EX1; Excitable Cells; Potentials Flashcards
This is a large transient change in membrane potential (neurons and muscle cells)
action potential
This change in the environment causes a change in the membrane potential of a resting cells in the depolarizing direction
stimulus (light, temp, pain, etc.)
What is the sequence of events after a stimulus leading to an action potential
stimulus –> depolarized membrane (dendrites of a neuron) –> depolarized cell body –> AP develops at initial segments then propagates along the axon
The first step to develop an action potential is to increase membrane permeability to what
Na+ ions
The Na ions enter through voltage regulated Na channels, driven by what
electrical and concentration gradients
Upon Na+ ions entering the cell, what happens to the membrane potential
it moves closer to 0mV (depolarizes)
If depolarization is sufficiently large, this point will be reached which causes additional Na channels to open
the membrane potential threshold
Voltage-regulated channels are in the open or closed state determined by what
the prevailing membrane potential
As more Na+ enters the cells, it is a positive feed back cycle termed the rising phase; what does this mean
the opening of voltage gated Na channels
increases membrane Na permeability
increasing flow of Na into cell
decreasing the membrane potential (depolarization)
which opens the voltage gates Na channels
The membrane potential is very rapidly moves toward 0mc resulting in what
an overshoot of 0mV, reaching 40mV
Upon the membrane potential overshoot, what voltage regulated channels open
K+; go from the inside to outside
Upon K+ leaving the cell, the membrane potential abruptly reverses direction and returns to what
resting value and K+ ions diffuse out, carrying their + charge with them; referred to falling out phase
Movement of K+ is driven by what
concentration gradient and initially by electrical gradient as long as potential is positive
During the falling phase, what becomes of the Na channels
the Na channels close due to the membrane becoming more negative; “Na inactivating”
This is a phase of hyperpolarization; the rapid depolarization and repolarization, complete in ~1ms but overall talks >10ms (shoot past -70mV to ~100mV, then back to -70mV)
afterpolarization
The movement of a small/large number of ions results in a large change in membrane potential
small
This is a very brief period between applying a stimulus and the beginning of depolarization during rising phase of an AP
latent period
The latent period precedes the “foot” of AP, which is what
the portion of the rising phase before threshold is reached; channel opening
Why does the peak of the action potential stop at approximately 40mV
the peak of AP(40) approaches the E (equilibrium voltage) of Na (58)
Na is free to cross the membrane (during rising phase) until its ionic gradient is in equilibrium with membrane potential; the concentration and electrical gradient nearly balance each other at peak of AP
The end of the repolarization is close to what
the equilibrium voltage of K+; K+ freely crosses membrane during falling phase until its ionic gradient is in equilibrium with membrane potential, the concentration and electrical gradient nearly balance each other at the end of AP
This type of stimulus is insufficient to take a membrane to threshold
subthreshold stimulus
This type of stimulus is just sufficient to take membrane to threshold
threshold stimulus
This type of stimulus is greater than a threshold stimulus
suprathreshold stimulus
Events (potential changes) resulting from a sub threshold stimulus are confine to what
the immediate region of membrane
These are small depolarization or hyper polarization which do not move along the membrane
local responses
This response is proportional to the stimulus strength; can be relatively weak and elicit changes in membrane potential that are subthreshold and not propagated
graded responses
A threshold stimulus cause and action potential to occur and once it passes the threshold level, what occurs
it continues to completion and propagates along the entire length of an axon
Once an AP crosses the threshold level, and continues to completion this is termed what
all-or-none
This is a brief period when a second threshold stimulus or even a supra threshold stimulus cannot elicit a second AP
absolute refractory period
For this longer period after an AP, a suprathreshold stimulus can elicit another AP but a threshold stimulus still cannot
relative refractory period
The refractory periods impose what
an upper limit on the frequency at while cells can fire APs
The transition from the closed to open state of the ion channels is dependent upon what; whether the stimulus be instant or slow
the rate of stimulus change; adaptation
referred to accommodation
Adaptation is a property of what and accommodation is a property of what
adaptation = neuron accommodation = ion channel
What are the four parameters of a stimulus
intensity (amplitude)
duration
rate of change
frequency
The stimulus strength-duration curve relates what
strength (intenisty) of an instantaneous stimulus to the duration of the same stimulus that is required to elicit a response (AP)
This is the magnitude of the least intense stimulus that can elicit a response
rheobase
This is the duration required to elicit a response by a stimulus with a rheobase magnitude
utilization time
This is the duration required to elicit response for a stimulus that has a magnitude that is twice the rheobase magnitude; can be used to compare excitability of different cells
chronaxie
These are currents that occur at the immediate site of the stimulating electrodes, they do not propagate (passive currents), will give rise to AP if sufficient magnitude
electrotonic currents
What is the potential change at the cathode
depolarizing; cathode causes cations (CCC) to move toward it, in both ECF and inside cell, that + ions inside cell are trapped and results in depolarization
What is the potential change at the anode
hyperpolarizing potential change; anode attracts anions
The stimulus that occurs at the site of the cathode which results in a depolarizing potential change at the site, causing local currents, this in turn cues what
depolarization of adjacent regions, this, if sufficient, will trigger an AP
One AP does not move along the axon, rather, what occurs
every site along an axon undergoes a change in membrane potential (unless myelinated)
What drives the AP in one direction
Na channel inactivation
These cells surround axons, wrapping an extensive layer of plasma membrane around the axon
Schwann cells
Where are Schwann cells not located
periodic nodes; nodes of Ranvier
The layer of the Schwann cell is what; an excellent electrical insulator
myelin
True or False
Local currents inside axon spread much further in the presence of myelin, allowing the AP to be only generated at the nodes
True
What is the term when an AP skips along the axon; increasing the velocity of AP
saltatory conduction
What is the breakdown of myelin, resulting in gross motor abnormalities
multiple sclerosis
This contains many neurons
peripheral nerve
Velocity of an AP along the axon is dependent upon what
diameter; those with larger diameter have higher velocities
