02/03/26 - Nervous Tissue (slides b)

cell membrane

a barrier that separates the cytoplasm of the cell from the enviroment

membrane potential

the difference in electrical charges across the membrane

• created when the positive and negative charges are separated apart by the plasma membrane

• an electrochemical gradient

• varies from time to time

the resting membrane potential

the membrane potential in an unstimulated or undisturbed cell

current

a movement of charges to eliminate a potential difference

resistance of the membrane

a measure of how difficult it is for a particular ion to cross the membrane

• can change as ion channels open or close

permeable

when a type of ion can cross the plasma membrane through its opened ion channels

leak ion channels

membrane channels that always open

• important in establishing the resting membrane potential of the cell

regular/gated ion channels

membrane channels that always remain closed unless the proper stimulus is present

chemically gated ion channels (ligand-gated channles)

open or close when they bind specfic chemicals or ligands

• are most abundant on the dendrites and cell body of a neuron

voltage gated ion channels

open or close in response to changes in the membrane potential

mechanically gated ion channels

open or close in response to physical distribution of the membrane surface, such as when pressure is applied due to the touch of a hand.

graded (local) membrane potentials

are changes in the membrane potential that cannot spread far from the site of stimulation

• local, gets diminished with distance, and does not spread far

repolarization

the process of restoring the normal resting membrane potential after depolarization

• involves a combination of ion movement through membrane channels and activities of the Na-K exchange pump

action potentials (nerve impulses)

changes in the membrane potential that are intiated, after a continous excitable membrane

• propagated along the surface of an axon to the axon terminals, it does not diminish as it moves away from its intitation site

all-or-none principle

a given stimulus triggers either a typical action potential or none