Lab 2 Flashcards
Change in membrane potential during action potential propagation
Simulus gated sodium channels open
Sodium floods into neuron with the opening of more sodium channels
Voltage gate sodium channels close
Voltage gated potassium channels open
Returns to resting membrane prtential and both channels are now closed
Define conductance as it applies to ions moving through a cell membrane
Conductance is the inverse of electrical resistance - if the conductance of the membrane is low, then the resistance to movement of that ion across the membrane is high
Depends on permeability (ion channels) and equilibrium potential (driving force)
Changes in the membrane potential in a local area of a neuron’s membrane will result from …
changes in membrane permeability
Intracellular recordings
Recordings taken from inside of an axon or neuron
measurement of the electrical charge in the internal environment relative to the electrical charge in the external environment outside the membrane
Units that are normally used for membrane potential
mV
Why does an action potential peak at approximately +40mV?
Because it is going towards sodium conductance
Extracellular recordings
Recordings taken from electrodes placed at 2 different points on the outside of an axon or neuron
Records the electrical activity in the external environment of a group of axons such as a whole nerve
How do the properties of the individual axons within a nerve vary?
Myelination and diameter
Whole nerve potential
An action potential representative of the combined electrical activity of ALL the different axons within a nerve. All individual axons within a nerve summate electrically to produce a WNP
The summed electrical activity from all icons within the nerve
What feature in some axons might increase the membrane resistance (rm) and therefore aid in the spread of the electrical signal along the cable?
Myelin
Amplitude of WNP is
Phase 1 - upswing
2 phases of a WNP
Upswing and downswing
Whole nerve action potential is …
biphasic
Why is WNP biphasic ?
When you stimulate a whole nerve APs propagate at different speeds along different axons. Some axons are slow and some axons are fast. This means the WNP travels down the nerve as a wave, not a single point, with the APs from the fast neurons at the front and the APs from the slow neurons at the back.The biphasic trace occurs because of the way we record the wave of APs across two electrodes.
What is happening within each axon within the nerve during the whole nerve potential?
• If threshold is reached within a neuron, an action potential will propagate along its axon. • Not all neurons have the same threshold.
Latency
Time delay between the stimulus and the response
Are all the axons doing the same thing at the same time during a WNP?
No - APs propagate at different speeds along an axon according to axon diameter (rin) and the extent of axon myelination (rm)
Threshold response
The point at which you first see a response after seeing no response below that threshold on the wave form
Maximal response
The point at which increasing the pulse height no longer causes an increase in the amplitude of the response