Special Senses

Special Senses

• Allows the human body to react to environment
• Allows body to see, taste, smell, touch and maintain balance
• Nerves carry sensory messages to the brain, brain interprets and responds to the message

General Senses

• various senses scattered throughout the body in various regions
• heat, cold, pain, nausea, hunger, thirst, and pressure or deep touch

Common Sense

• Intuition
• Just knowing how to do a certain task
• What are we born knowing?
• Instinct

Eye

• controls special sense of sight
• Receives light rays and transmits the rays to the optic nerve, which carries the rays to the brain where they are interpreted as vision or sight

Vision

• Good vision: adds to quality of life & contributes to one's independence
• Challenged vision: impacts our sense of well-being and independence. More than 11 million Americans have a vision problem not improved with corrective lenses.

Protection of the Eye

• Partially enclosed in a bony socket of the skull
• Eye lids and lashes help keep out dirt and pathogens
• Lacrimal glands produce tears

Tears

• Produced by lacrimal glands
• Constantly moisten and cleanse the eye
• Tears flow across eye and drain through the Lacrimal duct into the nasal cavity

Conjunctiva

• mucous membrane that protects the eye
• Lines the eyelids and covers the front of the eye
• Provides protection and lubrication

Sclera

• Outermost layer
• Tough CT
• white of the eye
• maintains shape of the eye
• Extrensic muscles, responsible for moving the eye. Attached to sclera.
• Contains the cornea: allows light rays to enter

Choroid Coat

• middle layer of eye
• dark blue vascular layer of the eye between the sclera and retina
• has many blood vessels

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• Pupil: hole in the choroid coat & allows light rays to enter
• Iris: special part of choroid coat, colored portion of eye, a muscle that controls size of pupil & regluates amount of light entering the eye

Retina

• Innermost layer of the eye
• Made of many layers of nerve cells that transmit the light impulses to the optic nerve
• delicate membrane

2 special light-sensing cells in the retina

• Cones: used for light vision, sensitive to color, 3 million, we see about 7 million shades of color
• Rods: provide black and white images
• About 100 million rods

Lens

• circular structure located behind the pupil
• suspended in position by ligaments
• Refracts or bends light rays so the rays will focus on the retina

Aqueous humor

• Clear watery fluid
• fills space between the cornea and iris
• helps maintain the forward curvature of the wyeball
• bends or refracts light rays

Vitreous humor

• jelly like substance
• fills the area behind the lense
• helps maintain shape of the eyeball
• bends and refracts light rays
• series of muscles located in the eye provide for eye movement

Refraction of Light Rays

• When light enters the eye they pass through a series of parts that bend or refract the rays
• Allows the rays to focus on the retina
• Rays pass through the cornea, the aqueous humor, the pupil, the lense, and the vitreous humor to focus on the retina

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• In the retina, the rays or images are picked up by the rods and cones, changes into nerve impulses, and trasmitted by the optic nerves to occipital lobe of cerebrum, where site is interpreted
• If rays are not refracted correctly by the various parts, vision can be distorted or blurred.