Special Senses: Equilibrium & Hearing

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:80-100 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 • 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 LanguageCan you spell your name?