Electrochemical Impulse

sodium potassium pumps

need ATP, pump 3Na+ out, 2K+ in

non-gated channel proteins

(leak channels) (slides) allow facilitated diffusion of ions

voltage gated channel proteins

open in response to voltage change, once open → open on both ends, allows facilitated diffusion of ions

ligand-gated channel proteins

open in response to ligand binding, once open → open on both ends allows facilitated diffusion of ions

nerve impulses

electrical signal used by nerves to communicate w other neurons, muscles and glands

resting neuron

cytoplasmic side of membrane is negative relative to th extracellular side; charge seperation across membrane is a form of potential energy called membrane potntial

resting membrane potential

potential diff across a membrane in a resting neuron; about -70mV, provides energy for generating a nerve impulse

polarized membrane

membrane charged by unequal distribution of positively charged ions inside and outside the nerve cell

3 main factors that influence resting membrane potential

large negatively charged proteins in cell, channels in membrane allow K+ to diffuse out more easily than Na+ can move into the cell, sodium potassium pump moves Na+ and K+ ions across the cell membrane in different ratios

what does resting mean

no nerve impulses are being transmitted along the axon. The resting potential maintains the axon membrane in a condition of readiness for an impulse to occur.

depolarization

occurs when the cell becomes less polarized During depolarization, the inside of the cell becomes less negative relative to the outside of the cells.

action potntial

rapid temporary shift (depolarization) in th neuron’s membrane potential (from negative to positive) caused by a sudden influx of positive ions triggered by a stimulus since stress activatd ion channels in the membrane of sensory receptors open in response to physical stimulus

all or nothing phenomenon

if stimulus causes the axon to depolarize to a certain level to the threshold potential, an action potential occurs

threshold potential

-55mV

strong stimulus

does not chang strength of action potential, allows axon to start an action potential more offten

action potentials purpose

series of action potentials move along plasma membrane of an axon to create a nerve impulse

steps of action potentials

initiation, depolarization, repolarization, hyperpolarization, refractory period

initiation

an action is triggered when positive ions caused by stimulus rais membrane potential past threshold potential, generating an action potential

depolarization

voltage-gated sodium channels open when threshold potental is reached, Na+ moves down concentration gradient and rushes insto axon, causing depolarization of membrane (40mV)

repolarization

voltage-gated sodium channels close due to change in membrane potential and voltage gated potassium channels open, move down gradient and exit the axon, causing membrane to repolarize

hyperpolarization

K+ channels are slow to close, causing membran to become hyprpolarized to -90mv

refractory period

voltage-gated potassium channels closed, resting potntial is restored by the sodium potassium pump pumping Na and K ions across membran to rebuild concentration gradient; time it takes for resting potential to be restored

saltatory conduction

conduction of nerve impulse along myelinated neuron where action potentials jump from one node of Ranvier to the next

nodes of ranvier

exposed areas of the neuron that have voltage gated sodium channels 

speed myelinated vs unmyelinated

120m/s vs 0.5m/s