Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 11: Auditory System (Inner Ear: Cochlea with 3 chambers (Organ of…
Chapter 11: Auditory System
Sound is a pattern of variation in air pressure
Outer Ear: up to Tympanic membrane
Middle Ear: Tympanic membrane to stapes
Ossicles (3);
Incus (Anvil)
Stapes (Stirrup)- footplate is bottom portion that transmits vibrations to oval window (pressure 20x greater than eardrum)
Malleus (Hammer)
Inner Ear: Cochlea with 3 chambers
Scala media
Scala tympani
Scala vestibuli
Basilar Membrane
Reissner's Membrane
Organ of Corti: sits on basilar membrane, contains auditory receptor cells
Tectorial Membrane hangs over organ of corti
Fluids of the Inner Ear
Perilymph (in vestibuli & tympani); low K+, high Na+
Endolymph: found in scala media; High K+, low Na+
Ek= 0mV; Stria vascularis generates ionic difference
Helicotrema: hole at apex of basilar membrane- connects scala vestibuli & scala tympani
Basilar Membrane- Stiffer at base, thinner at base. Lower frequencies resonate farther out
Outer Hair Cells: bent back & forth by tectorial membrane
Inner hair cells: move in response to moving endolymph
Hair Cells: Tension allows K+ to flow in, leading to NT release to spiral ganglion
Outer hair cells: multiple feed one neuron. Inner hair cells: Feed multiple neurons each
Outer Hair Cell Amplification (Two mechanisms)
Motor Proteins change length of outer hair cells (Prestin)
Myosin attached to upper tip links
Ototoxicity: deafness caused by antibiotics due to damage to cochlear amplifier
Central Auditory Pathway
CN8
Spiral Ganglia
Dorsal & Ventral Cochlear Nuclei
Superior Olive
First binaural neurons
Rostral Medulla
Most spiral ganglia receive input from one hair cell at specific locale on basilar membrane (Characteristic Frequency)
Encoding Sound Frequency
Intermediate Frequencies: (200Hz-5kHz): Phase Locking and Tonotopy
High Frequencies: (>5kHz)
Low Frequencies (<200 Hz): phase locking only
Sound Localization
Horizontal
Interaural Time Delay (20-2000Hz)
For continuous tones: Interaural Intensity Difference (2000-20000Hz)
Vertical
Reflections from the Pinna
Auditory Cortex- From MGN via internal capsule in ACOUSTIC RADIATION
Layer IV: MGN neurons terminate, densely packed granule cells
Layer V & VI: Mostly pyramidal cells
Layers II and III: small pyramidal cells
Layer I: Few cell bodies
Auditory Disorders
Unilateral lesion in auditory cortex: almost normal auditory function
Two types of deafness
Conduction Deafness: disruption in sound from outer ear to cochlea
Nerve Deafness: loss of auditory nerve neurons or cochlear hair cells
Bilateral Ablation of auditory cortex leads to deafness
Vestibular System-evolved from lateral line organs in fish/amphibeans
Otolith Organs (Utricle and Saccule)- linear acceleration
Macula- sensory epithelium oriented vertically with saccule, horizontally with utricle
Otoconia: calcium carbonate crystals on top of macula
Semicircular Canals- rotational acceleration
Filled with endolymph
Hair cells clustered within the crista wihtin bulge called the Ampula
Cilia project into gelatinous cupula
Vestibular Pathway- primary axons project to ipsilateral medial and lateral vestibular nuclei, and to cerebellum