Sensory System

Sensory System TABLE OF CONTENTS Lessons 1. Intro to the Sensory System Go 2. Vision Go 3. Hearing Go 4. Smell, Taste, and General Senses Go 5. Sensory System Diseases and Disorders Go TABLE OF CONTENTS

Lesson 1– Sensory System vision hearing smell taste touch Receives stimuli and sends impulses to the brain to be interpreted. Recognizes changes in the environment Sensory System The sensory system refers to the special senses associated with vision, hearing, smell, taste, and touch. It consists of receptors in specialized cells and organs. The sensory system receives stimuli and sends the impulses to the brain to be interpreted. It performs the function of recognizing changes in the internal and external environment to allow the body to react.

Lesson 2– Vision and the Eye Eye carries information to the brain where it is translated into vision, or sight. Vision is considered to be the most important sense. Vision and the Eye Vision is one of the five special senses. The eye is the organ that controls this sense. Like all special senses, it receives stimuli and sends the impulses to the brain to be interpreted. After receiving light rays, the eye carries the information to the brain where it is translated into vision, or sight. Vision is considered to be the most important sense. About 90% of the information about a person’s surroundings reaches the brain through the eyes.

Lesson 2– Layers of the Eye Sclera – outer eye Choroid coat – middle eye Retina – inner eye Layers of the Eye The three main layers of the eye are the sclera (outermost), choroid coat (middle), and retina (innermost). The sclera is made of tough connective tissue and is often referred to as the “white” of the eye. It gives shape to the eye. Muscles attached to the sclera help the eye move. The cornea is a clear, circular part at the front of the sclera that allows light rays to enter. The choroid coat contains many blood vessels that nourish the eyes. The ciliary muscles in this layer help to focus the eyes. The retina contains many layers of nerve cells that transmit the impulses from the light rays to the optic nerve. Two special cells in this layer are cones and rods. Cones sense color and are mainly used for vision in bright light. Rods are used for vision in the dark or dim light.

Lesson 2– Other Parts of the Eye Iris Pupil Lens Aqueous humor Vitreous humor Other Parts of the Eye The iris is the colored portion of the eye, located behind the cornea on the front of the choroid coat. The pupil is the opening in the center of the iris. Two muscles in the iris control the size of the pupil and how much light enters the eye. The lens is a clear, circular structure located behind the pupil. It refracts, or bends, the light rays so they focus on the retina. The aqueous humor is a clear, watery fluid that fills the space between the cornea and the iris. The vitreous humor is the jellylike substance that fills the area behind the lens. Both the aqueous humor and vitreous humor help give shape to the eyeball and refract light rays.

Lesson 2– Pathway of Light through the Eye In order: Cornea Aqueous humor Pupil Lens Vitreous humor Pathway of Light through the Eye The pathway of light goes through these parts of the eye in order: Cornea Aqueous humor Pupil Lens Vitreous humor As the light passes through these parts, it is refracted to focus on the retina. Then the cones and rods pick up the stimulus and pass it on to the optic nerve, which sends it to the brain to be interpreted.

Lesson 2– Protection of the Eye Partly enclosed in a bony socket in the skull. Lacrimal glands Eyelids and eyelashes help keep out foreign materials. Conjunctiva Protection of the Eye The eye is well protected. It is partly enclosed in a bony socket in the skull. Tears produced in the lacrimal glands constantly clean the eye and keep it moist. The tears flow across the eye and drain through the lacrimal duct into the nasal cavity. Eyelids and eyelashes help keep out foreign materials. Conjunctiva, a mucous membrane, lines the eyelids and covers the front of the eye to provide added protection and moisture.

Lesson 3– Hearing and the Ear Controls hearing and sense of balance Ear carries sound waves to the brain Three main sections: Outer ear Middle ear Inner ear Hearing and the Ear Hearing is one of the five special senses. The ear is the organ that controls this sense as well as the sense of balance. Like all special senses, it receives stimuli and sends the impulses to the brain to be interpreted. After receiving sound waves, the ear carries the information to the brain where it is translated into hearing. The ear is divided into three main sections: the outer ear, middle ear, and inner ear.

Lesson 3– Outer Ear Pinna Auditory canal Tympanic membrane Outer Ear The pinna, or auricle, is the visible part of the outer ear. It leads to the auditory canal, also known as the external auditory meatus. This canal contains special glands that secrete wax to protect the ear. Sound waves are collected and channeled through the canal to the tympanic membrane, or eardrum. This membrane vibrates when sound waves hit it, and it separates the outer ear from the middle ear.

