Action Potential Practical Flashcards
What are the 2 types of electrical recording?
- Transcellular recording
- Extracellular recording
How does transcellular recording work? What does it measure?
- The potential difference across a membrane may be recorded by inserting one electrode into a cell and placing the other on the surface of the cell or in the extracellular fluid.
- It measues the electrical activity of a single cell.
How does extracellular recording work? What does it measure?
- Electrical activity can be recorded by placing two electrodes on the surface of a nerve trunk
- It measures the electrical activity of all cells adjacent to the electrodes
What are the 4 reasons while the extracellular recording is used?
- the measurement of nerve conduction velocity.
- the effect of temperature on the excitability of the nerve.
- the changes in excitability of the nerve that occur after it has been stimulated (refractory periods).
- some relationships between nerve and muscle activity. (Here, the muscle compound action potential and resulting contraction are also recorded).
What is recorded when a microelectrode pierces the nerve cell membrane? Why?
A potential between the inside and outside of the cell = transmembrane potential.
What happens to this transmembrane potential when the nerve is stimulated? What ions are involved?
Action potential occurs, once reaching the threshold.
Na2+ and K+
Why does the passage of a nerve impulse normally take place only in one direction?
Even though the impulse travels in both directions in the first nerve, it can only be transmitted across a synapse where the neurotransmitter is released (only neurotransmitter on one side)
What sort of record is produced by recording from the extracellular fluid surrounding a nerve? Why?
A small current (through extra-cellular recording)
If two simple wire electrodes are placed close to the outside surface of the nerve, any change in polarity of charge across a membrane can be detected.
What is a compound action potential? What is the magnitude of the potential related to?
The sum of action potentials in one nerve
Number of axons that respond with an action potential.
The sum of electrical activity resulting from the action potentials occurring simultaneously in a number of axons.
How does COLD Ringer affect the compound action potential?
Cold- delays action potential (channels open later, threshold later)
What is meant by the refractory period of a nerve? What happens to the recorded compound action potential if the nerve is stimulated in its refractory period?
During much of the action potential the membrane of a nerve is completely refractory to further stimulation i.e. will not fire a second action potential in response to a stimulus no matter how strong = absolute refractory period
During the last part of the action potential, a second action potential can be triggered but the stimulus must be stronger than normal to elicit it = relative refractory period
What is the stimulus artefact?
The time of first stimulation
What does the amplitude and duration of the stimulus artefact reflect?
The amplitude and duration of the stimulus artefact reflect the strength and duration of the stimulus applied to the nerve.
What happens to the transmembrane potential, when a cell is depolarised?
made less negative
An active response (the action potential) occurs when the membrane potential reaches a critical (threshold) level. This is due to the ______ (opening/closing) of sodium channels in the membrane by the ______ in the voltage field across them (that is, the channels are voltage sensitive). Sodium ions enter the cell through these channels making it even ______ (more/less) negative inside, until the transmembrane potential reverses so that the inside is ______ (positive/negative) relative to the external solution.
opening; change; less; positive
This change of making the inside of the cell more positive than the outside only occurs for a short period because of 3 reasons. List them
(i) the sodium equilibrium potential (ENa) is approached, (ii) the sodium channels close (they inactivate), and (iii) voltage - sensitive potassium channels open, K+ ions exit and the membrane repolarizes.
How can changes in voltage be recorded?
inserting a micropipette inside the nerve or muscle cells
How can changes in polarity of charge across the active membrane be detected?
Extracellularly- as a small current is generated in the extracellular fluid
If two simple wire electrodes are placed close to the outside surface of the active membrane, this current can be detected as a voltage difference between the two points in the extracellular space.
If many nerve or muscle fibres discharge (that is, fire action potentials) at the same time, then the response will be _____ (large/small).
large
What is the threshold stimulus?
the minimum stimulus required to initiate an action potential in the axon
As the stimulus voltage applied to a compound nerve is increased, ______ (more/less) axons, with _____ (higher/lower) thresholds, will be stimulated
more; higher
As more individual action potentials reach the recording electrode, a compound action potential of ______ (higher/lower) amplitude is recorded, consequently there is a relationship between the strength of the stimulus applied to the compound nerve and the _____ of the response.
higher; size
Why is there an upper limit to how big the compound action potential can get?
This is the point at which the stimulation threshold for all available axons has been exceeded and thus all axons have been recruited. Each axon arising from a motoneuron makes synaptic contact with a number of muscle fibres. The actual number of muscle fibres innervated by a motor neuron varies with the size of the muscle.
What is the principle of a strength duration curve?
Stimuli of very short duration will not evoke an action potential in an axon no matter how intense the stimulus is. With stimuli of longer duration, the strength of the stimulus which excites a population of axons is related to its duration.
In a strength duration curve, stimuli of very short duration ______ (will always/ will never) evoke an action potential in an axon no matter how intense the stimulus is. With stimuli of longer duration, the strength of the stimulus which excites a population of axons is related to its duration.
will never
Briefly explain why there is a minimum voltage (1) and duration of stimulus (2) required to generate an action potential.
2 step process
- need min voltage –> activate gated voltage channels –> Na+ channels open –> depol –> enough depol –> action potential
- need duration to be processed -> activate gated voltage channels –> Na+ channels open –> depol –> enough depol –> action potential
What is the principle of an absolute refractory period?
During much of the action potential the membrane is completely refractory to further stimulation i.e. it will not fire a second action potential in response to a stimulus no matter how strong.
What is the principle of a relative refractory period?
During the last part of the action potential, a second action potential can be triggered but the stimulus must be stronger than normal to elicit it
During which part of the action potential is the second stimulus delivered?
- during relative refractory period
- during relative refractory period
- outside the refractory period
- during the absolute refractory period
