CPG's - Central Pattern Generator

Question 1

Advantages of invertebrate models

Answer 1

Very simple nervous systems –only a few 1000’s of neurons per ganglion

Relatively small numbers of types of neurons and only small numbers of each type involved in

“Identified neuron” concept

Possibility of in vivo/semi-intact preps where neurons can be recorded during the motor behavior while it is physically happening.

Question 2

Disadvantages of invertebrate preps

Answer 2

Experimental disadvantages

Neurons may have complex morphology -it may not be possible to record close to the postsynaptic and integrative sites.

Molecular/genetic techniques not developed for many invertebrate species (Drosophila being the big exception –but this has major disadvantages of the type above).

Biological disadvantages

Signalling systems somewhat different from vertebrates (transmitters, receptors etc).

Organization of the nervous system very different from vertebrates –generality of results?

Question 3

Advantages of vertebrate preps

Answer 3

Results of direct applicability to the human condition. Basic organisation of the nervous system shared.

Easier to exploit molecular genetic techniques and genomics (esp. true for mouse).

Better pharmacological agents available, better antibodies, cDNA probes…

Question 4

Disadvantages of vertebrate preps

Answer 4

Complexity –many neurons and many types of neurons. (Lower vertebrates such as lamprey and tadpole offer major advantage of reduced complexity)

Great redundancy –100’s to 1000’s of each type of neuron. How do you manipulate these populations?

Much harder to record in situ during behavior –how do you relate neural action to behavioral function?

The problem of anesthesia for in vivo work

Question 5

How are is motor pattern generation studied?

Answer 5

We have to be able to relate activity of neurons and circuits to behaviour, this is impossible to do without first defining the behaviour

Kinematic studies –the sequence of movements, information about efficiency and power

Getting to the neural machinery –recordings from muscles/motor nerves. Can the activation of muscles etc explain the physical movement?

Question 6

Locomotion in cat

Answer 6

PEP: posterior extreme position
AEP: anterior extreme position
Sw: Swing phase
St: Stance phase

Question 7

Explain the reflex hypothesis

Answer 7

Rhythmic movements generated through a sequence of reflexes

Question 8

Explain the central hypothesis

Answer 8

Central circuits exists which have the right connectivity and properties to generate in the absence of any sensory feedback the correct sequence of muscle contractions and movements.

Question 9

Issue with hypotheses

Answer 9

Rhythmic motor behaviours are indeed centrally generated and are controlled by circuits commonly called Central Pattern Generators

However to varying extents, movement related feedback does play a role in correct generation and coordination of behaviour. Two lines of evidence are important:

Removal of sensory feedback can alter the motor pattern,

Imposed feedback can entrain the centrally generated pattern

Question 10

Types of edge cells

Answer 10

One type has contralateral axons and is inhibitory

The other type has ipsilateral axons and is excitatory