Nervous and Hormonal Systems

Comparison of main features

Hormonal System Nervous System

Communication is by chemicals called hormones

Communication is by nerve impulses

Transmission is by the blood system Transmission is by neurones

Transmission is relatively slow Transmission is very rapid

Hormones travel to all parts of the body but only target organs respond

Nerve impulses travel to specific parts of the body

Response is widespread Response is localised

Response is slow Response is rapid

Response is often long lasting Response is short-lived

Effect my be permanent and irreversible Effect is temporary and reversible

Chemical Mediators

These are chemicals that are released from cells (typically infected or injured cells) and have an effect on the cells in the immediate vicinity

Two examples:

• Histamine – stored in certain white blood cells and released following injury or in response to an allergen (such as pollen) it causes dilation of small arteries and increased permeability of capillaries. This leads to localised swelling redness and itching

• Prostaglandins -Found in cell membranes and cause dilation of small arteries and increased permeability of capillaries. They are released following injury and affect neurotransmitters and in doing so affect the pain sensation

(c) myrevisionnotes