MOTOR SYSTEMS Flashcards
Rhythmic motor patterns are…
- complex
- stereotyped
- repetitive
Describe how pendulums are an example of rhythmic behaviour.
- swings back and forth
- momentum and potential energy are the two processes sequentially increasing and decreasing
- starting position is hanging straight down
What type of CPG is lobster pyloric rhythm?
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
What are electrical connections?
cells coupled by gap junctions – their activity is tightly linked to each other
What type of CPG is the leech heartbeat?
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
Is there an organization to the circuits controlling mammalian locomotion (and other movement)?
yes – there is a hierarchical organization
What is the motor cortex involved in?
planning, initiation, and directing voluntary movements
What is the basal ganglia involved in?
initiation of movement and behaviours
What is the cerebellum involved in?
coordination of movement
What are spinal cord circuits?
networks of neurons that generate rhythmic activity that underlies locomotion
What are the local circuit neurons of the spinal cord circuits?
CPGs for locomotion – receive proprioceptive feedback
What are the motor neuron pools of the spinal cord circuits?
lower motor neurons – project to skeletal muscle
How do flexor and extensor muscles contract during walking? What type of CPG?
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
What happens to locomotion of cats with spinal cord transection (cut)?
they will still maintain phasic muscle contractions on a treadmill, even in absence of descending inputs from the brain
How do pattern of horse leg movements (gait) shift?
shifts through discrete transitions as speed increases (walk, trot, pace, gallop)
Where is the primary motor cortex (M1) located?
just posterior to premotor cortex
What functions does dopamine from substantia nigra (SNc) and ventral tegmental area (VTA) contribute to?
- motivation
- reward
- reinforcement
- voluntary movement – dysfunction of dopaminergic system leads to Parkinson’s disease
- extraversion
- lactation
- sexual gratification
- sleep
- mood
- attention
- working memory
- learning
Monkeys learn that reward starts to take on different meanings. What sort of meanings?
neurons begin to signal expectation for reward (not the reward itself) and the prediction, and whether the result meets the expectation
What is Parkinson’s disease?
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
BMI can control robotic prosthetics or patient limbs. What are the barriers to this outside the lab?
- portability
- length of time implant can be left
Where is the premotor cortex located?
adjacent to primary motor cortex
What are neural rhythms generated by?
endogenous oscillating neurons
What are the two requirements of rhythm?
- two or more processes sequential increase and decrease
- system repeatedly returns to starting state
Cell-Autonomous Oscillator – How Single Cell Generates Rhythm
Consider a cell that has…
- 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
What do cortical neurons project to and why?
project to spinal motor circuits to control movement
Synapses
- one away from each other: out of phase
- two away from each other: in phase
- positive: sign-conserving synapse
- negative: sign-inverting synapse
What does the basal ganglia provide input to?
upper motor centres
Describe basal ganglia circuits.
circuits (connections between each neuron and role each neuron plays) are very well-defined
What are the two parts of the striatum?
- caudate
- putamen
Dopamine has different effects on neurons depending on receptors present.
-
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?
- neurons in primary motor cortex fire during the task
- some neurons in premotor cortex fire at appearance of the cue (signals intention)
What is the Theory of Mind?
idea that an individual is aware that someone else is aware of things
What is cerebellar gait?
unsteady and halting
What is halorhodopsin?
light-activated inhibitory chloride channel
What is channelrhodopsin (ChR2)?
excitatory light-gated cation channel
What do motor commands also required?
proprioception, vestibular info, etc.
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?
- 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)
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.
- 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
