Neural Circuits (CPG, Respiration, Sleep) Flashcards
central pattern generators
neuronal circuits that when activated can produce rhythmic motor patterns such as walking, breathing, flying, and swimming in the absence of sensory or descending inputs that carry specific timing information
why are motor circuits easy to study and measure?
motor behaviours are easy to define and measure unlike cognitive
invertebrate examples for CPG models
lecture 11 first page
lobster/crab - stomach chewing crayfish - escape clione - swimming tritonia - escape (bend + jump) leech - muscle activation locust - complex, flight/kick
advantage of invertebrate models of CPG
disadvantages
simple NS (few Ns and small no.types), can record during motor behaviour
may be complex with electrical signals in places where might not see, may not be possible to record close to postsynaptic and integrative sites, techniques not developed for many species, signalling differs for vertebrates so generalisation issue
advantages of vertebrate models of CPG
disadvantages
applicable to humans, use molecular genetic techniques, better Abs and pharmacological agents
complexity (tadpole/lamprey better), great redundancy (lots each type), harder to record in situ, anaesthesia in vivo changes activity
vertebrates examples for CPG model
cats - locomotion, plot limb movement
lamprey - swim, primitive NS
tadpoles - swim, simple in early development
rat/mice - use gene knockouts
how to study motor pattern generation
1) define behaviour - measure
2) neural machinery - record muscles/nerves
see if movement related to neural activity
Leech swimming motor pattern
waves of bending and how fast travel along length
measure tension and nerve recordings
left segments activity before right so head to tail bending (delay)
Cat locomotion (phases)
swing phase - from PEP to AEP (posterior extreme position to anterior)
stance phase - foot on ground so hip move and other foot move
measure angles and see change in neural activity
Humans walk/run
record angles and activation of muscle groups
Reflex Hypothesis
rhythmic movements generated through sequence of reflexes (dependent on feedback)
Central Hypothesis
central circuits generate without sensory feedback so reflexes not important
which hypothesis is correct? (reflex or central)
removing all sensory feedback shows all rhythmic motor behaviour like laughing is controlled by central networks -> CPGs
but movement feedback coordinates behaviour because removing sensory feedback alters motor pattern (but is still generated) so it entrains motor pattern that is centrally generates
e.g. human disease w/o feedback means can still walk but differs
Lamprey (categories, entrain, CC)
swim, wiggle spinal cord left right (oscillations in membrane potential match motor nerve recordings)
categories of neurones - 2 motor, CC interneurones, edge cells, dorsal cells, giant interneurones, lateral interneurones, excitatory interneurones
imposing slower movement slows CPG because stretch receptors in spinal cord
killing opposite side of spinal cord disturbs rhythm of other side - CC role
modern view on CPGs (conclusion)
central circuit has everything for motor activity
turned on/off by higher command centres (decision)
coordinate sensory input (if in at wrong time)
stretch receptors in muscles fine tune and entrain patterns
Xenopus embryo (tadpole) (HRP, classes, origins of drive)
lower vertebrate model of swimming used HRP (horse radish peroxidase) to see if it would cross the spinal cord from one side to other categorise types of neurones (lecture 12 first page)
2 classes of C motor neurones - d descending interneurone and c commissural interneurones on opposite sides of spinal cord and form neural circuit for swimming
reciprocal inhibitory interneurones - commissural with crossed axon, important in circuit because glycinergic inhibition (it uses glycine NT) will change speed of swimming/block
immunocytochemistry to identify neurones
stain with glycine Ab so show neurones that use glycine as NT
criteria to determine if neurone contributes to CPG
lecture 12 bottom first page and top second page
is it active during motor behaviour? (some copy rhythm not generate) - necessary but not sufficient
is it used to reset rhythm? - sufficient but not necessary
if inactivate/destroy/block activity does the generation stop?
need to demonstrate all 3
tonic and phasic
slow and fast
V2a in Zebrafish
excitatory interneurones, removing cells affects ability to produce swimming and NMDA which usually excites neurones and swimming has a weaker effect
activation of these cells sufficient for swimming (blue light experiment - have light sensitive ion channels
the wiring diagram
lecture 12 page 3
post-inhibitory rebound
inject -ve current so hyperpolarises, then fires AP when recovers (rebound) so circuit carries on
pacemaker neurones in Clione
carry on generating rhythm without input (endogenously)
carries on if drag cell out ganglion so endogenous pacemaker
mid-cycle inhibition
between APs
lamprey spinal neurones pacemaker properties
some cells still oscilate w/o AP (NMDA and TTX to stop AP)
injecting current changes speed/freq of oscillations
computational and mathematical models of neural circuits
uses?
want simple model to understand complex
combine models of body and movement to neurones
understand roles of cells and components
make predictions on function
extract general principles of circuit behaviour
breathing disorders
Joubert syndrome (rapid breath) Rett syndrome (difficult while awake) Ondine's curse (while asleep) Sleep apnoea (obstructive) Sudden Infant Death Syndrome (don't know cause)
phases of respiratory pattern
inspiratory (phrenic nerve innervates diaphragm)
expiratory (post-inspiratory)
then active expiration (induced by exercise, cough, sneeze, force air out)
The pre-Bötzinger complex (preBötC)
a central pattern generator in brain stem in medulla oblongata that is important for the generation of respiratory rhythm
with long columns of cells going from cVRG (caudal ventral respiratory group) to rVRG (rostral)
and a few nuclei in pons
NTS
sensory control of breathing
damage to medulla
severely compromise breathing
experiment in rodent neonates showing breathing CPG
record from nerves equivalent to phrenic, shows rhythmic bursts of respiration
without pons the brainstem can generate rhythm but speeds a bit
