Cell Physiology Part 5 Flashcards
What is the overshoot in an action potential?
When the inside of the cell becomes positively charged (above 0 mV)
What is the spike potential?
Rapid rise and fall of action potential to form sharp spike typically around +35 mV
What is after-hyperpolarization?
A temporary increase in negativity after repolarization before returning to resting potential.
Membrane potential is more negative than resting potential.
What is a threshold stimulus?
The minimal depolarization needed to trigger an action potential (about -55 mV)
What initiates an action potential?
A transient change in membrane ion permeability .A chemical signal makes the channels open, allowing greater ionic current across the membrane
When does Action potential occur?
Action potentials occur only when the net movement of positive charge through ion channels is inward
How do ion channels contribute to an action potential?
They open in response to a signal, allowing inward movement of positive ions, especially Na⁺
What is the ionic basis of the action potential?
• Depolarization: Na⁺ channels open → Na⁺ influx
• Repolarization: K⁺ channels open → K⁺ efflux
• Hyperpolarization: Continued K⁺ efflux before channels close
What is the resting membrane potential close to?
The equilibrium potential of potassium (K⁺)
What causes the rising phase of the action potential?
Influx of sodium (Na⁺) ions into the cell
What causes the falling phase of the action potential?
Efflux of potassium (K⁺) ions out of the cell
What does the peak potential of an action potential approximate?
The equilibrium potential of sodium (Na⁺)
What role does sodium diffusion play during rest?
Sodium ions continuously move into the cell through open sodium channels
What is the role of the sodium-potassium pump in membrane potential?
• Pumps 3 Na⁺ out and 2 K⁺ in
• Creates a net loss of positive charge
• Contributes approximately -4 mV to the resting membrane potential
What is a graded potential?
A local change in membrane potential in response to a subthreshold stimulus
Do graded potentials reach the threshold for an action potential?
No, they are subthreshold and do not trigger an action potential
What causes graded potentials?
Opening of some ion channels (not all), typically in response to a small stimulus
Where do graded potentials commonly occur?
In neurons and at synapses
How do graded potentials differ from action potentials?
Graded: variable amplitude, local, decremental (fade with distance)
• Action potentials: all-or-none, long-distance, non-decremental
