MOTOR SYSTEMS

Question 1

Rhythmic motor patterns are…

Answer 1

• complex
• stereotyped
• repetitive

Question 2

Describe how pendulums are an example of rhythmic behaviour.

Answer 2

• swings back and forth
• momentum and potential energy are the two processes sequentially increasing and decreasing
• starting position is hanging straight down

Question 3

What type of CPG is lobster pyloric rhythm?

Answer 3

cell-autonomous oscillator

• one cell is the endogenous cell-autonomous oscillator that is sufficient on its own to generate rhythmic activity, and drives the rhythm of the other cells in the network (“pacemaker”)
• can either couple or inhibit other cells
• each neuron has rhythmic activity
• phase of rhythms are set with respect to each other

Question 4

What are electrical connections?

Answer 4

cells coupled by gap junctions – their activity is tightly linked to each other

Question 5

What type of CPG is the leech heartbeat?

Answer 5

network of half-centre oscillators

• set of 3 half-centre oscillators connected into larger networks that burst in phases
• all cells are reciprocally inhibiting each other
• everything one away from each other is out of phase
• everything two away from each other is in phase

Question 6

Is there an organization to the circuits controlling mammalian locomotion (and other movement)?

Answer 6

yes – there is a hierarchical organization

Question 7

What is the motor cortex involved in?

Answer 7

planning, initiation, and directing voluntary movements

Question 8

What is the basal ganglia involved in?

Answer 8

initiation of movement and behaviours

Question 9

What is the cerebellum involved in?

Answer 9

coordination of movement

Question 10

What are spinal cord circuits?

Answer 10

networks of neurons that generate rhythmic activity that underlies locomotion

Question 11

What are the local circuit neurons of the spinal cord circuits?

Answer 11

CPGs for locomotion – receive proprioceptive feedback

Question 12

What are the motor neuron pools of the spinal cord circuits?

Answer 12

lower motor neurons – project to skeletal muscle

Question 13

How do flexor and extensor muscles contract during walking? What type of CPG?

Answer 13

in anti-phase (out of phase)

• not entirely conscious behaviour
• muscle movement is generated in rhythmic activity

half-centre oscillator – reciprocal inhibition between groups of neurons

Question 14

What happens to locomotion of cats with spinal cord transection (cut)?

Answer 14

they will still maintain phasic muscle contractions on a treadmill, even in absence of descending inputs from the brain

Question 15

How do pattern of horse leg movements (gait) shift?

Answer 15

shifts through discrete transitions as speed increases (walk, trot, pace, gallop)

Question 16

Where is the primary motor cortex (M1) located?

Answer 16

just posterior to premotor cortex

Question 17

What functions does dopamine from substantia nigra (SNc) and ventral tegmental area (VTA) contribute to?

Answer 17

• motivation
• reward
• reinforcement
• voluntary movement – dysfunction of dopaminergic system leads to Parkinson’s disease
• extraversion
• lactation
• sexual gratification
• sleep
• mood
• attention
• working memory
• learning

Question 18

Monkeys learn that reward starts to take on different meanings. What sort of meanings?

Answer 18

neurons begin to signal expectation for reward (not the reward itself) and the prediction, and whether the result meets the expectation

Question 19

What is Parkinson’s disease?

Answer 19

neurodegenerative movement disorder resulting from progressive loss of dopaminergic neurons (around 80%)

• affects ~1% of population over 65
• most cases late onset and sporadic (like AD), but there exists early onset cases with more genetic involvement
• most notable symptoms include bradykinesia (slowness of movement), resting tremor, rigidity, postural instability
• can also manifest in cognitive and psychiatric abnormalities

Question 20

BMI can control robotic prosthetics or patient limbs. What are the barriers to this outside the lab?

Answer 20

• portability
• length of time implant can be left

Question 21

Where is the premotor cortex located?

Answer 21

adjacent to primary motor cortex

Question 22

What are neural rhythms generated by?

Answer 22

endogenous oscillating neurons

Question 23

What are the two requirements of rhythm?

Answer 23

• two or more processes sequential increase and decrease
• system repeatedly returns to starting state

Question 24

Cell-Autonomous Oscillator – How Single Cell Generates Rhythm

Consider a cell that has…

Answer 24

• AP machinery
• low-threshold, voltage-activated, non-inactivating Ca2+ current
• Ca-activated K+ current
• leak current (non-voltage-dependent) with reversal potential more depolarized than Ca2+ activation potential

Question 25

What do cortical neurons project to and why?

Answer 25

project to spinal motor circuits to control movement

Question 26

Synapses

Answer 26

• one away from each other: out of phase
• two away from each other: in phase
• positive: sign-conserving synapse
• negative: sign-inverting synapse

Question 27

What does the basal ganglia provide input to?

Answer 27

upper motor centres

Question 28

Describe basal ganglia circuits.

Answer 28

circuits (connections between each neuron and role each neuron plays) are very well-defined

Question 29

What are the two parts of the striatum?

Answer 29

• caudate
• putamen

Question 30

Dopamine has different effects on neurons depending on receptors present.

Answer 30

-

Question 31

In monkeys trained to perform a task in response to a cue, when do primary motor cortex neurons fire? When do premotor cortex neurons fire?

Answer 31

• neurons in primary motor cortex fire during the task
• some neurons in premotor cortex fire at appearance of the cue (signals intention)

Question 32

What is the Theory of Mind?

Answer 32

idea that an individual is aware that someone else is aware of things

Question 33

What is cerebellar gait?

Answer 33

unsteady and halting

Question 34

What is halorhodopsin?

Answer 34

light-activated inhibitory chloride channel

Question 35

What is channelrhodopsin (ChR2)?

Answer 35

excitatory light-gated cation channel

Question 36

What do motor commands also required?

Answer 36

proprioception, vestibular info, etc.

Question 37

What are some major technical hurdles that would need to be overcome before optogenetic stimulation becomes a viable clinical treatment for PD or other neurological diseases?

Answer 37

• how to introduce ChR2 – viral vectors haven’t been proven in the clinic
• Thy1 expression in the paper was from a transgenic mouse line – not clear how
  to integrate that onto viral vector
• how to introduce fibers
• not clear that M1 finding from rodents will translate to humans
• unintended off-target effects of optically stimulating M1 (or other cells)

Question 38

As you test the BMI you attempt to train the monkey in two tasks: using the robotic arm to bring food to the monkey’s mouth; and using it to make a “peace” sign with its fingers. Despite the fact that both actions involve similar complexity of movement, the first action (feeding) works much better. Provide two potential explanations for this observation that are logical and based on information outlined in class.

Answer 38

• monkey has specific localized circuits to execute normal ethological functions like bringing food to the mouth
• reward of bringing food to the mouth reinforces this action