Special Senses

Pg. 115

Special Senses

Special senses are those organs and receptors that are associated with touch (sensory receptors), vision, hearing, equilibrium, smell, and taste

Sight, hearing, smelling are distance senses. They bring in information from far away

Touch and taste can only reveal information about things you come in direct contact with.

These special senses receive stimuli from the sensory receptors and transmit these impulses to the brain for interpretation

Sensory Receptors Sensory receptors are structures that are stimulated by

changes in the environment. Sensory receptors for pain, touch, temperature, and

pressure are found all over the body in the skin, connective tissue, and muscle.

Special sensory receptors including the taste buds of tongue, special cells in nose, retina of eye, special cells in inner ear (organ of Corti)

When a sense organ is stimulated, the impulse travels along nerve pathways to the brain where it is registered. Sensation actually takes place in brain but is mentally referred back to the sense organ. This is called projection of the sensation.

Sensory receptors become less sensitive with age (decrease in number of receptors make it difficult for elderly to feel pain or cope with changes in temperature)

Sight, Smell, Taste, Sound, Equilibrium(pg. 114)

Pgs. 117 and 119

The Eye

Human eye is a tender sphere about 1 inch in diameter.

Protected by orbital socket of skull, eyebrows, eyelids, and eyelashes

When we blink the eyes are bathed in fluid by tears secreted from lacrimal glands (underside of upper lid of each eye with duct at inner corner of each eye *also connected to nasal lacrimal duct*) Lacrimal secretions contain lysozymes which help

combat bacterial infections. Tears cleanse and moisten the eyes on a continuous basis

The Eye

Canthus is the angle where the upper and lower eyelids meet

Conjunctiva is the thin membrane that lines the eyelids and covers part of the eye. It secretes mucus that helps lubricate the eye

Location of eye allows for superimposition of images from each eye allowing us to see stereoscopically in three dimensions (length, width, and depth)

Wall of eye is made of three concentric layers, or coats (sclera, choroid, retina)

The External View of Eye (pg. 116)

The Internal View of Eye (pg. 116)

Sclera

Outer layer, or white of the eye Tough, unyielding, fibrous capsule that

maintains the shape of the eye and protects the delicate structures within

Muscles responsible for moving the eye within the orbital socket are attached to the outside of the sclera Muscles are referred to as extrinstic

muscles

Extrinsic Eye Muscles (pg. 116)

Cornea

Referred to as the “window” of the eye Transparent front of sclera to permit

passage of light rays Cornea consists of 5 layers of flat cells Possesses pain and touch receptors so

it’s sensitive to foreign particles No blood vessels so transplantation

can occur without rejection

Choroid Coat Middle layer of the eye Contains blood vessels to nourish the eye

and a non-reflective pigment rendering it dark and opaque Pigment darkens eye chamber preventing

light reflection within eye In front, choroid coat has a circular opening

called the pupil Colored, muscular layer surrounds the

pupil called the iris (may be blue, green, gray, brown, or black…related to number and size of melanin pigments cells in the iris

Intrinsic Eye Muscles

Within iris are two sets of antagonistic smooth muscles, the sphincter and dilator pupillae. These intrinsic muscles help iris to control amount of light entering the pupil. Sphincter muscles contract making

pupil smaller Dilator muscle contracts making

pupil larger

Lens Lens is crystalline structure located

behind iris and pupil Elastic, disc-shaped structure with

anterior and posterior convex surfaces that form a biconvex lens (posterior more curved than anterior) Curvature of each structure alters with age

Lens is held in place behind the pupil by suspensory ligaments from ciliary body of choroid layer

Retina

Innermost, or third coat of the eye Located between posterior chamber and

choroid coat Does not extend around the front portion of eye Light-sensitive layer that light rays from an

object form an image Contains pigments and specialized cells known

as rods and cones which are sensitive to light Rod cells are sensitive to dim light and cones

sensitive to bright light Cones also responsible for color vision Three varieties of cone cells and each type is

sensitive to a special color

Optic Disc

Part of retina where the nerve fibers enter the optic nerve to go to the brain is called the optic disc

Contains no rods or cones Unable to convert images into nerve

impulses Aka blind spot

Fovea

Focus point for light rays for best visual acuity

Composed mostly of cone cells which specialize in bright light

Pathway of Vision

Images in Light cornea pupil lens (where the light rays are bent or refracted) retina (rods and cones pick up the stimulus) optic nerve occipital lobe (cerebrum) of the brain for interpretation

