MCAT BIO/BIOCHEM: Neurons and Action Potentials Flashcards

Question 1

What is Neuron?

Accepted Answer

An excitable cell that receives, integrates and transmits information, using electrical signals along its membrane and chemical signals at its synapses.

Question 2

What is Dendrite?

Accepted Answer

A branched extension of a neuron's cell body that receives input from other neurons and conducts graded potentials toward the soma.

Question 3

What is Soma?

Accepted Answer

The cell body of a neuron, containing the nucleus and most organelles, where the neuron's proteins and neurotransmitter-making enzymes are produced.

Question 4

Define Axon Hillock.

Accepted Answer

The cone-shaped region where the axon leaves the cell body; its dense voltage-gated sodium channels make it the usual trigger zone for action potentials.

Question 5

What is Axon?

Accepted Answer

A single long projection of a neuron that conducts action potentials away from the cell body toward its terminals.

Question 6

Define Axon Terminal.

Accepted Answer

The swollen end of an axon branch, packed with neurotransmitter vesicles, where the electrical signal is converted into chemical release at a synapse.

Question 7

Define Myelin Sheath.

Accepted Answer

A layered, lipid-rich wrapping of glial cell membrane around an axon that insulates it, cutting leakage and capacitance so signals travel faster.

Question 8

Define Schwann Cell.

Accepted Answer

A glial cell of the peripheral nervous system that wraps one segment of a single axon in myelin and helps damaged peripheral axons regrow.

Question 9

What is Oligodendrocyte?

Accepted Answer

A glial cell of the central nervous system that sends out several processes, each wrapping a segment of a different axon in myelin.

Question 10

What is Astrocyte?

Accepted Answer

A star-shaped glial cell of the central nervous system that supports neurons, regulates the ions around them and helps form the blood-brain barrier.

Question 11

What is Microglia?

Accepted Answer

The resident immune cells of the central nervous system, acting as macrophages that engulf debris, dead cells and pathogens.

Question 12

Define Node of Ranvier.

Accepted Answer

A short unmyelinated gap between myelin segments, rich in voltage-gated sodium channels, where the action potential is regenerated.

Question 13

Define Saltatory Conduction.

Accepted Answer

The rapid propagation of an action potential along a myelinated axon, regenerated only at each node so that it appears to leap between nodes.

Question 14

Define Resting Membrane Potential.

Accepted Answer

The steady voltage across a neuron's membrane when it is not signaling, about -70 mV inside, set mainly by potassium leak and maintained by the sodium-potassium pump.

Question 15

Define Sodium-Potassium Pump.

Accepted Answer

A membrane ATPase that moves three sodium ions out and two potassium ions in for each ATP used, maintaining the gradients that resting and action potentials depend on.

Question 16

Define Equilibrium Potential.

Accepted Answer

The membrane voltage at which an ion's electrical and concentration gradients balance so that it has no net flow; it is calculated with the Nernst equation.

Question 17

Define Nernst Equation.

Accepted Answer

An equation giving one ion's equilibrium potential from its concentrations inside and outside the cell, its charge and the temperature.

Question 18

Define Goldman Equation.

Accepted Answer

An equation that predicts the resting membrane potential by weighting each ion's inside and outside concentrations by how permeable the membrane is to that ion.

Question 19

What is Threshold?

Accepted Answer

The membrane potential, typically around -55 mV, that a depolarization must reach to open enough voltage-gated sodium channels to trigger an action potential.

Question 20

Define Action Potential.

Accepted Answer

A brief, all-or-none reversal of membrane potential, from about -70 mV to about +30 mV and back, that propagates along an axon without losing strength.

Question 21

What is Depolarization?

Accepted Answer

A change in membrane potential toward a less negative value, as in the rising phase of an action potential when sodium rushes into the cell.

Question 22

What is Repolarization?

Accepted Answer

The return of membrane potential toward rest after depolarization, caused mainly by potassium leaving through voltage-gated potassium channels while sodium channels inactivate.

Question 23

What is Hyperpolarization?

Accepted Answer

A shift of membrane potential to a value more negative than rest, which makes the cell harder to excite.

Question 24

Define Absolute Refractory Period.

Accepted Answer

The interval during and just after an action potential when no stimulus, however strong, can trigger another, because voltage-gated sodium channels are open or inactivated.

Question 25

Define Relative Refractory Period.

Accepted Answer

The interval after the absolute refractory period when only a stronger-than-normal stimulus can trigger an action potential, because the membrane is still hyperpolarized.

Question 26

Define Voltage-Gated Sodium Channel.

Accepted Answer

A membrane channel that opens when the membrane depolarizes to threshold, letting sodium flood in, then shuts its inactivation gate until the membrane repolarizes.

Question 27

Define Graded Potential.

Accepted Answer

A small, local change in membrane potential whose size varies with stimulus strength and which fades with distance, unlike an all-or-none action potential.

Question 28

Define Excitatory Postsynaptic Potential (EPSP).

Accepted Answer

A graded depolarization of the postsynaptic membrane that brings it closer to threshold, usually caused by sodium entering through ligand-gated channels.

Question 29

Define Inhibitory Postsynaptic Potential (IPSP).

Accepted Answer

A graded hyperpolarization of the postsynaptic membrane that moves it further from threshold, usually caused by chloride entering or potassium leaving.

Question 30

What is Summation?

Accepted Answer

The adding together of postsynaptic potentials: temporal summation combines rapid inputs at one synapse, while spatial summation combines inputs at different synapses.

Question 31

What is Synapse?

Accepted Answer

The junction where a neuron passes a signal to another cell, usually by releasing neurotransmitter across a narrow cleft onto receptors on the postsynaptic cell.

Question 32

What is Neurotransmitter?

Accepted Answer

A chemical released from an axon terminal into a synapse that binds receptors on the postsynaptic cell to excite or inhibit it.

Question 33

What is Acetylcholinesterase?

Accepted Answer

An enzyme in the synaptic cleft that rapidly splits acetylcholine into acetate and choline, ending its signal at neuromuscular junctions and other cholinergic synapses.