1. Special Senses: Equilibrium & Hearing
Honors Anatomy & Physiology

2. Ear Anatomy External Ear Pinna (Auricle)
elastic cartilage covered w/thin skin
Directs sound waves into auditory canal
External Acoustic Meatus (auditory canal)
Short curved tube carved into temporal bone
Lined w/Ceruminous glands – secrete cerumen (ear wax) to repel insects and trap pathogens
Tympanic Membrane (Ear Drum)
Connective tissue membrnae
Sound waves cause it to vibrate

3. Ear Structures Middle Ear Air-filled mucosa-lined cavity
Phargnotympanic (Eustachian) tube
links middle ear to nasopharynx
Flattened until needed to equalize w/external air pressure
Important for free vibrations of ear drum
Auditory Ossicles (smallest bones in body)
Malleus (Hammer)
Incus (Anvil)
Stapes (Stirrup)
Transmit vibrations to oval window (small opening) of inner ear

4. Internal Ear (Labyrinth)
Osseous Labyrinth
Filled w/perilymph (similar to CSF)
Vestibule
Houses receptors that respond to gravity & changes of head position
Cochlea
Snail coil the size of a split pea
Spiral organ of Corti – receptor organ for hearing
Semi-Circular Canals
Oriented in X,Y,Z planes
Receptors respond to rotational movements of the head
Membranous Labyrinth
Sacs & ducts contained w/in the bony labryinth
Filled w/endolymph – K+ rich intracellular fluid

5. Properties of Sound
Sound – alternating areas of high and low pressure causing molecules to vibrate…travels slower than light
Illustrated as a sine wave defined by:
Frequency – number of waves that pass a given point in a certain time
Human hearing 20-20,000 waves per second (Hz)
Wavelength – distance between 2 consecutive crests
Pitch – perceived sound frequencies (higher freq = higher pitch)
Amplitude – height of sine wave – sound intensity…interpreted as loudness measured in decibels (dB)

6. Physiology of Hearing
Sound waves vibrate tympanic membrane transferred to auditory ossicles and then the oval window
Bulging membrane of round window creating pressure waves within perilymph of vestibular duct
Pressure waves distort basilar membrane, vibrating hair cells against tectoral membrane
Information relayed via cochlear nerve
Hair cells – receptors of inner ear
Stereocilia: microvilli on free surface moved by external forces causing displacement in one direction increasing neurotransmitter release, displacement in opposite direction decreases neurotransmitter release
Pitch determined by which part of cochlear duct is stimulated
Volume determined by how many cells are stimulated

8. Vestibular Apparatus: Equilibrium & Orientation
Dynamic Equilibrium
Maintains balance during sudden movements
Semicircular Ducts (anterior, posterior & lateral)
Rotational Motion
Ampulla – swollen region w/sensory “hair” cells
Movement of endolymph stimulates hair cells
Static Equilibrium
Maintains posture and stability when motionless
Vestibule
Gravity & Linear Acceleration
Osteolith (CaCO3) sits on hair cells and can shift
Vestibular branch of vestibular cochlear nerve integrate sensory info from both sides, and relay info to cerebellum, cerebral cortex, & brain stem

9. Dynamic Equilibrium
Static Equilibrium

10. Hearing Deficits Conduction Deafness Sensorinueral Deafness
Blocks transfer of vibration from tympanic membrane to oval window
Ear wax buildup, trapped water, scarring or perforation of tympanic membrane, overgrowth of ossicles
Sensorinueral Deafness
Within the cochlea or auditory pathway
Broken sterocilia (loud sounds), drugs destroy hair cells, bacterial infection kill hair cells
Cochlear implants convert sound into electrical signals can be inserted into temporal bone

11. American Sign Language Can you spell your name?