Sensitivity

• A neurone is a cell that sends electrical signals through the body. A bundle of neurones is a nerve.
• Neurons have a long fibre (axon) to send the electrical impulses down
• Sensory neurones carry impulses from sense organs to the CNS
• Relay neurones are found inside the CNS and connect sensory and motor neurones.
• Motor neurones carry impulses from the CNS to effectors (muscles or glands)
• A voluntary response begins in sensory neurones and are processed in the brain before releasing an outward signal to the effectors.
• Involuntary responses are faster and do not reach the brain. They are essential to survival and are rapid.
• The synapse is the junction between two neurons where a nerve impulse is transferred.
• The cornea is a transparent lens that refracts light as it enter the eye
• the iris controls how much light enters the pupil
• the lens are a transparent disc that can change shape to focus light onto the retina
• the optic nerve is a sensory neurone that carries impulses between the eye and the brain
• the pupil is a hole that allows light to enter the eye
• accommodation is when the eye muscles contract and extend to focus on closer and further distances through the lens.
• In bright light, the pupil contracts to restrict the amount of light entering the eye in order to protect the cones and rods from burning
• A hormone is a chemical substance that is produced by a gland or organ and is carried by the blood. it alters the activity of one or more specific target organs.
• a nerve impulse is an electrical signal that passes along neurones.
• The nervous system consists of two main parts; the central nervous system (CNS) which includes the brain and spinal cord and the peripheral nervous system (PNS).