Special Senses 2

Disorders & Conditions of the Eye

Inflammation of the conjunctiva leads to red irritated eyes.
Conjunctivitis is caused by bacteria or viruses is contagious and called pink eye.

Conjunctivitis that is not contagious may be caused by allergies or chemical agents that have irritated the eyes.

​

Conjunctivitis & Pink Eye

• A red, painful bump along the edge of the eyelid

• Caused by a blocked sweat or sebaceous gland

​

​Stye

Most common type of colorblindness is caused by a lack of red or green receptors

Makes it difficult to distinguish between red and green

Inherited almost exclusively by males

​Colorblindness

​​Normal Vision

​Caused by an eyeball that is too short or a lens that is too strong.

Myopia

​Caused by an eyeball that is too long or a lens that is too weak

Hyperopia

​Caused by an irregular cornea that scatters light

Astigmatism

​​Cataracts

Glaucoma

​​Macular Degeneration

​​Diabetic Retinopathy

Hearing and Balance

The Ear

Human Ear

• External part is called auricle or pinna

• Gathers sound waves and directs them toward the eardrum

• The outer ear includes the auricle and auditory canal or external acoustic meatus

• The skin lining the external acoustic meatus contains ceruminous glands which produce cerumen or earwax, a waxy brownish-yellow substance.

• The function of earwax is to trap foreign debris and dead skin cells, and also to lubricate the auditory canal

Multiple Choice

These glands produce wax.

• sudoriferous glands

• ceruminous glands

• sebaceous glands

• sweat glands

Multiple Choice

The outer part of the ear is called the

• earlobe
• eardrum
• ear canal
• pinna

• Also known as the tympanic membrane

• Thin membrane between the outer and middle ear

• Vibrates in response to sound waves

​

​Ear Drum

Multiple Choice

The ear drum is also known as

• tympanic membrane
• earlobe
• auditory canal
• cochlea

Transfers sound wave vibrations of the ear drum to fluid waves in inner ear structures.

​

​

​Middle Ear

• Malleus (hammer)

• Incus (anvil)

• Stapes (stirrup)

These tiny bones actually move as they transfer sound waves to the oval window.
The auditory ossicles also amplify sound waves as they travel through the middle ear

​

​Auditory Ossicles

• Also called the pharyngotympanic or auditory tube

• Connects the middle ear with the nasopharynx

• Helps equalize pressure in the middle ear, keeping it equal with air pressure outside the body 

​

​Eustachian Tube

Multiple Choice

The Names of the auditory ossicles are

• malleus, incus, and stapes
• tibia, fibula, and patella
• hammer, anvil, and stirrup
• malleus, incus, and staples

Multiple Choice

What is the function of the Eustachian Tube

• Filter dust and debris
• Drain fluid from the ear
• Regulate body temperature
• Equalize pressure

Vibrations of the stapes are transmitted into the vestibule through the membrane-covered oval window 

The membrane of the round window vibrates in opposite phase to oval window vibrations

​Two openings to inner ear

• A maze of bony chambers also called the bony labyrinth

• The bony labyrinth is a cavity in the temporal bone

• This cavity is filled with a fluid called perilymph which supports a system of membrane sacs called the membranous labyrinth that follows the shape of the cavity

• The vestibule is the cavity medial to the tympanic membrane and tympanic cavity between the semicircular canals and the cochlea

• The vestibule is separated from the middle ear by the oval window

Inner Ear

• 3 areas:

  • cochlea

  • vestibule

  • semicircular canals

Inner Ear

Multiple Choice

Which "window" does the stapes vibrate

• round window
• oval window
• square window
• triangle window

Multiple Choice

The Inner Ear includes which structure

• trachea, bronchi, and alveoli
• cochlea, vestibule, and semicircular canals
• eardrum, auditory nerve, and ossicles
• retina, optic nerve, and lens

Static Equilibrium

• Receptors in the vestibule report on the position of the head with respect to gravity when the body is not moving

• Tiny stones called otoliths stimulate hair cells which inform the brain of head position

• When the head moves, the fluid moves and causes hair cells to bend which activates them to send impulses to the cerebellum

Dynamic Equilibrium

• Dynamic equilibrium refers to maintaining proper head position when the body is moving.

• Arranged in 3 planes, semicircular canals are filled with thick fluid that moves in response to body movement

• Fluid stimulates hair cells which send impulses along the vestibular nerve to the cerebellum

Multiple Choice

Which is the part of the ear that maintains static equilibrium?

• Semicircular canals
• Cochlea
• Eustachian tube
• Tympanic membrane

How sound travels through the ear

​

1. Sounds enter the ear (captured and directed by the auricle, they travel through the external acoustic meatus, and cause vibration of the tympanic membrane)

2. Tiny middle ear bones amplify sound (malleus, incus, and stapes)

3. Cochlea sorts sounds by frequency (hair cells in the organ of Corti detect various frequencies based on their length and position)

4. Impulses from hair cells in the cochlea travel along the cochlear (auditory) nerve to the brain stem (The cochlear nerve merges with the vestibular nerve coming from the vestibule and semicircular canals, which is carrying sensory information about equilibrium. When these two nerves merge, they form the vestibulocochlear nerve, also known as the 8th cranial nerve)

5. Signal travels through brain getting decoded along the way 

6. Auditory cortex recognizes, processes sound (located in the temporal lobe)

• The cochlea contains fluid called endolymph

• When sound waves reach the oval & round windows, cochlear fluid is set in motion

• Hair cells, located in the organ of Corti, are stimulated to transmit impulses along the cochlear nerve

​Hearing

• Vibrations in the cochlea cause movement of the tectorial membrane which stimulates the hair cells just below the membrane

• Different sound pitches are detected by different hair cells; high-pitch sounds stimulate shorter hair cells and low-pitch sounds stimulate longer hair cells

• Tiny projections called stereocilia are found at the tips of the hair cells in the organ of Corti.

• Sounds are interpreted in the auditory cortex of the temporal lobe
  

​

Reorder

Reorder the following to show how sound moves through the ear.

• Sound enters through the Pinna

• Sound waves cause the tympanic membrane to vibrate

• tiny bones amplify sound

• Couchlea sorts sounds

• Impulses from hair cells travel along the auditory nerve to the brain stem

1

2

3

4

5

• 1
• 2
• 3
• 4
• 5