27b Nervous System Flashcards
what is the membrane potential?
the electival potential differences (voltages) that exists from intracelluar to extracelluar. due to unequal distrubution of ions across membrane (ionic gradient)
what is the resting potential?
the potential difference when the cell is not transmitting any signals.
depends on the ionic gradient (unequal distribution of ions across the membrane)
what is the ionic gradient in the RESTING POTENTIAL due to?
changes in membrane permeabilities for potassium, sodium, calcium, and chloride ions
what is the typical resting potential in a neuron?
what does the negative sign mean?
resting potential of -60 to -80 millivolts
negative sign means that the inside of the neuron is NEGATIVE compared to the outside - concentration gradient.
what is an electrical gradient?
develops in the opposite direction to the concentration gradient. the excessive negative charge inside the cell attracts positive K+ (potassium+) ions from the outside, back inside.
what is the equilibrium potential?
the size of the membrane voltage when that ion is at an equilibrium across the membrane.
under what circumstances could ions flow through ion channels from a region of low ion concentrtation to a region of high ion concentration?
ions can flow against the concentration gradient if there is an electical gradient because of a highly charged ion (eg K+ being attracted back into the cell because of the excessive negative charge inside the cell)
why is the resting potential of neurons different from the equilibrium potentials of K+ and Na+?
the resting potential is simly the DIFFERENCE WHEN THE CELL IS NOT TRANSMITTING A SIGNAL. this results in ionic graidents across the membrane.
however the equilibruium potential occurs after a resting potential has gone through an electrical gradient to alter the concentration gradient, resulting in NO NET DIFFUSSION OF IONS ACROSS THE MEMBRANE
define hypepolarisation
is triggered by a stimuli which changes the membrane potential to become more negative. hyperpolarisation occurs when K+ gated channels open, increasing transfer of potassium through the membrane.
membrane potential moves closer to Ek (-92mV)
define depolarisation
decreases the size of the membrane potential - makes inside of cell become less negative. due to opening of sodium + channels - increase sodium permability through the membrane.
membrane potential moves closer to Ena (62mV)
define a graded potential
the shift in the hyperpolarisation or depolarisation in the membrane potential
what happens when depolarisations have reached their threshold?
an action potential is generated. this is when the membrane potential changes from negative to positive
what are the 5 steps for the action potential?
r
d
r
f
u
resting state - resting potential
depolarisation - stiumulus opens some sodium+ activation gates allowing sodium+ to enter the cell (inside becomes less negative
rising phase - depolarisation continues to open more soidum+ activation gates (positive feedback) when depolrisation reaches threshold - action potetial is made
falling phase - cell becomes more negative inside again (repolarisation) this is to stop depolarisation to reach Ena (62mV)
undershoot - potassium+ channels close slowly - membrane potential becomes more negative
how are action potentials conducted along axons?
the action potential is intiatiated along the axon hillox
what are the two types of synapses? why are synapses important?
electical synapses
chemical synapse
synapses are necessary for neurons to communicate with each other cells
what does an electical synapse do?
contains gap junctions that DO ALLOW electrical currents to flow from cell to cell
what does a chemical synapse do?
transmit information between cells by the release of neurotransmitters from the pre-synaptic cell
