Midterm 2: Motor Systems Flashcards
What can neural rhythms be generated by?
endogenous oscillating neurons
What are the 2 requirements of rhythm?
- two or more processes sequentially increase and decrease
- as a result, system repeatedly returns to starting state
What is a central pattern generator (CPG)?
neural network with rhythmic activity in absence of any outside input
What are the two types of CPGs?
- cell-autonomous CPG
- synaptic networks
How do cell-autonomous CPGs work?
spike-bursting – rhythm generated by single cell, then propagate to other neurons
How do synaptic network CPGs work?
bursts produced through interactions of multiple connected neurons (synaptic properties)
Lobster Pyloric Rhythm
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What are electrical connections between cells?
cells coupled by gap junctions – their activity is tightly linked to each other
How does a single cell generate a rhythm?
- cell starts out hyperpolarized
- leak currents cause depolarization
- membrane potential crosses Ca2+ activation potential, Ca2+ rushes into cell
- membrane potential crosses AP threshold and APs fire
- Ca-activated K+ current hyperpolarizes cell
What is a half-centre oscillator?
simplest network oscillator (CPG) where reciprocal inhibitory connections create rhythm
Describe how reciprocal inhibitory connections create rhythm in half-centre oscillators.
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)
How is the leech heartbeat network organized?
set of three half-centre oscillators connected to form a larger network that bursts in phases
What does the motor cortex control?
planning, initiation, and directing voluntary movements
What does the basal ganglia control?
initiation of movement and behaviours
What does the cerebellum control?
coordination of movement
What are spinal cord circuits?
networks of neurons that generate rhythmic activity that underlies locomotion
What are local circuit neurons (of the spinal cord circuit)?
CPGs for locomotion – receive proprioceptive feedback
What are motor neuron pools (of the spinal cord circuit)?
lower motor neurons – project to skeletal muscle
What is the model for reciprocal inhibition of flexor and extensor muscles?
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
What controls movement?
cortical neurons project to spinal motor circuits to control movement
How are motor neurons mapped in the primary motor cortex?
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
What is the problem with studying M1 compared to S1?
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)
Where does basal ganglia provide input to?
to upper motor centres
Describe basal ganglia circuits.
very well-defined – connections between each neuron and role each neuron plays is well-defined
