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Where does a graded depolarization occur and how?
How: From sensory stimilus. the amount of stimilus varies resulting in different levels of graded potentials
Where: Dendrites, Cell body
Describe a graded depolarization
when the type of neurotransmitter binding to its receptor causes sodium channels to open, then sodium ions would move into the cell and the resulting graded potential would be depolarization
Define summation of graded potentials
- Summation is the additive process of graded potentials.
- One single graded potential is not enough to generate action potential, graded potentials can accumulate due to multiple locations of simultaneous inputs
Define Spatial Summation
Effects of stimuli from multiple sources occurring close together in time arriving at the axon hillock (trigger zone) at the same time
Define Temporal Summation
Stimuli applied in rapid succession, such that stimulus from one graded stimulus does not dissipate before the next stimulus applied
Threshold is the level of depolarization necessary to induce action potential
The level of depolarization insufficient to induce action potential
Level of depolarization in excess of threshold. It is sufficient to induce action potential.
-Does not produce a stronger action potential
Put the following in order and label with correct phase: describing the sequence of events that occur during an action potential.
activation of Na+ channels and rapid depolarization (positive feedback)
Return to resting membrane potential
Depolarization to threshold -70 to -55
Repolarizaton with the activation of K+ channels
- 1. Depolarization to threshold -70 to -55
- 2. Activation of Na+ channels and rapid depolarization phase 13. Repolarization with the activation of K+ channels phase 24. Hyperpolarization phase 35. Return to resting membrane potential
Describe absolute refractory peroids
During the absoult refractory peroid NO
stimulus of any strength can generate a second action potential
- No influx of sodium (Na+) possible: inactivation gate closed and incapable of opening until return to resting state.
- K+ channels are open
Prevents summation of action potentials
Define Relative refractory peroid
Stronger than normal stimulus needed for another immediate action potenial
Na+ channels ready but K+ channels still open
This offsets Na+ influx
True or false:
Action potentials are dependent upon threshold; all or nothing?
True or false:
The following are true of action potentials:
-all or nothing
-action potentials are identical
-action potentials do not diminish in strength over distance
-action potentials cannot be summated
What factors influence conduction velocity of action potentials?
- Larger diameter axons carry faster signals
- Myelinated axons carry faster signals. The action potnetial jumps across myelinated segments
- Nodes of Ranvier- greatest concentration of voltage gated sodium and potassium channels
- conserves energy- requires less energy to re-establish sodium/potassium distribution by Na/K pump at nodes only
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