S-Cool Revision Summary

S-Cool Revision Summary

The nervous and hormonal systems are critical in maintaining careful control of animal life.

Nervous System: uses receptors to gather information about the function of the body and the world outside. It then provides fast response to that information, by acting on glands or muscles.

Hormonal System: made up of a number of glands throughout the body, which secrete hormones directly into the blood stream. These control a wide range of functions within the body. The action of the system is slower than the nervous system but has a more widespread and longer-lasting action.

The body is a complex interconnection of many different systems.

Nervous System

Your nervous system is divided into two parts:

The central nervous system (CNS) is made up of the brain and the spinal cord.

The peripheral nervous system is all the other nerve fibres that connect to it.


Receptors are specialised nerve cells, which are adapted to respond to a stimulus.

Receptors pass electrical impulses to other neurones at tiny junctions called synapses.

These signals allow the nervous system to co-ordinate a response.

What happens at a synapse?

Neurones 'talk' by passing a small amount of a chemical messenger between them across the synapse. This neurotransmitter then sets up the electrical impulse in the second neurone, and so it carries on.

Drugs, poisons and other chemicals can effect synapses by interfering with how the neurotransmitter is dealt.

Relfex Action

A reflex is a very fast, pre-programmed response to a stimulus. They are automatic so that you don't need to think about it beforehand. They act to protect the body.

The stimulus is picked up by a receptor, which transmits an impulse to a sensory neurone.

The Eye

The eye is a great example of a receptor and it also illustrates some reflex arcs too.

Structure of the eye

Hormonal System

The hormonal system is the second important control system in the body. It is closely connected with the nervous system, but is also distinct.

What are Hormones?

Hormones are proteins that act as chemical messengers.

They are secreted - that is they are released from glands into the blood stream. Hormones are then carried around the blood so that they can reach every cell.

Hormones in action

Hormones control a wide variety of things in the body including the amounts of water and glucose.

Hormones also control important functions including the production of eggs and sperm. They effect our growth, repair our cells, produce heat, and so on.

The pituitary gland controls the volume of water in the body by secreting anti-diuretic hormone (ADH) as part of homeostasis. The pituitary gland also controls other glands throughout the body.

Hormones form an essential part of our body's control system.

The Pancreas

The pancreas is a leaf-shaped organ just below the stomach. It has a complex function in the body. It secretes an alkaline solution containing enzymes into the digestive tract. But it also contains cells that secrete hormones into the blood stream.

Two of these are important in controlling the level of glucose in the blood stream.

Why is Glucose Important?

Glucose is the basic fuel for aerobic respiration and is needed by all cells. The heart and brain use glucose as their sole fuel supply.

Too little glucose

When there is too little glucose in the blood, it is detected. The pancreas secretes the hormone glucagon.

This causes the liver to convert glycogen back into glucose.When this gets back into the blood it returns the glucose level to normal.

Too much glucose

When we have too much glucose in our blood, we secrete insulin to store it for later.


Diabetes mellitus is a disease in which the pancreas cannot produce enough insulin.

As a result, a diabetic cannot store glucose as glycogen for later use. So they use up all the glucose in their blood and then go into a coma.

One treatment is to inject insulin after a meal. This stores the extra glucose as glycogen. Therefore they will have enough glucose for later on.

Diabetics have to test their blood regularly to monitor their blood glucose. When it gets too high they inject insulin. If it is too low, they eat something.