Flashcards in CPG Deck (18)
what is CPG? Give three examples in vertebrates
Neural network that can produce a rhythmic pattern all by itself. Does not need sensory input.
why does the absence of rhythmic activity not imply the absence of a CPG?
the CPG can be turned off by other inputs
what are the four intrinsic membrane properties of CPG neurons that can lead them to oscillatory behavior?
(i) Burst firing (endogenously or via neuromodulation)
(ii) Intrinsic oscillatory behavior, which can provide important timing inputs for circuits (but it may be difficult to entrain or reset their activity). Strong, intrinsically oscillatory neurons are relatively rarely found in circuits
(iii) Bistability, where plateau potentials are triggered by a depolarizing input and terminated by a hyperpolarizing event. Bistable neurons can act as intrinsic ‘memories’ of their last synaptic input, and also can produce a discharge pattern that long outlasts their excitatory drive
(iv) Post-inhibitory rebound - Many synaptic interactions in CPG circuits are inhibitory whereby pattern-generating neurons fire on rebound from inhibition that is crucial for the timing of their firing. (v) Spike-frequency adaptation, is a decrease in the frequency of firing during a constant depolarization; (vi) Other neurons have other properties that play a role in governing how neurons in circuits will respond to a particular pattern of synaptic inputs.
what are the two factors that contribute to making CPGs rhythmic?
1. intrinsic properties of neurons that make up the network: neurons can act as core oscillator, causing the rest of the circuit to oscillate
2. properties of synapse (strength, time): synaptic interaction makes the oscillation. Typically reciprocal inhibition
describe reciprocal inhibition
two neurons that fire non-rhythmically in isolation fire in alternating bursts when they inhibit each other. part of synapse-based rhythms
describe circuitry of CPG network responsible for axial-based swimming in lamprey
Left and right compartments receive inputs from reticulospinal tract
burst generation is provided by the excitatory interneurons (EIN)
commissural INs (CINs) provide reciprocal inhibition
Each compartment has excitatory interneurons (EIN), inhibitory interneurons (IIN), commisural interneurons (CIN), and motoneurons (MN).
1. EIN on one side gets excited > excites CIN, IIN, MN
2a. CIN inhibits opposite compartment
2b. IIN inhibits EIN and MN
2c. MN fires
3. CIN is inhibited by the inhibition of EIN, so other side becomes less inhibited
check the slide for the picture
what are the two different neuronal populations cover the range of swimming in zebrafish?
High freq. range (fast, low resistance) = fight or flight response
Low freq. range (slower, high resistance) = normal locomotion
what does the frog metamorphosis process say about CPGs?
When both tail and legs are present:
5-HT and NA can synchronize/couple the tail CPG to the leg CPG. Without neuromodulation, they are doing their own thing and swimming is impaired.
In cat locomotion, ________ are active during the swing phase (feet off ground) and _______ are active during the stance phase (feet contact ground)
flexion (F) then first extension (E1), second (E2) and third extension phase (E3)
what is a piece of evidence for the existence of half-center in the spinal cord?
In spinal cats treated with L-Dopa, brief trains of stimulation of small-diameter, high-threshold cutaneous and muscle afferents (collectively known as flexor reflex afferents, or the FRA) evoked long-lasting bursts of activity in either flexor or extensor motor neurons and often resulted in short sequences of rhythmical reciprocal activity in flexor and extensor motor neurons.
This shows reciprocal inhibition between ipsi- and contralateral half-centers
check slide 29 for the picture
what is the unit burst generator hypothesis?
CPG circuits can be coupled together to produce complex motions. I.e. the circuits can burst on their own but depending on what motion you want to do, additional circuits can be recruited.
what are the two hypotheses of patterned limb movement generation?
2.unit burst generator
check slide 31 for limb generator as flexor/extensor and left/right rhythm-generating half-centers
what are the four features of locomotion?
1. Supraspinal structures are not necessary for basic motor pattern generation
2. Rhythm produced by circuits entirely in the spinal cord
3. Circuits are activated by tonic descending signals from the brain (i.e. non-oscillating input)
4. CPG networks do not require sensory inputs but are modulated by them
what molecules have been shown to generate locomotion when applied to the spinal cord?
5-HT, NMDA, DA
when the spinal cord is removed from neonatal rats (0-5 days after birth) and placed in a saline bath, it will generate coordinated bursts of activity in hindlimb motoneurons when exposed to NMDA and serotonin (5HT).
what are two types of motor system controls? (not in the lecture)
1. feedforward (CPGs, rhythm generation)
measures used to quantify and compare rhythmic motor patterns
duty cycle = burst duration/period (fraction of time active in a cycle)
phase = delay/period (provides relative timing information)
check the slides
two general mechanisms for rhythm production
1. pacemaker neurons that drive neural networks. In a pacemaker driven network, a neuron or several neurons act as a core oscillator, driving neurons that are not themselves bursting, into a rhythmic motor pattern. The pyloric rhythm of the crustacean STG and the vertebrate respiratory rhythms are pacemaker driven.
2. emergent rhythms can arise as a consequence of synaptic connections among neurons that are not themselves intrinsically rhythmic. The simplest emergent rhythm is often termed a ‘half-center oscillator’ where two neurons reciprocally inhibit each other. When isolated these neurons do not fire in bursts, but when coupled they produce alternating patterns of activity. The dynamics of alternation in half-centers requires an understanding of how each neuron makes its transitions between activated and inhibited states. These transitions can occur via a number of mechanisms. For example, if the neurons show spike-frequency adaptation, the active neuron may slow down or stop firing, thus releasing the other neuron from inhibition. Alternatively, the inhibited neuron may escape from the inhibition due to its intrinsic membrane properties, cross its spike threshold, and in turn inhibit the first neuron.