PNB Lab Quiz Prep - Earthworm Action Potential

What characteristic of the axon is essential for the fast propagation of action potentials in invertebrates?

the size

What anatomic feature enables continuous recording of electrical activity in the earthworm?

electrical connections between fibers 

How is action potential elicited in the earthworm experiment recording?

electrical stimulation

The biphasic nature of the action potential recorded extracellularly is a consequence of:

the use of two extracellular electrodes spaced some distance apart to record the potential

How is the all or none phenomena demonstrated in earthworms?

each axon represents a single unit

What is absent in properly anesthetized worm?

constant moving 

During absolute refractive period, a stronger stimulus will be required to reach the threshold voltage, and thus, initiate another action potential. T or F

false

If earthworm you are using in your lab is frequently moving, what would be the best advice to proceed the experiment?

to use additional ethanol to anesthetize the worm

What recording will be used to investigate the action potential propagation of earthworms?

extracellular 

What will be needed for this lab?

needle recording electrodes

What does the black recording lead connect to?

channel 1 positive (POS)

What does the white lead connect to?

channel 1 negative (NEG) input 

What does the green lead connect to?

EARTH pin of the Bip Amp cable 

What should be grounding the pan and connecting to back of power lab?

alligator clip

What must be done to anesthetize the worm?

place in dish, fill dish with sufficient ethanol to cover worm, don’t drown the worm

How long should the worm be left in the ethanol/ringer’s solution?

until it has stopped moving (approx. 5 minutes) 

How do you test if the worm is sufficiently anesthetized?

prodding it gently with a blunt instrument

What happens if the worm reacts when touched?

leave it in the solution for a further 3-5 minutes

What will damage the nerve fibers of the worm?

stretching 

How should the worm be placed on the dissecting tray?

not twisted at all, dorsal side facing up

How does one ensure the worm is placed correctly?

dark line running along the back of the worm, should be straight

How do you keep the worm anesthetized?

apply a few drops of the ethanol/ringer’s solution along its length with the dropper 

What can a large puddle of solution result in?

can interfere with the recording

What is the head end of the worm?

end nearest the saddle (clitellum); the smooth, non-segmented band

What needs to happen when placing the three needle electrodes into the body of the worm?

stay just off the center line to avoid damage to the nerve cord 

What must the green wire pin (ground electrode) attach to?

an area after the clitellum (1 cm away)

What is the white wire pin?

negative electrode

What is the green wire pin?

the ground electrode 

Where does the white wire pin attach?

further posterior, approx. 3-4 cm away from the ground electrode

What is the black wire pin?

positive electrode

Where will the black wire pin be positioned?

further down the worm, 0.5-1 cm away from the white pin 

What is critical in terms of wires?

no touching/contact

What do the recordings demonstrate?

biphasic waveform that is a result of an action potential propagating past negative and positive electrodes (NOT action potentials)

Where is threshold voltage entered?

median giant fiber row 

How do the lateral fibers differ from the medial giant fiber in terms of threshold and conduction?

higher threshold & slower conduction

What are medial and lateral giant fibers in the earth worm?

collection of nerve cells or neurons

What is the nerve fiber made up of?

axons of neurons 

What is a nerve?

bundle of nerve fibers

What are giant fibers?

nerve cells are electrically coupled through gap junctions, each fiber behaves as if a single axon

What are intracellular recordings?

direct; records voltage potential across the membrane, accurate assessment of electrical activity 

What are extracellular recordings?

indirect; records potential changes at the membrane surface, requires electrode placement near excitable cell 

What will each giant fiber result in?

all-or-none response

What does an intitial stimulus cause?

action potential propagation down the medial giant fibers

What is a stronger stimulus?

cause recruitment of the lateral giant fibers 

What must be used for lateral giant fibers?

overlay data mode (NOT “solo”) when you are recording to ensure the signal you are seeing is real and not noise

What is absolute refractory period?

Na+ channels are inactivated, no stimulus will reopen channels

What are relative refractory periods?

some Na+ channels are still inactivated but some have reopened, strong stimulus in order to fire an action potential 

What should not be placed on the dorsal side of the worm?

pin in the middle of an earthworm

Where should metal pins be stuck?

into the blue pad

What must not be thrown away?

plastic pipette and petri dish