Eye as a receptor and nervous system

what is a synapse

a junction between two neurones

role of neurotransmitters

• when an electrical impulse travels to the end of the presynaptic neurone

• triggers the release of neurotransmitters

• these travel/diffuse through the synaptic cleft

• bind to the postsynaptic neurone

• triggers new impulse

• impulse=travels one way ONLY

what are neurotransmitters

chemicals that carry signals across the synaptic cleft between neurones

simple reflex arc illustrated by withdrawal of finger from a hot object

• stimulus received (heat)

• receptor detects

• signal sent to CNS which consists of spinal cord and brain via sensory neuron

• impulse crosses sensory neuron to motor neuron

• motor neuron sends signal to effector e.g. muscle in this case to withdraw hand

what is the purpose of the cornea

refracts light as it enters the eye to help focus it

purpose of iris

controls the SIZE of pupil —> how much light enters your eye

• in BRIGHT light —> constricts/gets smaller

• in DARK —> dilate/get bigger to take in more light

purpose of lens

changes shape to focus light on the retina

• NEAR —> thicker

• FAR —> thinner

purpose of retina

contains photoreceptor cells:

• cone cells —> colour and work in bright light

• rod cells —> dim light BUT no colour

converts light into electrical impulses

purpose of optic nerve

carries electrical impulses from retina to brain —> image is processed

what is the eye’s response to distant objects

• ciliary muscles relax

• suspensory ligaments tighten

• lens get thinner

• less bending of light needed

what is the eye’s response to close object

• ciliary muscles contract

• suspensory ligaments relax

• lens is more curved

• more bending of light needed

eye’s response to dim light

• circular muscles contract

• radial relax

• pupils dilate

eye’s response to bright light

• circular muscles relax

• radial muscles contract

• pupils constrict