Thus a record of the stimulating event and the time when the Action Potential appears (latency) can be measured.
It is possible to "trigger" the computer, to begin to collect data (to sweep), at the same time as the stimulus is applied. The trigger allows you to capture the time period immediately after an event. A useful feature of PowerLab is that the operator can initiate a sweep of the screen (i.e. Time and sensitivity can be adjusted on each channel. Time will be recorded on the X axis and voltage on the Y. Powerlab will act as a digital 2-channel oscilloscope. You will not only visualize the action potential but also determine the speed at which the action potential travels along a nerve in each of these organisms. In the Earthworm, you will be recording from giant axons. In today's laboratory you will be using extracellular recording: In the frog and human you will be recording from a nerve, which is a bundle of neurons each with its own threshold, rather than from a single neuron. This method has the distinct advantage that it can be used to record the passage of an action potential (as in a muscle) from the surface of the body and is also used to record action potentials from whole nerves (in contrast to having to puncture individual neurons). This method does not measure ion flow but the net difference in potential as the action potential passes first one electrode and then the other electrode. A change in potential between the two electrodes is measured and recorded as a biphasic AP as the action potential passes along the neuron. Extracellular Recording: A pair of electrodes is placed on the outside of the neuron. This technique is performed on large, isolated neurons.Ģ. A change in potential difference between the electrodes is recorded as the ions move into and out of the cell.
Intracellular Recording: Two electrodes are placed on either side of the membrane of the neuron, one inside the cell and one outside. Changes in electrical potential can be experimentally detected as the action potential passes along the axon of the neuron.Ĭhanges in electrical potential of the axon can be detected and displayed on a recording device in the laboratory by one of two basic methods:ġ. The change in distribution of ions leads to a change in electrical charge (potential) across the membrane. This change in permeability results in a change in distribution of ions across the membrane. The action potential is caused by a change in the neuron membrane permeability. Neurons have the property of being able to generate action potentials.
An action potential may be transmitted to a muscle cell, causing muscle contraction. An Action potential may originate in the brain and result in a deliberate movement or they may be involved in a reflex arc that is independent of the brain. The axon is the part of the neuron that conducts impulses the axon is usually a long outgrowth, or process, that carries impulses away from the cell body of a neuron toward target cells.Ī nerve impulse, also called an action potential, is the signal that is transmitted along an axon that enables nerve cells to communicate and to activate many different systems in an organism. To measure the conduction velocity of the human sciatic nerve through external recording electrodes (extracellular recording).Ĭonduction Velocity in Nerves: BackgroundĪ neuron is a cell that is specialized for the transmission of nervous impulses.To measure the threshold and conduction velocity of an earthworm giant axon through external recording electrodes.To measure the threshold, conduction velocity, and refractory period of the sciatic nerve of a frog nerve by stimulating the nerve and measuring the response through external recording electrodes (extracellular recording).To measure conduction velocity in a human reflex arc, using the Achilles tendon as the initiator of a reflex and contraction of the gastrocnemius muscle as the response (extracellular recording).5 Conduction Threshold and Velocity in Earthworm Nerves.4 Conduction Velocity in a Frog Sciatic Nerve.3 Conduction Velocity in a Human Reflex Arc.2 Conduction Velocity in Nerves: Background.
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