Pathway of Vision (pg. 118)

Visual Acuity Clearness/sharpness of visual

perception recorded as two numbers First number represents the

distance in feet between the subject and the test chart (Snellen Chart)

Second number represents the number of feet a person with normal acuity would stand to see clearly

20/20 is considered normal acuity 20/200 or worse is considered

legally blind

Homeostatic Imbalances of Eye (pg. 118)

Myopia: nearsighted (focus falls short of retina) Hyperopia: farsighted (focus falls behind retina) Astigmatism: focused image is distorted (cornea is not

spherical) Color blindness: congenital lack of one or more types of

cones; sex-linked Conjunctivitis: pink eye (inflammation of conjunctival

membranes) Glaucoma: destruction of retina and atrophy of optic nerve

(excessive intraocular pressure) Cataract: gradual blurring and loss of vision (lens becomes

cloudy) Macular degeneration: dimming or distortion of vision that

is most obvious when reading (gradual thinning of retina) Detached retina: loss of peripheral vision and then loss of

central vision (tear in retina) Sty: eye is red, swollen, and painful (tiny abscess at base of

eyelash caused by inflammation of sebaceous gland of eyelid)

Strabismus: crossed eyes (muscles of eyeball do not coordinate their action)

Pgs. 121 and 123

The Ear

Adapted to pick up sounds waves and send these impulses to the auditory center of the brain Auditory center is located in the temporal area just

above the ears Receptor for hearing is the delicate organ of Corti which

is located within the cochlea of the inner ear Also involved with equilibrium

Receptors in inner ear send message to cerebellum in the brain about head position, to help maintain balance

Other receptors in our eyes and around our joints pick up information and it’s processed in the cerebellum and cerebral cortex to enable the body to cope with changes in equilibrium

Three parts: external ear, middle ear, and inner ear

The Ear (pg. 120)

Outer/External Ear

Auricle/Pinna: the flap that funnels sound waves helix=rim lobule=lobe

External auditory meatus: opening to auditory canal; lined with sebaceous or ceruminous glands that secrete a wax-like or oily substance called cerumen which protects the ear

External auditory canal: short, narrow chamber extends from auricle to tympanic membrane

Tympanic membrane/Eardrum: stretches across canal; vibrates in response to sound waves and transmits them to middle ear

Middle Ear

Cavity in the temporal bone Connects with pharynx (throat) by

means of the eustachian tube Tube serves to equalize air pressure in

middle ear with that of outside atmosphere

Chain of three tiny bones: malleus (hammer), incus (anvil), and stapes (stirrups) Transmit sound waves from eardrum to

inner ear by vibration

Inner Ear Labyrinth: hollowed out structure of inner ear Vestibule: central egg-shaped cavity of labyrinth Oval window: separates middle ear from inner ear;

located just under the base of the stapes; vibrations reach the inner ear through this structure

Cochlea: snail-shaped structure where sound vibrations are converted into nerve impulses Organ of Corti: pick up nerve impulses and transmit them

through auditory nerve to the hearing center of the cerebrum Semicircular Canals: three canals that contains a liquid, and

delicate hairlike cells that bend when the liquid is set in motion by head and body movement; these impulses are sent to the cerebellum, helping to maintain body balance or equilibrium (NOTHING to do with the sense of hearing)

Pathway of Hearing

Sound waves pinna, or outer ear auditory canal tympanic membrane ear ossicles (hammer, anvil and stirrup stimulate the receptors in the cochlea) cochlear nerve (part of vestibulocochlear nerve) temporal lobe of the brain for interpretation

Pathway of Hearing (pg. 122)

Pathway of Equilibrium

Movement of head equilibrium receptors in the semicircular and vestibule areas of the inner ear vestibular nerve (part of vestibulocochlear nerve) cerebellum of brain for interpretation

Loud Noise and Hearing Loss

If the delicate hair cells in the organ of Corti become overstimulated, they will become damaged

When the same sound keeps reaching the ears, the auditory receptors adapt to the sound and we do not hear it

Sound is measured in decibels (dB). The scale runs from the faintest sound the human ear can hear at 10 dB to over 165 dB.

