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1

Neurophysiology

The study of the life processes of neurons

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Polarized

Exhibiting a difference in electrical charge between the inside and outside of the cell

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Ion

An atom or molecule that has acquired an electrical charge by gaining or losing one or more electrons

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Anion

A negatively charged ion, such as a protein or a chloride ion

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Cation

A positively charged ion, such as a potassium or sodium ion

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Intracellular fluid

The watery solution found within cells

Also called cytoplasm

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Extracellular fluid

the fluid in the spaces between cells (interstitial fluid) and in the vascular system

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Cell membrane

The lipid bilayer that ensheathes a cell

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Microelectrode

An especially small electrode used to record electrical potentials in living cells

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Resting potential

A difference in electrical potential across the membrane of a nerve cell during an inactive period

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Ion channel

A pore in the cell membrane that permits the passage of certain ions through the membrane when the channels are open

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Millivolt (mV)

A thousandth of a volt

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Potassium ion (K+)

A potassium atom that carries a positive charge because it has lost one electron

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Selective permeability

The property of a membrane that allows some substances to pass through, but not others

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Diffusion

The spontaneous spread of molecules until a uniform concentration is achieved

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Electrostatic pressure

The propensity of charged molecules or ions to move, via diffusion, toward areas with the opposite charge

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Sodium-potassium pump

The energetically expensive mechanism that pushes sodium ions out of a cell, and potassium ions in

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Sodium ion (NA+)

A sodium atom that carries a positive charge because it has lost one electron

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Equilibrium potential

The point at which the movement of ions across the cell membrane is balanced, as the electrostatic pressure pulling ions in one direction is offset by the diffusion force pushing them in the opposite direction

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Axon hillock

The cone-shaped area on the cell body from which the axon originates

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Hyperpolarization

An increase in membrane potential (the interior of the neuron becomes even more negative)

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Depolarization

An increase in membrane potential (the interior of the neuron becomes less negative)

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Local potential

An electrical potential that is initiated by stimulation at a specific site, which is a graded response that spreads passively across the cell membrane, decreasing in strength with time and distance

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Threshold

The stimulus intensity that is just adequate to trigger an action potential at the axon hillock

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Action potential

A rapid reversal of the membrane potential that momentarily makes the inside of the membrane positive with respect to the outside

Also called spike

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All-or-none property

The fact that the size (amplitude) of the action potential is independent of the size of the stimulus

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Afterpotential

The positive or negative change in membrane potential that may follow an action potential

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Voltage-gated Na+ channel

A NA+-selective channel that opens or closes in response to changes in the voltage of the local membrane potential; it mediates the action potential

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Refractory

Temporarily unresponsive or inactivated

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Absolute refractory phase

A brief period of complete insensitivity to stimuli