Chapter 17, Part 2! The Special Senses! Hearing and Equilibrium! SECTION 17-5! Equilibrium sensations originate within the inner ear, while hearing involves the detection and interpretation of sound waves! 2! 1!
The Anatomy of the Ear Figure 17-21! AIR! 3! Middle Ear! Air-filled; Epithelial lining! Auditory ossicles! Malleus, incus, stapes! Auditory tube (Eustachian or pharyngotympanic)! Connects with nasopharynx! Equalizes air pressure! Ear infections from nasopharynx! Muscles - Prevent damage due to prolonged loud noises! Tensor tympani inserts on malleus! Stapedius inserts on stapes! 4! 2!
Middle Ear Figure 17-22! The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. 5! Inner Ear Bony Labyrinth! 1. Bony labyrinth! Cavities within temporal bone! Dense bony shell in petrous portion! Lined with periosteum, epithelium! Contains perilymph! Secreted by epithelial lining! Similar to cerebrospinal fluid! A. Semicircular canals! B. Vestibule! C. Cochlea! 6! 3!
Membranous Labyrinth! 2. Membranous labyrinth! Lined with epithelium! Contains endolymph! Secreted by stria vascularis (of cochlear duct)! Has high [K + ] Endolymphatic duct and sac! Sac projects to dura! Returns endolymph to circulation! 7! The Inner Ear Figure 17-23! 8! 4!
! Chapter 17 Part 2 Special Senses! Receptor Function Big Picture! Receptors = hair cells! Surrounded by supporting cells! Receptors synapse with sensory neurons! Cochlea and vestibule hair cells have many stereocilia! Vestibular hair cells also have one kinocilium! Displacement of cilia opens or closes mechanically-gated ion channels 9! Receptor Function Hair Cells! Cilia of hair cells are actually microvilli! Endolymph: High [K + ]! Displacement of cilia opens or closes mechanically-gated ion channels! When channels open:! K + enters cell from endolymph! Depolarization occurs (receptor potential)! Ca 2+ channels open! Neurotransmitter released! Sensory neuron stimulated! Cytoplasm: Low [K + ]! CN VIII! 10! 5!
The Vestibular Complex Figure 17-24! 11! Equilibrium Semicircular Canals! A. Semicircular ducts (in canals)! Oriented in 3 different planes! Sense angular acceleration! and rotation! Crista (ampullaris) with cupula! Cupula is a jelly-like, elastic! Floats in endolymph! Endolymph! Bend in one direction ion channels open! Bend in other direction ion channels close! 12! 6!
The Vestibular Complex Figure 17-24c! Endolymph! 13! Equilibrium Vestibule! B. Utricle and saccule! Static equilibrium: detect gravity! Dynamic equilibrium: linear acceleration! Tilting head, car acceleration, elevator ride! Contain maculae! Utricle macula oriented in horizontal plane! Saccule macula oriented in vertical plane! Maculae contain otoliths (statoconia)! 1. CaCO 3 crystals! 2. Embedded in glycoprotein gel! 14! 7!
The Vestibular Complex Figure 17-25! 15! Pathways for Equilibrium Sensation Fig. 17-26! Vestibular! branch! Cochlear branch! Vestibulocochlear nerve (VIII)! 16! 8!
Audition The Cochlea Figure 17-27! 17! Cochlear Duct (Scala Media)! Contains endolymph Oval window articulates with stapes, communicates with scala vestibuli! Round window communicates with scala tympani! Scala vestibuli and tympani connected at helicotrema! Helicotrema! Uncoiled cochlea! 18! 9!
Organ of Corti (Spiral Organ) Figure 17-28! Sits on basilar membrane (or lamina, or plate)! Membrane moves in response to pressure waves in perilymph! Hair cells! Have stereocilia! Tectorial membrane! Contacts stereocilia! 19! Auditory Events 1! 1. Sound waves vibrate tympanum! 2. Malleus, incus, stapes move! Amplify vibrations! 3. Oval window moves! Sets up pressure waves (traveling waves) in perilymph! Pressure transmitted from scala vestibuli to scala tympani through scala media! Round window acts as shock absorber! 20! 10!
Auditory Events 2! 4. Pressure waves distort basilar membrane! 5. Vibration of basilar membrane moves hair cells against tectorial membrane! 6. Stereocilia bend! 7. Mechanically-gated K + channels open! 8. Receptor potential neurotransmitter release (VIII)!!"""! 21! Sound Waves Figure 17-29! Sound waves striking an object cause it to vibrate at a resonant frequency.! 22! 11!
Sound and Hearing Figure 17-30! Helicotrema! Video 23! Basilar Membrane 1! Fibrous membrane! Fibers = stiff, reed-like structures! One end attached to modiolus (bone)! One end imbedded in the flimsy basilar membrane! i.e. fibers can move up and down! Fibers get longer moving away from the oval window (towards helicotrema)! Fibers get less stiff in the same direction! 24! 12!
Basilar Membrane 2! A. Near oval window:! Short, stiff (rigid) fibers! Respond to high frequency sounds! B. Near helicotrema:! These contain a lot of energy! Longer, more pliable fibers! Respond to low frequency sounds! These contain less energy! C. Traveling waves peak at the resonant frequency for a particular portion of the basilar membrane! 25! Hair Cells! Attached to tectorial membrane! Stereocilia connected to mechanically-gated channels! 1. Upward movement! Gates open! K + enters receptor receptor potential! Voltage-gated Ca 2+ channels open! Neurotransmitter released by hair cell (glutamate or GABA?)! 2. Downward movement - Opposite effect! 26! 13!
Cochlear Response to Sound Figure 17-31! Helicotrema! Fibers short! and stiff! Fibers longer,! more pliable! 27! Sound and Hearing Figure 17-30! Helicotrema! 28! 14!
Auditory Pathways Figure 17-32! Note organization of cortex.!! Look familiar?! 29! Awesome Basilar Membrane Videos! The basilar bembrane responds to Bach! The Organ of Corti! Auditory Transduction! These are the first three links under Audition on the Links page.! 30! 15!