Answer 22

Disproportional
representation of body
parts in the brain.
 Proximity matters.
 Loops between sensory
and motor areas.

Question 23

what about extrapyramidal tracts?

Answer 23

wikipedia: Extrapyramidal tracts are chiefly found in the reticular formation of the pons and medulla, and target lower motor neurons in the spinal cord that are involved in reflexes, locomotion, complex movements, and postural control

Prashanti: Extrapyramidial tracts are responsible for indirect control of spinal cord activity