In: Biology
Describe the sequence of steps for an action potential of one neuronal cell leads to the action potential in a postsynaptic cell.
A resting neuron is in polarised state, it means there is a
charge difference across the membrane of a neuron. Positive charge
is more outside and negative charge is more inside. This charge
difference generates a membrane potential known as the resting
membrane potential. The resting membrane potential of a neuron is
-70mV. This charge difference is mainly generated by the
sodium-potassium ATPase. Sodium-potassium ATPase pumps 3 Na+ ions
outside and takes in 2 K+ ions. So, a resting neuron has more K+
ions inside and more Na+ ions outside.
Membrane of a neuron also has sodium and potassium voltage gated
channels due to these channels depolarisation and repolarisation
takes place. An action potential or a wave of depolarisation is
generated when opening of voltage gated channels cause huge influx
of Na+ ions. Voltage gated Na+ channels open when the membrane
potential reaches threshold potential. Influx of Na+
ions via voltage gated sodium channels first depolarises the
membrane near the axon hillock and from the axon hillock wave of
depolarisation moves towards the axon terminal. At the axon
terminal neurotransmitters are stored in the synaptic vesicles.
When the action potential reaches the axon terminals it opens the
voltage gated calcium channels and causes influx of calcium ions.
Calcium ions cause exocytosis of the neurotransmitter into the
synaptic cleft. Released neurotransmitter then binds to the
post-synaptic neuron and generates action potential.