1. 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