Mechanically gated channels
open or close in response to a mechanical force on the membrane (usually associated with sensory or visceral receptors located at the END OF AFFERENT NEURONS)
Repolarization
the return of a depolarized membrane to the resting potential to a more negative value
Because the membrane potential is a difference in potential across the membrane, the membrane is ___.
polarized
Membrane potential always refers to the potential ___ the cell relative to the potential ___.
inside, outside the cell
Hyperpolarization
a change in the more negative value and becomes more polarized
depolarization
a change from a negative charge to a more positive charge and becomes less polarized.
repolarization
when a membrane potential returns to the resting membrane potential following a depolarization.
2 different types of electrical signals in the neuron:
graded potentials and action potentials
graded potentials
small electrical signals that act over short ranges only because they diminish in size with distance
action potentials
are large signals capable of traveling long distances without decreasing in size
Graded potentials occur when ion channels open or close in response to a ______ acting on the cell.
stimulus
Some graded potentials are depolarizations, whereas others are ________.
hyperpolarizations
If Na channels open then Na ions would move into the cell and the resulting graded potential would be ______.
depolarization.
If K channels open then K ions would move out of the cell and the resulting graded potential would be __________.
hyperpolarization
What is the primary significance of graded potentials?
They determine whether a cell will generate an action potential.
Graded potentials generate action potentials if they depolarize a neuron to a certain level of membrane potential called the ____.
threshold
Graded potentials that are depolarizations are described as _____.
excitatory
Graded potentials that are hyperpolarizations are described as ____.
inhibitory
decremental
describes how the change in the membrane potential decreases in size as it moves along the membrane away from the site of stimulation.
Electronic conduction
spread of voltage by passive charge movement
As the graded potential spreads from the site of the stimulation, the current is spread over a larger area, and some current leaks across the plasma membrane. This results in the size of the membrane potential to _____ as it moves from the site of the ini
decrease
A single graded potential is generally not of sufficient strength to elicit an ___ ____.
action potential
temporal summation
when stimuli are applied in such rapid succession that the graded potential from one stimulus does not dissipate before the next graded potential occurs. (effecting the potentials sum)
The greater the stimuli overlap in time, then the ___ the summation.
greater
spatial summation
the addition of graded potentials generated at different locations that occurs when they are stimulated more or less simultaneously.
Where do action potentials occur?
in the membranes of excitable tissue (nerve or muscle)
Action potential occur when:
a graded potential reaches threshold.
What happens during an action potential?
A large rapid depolarization occurs where the polarity of the membrane potential reverses, becoming + for a brief period of time. Changes from -70mV to +30mV (change of 100mV)
Once an action potential is initiated it is capable of being propagated _____ _____ along the length of an axon without any decrease in strength, unlike the graded potentials.
long distances
The action potential depends on these 2 factors:
The selective permeability of the plasma membrane and the Na+ and K+ electrochemical gradients that exist across the membrane.
The plasma membrane is __ times more permeable to K ions than to Na ions, because there are more K leak channels than Na leak channels.
25
What are the 3 distinct phases for an action potential in a neuron?
1) Depolarization 2) Repolarization 3) After-hyperpolarization
During depolarization the membrane potential changes from ____mV to ___mV. This is caused by a sudden increase in the permeability to ___ followed by a sudden movement of those ion into the cell.
-70mV to +30mV; Na
During repolarization the membrane potential goes from ____ to _____.
+30mV to -70mV
During repolarization, 1 msec after the Na permeability increases it begins to decrease rapidly. At the same time K permeability ____ and begins to move down the electrochemical gradient ___ of the cell.(bringing it back to resting levels)
increases; out
After the repolarization occurs, K permeability remains ____ for 5-15 msec after reaching resting membrane potentials which results in _______.
elevated; after-hyperpolarization
The location of graded potentials are:
dendrites, cell body, sensory receptors
the location of action potentials are:
on the axon
the strength of graded potentials are:
relatively weak, proportional to strength of stimulus; dissipates with distance from stimulus
the strength of an action potential is:
100mV (All-or-none)
The summation of a graded potential is:
spatial or temporal
What are the refractory periods for a graded potential? What about for action potentials?
none; absolute and relative
What are the channel types that are used during a graded potential?
ligand-gated and mechanically gated
What are the channel types that are used during an action potential?
voltage-gated
What ions are involved with a graded potential?
Na+, Cl-, and K+
What ions are involved with an action potential?
Na+, and K+
What is the duration of time of a graded potential?
few msec to seconds
What is the duration of time of an action potential?
1-2 msec (after-hyperpolarization may last 15 msec)