Special Senses 7.7

Special Senses

-Allow body to react to the environment

-Sight, hearing, taste, smell, and maintain balance

The Eye:

-Organ that controls the special senses of sight

-Light rays transmitted to the optic nerve

-The optic nerve relays information to the brain.

Lacrimal glands (parts of the eye)

Produce tears, which constantly moisten and cleanse the eye.

Conjunctiva (parts of the eye)

Mucous membrane that lines eyelids and covers the front of the eye to provide additional protection and lubrication.

Sclera (parts of the eye)

White outer coat of the eye: maintains shape.

Cornea (parts of the eye)

The transparent section of the sclera; allows light rays to enter.

Choroid coat (parts of the eye)

Middle layer of eye; nourishes the eye

Retina (parts of the eye)

Innermost player of eye; transmits light impulses to the optic nerve.

Iris (parts of the eye)

Locate behind the cornea; colored portion of the eye.

Eyelids and Eyelashes (parts of the eye)

Helps to keep out dirt and pathogens.

Pupil (parts of the eye)

Opening in the center of the iris; regulates amount of light.

Lens (parts of the eye)

Circular structure behind the pupil; held by ligaments.

Aqueous humor (parts of the eye)

Clear watery fluid that fills the space between the cornea and iris and gives the forward curvature of the eyeball.

Vitreous humor (parts of the eye)

Jellylike substance that fills the area behind the lends: helps maintain shape.

Ligaments (parts of the eye)

Muscles located in the eye that provide for eye movement.

Rods (parts of the eye)

Used for vision when it is dark or dim.

Cones (parts of the eye)

Sensitive to color and are used mainly for vision when it is light.

Amblyopia

Lazy eye”; poor vision in one eye caused by the dominance of the other eye.

Astigmatism

Warping or curvature of the cornea that causes blurred vision at any distance. 

Cataract

Occurs when the normally clear lens becomes cloudy or opaque.

Conjunctivitis

Pink eye, a highly contagious inflammation

Glaucoma

A condition of increased intraocular pressure caused by an excess amount of aqueous humor. 

Hyperopia

Farsightedness, objects far away are seen clearly. Things up close are blurry. 

Macular degeneration

A major cause of vision loss and blindness; age-related. No cure, affects the most sensitive section of the retina.

Myopia

Nearsightedness, sight is clear up close. Objects far away are blurry

Presbyopia

Farsightedness caused by a loss of lens elastically. Results from the normal aging process. 

Strabismus

A disorder in which the eyes do not move or focus together. Cross-eyes.

The Ear

• The organ that controls the special senses of hearing and balance. 

• The ear is divided into three main sections:

1. Outer ear

2. Middle ear

3. Inner ear

The Outer ear

• Contains the visible part of the ear

1. Pinna or Auricle- Elastic cartilage covered by skin

2. External auditory meatus or auditory canal- Canal that leads from the pinna

3. Tympanic membrane (ear drum)- Vibrates when sound waves hit it and transmits the sound waves to the middle ear. 

The Middle ear

• A small space or cavity in the temporal bone

• Has three small bones (ossicles)

1. Malleus 

2. Incus

3. Stapes

• The middle ear is connected to the pharynx (throat) by a tube called the Eustachian tube to equalize pressure on both sides of the tympanic membrane.

The Inner ear

• Most complex portion of the ear

• Separated from the middle ear by a membrane called the oval window.

• Cochlea- is the snail-like shape.

Cerumen

wax that protects the ear produced by special glands. 

Hearing loss and deafness

classified as either conductive or sensory hearing loss.

Conductive

Sound waves are not conducted to the inner ear. (causes: was plug, foreign object obstruction infection or ruptured tympani membrane. 

Sensory

there is damage to the inner ear. Cannot be corrected (cochlear implants can improve severe loss)

Meniere’s disease

results from a collection of fluid in the inner ear

Otitis externa

an inflammation of the external auditory canal. (swimmers ear, inserting bobby pins, fingernails, or cottenswabs)

Otitis media

Ear infection

Otosclerosis

An inherited disease. Staples become immobile cause hearing loss. May remove staples and insert artificial stapes to correct the condition.

The tongue and sense of taste:

• The tongue is a mass of muscle tissue

• Contains projections called papillae

• The papillae contain taste buds that stimulate flavors of foods moistened by saliva (5 main taste):

1. Sweet- tip of the tongue.

2. Salty- sides of the tongue.

3. Bitter- back of the tongue.

4. Sour-  back sides of the tongue.

5. Umami- detects meaty or savory sensations. Your taste is influenced by the sense of smell. Middle of tongue

The Nose andSense of Smell:

• The organ of smell

• Smell made possible by the olfactory chemoreceptor cells located in the upper part of the nasal cavity

• The human nose can detect more than 6,000 scents.

The Skin and General senses:

• General sense receptors for pressure, heat, cold, touch, and pain are located throughout the body in the skin.

• Each receptor perceives only one type of sense

1. Thermoreceptors- heat and cold

2. Mechanoreceptors- pressure and touch

3. Nociceptors- react to pain.