Lecture 17; Respiratory Rhythm Generation Flashcards
What is rhythm?
Co-ordinated activity
Give an example of processes in the body that are rhythmic?
- Breathing
- Walking
- Heart beating
How is walking rhythmic?
Neuronal activity in the spinal cord is the source of rhythm. Switches between left/right, off/on to generate movement
Simple circuit
What does activation of the respiratory muscles require?
(Baseline) - Rhythm generator (Firing, deactivation, firing etc (in,out,in,out)
(Modulation) - Patterns of firing (fast,slow…)
(Feedback) - Neuronal inputs to alter activity
What can alter respiration?
Feedback can alter at all various levels i.e rhythm generation etc
Conscious control of respiration i.e anticipation
Noxious stimuli alters rhythm i.e sneezing
All these are included in the circuitry that alters burst activity (this is the respiratory network)
What are the two groups of respiratory cells in the medulla?
preBOTC
RTN/pFRG
Describe the respiratory network;
Rhythm generation
Burst pattern formation
Motor neurons
Co-ordinated activity in respiratory muscles
With afferent chemo and mechanoreceptor feedback mechanisms to the burst pattern formation level
What did in vivo studies initially reveal?
Rhythm derived from diffuse network
Also;
Combination of neurons firing to create two distinct events to generate breathing
What sort of activity was found at the phrenic nerve?
Augmented activity.
i. e Neuron outputs integrated to increase potential then rapid decline
i. e activity of lots of different nuclie neurons together to generate inhalation exhalation
How many respiratory nuclie contribute to rhythm generation?
Lots of nuclie, but integration is key to form a respiratory network
- Can destroy the nuclie and the output becomes altered (i.e waveform) but the rhythm is the same / in sync with respiration
- All fire at specific frequencies, differing firing patterns, but same rhythm
(but if main centre is lost everything is shut off)
What does the three preparations of phrenic nerve show you?
Three distinct wave forms;
- Augmented (intact prep)
- Constant (Medullary prep)
- Decreasing (PreBOTC preparation)
What is the point of the three preparations?
To demonstrate that all brain regions work together to determine the output and removing them changes this
What are the hypothesis’ of pacemaker generation for respiration?
Pacemaker Hypothesis
Network Hypothesis
Hybrid Networks
What is the pacemaker model?
Pacemaker cells with inputs altering outputs
What is the hybrid model?
Pacemaker cells wont work without Network input
What is the role of synaptic inhibition in the network model?
Critical for oscillation: responsible for phase transition
What is the role of synaptic inhibition in the hybrid model?
Contributes to phase transition and but not essential for rhythm generation
What is the role of intrinsic membrane properties in the network model?
Contribute to bursting behavior of neurons but not essential for rhythm generation
What is the role of intrinsic membrane properties in the hybrid model?
Convey voltage-dependent oscillatory properties to pacemaker neurons and these are the source of the rhythm
Are networks needed for exhalation?
No they are not needed for passive exhalation only forced
What is the browns centre hypothesis?
Initiating stimulus
Reciprocal inhibition (prevents both halves from being coactive)
Terminating signal
What is a crucial component of both the network and hybrid models?
Both systems must be able to switch off inhalation or exhalation
note; In the hybrid model inhibitory neurons only needed to switch between exh. and insp. i.e running
Describe the firing of the pacemaker cells in the pacemaker hypothesis and the hybrid hypothesis;
In regards to insp. and exp. cell groups
Pace hyp: Continuous firing from pacemaker cells
Hybrid; Continuous firing from all inputs feeding back
What exists between exp. and insp. cell groups?
Greater activity wins (reciprocal inhibition)
