Psyc 4442 Notes Gwen PDF

Chapter 11: The Auditory and Vestibular Systems  The Nature of Sound Audible variations in air pressure Cycle: distance between successive compressed patches of air Sound frequency: number of cycles per second expressed in hertz (Hz) Audible Sound Ra...

Chapter 11: The Auditory and Vestibular Systems  The Nature of Sound Audible variations in air pressure Cycle: distance between successive compressed patches of air Sound frequency: number of cycles per second expressed in hertz (Hz) Audible Sound Range: 20 Hz to 20,000 Hz Amplitude - volume Frequency - pitch  Auditory Pathway Sound waves Tympanic membrane Ossicles Oval window Cochlear fluid Sensory neuron response  The Middle Ear Sound force amplification by the ossicles The attenuation reflex (acoustic reflex) Onset of loud sound causes tensor tympani and stapedius muscle contraction Function: adapts ear to loud sounds, protects inner ear, enables us to understand speech better  The Inner Ear/The Cochlea Perilymph: fluid in scala vestibuli and scala tympani Endolymph: fluid in scala media Endocochlear potential: endolymph electrical potential 80 mV more positive than perilymph Motion at oval window pushes perilymph into scala vestibuli, makes round window membrane bulge  The Basilar Membrane Traveling Wave Response of Basilar Membrane to Sound The Organ of Corti Bending of Stereocilia  Transduction by Hair Cells Sound: basilar membrane upward, reticular lamina up, and stereocilia bend outward 1. Sheering force opens K+ channels. 2. Cell depolarizes. 3. Voltage-gated Ca2+ channels open. 4. Depolarizes further because of Ca2+. 5. Exocytosis (vesicles join the membrane and release NT).  Hair Cells The innervation of hair cells One spiral ganglion fiber synapses with one inner hair cell, numerous outer hair cells Amplification by outer hair cells— cochlear amplifier Function: sound transduction Motor proteins: change length of outer hair cells Prestin: protein required for outer hair cell movements Auditory Pathways  Properties of Auditory Neurons Characteristic frequency Frequency at which a neuron is most responsive - from cochlea to cortex Response properties more complex and diverse beyond the brain stem Binaural neurons are present in the superior olive.  Encoding Sound Intensity Membrane potential of activated hair cells more depolarized or hyperpolarized Firing rates of neurons Loudness perceived is correlated with number of active neurons. Tonotopic maps on the basilar membrane and cochlear nucleus  Tonotopy Tonotopic maps on the basilar membrane, spiral ganglion, and cochlear nucleus From the base to apex, basilar membrane resonates with increasingly lower frequencies. Tonotopy is preserved in the auditory nerve and cochlear nucleus. In cochlear nucleus, bands of cells with similar characteristic frequencies increase from anterior to posterior. Phase Locking Low frequencies: phase locking on every cycle or some fraction of cycles High frequencies: not fixed Mechanisms of Sound Localization Localization of sound in horizontal plane Interaural time delay: difference in time for sound to reach each ear Interaural intensity difference: sound at one ear less intense because of head’s sound shadow Duplex theory of sound localization: Interaural time delay: 20–2000 Hz Interaural intensity difference: 2000–20,000 Hz Delay Lines and Neuronal Sensitivity to Interaural Delay Sound from left side, activity in left cochlear nucleus sent to superior olive Sound delayed to right ear, activity in right cochlear nucleus Impulses reach olivary neuron at the same time → summation → action potential Localization of Sound in Vertical Plane Based on reflections from the pinna  Primary Auditory Cortex Axons leaving MGN project to auditory cortex via internal capsule in array called acoustic radiation. Structure of A1 and secondary auditory areas: similar to corresponding visual cortex areas  Principles of Auditory Cortex Tonotopy, columnar organization of cells with similar binaural interaction Frequency tuning in neurons: similar characteristic frequency Unilateral lesion in auditory cortex: almost normal auditory function Different frequency bands processed in parallel  The Vestibular System Balance, equilibrium, posture; head, body, eye movement Vestibular labyrinth Otolith organs— gravity and tilt Semicircular canals— head rotation Use hair cells, like auditory system, to detect changes  The Otolith Organs Detect changes in head angle, linear acceleration Macular hair cells responding to tilt Semicircular Canals Three on each side Help sense all possible head rotation angles Each paired on opposite side of head. Push–pull activation of vestibular axons Cupula Fluid doesn’t move as quick as the head, pushing the cupula in the opposite direction, deflecting the stereocilia and creating a nerve impulse. Causes depolarization of the hair cells on one side of the body and hyperpolarization on the other side. Comparison establishes movement within three- dimensional space. Central Vestibular Pathway The Vestibulo-Ocular Reflex (VOR) Function: fixate line of sight on visual target during head movement Mechanism: senses rotations of head, commands compensatory movement of eyes in opposite direction Connections from semicircular canals, to vestibular nucleus, to cranial nerve nuclei → excite extraocular muscles