Chapter 11A The Human Eye Flashcards
Describe and explain how the pupil of the eye responds to an increase in light intensity [4] (2015/B10 OR)
- The response of the pupil to an increase in light intensity is a reflex action known as pupil reflex.
- Increase in light intensity stimulates photoreceptors on the retina which will generate nerve impulses [1];
- which are transmitted via the optic nerve to the brain and then along the motor neurone to the iris muscles [1];
- the circular muscles of the iris contract while the radial muscles of the iris relax, [1]
- causing the pupil to constrict; reducing the excessive amount of light entering the eye and damaging the retina [1]
Describe how a focused image is produced in the retina of the eye [6] (2015/B10 OR)
- When light reaches the eye, it is refracted by the cornea, the aqueous humor, lens and vitreous humor
- Light falling on retina is detected and nervous impulse transmitted to brain and directly back to ciliary muscles (involuntary action)
- To produce a focused image of near objects on the retina, ciliary muscles contract and suspensory ligaments
slackens; relaxing the pull on the lens, making the lens thicker and more convex, decreasing the focal length. - Light rays from near objects bend more and focus to a point on the fovea of the retina, forming a clear image.
- To produce a focused image of distant objects on the retina, ciliary muscles relax and suspensory ligaments pull taut; the Lens becomes thinner and less convex, increasing the focal length.
- Light rays from the distant object bend less and focus to a point on the fovea of the retina, forming a clear image. [1]
A person was kept in darkness for 30 min. After that light was shined into his eye. The diameter of the pupils of the eye decreased.
Describe how the decrease in the diameter of the pupils was brought about. [3] (2018/B8)
- Increase in light intensity stimulates photoreceptors on the retina
and nerve impulses are generated; - which are transmitted along the optic nerve across a synapse to the relay neurone in the brain and across another synapse to the motor neurone and to the iris muscles;
- Circular muscles of the iris contract while radial muscles of the irisrelax and pupil constricts, bringing about the decrease in the diameter of the pupil to reduce the amount of light entering the eye;
The “white of the eye is known as the? (self)
Sclera
The _____ (yellow spot) is the site where images are focused. It contains the most number of photoreceptors. (self)
Fovea
The ________ contains numerous blood vessels to transport oxygen and nutrients to the eye and remove metabolic waste products. (self)
Choroid
What is the function of the choroid? (self)
It contains numerous blood vessels to transport oxygen and nutrients to the eye and remove metabolic waste products.
The ______ has photoreceptors called rods and cones that detect light and is where images are formed (self)
Retina
The ______ is transparent and dome-shaped to refract light into the eye to focus on the retina. (self)
Cornea
What is the structure and function of the iris? (self)
Iris is a circular sheet of muscles, consisting of circular muscles and radial muscles which work antagonistically to control the size of the pupil and the amount of light entering through the pupil. It contains pigment, which gives the eye its colour.
The _____ is a hole in the center of the iris which allows light to enter. (self)
Pupil
The ______ ____ is the site at which the optic nerve leaves the eye and no photoreceptors are present. The optic nerve transmits nerve impulses via a sensory neuron to the brain. (self)
Blind spot
The _______ _______ found in the ciliary body controls the thickness/curvature of the lens. (self)
Ciliary muscles
The __________ _________ attaches the lens to the ciliary muscles/transmits the force from the ciliary muscles to the lens. (self)
Suspensory ligaments
