How the nervous system works Flashcards
polarised
the condition of a neurone when the movement of positively charged potassium ions out of the cell down the concentration gradient is opposed by the actively produced electrochemical gradient, leaving the inside of the cell slightly negative relative to the outside
resting potential
the potential difference across the membrane of around -70mV when the neurone is not transmitting an impulse
neurotransmitter
a chemical which transmits an impulse across a synapse
sodium gates
specific sodium ion channels in the nerve fibre membrane that open up, allowing sodium ions to diffuse rapidly down their concentration and electrochemical gradients
depolarisation
the condition of the neurone when the potential difference across the membrane is briefly reversed during an action potential, with the cell becoming positive on the inside with respect to the outside for about 1 millisecond
action potential
when the potential difference across the membrane is briefly reversed to about +40mV on the inside with respect to the outside for about 1 millisecond
threshold
the point when sufficient sodium ion channels open for the rush of sodium ions into the axon to be greater than the outflow of potassium ions, resulting in an action potential
refractory period
the time it takes for ionic movements to repolarise an area of the membrane and restore the resting potential after an action potential
absolute refractory period
the first millisecond or so after the action potential during which it is impossible to re-stimulate the fibre, the sodium ion channels are completely blocked and the resting potential has not been restored
relative refractory period
a period of several milliseconds after an action potential and the absolute refractory period during which an axon may be re-stimulated, but only by a much stronger stimulus than before
