Exam 2 Action potentials

two states of membrane potential

1. transmembrane potential 2. dipole potential

Describe the amplitude of an action potential

Does this differ between action potentials?

membrane potential

The voltage across a cell's plasma membrane.

two types of postsynaptic potentials

and the change in the membrane potential associated with each

ion channels

channel proteins that transport ions

anion

negatively charged ion

hyperpolarization

(increased polarization): Occurs when the negative charge inside the axon increases (e.g., -70mV becomes -80mV).

cell membrane

A cell structure that controls which substances can enter or leave the cell.

equilibrium potential

Describe in terms of the following: diffusion, electrostatic pressure, sodium-potassium pump

depolarization

Loss of a state of polarity; loss or reduction of negative membrane potential (decreasing polarization towards zero): Occurs when the negative charge inside the axon decreases (e.g., -70mV becomes -55mV)

What happens (and how) to Na+ ions during an action potential?

Move inside of cell

What happens (and how) to K+ ions during an action potential?

Move outside of cell

Where (on the neuron) does an action potential start? Where does it end?

Starts on the axon Ends at the axon terminals

What does it mean if there is no difference in the electrical charge inside and outside of a cell?

The cell is depolarized. If neuron is stimulated enough (threshold of excitation), sudden, massive depolarization of membrane and action potential occurs.

Why are action potentials uni-directional along the axon?

The sodium channels have a mechanism that avoids "back propagation" of the action potential, which would result in a confused signal. After opening, the sodium channels become inactivated as the potential becomes more positive, and they cannot open again until they are "reset" by hyperpolarization at the end of an action potential. This brief period of sodium channel inactivation, called a refractory period, prevents bidirectional propagation of the action potential, constraining it to go in only one direction.

amplitude of an action potential

Voltage over time. Generally, the same amplitude, but amplitude of action potential depends on properties of ion channels, at what potential, for example, K+ channels will open to start repolarization (peak of AP). Duration also depends on properties of ion channels. But since there are not a lot of variability in ion channels and extracellular ion composition is mainly same in animals, most of APs will have same shape/duration/amplitude.

polarized cell

cell that exhibits a membrane potential

How does the rate of action potentials affect neuronal communication?

faster action potentials means more efficient neuronal communcation

cation

positively charged ion

saltatory conduction

rapidly jumping from node to node; occurs only in myelinated axons and is about 30 times faster

threshold of excitation

the level of depolarization necessary to generate an action potential, usually about -65 mV How does a neuron reach the threshold? (Explain in terms of postsynaptic potentials)

Differentiate between an afterpotential and refractory phase

the sequence of electrical events that follows the action potential of nerve activity and that usually takes the form of a negative followed by a positive potential with both being of much smaller amplitude than the action potential Refractory period by order: 1) absolute refractory period - the membrane cannot produce an action potential, regardless of how strong a stimulus is 2) relative refractory period - a stronger than usual stimulus could initiate an action potential

all-or-none law

when an action potential occurs, the speed and size/range of the action potential is the same, no matter how weak or strong the stimulus was that caused the action Ex) Whether someone pokes you with a pencil eraser or smacks you with a boat oar, the action potential would be the same, i.e., the stimulus wass strong enough to cross the threshold of excitement in the first place, the action potential would occur the same way every time. (Other factors, such as the timing of action potentials, are what allows us to determine the strength of a stimulus.)

resting membrane potential

• voltage (charge) difference across the cell membrane when the cell is at rest. • when a neuron is not sending a signal (resting) • inside of neuron is negative relative to outside • -70 mV less than the outside • Pump that moves 3 Na+ ions out for every two K+ ions in • At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.