The Nervous System

GCSE Biology Revision   The Nervous System   Reflex Actions   Reflex reactions only contain three types of neurones – Sensory neurons, Motor neurons and Relay neurons. Reflex neurons are used when the skin comes into contact with something harmful. For example, if a finger touches a hot iron, the stimulus would travel to the sensory neurone, to the relay neuron which does not pass to the brain (the Central Nervous System - CNS) to the motor neuron which gets to the effector which is a gland or muscle. This is a reaction done without thinking and is helpful to stop causing harm to the body.   How is this different from a normal reaction?   Synapses In order for the impulse to pass from one neuron to the other, it has to pass the synapse. The impulse travels along the neuron axon, when it reaches the end, the synaptic vesicles secrete neurotransmitters (chemical messengers) across the synapse to the other neuron. The neurotransmitters travel to the dendrite of the next neuron.          

GCSE Biology   The Nervous System   The Eye  

Cornea = Refracts light and protects the eye Iris = Controls how much light enters the pupil Lens = Focuses light onto the retina Axon = The bundle of sensory neurones that carry the impuylses to the brain Rod Cells = Layer of tissue at the back of the eye that contains photoreceptor cells called rods and cones Fovea = Area of the retina with highest concentration of cone cells that provides sharp vision Aqueous Humour = Maintains the pressure in the eye and nourishes the cornea Vitreous Humour = Maintains the shape of the eye and attaches the retina Ciliary Muscles = Help change the shape of the lens in accommodation Sclera = Tough outer layer that extraocular muscles can attach to. Pupil = Hole in the center of the eye that lets light in https://www.goconqr.com/en-GB/p/13852005