Lesson 3– Middle Ear Small chamber in the temporal bone Ossicles Eustachian tube Middle Ear The middle ear is a small chamber in the temporal bone. It contains three small bones called ossicles. They receive sound from the vibrations of the tympanic membrane and in turn transmit the sound waves to the inner ear. The eustachian tube connects the middle ear to the pharynx, or throat. This tube allows air to enter the middle ear and helps equalize pressure on both sides of the tympanic membrane.

Lesson 3– Inner Ear Cochlea Semicircular canals Inner Ear The inner ear is the most complex section of the ear. It contains the cochlea, which is shaped like a snail shell. Inside the cochlea, delicate, hair-like cells make up the organ of Corti. The cells pick up sound waves and pass them on to the auditory nerve, which sends the impulse to the brain to be interpreted. Three semicircular canals are also part of the inner ear. They contain fluid and delicate, hair-like cells that bend when the liquid moves with head and body movements. These impulses are sent to the cerebellum to help maintain balance.

Lesson 4– Sense of Smell The nose is the organ that controls smell. Olfactory receptors Cilia The sense of smell is closely related to the sense of taste. Sense of Smell Smell is one of the five special senses. The nose is the organ that controls this sense. Olfactory receptors at the top of the nasal cavity make the sense of smell possible. They are nerve cells covered with tiny hairs called cilia. These cells receive stimuli from gases in the air. Then the impulses are carried by the olfactory nerve to the brain, where they are translated into smell. The sense of smell is closely related to the sense of taste, although it is more sensitive than taste.

Lesson 4– Slide Title Taste buds The receptors in the taste buds send a signal to the brain to detect the flavor of the food. The four basic tastes: Sweet Salty Sour Bitter Taste and the Tongue Taste is one of the five special senses. The tongue is the organ that controls this sense. It is a mass of muscle tissue that contains projections called papillae, which contain “taste buds.” When food is moistened in fluid or saliva, taste buds are activated. The receptors in the taste buds send a signal to the brain to detect the flavor of the food. The four basic tastes and their regions of the tongue are: Sweet tastes at the tip. Salty tastes near the tip. Sour tastes at the sides. Bitter tastes at the back. The sense of smell also influences taste.

Lesson 4– General Senses Touch Temperature Pressure Pain General sense receptors are located throughout the body in the skin and connective tissue. Each receptor perceives only one type of feeling. General Senses General senses are involved in feeling touch, temperature, pressure, and pain. General sense receptors are located throughout the body in the skin and connective tissue. Each receptor perceives only one type of feeling. For example, receptors in the skin that detect heat are distinct from those that detect cold. Messages from these receptors allow the body to respond to the environment and avoid possible harm.

Lesson 5– Diseases and Disorders of the Sensory System Conjunctivitis Cataract Hearing Loss Otitis Media Common Cold Diseases and Disorders of the Sensory System Conjunctivitis is also called “pink eye.” It is an inflammation of the eyelid caused by a bacteria or virus, and it is extremely infectious. Symptoms include reddening of the eyelids and sclera. In addition, pus may form and lead to the closing of the eye. Treatment involves antibiotics. Cataract is a condition where the lens of the eye gradually becomes cloudy, which causes blurred or partial vision. The cause is not known. If left untreated, cataracts may lead to blindness. Treatment involves surgical replacement of the lens. Hearing loss or deafness has two classifications, conductive or sensory. Conductive hearing loss occurs when sound waves are not carried to the inner ear. It is caused by a ruptured tympanic membrane or blockage in the ear, such as from wax, a foreign body, or an infection. Treatment involves removing the cause. Sensory hearing loss occurs when the inner ear or auditory nerve is damaged. Usually this type of hearing loss cannot be corrected. Otitis media is an infection of the middle ear caused by a bacteria or virus. It is common in young children and often follows a sore throat. Symptoms include pressure or pain in the ear and fever. If left untreated, otitus media may lead to hearing loss. Treatment involves antibiotics and possibly inserting tubes to relieve the pressure and fluid in the ear. A cold is a respiratory infection. It may be caused by 1 of more than 200 viruses that are highly contagious. Symptoms may include sneezing, runny nose, sore throat, congestion, and cough. The symptoms typically last for one to two weeks. There is no cure for a cold. Treatment involves rest and medications to relieve symptoms.