Sensitivity and Response in Animals

• The receptor is stimulated - we have receptors sensitive to sight, sound, touch etc.
• Info is sent from the receptor to the Central Nervous System(brain and spinal cord) which is a coordinator and determines what response is requires. This info is sent to an effector.
• An effector (usually a muscle) produces a response.
• 

Neurones are nerve cells which carry the information between the receptors, coordinators, and effectors.

Ciliary Muscles - contract or relax to alter the shape of the lens

Cornea - transparent cover that does most of the light refractions

Iris - alters the size of the pupil to control the amount of light entering the eye

Lens - Changes shape to focus light onto the retina

Humour - clear jelly that fills the inside of the eye

Retina - contains light sensitive receptor cells( rods for dim light and black and white, and cones for bright light and colour) which change the light image into electrical impulses

Sclera - tough outer layer

Suspensory Ligaments - Hold the lens in place

Optic Nerve - Carries electrical impulses to the brain

The iris (the coloured part of your eye) controls the amount of light entering your eye by controlling the size of the pupil.

The Iris contains circular and radial muscles. In bright light, the circular muscles contract while the radial muscles relax, and in dim light, the reverse happens - the radial muscles contract while the circular muscles relax.

The eye is protected by:

• Conjunctiva -stops dust and dirt from damaging the cornea
• Eyelids and eyelashes - stops dust and dirt from entering the eye
• Blinking
• Tears -wash dust particles out of the eye ;also contain the enzyme lysozyme that destroys bacteria

The biceps muscle flexes the arm and the triceps muscle extends the arm. The muscles are effectors and the elbow joint is the pivot. Muscles that act in opposite ways are called antagonistic.

The different parts of the nervous system may all be involved when we respond to a stimulus. The simplest type of response is a reflex. Reflexes are rapid, automatic responses which often act to protect us in some way - for example blinking if something gets in your eye.

The pathway that signals travel along during a reflex is called a reflex arc:

stimulus-receptor-sensory neurone-CNS-motor neurone-effector-response

An example of standing on a pin can be used:

stand on a pin-nerve endings-sensory neurone-spinal cord-motor neurone-leg muscles-leg moves.

In heat, the hairs on your arms lie flat against the skin surface, because no air of insulating air is trapped. Blood travels through the surface capillaries and not through the shunt vessel-therefore more blood is close to the skin surface - vasodilation. Sweat is produced to cool the body down.

In cold conditions, hairs rise to trap a layer of insulating air, sweat is no longer produced, and blood is directed through the shunt vessel - vasoconstriction - and not though the surface capillaries.

Hormones are chemicals produced by special glands in the body that release the hormones directly into the blood. Different hormones are:

• Insulin - a hormone that regulates blood glucose level
• Adrenaline - a hormone that prepares that body for action at various times
• Testosterone - a male sex hormone
• Oestrogen - a female sex hormone