Lecture 26- Membrane Potential Flashcards
Voltage
Measure of the amount of difference in electrical charge between two points called the potential difference
Current
Flow of electrical charge from point to point
Dependent on voltage and resistance
Types of ion channels
Leakage (non gated) channels - always open
Chemically gated (ligand-gated) channels- open when correct chemical binds to channel
Mechanically-gated channels- open when membrane receptor is physically bent or stretched
Voltage gated channels- open in response to a change in membrane potential
When ion channels are open…
Ions diffuse through channels to other side along their electrochemical gradients
When ions channels close…
Ion pumps use ATP to put the ions back where they were before the channels open
Resting membrane potential
Difference in electrical charge across cell membrane (approx. -70mV)
This point the cell is polarized
Only exists across the membrane
What causes resting membrane potential?
Differences in the ion concentration of intracellular and extracellular fluids
Differential membrane permeability tot nose ions because of different channels and pumps
Resting membrane potential sodium and potassium
Inside of cell has lower concentration of sodium ions and higher potassium ions
More leakage channels for potassium than sodium, easier for potassium to leak out than for sodium to leak in
Because of potassium leaking out along membrane, more cations on outside and more anions on inside
ATP pumps move sodium to outside and potassium to inside , leakage moves some potassium back to outside, ends up slightly more positive than outside
Changing membrane potential
Neurons use changes in membrane potential as communication signals and can be brought on by changes in membrane permeability to any ion/ ion concentrations on the two sides of the membrane.
What can changes in membrane potential produce?
Grade potentials (short distance)
Action potentials (long distance)
Depolarization
Inside of membrane becomes less negative
Increase probability of nerve impulse
Hyperpolarization
Inside of membrane becomes more negatively charged
Decrease probability of nerve impulses
Graded potentials
Short lived changes in membrane potentials
Can be depolarized or hyperpolarized
“Graded” because the magnitude of stimulus corresponds to magnitude of response
Receptor potentials
Graded potentials occurring on receptors of sensory neurons
postsynaptic potentials
Graded potentials occurring in response to neurotransmitter released from another neuron
Action potentials
all-or-none phenomena: they either happen completely, in the case of a threshold stimulus, or not at all, in the event of a subthreshold stimulus.
Higher-stimulus intensity is from the increased frequency of action potentials
One size
Resting state
All voltage-gated Na+ and K+ channels are closed.
The axon plasma membrane is at resting membrane potential:
small buildup of negative charges along inside surface of membrane and an equal buildup of positive charges along outside surface of membrane.
Depolarizing phase
When membrane potential of axon reaches threshold, the Na+ channel activation gates open.
As Na+ ions move through these channels into the neuron, a buildup of positive charges forms along inside surface of membrane and the membrane becomes depolarized.
Repolarizing phase
Na+ channel inactivation gates close and K+ channels open.
The membrane starts to become repolarized as some K+ ions leave the neuron and a few negative charges begin to build up along the inside surface of the membrane.
Repolarization continues to hyperpolarization
K+ outflow continues.
As more K+ ions leave the neuron, more negative charges build up along inside surface of membrane.
Na+ channel activation gates close and inactivation gates open. Return to resting state when K+ gates close.
