Membrane Potential:
all living cells have membrane potential; means polarized electrically; membrane potential; is the separation of opposite electrical charges across the plasma membrane. membrane potential is due to the difference in concentraction and permeability of key ions such as Na, K, Cl and proteins.
action potential:
are brief, rapid, large changes in membrane potential once initiated are conducted through out nerve fibers. action potential starts by change in permeability of cell membrane to ions by trigger event result in decrease membrane potential (depolarization) until reaching threshold potential then rapid large increase in permeability of cell membrane along with NA influx then after reaching peak there will be increase in membrane potential "re-polarization" along k efflux.
In neurons:
- input zones (cell body & dendrities): part where incoming signals from other neurons are received
- trigger zones (axon hillock): part where action potentials are initiated or started
- conducting zone (axon): part that conducts action potentials in undiminishing or undecreasing fashion from trigger zone to branches of axon
- outpout zone (axon terminals): parts that release neurotransmitter that influence other cells then action potential will be transmitted from previous nerve to next one (cell bodies & dendrites) through synapse.
synapse is guard or junction between presynaptic & post-synaptic neurons.
action potential to be transmitted from one nerve ending to other has to be transmitted by way of releasing chemical transmitters.
steps in transmission of action potential at synapse:
- an action potential is propagated to the terminal of presynaptic neuron results in opening of voltage gated Ca channels.
- Ca enters the synaptic knob (presynaptic terminal)
- neurontranmitter is released by exocytosis (triggered by Ca entering) into synaptic cleft from their stores
- after release, neurotransmitter will interact with either presynaptic or post synaptic receptor
- specific ion channels open in the subsynaptic membrane results in initiating a pharmacologic effect or action.
