Nervous system

The nervous system is the part of an animal that coordinates its voluntary and involuntary actions by transmitting signals to different parts of the body. Nervous systems are found in most multicellular animals but vary greatly in complexity.

At the cellular level, the nervous system is defined by the presence of a special type of cell, called the neuron, also known as a "nerve cell". Neurons have special structures that allow them to send signals rapidly and precisely to other cells. They send these signals in the form of electrochemical waves traveling along thin fibers called axons, which cause chemicals called neurotransmitters to be released at junctions called synapses. A cell that receives a synaptic signal from a neuron may be excited, inhibited, or otherwise modulated. The connections between neurons can form neural circuits and also neural networks that generate an organism's perception of the world and determine its behavior.


1   Substance

In vertebrates, the nervous system consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

1.1   Central nervous system

The central nervous system consists of the brain and `spinal cord`_.

1.2   Peripheral nervous system

The peripheral nervous system consists mainly of nerves that connect the CNS to every other part of the body.

The PNS includes motor neurons, mediating voluntary movement; the autonomic nervous system, comprising the sympathetic nervous system and the parasympathetic nervous system, which regulate involuntary functions, and the enteric nervous system, which functions to control the gastrointestinal system.

Nerves that transmit signals from the brain are called motor nerves, while nerves that transmit information from the body to the CNS are called sensory nerves.

1.2.1   Nerve

A nerve is an enclosed, cable-like bundle of axons (the long, slender projections of neurons) in the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons to peripheral organs.

Pinching a nerve in a limb which makes it go to sleep. That tingly feeling when it comes back is your peripheral nervous system starting back up in that limb (more or less). No harm has been done. What happens is the compression of the nerve causes compression of the vasa nervorum (small blood vessels within the nerve sheath responsible for blood flow to the nerve itself). Once you compromise the blood supply of the nerve, you begin to compromise the nerve itself.

2   Transduction

Transduction is what takes place when many sensors in the body convert physical signals from the environment into encoded neural signals sent to the central nervous system; the process of sensory organs transforming input energy into neural activity.