It answers to stress by augmenting the heart rate and flow of blood to the muscles. It encompasses quick response and hence concerned with “fight or flight”.
Parasympathetic nervous system, encompass cranial nerves (nerves of brain) and also the lower spinal nerves i.e. nerves of sacral region. Action of this system counteracts the sympathetic actions by increasing digestive secretions and decreasing the heartbeat. It is concerned with “rest and digest”.
It is evident that ANS encompass afferent pathways that includes information from the viscera and brain and hence maintains the homeostasis. It has both sensory and motor neurons to carry the information to and from the brain and spinal cord.
An action potential along the axon is dependent on influx of sodium ions and efflux of potassium ions. The phases of action potential are: rising phase- In the resting state the inside of the neuronal cell is polarized (-70mv) as compared to its outside charge. Therefore, it is polarized.
Excitatory neurotransmitters like aspartate and glutamate released from their pre-synaptic neurons attach to post-synaptic dendrites, sodium channels open up leading to influx of positively charged sodium ion gradually more and more sodium ion channel open up resulting in positive charge inside the cell (+40mv inside cell) and the cell is said to be depolarized.
Falling phase- sodium ion channels are closed and potassium ion channels open up as a result potassium being an intracellular ion moves out through these channels and by this process there is a net loss of positive charge as potassium is positively charged ion.
Myelinated axons prevent the back diffusion of ions to outer space and ensure a fast and rapid conduction of action potentials. Myelinated neurons contains nodes of Ranvier, through this action potential jumps, this is called salutatory conduction.