Sensory System Health Science I Michelle Garon, RN

Our Senses Special senses allow the human body to react to the environment Body is able to see, to hear, to taste, to smell, and to touch Senses occur because the body has structures that receive the sensation, nerves that carry the sensory message to the brain that can interpret and respond to the message (1.sensory structures---2. nerves carry message to brain---3. Brain reads message & responds)

The Eye Protected by the orbital socket of the skull and by the eyebrows, eyelids, and eyelashes. Moved by muscles Continuously bathed in fluid by tears secreted by lacrimal glands. The tears flow across the eye into the nasal cavity, causing an increase in fluids.

The Eye Cont … Tears cleanse and moisten the eyes on a continuous basis 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 Conjunctiva is the mucous membrane that protects the eye. It lines the eyelids and covers the front of the eye.

The Eye Cont … Three main layers: 1. Sclera Outermost layer Tough connective tissue Frequently referred to as the white of the eye Maintains the shape of the eye Extrinsic muscles, responsible for moving the eye within the socket, are attached to the outside of the sclera Cornea: a circular transparent (no blood vessels) part on the front of the sclera that allows light rays to enter the eye. Sometimes referred to as the “ window ” of the eye. Since there are no blood vessels the corneal cells are fed by the movement of lymph through interstitial, or lymph spaces

The Eye Cont … 2. Choroid Middle layer of the eye Interlaced with many blood vessels that nourish the eyes Pupil: Hole in the front of the choroids coat, Allows light rays to enter Iris Special part of the choroids coat Colored portion of the eye It is two sets of antagonistic smooth muscles, sphincter and dilator pupillae. Called intrinsic muscles and help the iris to control amounts of light entering the pupil. When the eye is focused on a close object or stimulated by bright light, the sphincter pupillae muscle contracts, thus making the pupil smaller

The Eye Cont … 3. Retina Innermost layer of the eye Made of many layers of nerve cells that transmit the light impulses to the optic nerve Two special types of cells in retina: Rods which are used for dark or dim vision. Cones: used mainly for light vision, are sensitive to color, and located in a depression on the back surface of the retina called the fovea centralis. Optic Disc is a pale disc that is slightly to the side of Fovea. Nerve fibers from the retina gather here to form the nerve.

Other Special structures of the eye Lens Crystalline circular structure located directly behind the pupil Suspended in position by ligaments Refracts or bends light rays so the rays will focus on the retina Another function of lens = Accommodation (adjustment for variations in distance) Located between the anterior and posterior chambers.

Other Special structures of the eye Cont … Aqueous Humor Anterior chamber is filled with watery fluid called aqueous humor. Helps maintain the forward curvature of the eyeball Bends or refracts light rays

Other Special structures of the eye Cont … Vitreous humor Transparent jellylike substance that fills the posterior chamber (area behind the lens) Helps maintain the shape of the eyeball Also bends or refracts light rays

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 lens, and the vitreous humor to focus on the retina In the retina, the rays or image are picked up by the rods and cones, changed into nerve impulses and transmitted by the optic nerves to occipital lobe of cerebrum where sight is interpreted If rays are not refracted correctly by the various parts, vision can be distorted or blurred.

Pathway of Vision 1.Images of light 2.Cornea 3.Pupil 4.Lens 5.Retina 6.Optic Nerve 7.Optic chiasm (where 2 optic nerves cross) 8.Optic Tracts 9.Occipital Lobe

THE EAR

The Ear Organ that controls hearing and balance Transmits impulses from sounds waves to the auditory nerve (vestibulocochlear), which carries the impulses to the brain for interpretation as hearing. Divided into three main sections: the outer, middle, and inner ear.

The Outer Ear Contains the visible part of the ear called the pinna or auricle. This part collects the sound waves and directs them into the auditory canal. Auditory canal leads to the eardrum or tympanic membrane, which separates the outer and middle ear. Sebaceous glands line the auditory canal and secrete cerumen. This is a wax like substance that protects the ear.

