Human Eye Flashcards
What do receptors/sensory organs do?
Sensory organs or receptors receive stimuli from the environment and inform the body of any changes in the environment, by generating nerve impulses
List all the parts of the human eye
Cornea, conjunctiva, sclera, iris, pupil, eyelid, eyelashes, tear glands
Retina, choroid, lens, blind spot, optic nerve, ciliary muscle, suspension ligament, aqueous humour and vitreous humour, rectus muscles
What is the cornea and its function?
Transparent refractive layer covering the front of the eye
Refracts light
Connected to the sclera layer (outermost), but clear over the iris to let light through
What is the conjunctiva and its function?
It is a thin transparent membrane covering the sclera that helps lubricate the eye
What is the sclera and its function?
It is a tough white outer layer of connective tissue (white part of eyeball), becomes the cornea (transparent) over the iris
What is the iris and its function?
It consists of circular and radial muscles (antagonistic) of the iris (an effector), controls size of the pupil
What is the pupil and its function?
It is the circular opening of the eye that allows light to enter
What is the eyelid and its function?
It protects the cornea from mechanical damage
Blinking spreads tears and wipes off dust from the cornea
What is the eyelashes and its function?
Helps shield eye from dust particles
What is the tear glands and its function?
It secretes tears (via tear duct) to:
Wash away dust particles
Keep cornea moist
Lubricate conjunctiva to reduce friction when eyelids move
What is the retina and its function?
It is the innermost layer of the eye Contains photoreceptors (rods and cones), which generate nerve impulses which are transmitted towards the brain along the sensory neurones in the optic nerve
What (and where) is the fovea and its function?
Forvea is in the retina, and it contains the highest concentration of photoreceptors
What is the choroid and its function?
It is the middle layer of the eye
It is black in colour and absorbs light, to prevent internal reflection of light inside the eye (why iris seems black)
Contains blood vessels that provide oxygen and glucose to eye
What is the lens and its function?
The lens is elastic and flexible and its curvature can be changed to look at things at different distances
Helps to refract and focus light onto retina
What is the blind spot?
There are no photoreceptors in the area of the retina where the optic nerve leaves the eye, nothing can be seen there (not light sensitive)
What is the optic nerve and its function?
It contains sensory and motor neurones
Sensory: transmits nerve impulses from retina to the brain
Motor: transmits nerve impulses from the brain to effectors (circular and radial muscles of the iris in pupil reflex, or ciliary muscles during accommodation)
What is the ciliary muscle and its function?
Ciliary muscles can contract or relax, to make the suspensory ligament taut or slacken and change the curvature of the lens and focus
What is the suspensory ligament and its function?
It connects the ciliary muscles to the lens, can be taut or slackened to change the curvature of the lens
What are the aqueous humour and vitreous humour and their functions?
Maintains the shape of the eyeball by providing an internal fluid pressure
Aqueous humour: in the pupil (small area)
Vitreous humour: behind the lens (big area)
What is the rectus muscle and its function?
It is attached to the outside of the eyeball and controls its movement
What happens when light rays enter the eye? (Nervous system explanation)
Light rays from an object entering the eye are refracted by the cornea and the lens
The light rays stimulate the photoreceptors on the retina, which generate nerve impulses which travel up the optic nerve to the brain
What are the types of photoreceptors in the retina of the eye and what were their functions?
There are rods and cones.
Rods function in dim light, detecting shape and movement (not colour sensitive)
Cones function in bright light, detecting colour (sensitive to different wavelengths of light). Three pigments in cones are blue, green and red
What is colour blindness caused by?
Mutations in the genes for the pigment proteins
What is the image on the retina like?
Upside down
Laterally inverted
Diminished
Real
Two functions of the eye
Focusing / accommodation on near and far objects
Pupil reflex: controlling light entering the eye and falling onto the retina
What happens when focusing on a near object?
Light rays from a near object are diverging, and are refracted by the cornea through the pupil
Ciliary muscles contract, causing suspensory ligaments to slacken and reducing their pull on the lens, so it becomes thicker and more convex
Photoreceptors on the retina are stimulated and nerve impulses are transmitted along sensory neurones in the optic nerve to the brain, which interprets the information
What happens when focusing on a distant object?
Light rays from a distant object are nearly parallel, and are refracted by the cornea through the pupil
The ciliary muscles relax, causing the suspensory ligaments to become taut and pull on the lens, causing it to become thinner and less convex
Photoreceptors on the retina are stimulated, and nerve impulses are transmitted along sensory neurones in the optic nerve to the brain, which interprets the information
What is pupil reflex and what happens under different light intensities?
The pupil reflex is an involuntary action where the pupils contract or dilate in response to changing light intensities
Under low light intensities, the pupil dilates so more light enters the eye
Under high light intensities, the pupil constricts so less light enters the eye
What is the reflex arc of the pupil reflex?
Photoreceptors in the retina are stimulated, generating nerve impulses that travel along the sensory neurone in the optic nerve to the brain, which interprets the information that is transmitted across synapses to the relay neurone. The brain then generates a nerve impulse that travels across another synapse and along the motor neurone in the optic nerve to the antagonistic muscles of the iris (circular and radial, which are effectors)
How do the effectors of pupil reflex change under light conditions?
Dim: circular relaxes, radial contracts, dilate
Bright: circular contract, radial relax, constrict
Bright circular contract: BCC
