Lab Manual
Contents
Lab Manual¶
Today, you will primarily be recording activity of Motor Neurons in N1 of the abdominal ganglia of the crayfish.
These motor neurons control movement of the swimmeretts. Movement in each direction is controlled by independent branches (anterior and posterior) of N1.
Centrally, a relatively simple central pattern generator (CPG) circuit orchestrates coordinated motor output within and between segments.
Experiment 1. CPG¶
First, suction a nerve loop.
Then cut the nerves and suction onto the cut tip (at the end of the nerve root still attached to the ganglia).
Any differences? What do you think the differences are due to (what is different between these two configurations)?
If time, suction bilateral pair or intersegmental pair.
Experiment 2. disynaptic stimulation¶
“As an optional exercise, in addition to observing spontaneous activity, we can electrically stimulate motoneurons to increase their firing. In each ganglion, the motoneurons receive synaptic inputs from interneurons, many of which run the length of the nerve cord and excite groups of motoneurons in each segment. We can drive some of these interneurons by stimulating the anterior end of the cord. This will evoke firing in the postsynaptic motoneurons whose axons we monitor in the roots.
To interpret what we see at the recording electrode, it is necessary to understand that there are several types of pathways between the stimulating and recording points. The second root, for example, carries sensory axons that enter the ganglion and continue directly up the nerve cord toward the brain. Electrical stimulation of a connective creates antidromic (“backwards travelling”) action potentials in these “straight-through” axons. The antidromic action potentials appear at the recording electrode with very little “jitter,” since there are no intervening synapses. The electrical stimulus also excites interneurons that synapse (directly or through one or more intervening neurons) on motoneurons and excite action potentials. Because of the intervening synapse(s), the action potentials in postsynaptic units have a variable delay, and may drop out completely at high rates of stimulation. Both “straight-through” and postsynaptic units are seen in the accompanying illustration.” From Smith course
Copy data to your Google Drive for analysis¶
Use the Neural-Circuits notebook to analyse your data and answer the questions in the Responses notebook.
Figures from Mulloney and Smarandache-Wellmann 2012.