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4 Cards in this Set

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The central nervous system

A stimulus is a change in an organisms environment. Animals respond to stimuli in order to keep themselves in suitable conditions for survival.



An animal's response is conditioned by the central nervous system. This part of the system is sometimes referred to as the processing centre the central nervous system is connected to the Body by the peripheral nervous system.



The peripheral nervous system consists of sensory neurones that carry impulses from receptors to the central nervous system and motor neurones that carry impulses from the central nervous system to effectors.

receptors and effectors

Muscle cells in a muscle:


Impulses travel along motor neurones and stop by the muscle cells causing muscle cells to contract



Light receptor cells in the retina of the eye:


The lens Focuses light onto receptor cells in the retina. The receptor cell are then stimulated and send impulses along sensory neurones to the brain.



hormone secreting cells in a gland:


An impulse travels along a motor neurone and Stops at the hormone secreting cells in a glands. This triggers the release of the hormone into the bloodstream.

Neurones

Neurons are specially adapted cells that carry an electrical signal when stimulated. They are elongated to make connections between different parts of your body. They have branched endings so that a single neuron can act on many other neurones or effectors.



In motor neurones the cytoplasm forms a long fibre surrounded by a cell membrane called an axon. Some axons are surrounded by a fatty sheath which insulate the neuron from neighbouring cells and increases the speed at which the nerve impulses are transmitted

Synapses

Synapses are the gaps between adjacent neurones. Impulse is transmitted between neurones in the following way:



A nerve impulse reaches the synapse through the sensory neurone.



The impulse triggers the release of chemicals called neurotransmitters into the synapse.



Neurotransmitters diffuse across the synapse and bind with receptor molecules on the membrane of a motor neurone.



the nerve impulse is sent through a motor neurone.



Receptor molecules only bind with certain chemicals to start a nerve impulse in the motor neurone.