excitable cells Flashcards
action potential: define the term action potential, list all cell types that are electrically excitable, and define threshold, refractory period, "all or nothing" behavior, depolarisation, repolarisation, hyperpolarisation and saltatory conduction
where do action potentials occur
excitable cells e.g. muscle cells for contraction or B-cells in pancreas for insulin release
properties of action potentials
reliable and rapid
gradation effect on action potential formation
if, after synapse, depolarising graded response is sufficient to reach threshold, action potential will occur in that cell; if hyperpolarising graded response also present, causes inhibition
mechanisms responsible for action potential
time-course voltage vs time, voltage-gated ion channels and ion movement, permeability changes vs time
what does permeability depend on
conformational state of ion channels and population of specific ion channels
how are ion channels opened, inactivated and closed
opened by depolarisation, inactivated by sustained depolarisation, closed by hyperpolarisation
where is action potential generated
axon
passive propagation
decremental; over distance, potential change declines
active propagation
non-decremental allows impulses to be conducted down axon due to local current depolarising adjacent area if reaches threshold
nodes of Ranvier
larger population of Na+ channels and no myelin; if sufficient depolarisation achieved at next node following local current, action potential generated
saltatory conduction
allows rapid velocity of action potential