A neuron is at rest when not sending signals. The resting membrane potential of a neuron is approximately -70millivolt. This indicates that the inside of the neuron is approximately 70millivolt less than the outside. When the neuron is at rest, there is more sodium outside the neuron and more ions of potassium inside the neuron. A graded potential is achieved when the ligand opens a ligand-gated avenue in the dendrites to allow ions to exit or enter the cell. Potassium ions leave the cell, and sodium ions enter the cell until equality is acquired. An action potential is triggered by stimuli of either suprathreshold or threshold superimposed to a neuron. An action potential starts at axon hillock leading to depolarization. Due to the electrical stimulation created during depolarization, voltage-gated sodium ion channels open up. Propagation is the process of sending a signal between action potential and neurotransmitter. During the process, it does not affect or decrease the state of the action potential. In any case, the target tissue receives the same impulse regardless of how far they are from the neuron. Secretion is the process of storing, synthesizing, and producing hormones within the neuron. The products that are generated are mostly functional proteins; sometimes, they can be a wide range of non-protein substances.
There are three mechanisms for removing neurotransmitters in the synaptic left: degradation, re-uptake, and diffusion. It is either removed or inactivated.
Diffusion
This process does not only affect neurotransmitters but all molecules. When all particles are equal, a group of particles will reduce in its order. When having more particles in the synaptic cleft than outside is a highly ordered state, and particles move until concentration equilibrium is attained.
Degradation
During this process, acetylcholinesterase in the synaptic cleft breaks down acetylcholine hence neurotransmitter is inactivated.
Re-uptake
The pre-synaptic neuron takes back serotonin through the transportation of protein into the neuronal membrane. Later, neurotransmitters are either recycled into vesicles or broken down by enzymes.