Homeostasis and response

Homeostasis in humans

Homeostasis is the regulation of the internal conditions in the body.

Internal conditions which are regulated include: body temperatures, water content of the body and blood glucose levels.

It is important that internal conditions are maintained for the cellular enzymes.

Enzymes control all function of a cell but work best at specific ph levels and temperatures.

Automatic control system detect and respond to changes in the environment.

The automatic control systems include nervous responses in the nervous system and chemical responses in the hormonal system.

All control systems need: receptors, coordination centres, effectors.

Receptors: cells that stimuli (changes) in the internal or external environment.

Coordination centres: areas that receive and process information received from the receptors.

Effectors: muscles or glands that bring about a response to the stimulus.

The human nervous system

The human nervous system has two parts: the central nervous system and the peripheral nervous system.

The central nervous system, includes the brain and spinal cord.

The peripheral nervous system includes nerve cells that carry information to or from the central nervous system.


Receptor, generally a protein, that receives signals for a cell.

Receptors are present in every parts of the body.

Receptors detect the signals and then send them to brain.

The coordination centre

The coordination centre process information received from the receptors around the body.


Effectors include muscles and glands, that produce a response to a detected stimulus.

Nerve cells

Cells of the nervous system, called nerve cells or neurones.

These are three main types of neurone: sensory, relay and motor.

Neuron is the primary working unit of the brain.

Neurons, are specialized to carry electrical impulses from one place to another.

Reflexes action

Reflexes action are automatic and rapid responses which take place before you have time to think. The nerve pathway followed by a reflex action is called a reflex arc. They minimises any damage to the body, such as touching something hot.

The brain

The brain is made of billions of interconnected neurones.

The brain has three parts: the cerebrum, cerebellum and medulla.

Brain is the command center for the human nervous system. The brain is the complex part of human body.

Human brain has approximately 86 billion neurons. The human brain weighs on average three pounds.

Neuroscientists have been able to map the regions of the brain to particular functions by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques.

Investigating brain function and treating brain damage is difficult, due to the complexity and delicacy of the brain.

The Eye

The eye is a sense organ containing receptors sensitive to light intensity and colour. It has many different structures within it.

Light passes through the eyeball to the retina.

Iris Muscles contract or relax to change the size of the pupil. The size of the pupil changes in response to bright or dim light.

Cornea the see-through layer at the front of the eye. Refracts light rays.

White outer layer of the eye is called sclera, which protect the eye from injury.

Optic nerve carries impulses between the eye and the brain to create an image.

To focus on a near object, the lens becomes thicker and refracts light rays strongly.

To focus on a distant object, the lens then becomes thinner and only slightly refracts light rays.