Sensory system: A sensory system is a considered as a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors to recognize the stimuli, neural pathways to carry that stimuli, and parts of the brain involved in sensory perception.

Sensory receptors: These are the structures that are specialized to respond to stimuli, or changes, in their environment by generating electrochemical messages caused by ions crossing the plasma membrane of the neuron.

Gustation: Taste receptor cells on the tongue and back of the mouth respond to chemical substances that bind to them.

Mechanoreceptors: They are responsible for the sensations we describe as touch, pressure, hearing, and equilibrium.

Pain receptors: Also known as Nociceptors respond to very strong stimuli, which usually result from physical or chemical damage to tissues. Instead of being classified in a category of their own, pain receptors are sometimes classified as chemoreceptors, because they often respond to chemicals liberated by damaged tissue, and occasionally as mechanoreceptors, because they are stimulated by physical changes, such as swelling in the damaged tissue.

Sensory adaptation: It is defined as the diminished sensitivity to a stimulus as a consequence of constant exposure to that stimulus.

Sclera: It is often referred as white of the eye, protects and shapes the eyeball and serves as an attachment site for the muscles that move the eye.

Cornea: In front and center of the eye, the transparent cornea bulges slightly outward and provides the window through which light enters the eye. As light passes through the curved surface of the cornea, it is bent toward the light-sensitive surface at the back of the eye. Unlike most tissues in the body, the cornea lacks blood vessels. Although the cornea has no blood supply, it does have pain receptors.

Choroid: The choroid is a layer that contains many blood vessels that supply nutrients and oxygen to the tissues of the eye. The choroid layer also contains the brown pigment melanin, which absorbs light after it strikes the light-sensitive layer. This absorption of light helps prevent the reflection of light within the eye, resulting in sharper vision.

Ciliary body: It is a ring of the tissue primarily muscle, that encircles the lens of the eye, holding it in the place and controlling its shape. As we will see, the shape of the lens is important in focusing light on the light-sensitive layer of the eye.

Iris: The colored portion of the eye that can be seen through the cornea, regulates the amount of the light that enters the eye. It is shaped like a flat doughnut. The doughnut hole is the opening through the center of the iris, called the pupil, through which light enters the eye.

Retina: The innermost layer of the eye is the retina, which contains almost a quarter-billion photoreceptors, the structures that respond to light by generating electrical signals. Retina is similar to film in a camera.

Blind spot: It receives light from an image we are looking at, and converts that light into electrical impulses which are sent through the fibers of the optic nerve to the brain. The optic nerve is mostly considered as the cable of nerve fibers which carries the electrical signals from the retina to the brain for processing. The point of departure of that optic nerve through the retina does not have any rods or cones, and thus produces a "blind spot".

Macula: At the retina's center is an especially critical area called the macula, which enables us to see anything directly in front of us, like words on a page, a person's face, the road ahead or the image on a screen.

Rods: The rods allow us to see in dimly lit rooms and in pale moonlight. By detecting changes in light intensity across the visual field, rods contribute to the perception of movements.

Cones: The cones are responsible for color vision

Fovea: The cones are most concentrated in a small region in the center of the retina called the fovea. Only the fovea contains a sufficient number of cones, about 150,000/mm2, to produce detailed color vision.

Vitreous humor: This fluid helps keep the eyeball from collapsing and holds the thin retina against the wall of the eye.

Aqueous humor: This clear fluid supplies nutrients and oxygen to the cornea and lens and carries away their metabolic wastes. In addition, the aqueous humor creates pressure within the eye, helping to maintain the shape of the eyeball.

Light refraction: In an eye of the right length, light rays are bent into a point of focus on the retina to achieve sharp vision.

Pinna: The part of outer ear visible on the outside of the head consists of a fleshy flap, called the pinna. Shaped like a funnel, the pinna gathers the sound and channels it into the external auditory canal, the canal that leads from the pinna to the ear drum.