Midterm 2: Motor Systems

Question 1

What can neural rhythms be generated by?

Answer 1

endogenous oscillating neurons

Question 2

What are the 2 requirements of rhythm?

Answer 2

• two or more processes sequentially increase and decrease
• as a result, system repeatedly returns to starting state

Question 3

What is a central pattern generator (CPG)?

Answer 3

neural network with rhythmic activity in absence of any outside input

Question 4

What are the two types of CPGs?

Answer 4

• cell-autonomous CPG
• synaptic networks

Question 5

How do cell-autonomous CPGs work?

Answer 5

spike-bursting – rhythm generated by single cell, then propagate to other neurons

Question 6

How do synaptic network CPGs work?

Answer 6

bursts produced through interactions of multiple connected neurons (synaptic properties)

Question 7

Lobster Pyloric Rhythm

Answer 7

-

Question 8

What are electrical connections between cells?

Answer 8

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

Question 9

How does a single cell generate a rhythm?

Answer 9

1. cell starts out hyperpolarized
2. leak currents cause depolarization
3. membrane potential crosses Ca2+ activation potential, Ca2+ rushes into cell
4. membrane potential crosses AP threshold and APs fire
5. Ca-activated K+ current hyperpolarizes cell

Question 10

What is a half-centre oscillator?

Answer 10

simplest network oscillator (CPG) where reciprocal inhibitory connections create rhythm

Question 11

Describe how reciprocal inhibitory connections create rhythm in half-centre oscillators.

Answer 11

firing of neuron A inhibits neuron B, but allows B to slowly escape inhibition

• when A is depolarized, it releases inhibitory transmitters GABA that inhibits B (hyperpolarizes B)
• B has internal hyperpolarizing-induced current that allows it to depolarize once it becomes hyperpolarized
• when B starts depolarizing, it releases GABA that inhibits A

(and vice versa)

Question 12

How is the leech heartbeat network organized?

Answer 12

set of three half-centre oscillators connected to form a larger network that bursts in phases

Question 13

What does the motor cortex control?

Answer 13

planning, initiation, and directing voluntary movements

Question 14

What does the basal ganglia control?

Answer 14

initiation of movement and behaviours

Question 15

What does the cerebellum control?

Answer 15

coordination of movement

Question 16

What are spinal cord circuits?

Answer 16

networks of neurons that generate rhythmic activity that underlies locomotion

Question 17

What are local circuit neurons (of the spinal cord circuit)?

Answer 17

CPGs for locomotion – receive proprioceptive feedback

Question 18

What are motor neuron pools (of the spinal cord circuit)?

Answer 18

lower motor neurons – project to skeletal muscle

Question 19

What is the model for reciprocal inhibition of flexor and extensor muscles?

Answer 19

reciprocal inhibition occurring at two levels:
- motor neurons reciprocally inhibit each other
- motor neurons reciprocally activate extensor muscles, but the same module will inhibit flexor muscles – keeps extensor and flexor muscles out of phase

Question 20

What controls movement?

Answer 20

cortical neurons project to spinal motor circuits to control movement

Question 21

How are motor neurons mapped in the primary motor cortex?

Answer 21

M1 was once thought to have a somatotopic organization similar to S1 – stimulation of different areas of M1 revealed similar map existed

BUT newer evidence suggests a coarser somatotopic organization of M1 – there are regions of M1 that encodes different areas of the body, but mapping position within those areas is not as precise as S1

Question 22

What is the problem with studying M1 compared to S1?

Answer 22

studying sensory cortex: can record from neurons and apply which stimulus you want, and ask how the activity of the neuron reflects the stimulus

studying motor cortex: there is no stimulus that are you are trying to correlate with – trying to correlate with behaviour or motor activity (contraction of muscles)

Question 23

Where does basal ganglia provide input to?

Answer 23

to upper motor centres

Question 24

Describe basal ganglia circuits.

Answer 24

very well-defined – connections between each neuron and role each neuron plays is well-defined

Question 25

What is the caudate?

Answer 25

part of striatum

Question 26

What is the putamen?

Answer 26

part of striatum

Question 27

Dopamine from substantia nigra and ventral tegmental area contributes to what functions?

Answer 27

• motivation
• reward
• reinforcement
• voluntary movement
• extraversion
• lactation
• sexual gratification
• sleep
• mood
• attention
• working memory
• learning

Question 28

What does dysfunction of dopaminergic system lead to?

Answer 28

Parkinson’s disease

Question 29

What is ArchT?

Answer 29

optogenetic channel expressed in dopaminergic neurons of SNc that inhibits neurons – therefore turning on the laser results in inhibition

Question 30

Are most cases of Parkinson’s disease early or late onset?

Answer 30

most cases late onset and sporadic (like AD), but there exists early onset cases with more genetic involvement

Question 31

What is Parkinson’s disease?

Answer 31

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

Question 32

What are the most notable symptoms of Parkinson’s?

Answer 32

• bradykinesia (slowness of movement)
• resting tremor
• rigidity
• postural instability

can also manifest in cognitive and psychiatric abnormalities

Question 33

What are 𝛼-Synuclein mutations?

Answer 33

• enriched at presynaptic terminals
• mutations associated with PD increase aggregation
• Lewy body protein aggregates (intracellular, found throughout the brain) include 𝛼-Synuclein as major component

Question 34

What are the pathogenic effects of 𝛼-Synuclein?

Answer 34

effects of 𝛼-Synuclein are unclear and likely complex