How nerves and hormones coordinate the human body
The nervous system sends fast electrical signals. Its basic unit is the neuron, which has dendrites to receive signals, a cell body and an axon to pass them on. At rest, the axon membrane is polarised, with the inside negative at about −70 mV, maintained by the sodium–potassium pump. A stimulus opens sodium channels, causing depolarisation and an action potential that travels along the axon; in myelinated fibres it jumps between nodes of Ranvier. At a synapse, neurotransmitters such as acetylcholine carry the signal chemically to the next cell.
The central nervous system includes the brain and spinal cord. The cerebrum controls thinking and voluntary actions, the cerebellum maintains balance, and the medulla controls breathing and heartbeat. Reflex arcs allow quick responses through the spinal cord. The endocrine system uses hormones, slower chemical messengers carried in blood. The hypothalamus controls the pituitary, often called the master gland. Insulin and glucagon from the pancreas regulate blood sugar, thyroxine controls metabolism, and adrenaline prepares the body for emergencies.
Why it matters
This topic explains conditions such as diabetes, caused by problems with insulin, goitre from iodine deficiency, and stroke or Parkinson’s disease affecting the brain. Anaesthetics and many medicines act on nerve signalling. Understanding hormones also explains growth during puberty and the body’s response to stress.
Key terms
- Action potential
- A rapid change in the membrane potential of a neuron that carries a nerve impulse.
- Synapse
- The junction between two neurons where signals are passed by chemical neurotransmitters.
- Hormone
- A chemical messenger secreted by an endocrine gland and carried by blood to target organs.
- Reflex arc
- The nerve pathway that produces a quick, automatic response to a stimulus.