anatomy unit 13 nervous system - membrane potential

electrical potential

difference in concentration of charged particles between one point and another

measured in volts

may be able to produce a current

current

the flow of changed particles fro one point to another

example flashlight battery

with a potential voltage the battery is polarized

resting membrane potential

the charge difference across the plasma membrane of an unstimulated, resting cell. in a neuron it is typically -70 millivolts.

when there is a negative sign it means there are more negatively changed particles on the inside of the membrane than outside

gate channels

channels that are normally closed, but can be stimulated to open

These channels are also specific for its specific ion.

electrical currents

are created by the flow of ions (Na+, K+, etc.) through gated channels in the membrane

Leak (passive) channels

always open. each is specific to one ion

(Ex: the Na+ leak channel only allows for Na+ to pass through the channel down its concentration gradient)

chemically-gated channel

opens when: a chemical (hormone, neurotransmitter, etc.) binds

found on neuron cell body and dendrites

voltage-gated channel

opens when: the membrane potential changes

found on: neuron’s axon; skeletal and cardiac muscle membrane

mechanically-gated channel

opens when: physical stress or deformation hits the plasma membrane

found on: sensory receptors (touch, pressure, vibration)

Closed (gated cannel)

normally shut but capable of opening

open gated cannel

activated channel

inactivated (gated cannel)

ions cannot pass through the channel but the channel is not considered closed

resting membrane potential

ions are unequally distributed between extracellular fluid and intracellular fluid

results from the diffusion of ions (NA + and K+) down their concentration gradient, selective permeability of the membrane, and electrical attraction of cations and anions to each other

potassium (K)

is more abundant in the ICF then ECF

K+

is the membrane more permeable to k+ or Na+

more K+

are there more K+ leak channels or Na+ leak channels

negative (positive ions are being lost)

when k leaves the cell do the insides become more negative or positive

negative change

what starts pulling the K+ back in

Sodium (Na+)

more abundant in the ECF but the membrane is less permeable to it

concentration gradient and negative charge inside

how does NA+ enter the cell

the NA+/K+ pump

•     Compensates for Na⁺ leaking in and K⁺ leaking out.

•     Uses ATP to move 3 Na⁺ out and 2 K⁺ in, concentrating Na⁺ outside and K⁺ inside.

•     Uses about 70% of the energy requirement of the nervous system.

•     Contributes about −3 mV to the RMP.

local potential

a small, reversible, short-distance change in a cell's membrane voltage

sensory neurons

can be stimulated by chemicals, light, heat, or mechanical forces. the stimulation triggers local, temporary change in membrane potential

graded

size varies with stimulus strength.

stronger stimuli keep gated channels open longer, causing a larger depolarization or hyperpolarization, depending on the channel

decremental

get weaker the farther they spread from the point of stimulation