circuits 3

Some Animals have a blank Escape Response

Rhythmic

Tritonia Escape “Reflex”

Referred to as a reflex but it’s not, it’s rhythmicity

Rhythmicity

(1) Two or more processes that interact such that each process sequentially increases and decreases, and that,

(2) as a result of this interaction, the system repeatedly returns to its starting condition.

Episodic

Short sequences

Ex. Tritonia

Continuous

Animal running or walking

Ex. Horse running

What are some other behaviors that are rhythmic?

Heart beat breathing sleeping contractions chewing panting swallowing nursing gasping

Fixed Action Pattern

A behavior that goes from start to finish when evoked

Rhythmic motor patterns underlie many fixed action patterns

Blank Generate Rhythmic Motor Output

Reflex chains which are motor nervous system contained a series of reciprocally inhibitory reflexes that had a final common pathway: the motor neuron

Sherrington

The rhythm persists after removing the sensory input!!

Graham Brown removed the Dorsal Root Ganglion and still found rhythmic outputs, which he called “narcosis rhythms.” But cat was still able to walk after signal was removed but sensory input needed to avoid obstacles in path

Two “Half-Oscillators” with Reciprocal Inhibition

Reflex Chains vs. Central Pattern Generators

Reflex chain requires sensory input

Central pattern generators does not require sensory input

How Do you Test Central Origin of the Rhythm?

Remove the sensory inputs!!!

“Deafferenting” the central nervous system (CNS)!

“Fictive” Motor Programs:

Spontaneous CPG Activity in the Absence of Any Sensory Input

Dogfish locomotion: spontaneous with rhythmic output for swimming

Mammalian locomotion: requires neuromodulators To modulate rhythmic output

How might a CPG keep a rhythm?

1. Intrinsic Membrane Properties

2. Emergent Network Properties of neurons (e.g., “Half Oscillators”) this needs two neurons with reciepient inhibition for rhythmic output

Plateau Potentials:

Generated by Certain Types of Voltage-Gated Ion Channels

2) Emergent Properties:

How neurons are coupling for rhythmic output

Can be unconnected or rhythmically connected to inhibit each other and give rhythmic output this works reliably with electrical synapses in more complex CPGs

So, what, if anything, does sensory Input do?

sensory (proprioceptive) input is not necessary for generating the rhythmic output of the nervous system, but it plays a role in shaping the output like avoiding obstacles

This can be called: “reflex modulation”

Integration of CPG with Sensory Input

Transected dogfish:

- Physically and chemically immobilized

- Tail is moved by experimenter in a rhythmic way like swimming

Increase frequency for tail movement increases the rhythm

The Nervous System has Many Distinct blank

CPGs

some CPGs can have more than one function

Often the same limbs, muscles, motor neurons, and even CPG interneurons are utilized for very different behaviors

Turtles using limbs for scratching and swimming and use the same CPGs in these limbs to do these actions they have four CPGS for each limb that change coordination with other limbs

CPGs often Show Plasticity: blank

Neuromodulation

Neuromodulators can activate, modulate, and terminate central pattern generators. Like changing speed, respiratory system with or without seratonin, the heart has its on CPG not in the brain

Why CPG Plasticity is Relevant

Research on it can help paraplegics to walk again

A CPG that Generates a 24-hour Rhythm!

~100 rhythmically active “basal retinal neurons” change their neuronal conductance over the course of ~24 hours, thereby creating a “clock” that measures time!

Neurons are coupled and fired together but what changes is the conductance