Electrophysiology (Action Potential and Synapses) Flashcards
Neuronal membranes consist of a lipid bilayer with proteins.
What do you call these proteins and what are some of the functions of the proteins that float in or penetrate the cell membrane?
These proteins are called transmembrane proteins.
They can function as ion channels or receptors for neurotransmitters or peptide hormones.
What is the “resting potential” a comparison of?
In neurons, what is the resting potential?
It is a comparison of the voltage of the inside of the cell at rest to the outside of the cell.
The resting potential of neurons is ~70 to 90 mV.
At rest, compare the concentrations of Na+ and K+ of inside and outside a cell.
At rest, Na+ will passively flow out of the cell and K+ will passively flow inside the cell. (Also, at rest, K+ has an easier time flowing inside than Na+.)
At rest, how do cells maintain and restore the concentration gradient?
Cells use ion pumps that require metabolic energy (ATP) to maintain gradients by pumping Na+ OUT and K+ INTO the cell.
Local changes in membrane potential occur near synapses.
- What is an EPSP?
- What is an IPSP?
EPSP - Excitatory post-synaptic potential
- A small depolarization (from -70 to -60 mV)
IPSP - Inhibitory post-synaptic potential
- A small hyperpolarization (from -70 to -80 mv)
Graded potential changes decay over time and distance and cannot travel long distances along the neuron membrane.
However, graded potentials can add together. What are the two ways that they can summate?
- Temporal summation: Multiple and rapid graded potentials at a single synapse can add together
- Spatial summation: Multiple graded potentials at different synapses can add together
Once an EPSP is large enough and reaches the cell’s threshold potential, an all-or-nothing action potential results.
What is a neuron cell’s threshold potential?
Around -55 mV
Where do graded potentials typically occur?
Graded potentials usually occur around unmyelinated membrane synapses.
(Ex: Soma’s, dendrites, and the receptive end of sensory neurons)
Why are nerve and muscle cells called excitable cells?
How can these cells be excited?
Nerve and muscle cells are called excitable cells because they can undergo transient, rapid changes in membrane potential.
These cells can be excited via synaptic input or electrical stimulation.
What occurs in a cell when the membrane potential depolarizes to -55 mV?
- What occurs at Na+ channels?
- What propagates down the axon?
At -55 mV, the threshold potential is reached and an action potential is formed.
This causes voltage gated Na+ channels to open and for an action potential to propagate down the axon.
Does Na+ membrane permeability increase or decrease during an action potential? How does this affect the membrane potential?
Na+ membrane permeability drastically increases.
This causes the membrane potential to DEPOLARIZE and go from -70 mV to (overshooting 0 mV) ~20 mV.
Why does the cell membrane need to be rapidly depolarized in order to develop an action potential?
Rapid depolarization is critical, because Na+ channels are time and voltage sensitive.
They will only open at certain voltages and for a certain period of time.
After depolarization of the membrane by Na+, what causes repolarization of the membrane potential?
Repolarization is caused by K+ efflux from the neuron.
Repolarization by a K+ efflux causes a period of hyperpolarization to occur.
What channels mediate this hyperpolarization and what is this period called?
K+ channels mediate the hyperpolarization.
This period is known as the refractory period (which limits the frequency of action potentials).
After an action potential, in order to return the cell to a resting state the ionic gradients must be restored to normal.
What ion pump accomplishes this?
What fuels this ion pump?
The sodium potassium ion pump accomplishes this, via ATP fuel.
This ion pump pumps Na+ OUT of the cell and K+ BACK into the cell.
In the CNS after an action potential, astrocytes assist in returning the cell to a resting state.
How do they assist?
Astrocytes help the cell return to a resting state by removing excess K+ from the extracellular environment and preventing K+ accumulation.