Coordination and the neural system

When you run, your breathing speeds up, your heart beats faster and more blood flows to your muscles, all at once. When you stop, everything slowly returns to normal. Organs working together like this, each supporting the others to keep the body's inside steady (homeostasis), is coordination.

Two systems coordinate the body. The neural system gives quick, point-to-point control, along nerves to exact places. The endocrine system gives slower chemical control through hormones carried in the blood.

The basic unit of the neural system is the neuron, a cell that can detect, receive and pass on stimuli. Simple animals like Hydra have just a loose network of neurons. Insects have a brain and several ganglia (clusters of neurons). Vertebrates have a much more developed system.

The human neural system has two parts:

• The central neural system (CNS): the brain and spinal cord. It processes information and is in control.
• The peripheral neural system (PNS): all the nerves joined to the CNS.

Nerve fibres carry signals in two directions. Put your hand on something hot: the feeling travels from the skin to the CNS along afferent fibres. The CNS decides "move the hand!", and that order travels out from the CNS to the muscles along efferent fibres.

The PNS is divided again. The somatic neural system carries impulses from the CNS to the skeletal muscles (the ones we move at will). The autonomic neural system carries them to the involuntary organs and smooth muscles, and itself has two parts: sympathetic and parasympathetic. The visceral nervous system is the part of the PNS that carries impulses between the CNS and the internal organs, both ways.