Lab 4:Neurophysiology

Nervous System Organization

Earthworm

Structure of a Typical Neuron

Membrane Potential

Intracellular-70 to -60 mV

Extracellular

Nerve Impulse: Action Potential

Action Potential Propagation

Precautions

• Careful with equipment• Anesthetize the worm (change to 3 minutes)• Ground the worm (to minimize cutaneous

voltage conduction)• Use aluminum foil under apparatus• Use Loggerpro for data collection

Experimental DesignRoom Temperature• Voltage threshold: What voltage is needed to stimulate action

potential? Time between rising edge of stimulus pulse and first electrical event in the worm.

• Saturation: determine voltage that results in no further increase in activity.

• Pulse Duration: what occurs when duration is extended (0.25 sec)?• Stimulus Polarity: place anode closer to recording electrode. What

happens?• Symmetry of axons: switch anode/cathode and move amplifier.

Observe and record results.• Conduction velocity = distance/time (meters/second) (2 amplifiers)

Experimental Design

Effect of cooling • Cool the worm (in the apparatus) in

refrigerator for 10 minutes• Measure conduction velocity • Determine voltage threshold

Earthworm Chamber Set Up

Lab

Open “Earthworm AP” in LoggerPro

Sensor Confirmation Table will OpenSelect Connect Twice

Computer Screen After Stimulator Reading