The Middle Ear Small space or cavity in the temporal bone. It connects with the pharynx by means of a tube called the Eustachian tube. This allows air to enter the middle ear and helps equalize air pressure on both sides Contains three small bones (ossicles): malleus (hammer) incus (anvil) and Stapes (stirrup)

The Inner Ear (Cochlea) Most complex portion of the ear Contains many channels Oval window- membrane that separates it from the middle ear Vestibule- First section that acts at the entrance to the two other parts of the inner ear. Organ of Corti (receptor for hearing) is located in cochlea

Pathway of Hearing Sound waves Pinna/outer ear Auditory canal Tympanic membrane Middle ear (hammer, anvil, stirrup) Cochlea Cochlear nerve Temporal lobe of brain

The Nose Determined by olfactory receptors in the upper part of the nasal cavity. This area is about the size of a postage stamp called the olfactory epithelium, which is plentiful supply of nerve cells with specialized receptors. The receptors send signals to the adjoining olfactory bulbs, and extension of the brain. The stimulus is transmitted by the olfactory nerve to the limbic system, thalamus, and frontal cortex The sense of smell is closely related to the sense of taste Smells account for 90% of what we think of taste

The Tongue It is a mass of muscle tissue which has structures called papillae. Our taste is dependent upon taste receptors. Located on the papillae are taste buds, which are stimulated by the flavors of foods (sweet, salty, sour, and bitter). The receptors in the taste buds send impulses through three cranial nerves to the cerebral cortex for interpretation

General Senses General sense receptors for pressure, heat, cold, touch, and pain are located through-out the body Messages from these receptors allow the human body to respond to its environment Help the body react to conditions that could cause injury.

Disorders of the Eye Conjunctivitis- inflammation of the conjunctival membranes in front of the eye. Commonly known as “ pink eye ” Usually starts with one eye and rapidly spread to the other by a wash cloth or hand. Since it is highly contagious, other family members should not share the same washcloths or towels with the infected person. Good hand-washing should be maintained.

Disorders of the Eye Glaucoma is the condition of excessive intraocular pressure resulting in the destruction of retina and atrophy of the optic nerve. It is measured with an instrument called an tonometer. Treatment involves miotic drugs which constrict the pupil and thus increases the outflow of aqueous humor, or drugs which reduce the amount of aqueous humor produced by the eye. Laser surgery or incisional surgery helps to increase the flow of the aqueous humor. All treatments are focused on lowering the intraocular pressure.

Disorders of the Eye Cataracts is a condition where the lens of the eye gradually becomes cloudy. Usually occurs in people over 70 years of age. Condition causes a painless, gradual blurring and loss of vision. Pupil turns from black to milky white. People may complain of seeing halos. Cataracts are treated by the surgical removal of the lens and postoperative substitution of contact lens or eyeglasses.

Disorders of the Eye Macular Degeneration- sometimes occurs with aging. The macula is located in the center of the retina and is responsible for sharp central vision. Symptoms include a dimming or distortation of vision. Two types: dry- gradual thinning of the retina. Wet- leakage develops under the retina causing blister formation which may involve blood vessels. Laser tx may be used with this type.

Disorders of the Eye Detached retina also occurs with aging or could be from an accident in younger ages. The vitreous fluid contracts as it ages and pulls on the retina, causing a tear. Peripheral vision is lost then central vision. Laser treatment can prevent further damage if caught early. Sty (hordeolum) is a tiny abscess at the base of an eyelash. The eye is red, painful and swollen caused by an inflammation of the tiny sebaceous glands. Treatment is warm, wet compresses to relieve pain and promote drainage.

Vision Defects Presbyopia- a condition in which the lenses lose their elasticity resulting in a decrease in ability to focus on close objects. It usually occurs after age forty. Hyperopia- (far sightedness) is a condition in which the focal point is beyond the retina because the eyeball is shorter than normal. Myopia (near sightedness) is a condition in which the focal point is in front of the retina, because the eyeball is elongated. Amblyopia is a reduction, or dimness, of vision.

Vision Defects Astigmatism is a condition in which there is an irregular curvature of the cornea or lens, which causes blurred vision and possible eyestrain. Diplopia is blurred vision. Strabismus ( “ Crossed Eyes ” ) is a condition in which the muscles in the eye do not coordinate their action.

Disorders of the Ear Otitis Media- infection of the middle ear. Otosclerosis is an inherited disorder in which the bone stapes if the middle ear first become sponge and then harden. A common cause of deafness in young adults. Tinnitus is a sensation of ringing or buzzing that is perceived in the ear in the absence of an actual sound stimulus. Causes may be impacted wax, otitis media, otosclerosis, loud noise, blockage of normal blood supply to the cochlea, or the effects of various drugs like the salicylates.

Disorders of the Ear Presbycusis is a condition which causes deafness due to the aging process. Can be helped with the use of hearing aids. Meniere ’ s Disease is a condition which affects the semicircular canals of the inner ear, causing marked vertigo (dizziness).

Disorders of the nose Rhinitis is an inflammation of the lining of the nose which may cause nasal congestion, nasal drainage, sneezing, or itching. Nasal Polyps are growths in the nasal cavity associated with rhinitis. Deviated Nasal Septum is a condition in which there is a bend in the cartilage structure of the septum.

The End!!!