Homeostatic Imbalances of Ear (pg. 122)

Oititis media: infection of the middle ear; causes earache Treatment--Myringotomy: opening made in tympanic

membrane…tubes may be placed in the ear to allow fluids to drain off)

Otosclerosis: stapes bone of middle ear becomes spongelike and then hardens so stapes becomes immovable; common cause of deafness in young adults

Meniere’s Disease: affects semicircular canals of inner ear, causing vertigo (dizziness)

Conductive hearing loss: sounds of inner ear blocked by earwax or fluid in middle ear

Sensorineural damage: damage to parts of inner ear or auditory nerve resulting in partial or complete deafness

Pg. 125

The Nose

Human nose can detect about 10,000 different smells

Smells account for about 90% of what we think of as taste

Sense of smell can alert us to environmental dangers

Olfactory Sense

Sensors responsible for smell are located in dime-sized area called the olfactory region, on the top side of each nasal cavity Sensors called olfactory receptor cells (neurons) When nasal cavity becomes congested with

mucus from a cold, the olfactory receptors are covered or partially blocked so sense of smell affected

Olfactory hairs extend from these neurons into the nasal cavity, where they are covered by a thin, protective layer of mucus

Olfactory Sense

When you inhale an odor, the chemicals that caused the odor dissolve in the mucous layer surrounding the olfactory hairs

This dissolving action stimulates the olfactory receptor cells, which send impulses through the olfactory filaments that make up the olfactory nerve

Olfactory nerve sends impulses to the olfactory cortex of the brain

Nerve pathway between the nose and the brain travels through limbic system, the part of the brain responsible for emotion Smell may trigger positive or negative emotion because

we have associated a particular experience with that scent

Nasal Cavity (pg. 124)

Homeostatic Imbalances of Nose

Rhinitis: inflammation of mucous membranes that line the nasal passage; most frequent cause is common cold, but other causes include infection, allergies, strong chemical odors, and certain illegal drugs Releases histamines that trigger a reaction that produces nasal

congestion and drainage Treatment is taking antihistamines to curb activity of histamines

Deviated septum: large shift in position of septum away from the center; can be surgically repaired Caused by injury or from birth

Perforated septum: one or more holes in septum; can be surgically treated Caused by injury, an ulcer, long-term exposure to toxic fumes, or

illegal drug use Nasal polyps: soft, noncancerous growths in lining of nasal

passages or sinuses; may result from chronic inflammation of nasal cavity

Pg. 127

The Tongue

Human mouth contains ~10,000 sensory receptors for the sense of taste

These taste buds scattered throughout the interior of the mouth, including the lips and sides, top and back of the mouth

Most taste buds, however, reside on tiny bumps on tongue known as papillae

Within each taste bud, gustatory cells send tiny gustatory hairs up through the taste pores, very small openings in the top of the taste bud

Gustatory Sense

Chemical molecules from food dissolve in saliva to produce compounds called tastants. The tastants stimulate the gustatory hairs to send nerve impulses to the brain

Three of the cranial nerves– facial nerve, glossopharyngeal nerve, and vagus nerve—are responsible for transmitting taste sensations to the brain

The Tongue (pg. 126)

5 Basic Tastes Sweet Salty Sour Bitter Unami: the taste of beef as well as the taste of

monosodium glutamate, a seasoning commonly added to processed foods to enhance their taste

*A single gustatory cell responds to only one of the five taste sensations. *Individual taste buds contain 50 to 100 gustatory cells which typically include all five taste sensations*Average person is able to distinguish approximately 10,000 different flavors*Flavor is a combination of taste, smell, texture or consistency, and temperature

Homeostatic Imbalances of Tongue

Discoloration: may appear black when taking bismuth preparations for upset stomach; may appear pale due to iron-deficiency anemia; white patches may accompany fever, dehydration or mouth breathing

Infection: may result from tongue piercing, or traumatic accident causing a severe bite of tongue; antibiotics are used to treat infections; tongue heals more quickly than any other part of body

Hairy tongue: unnatural growth of gustatory hairs of the tongue; most common cause is inadequate oral hygiene; other causes include certain medications, excessive drinking of coffee or tea, frequent tobacco use, or radiation treatment to head or neck region

Burning mouth syndrome: sensation of moderate to severe burning in the mouth, tingling, numbness, or dryness of the mouth and a bitter or metallic taste; caused by damage to taste and pain receptors, chronic dry mouth, nutritional deficiencies, hormonal changes, acid reflux, and infections; treatment is based on underlying cause

Cancer: unexplained red or white areas, sores, or hard lumps (especially if painless); most oral cancers grow on the sides of tongue or on the floor of the mouth