Neurons, Synapses, and Signaling Part 2 Flashcards
Gated channel
- causes a change in membrane potential to occur
-Opens or closes in response to stimuli
Voltage gated ion channel
Opens or closes in response to a shift in the volatage across the plasma membrane or the neuron
When gated K+ channels open, K+ diffuses out which makes the inside of the cell more___
negative
Hyperpolarization
an increase in magnitude of the membrane potential
opening other types of ion channels triggers Depolarization.
a reduction in the magnitude of the membrane potential
Graded potentials
changes in polarization where the magnitude of the change varies with the strength of the stimulus.
- Graded potentials decay with time and distance from the source
If a depolarization shifts the membrane potential sufficiently, it results in a massive change in membrane voltage called
action potential
Action potentials have a constant magnitude and transmit signals over
short and long distances
Action potentials occur whenever a depolarization increases the membrane potential to a particular valve called a
threshold
Action potentials are all or
none
First stage of action potentials
Resting stage- Most Na+ channels are closed, but not all, of the volatage-gated potassium (k+) channels are also closed
Second stage of action potentials
Depolarization-A stimulus opens some sodium channels. Na+ flows into the cell. If the stimulus is strong enough, more Na+ channels open increasing Na- diffusion even more. If the depolarization reaches the threshold, it triggers an action potential.
Third stage of action potential
Once the threshold is crossed, this positive-feedback cycle rapidly
brings the membrane potential close to E N a
▪ This is called the rising phase
Deplorization opens most sodium channels while the potassium channels remain closed. Na+ influx makes the inside the membrane positive with respect to the outside
The fourth stage of action potential: Falling stage
During the falling phase, voltage-gated Na+ Channels become inactivated;voltage-gated channels open,and flows out of the cell
Refractory Period
During this period after an action
potential, a second action potential cannot be
initiated
* The refractory period is a result of a temporary
inactivation of the channels
site where the action potential is initiated (usually the axon hillock)
an electrical current depolarizes the neighboring region of the axon
membrane
Action potentials travel only toward the
synaptic terminals
Inactivated channels behind the zone of depolarization___the action potential from traveling___
prevent
backward
How long do action potentials last in neurons
less than 2 milliseconds
Frequency of action potential conveys information
True or False
True
Speed of an action potential increases with
the axon’s diameter
