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Home , Basilar membrane, Endolymph, Spiral ganglion, Tectorial membrane, Vestibular ganglion

VESTIBULAR SYSTEM (Balance/Equilibrium) The vestibular stimulus is provided by Earth’s ______, and ______. Located in the ______of the inner , in two components: 1. Vestibular sacs - gravity & head direction 2. - angular acceleration (changes in the rotation of the head, not steady rotation) 1. Vestibular sacs ( organs) - made of: a) ______(“little pouch”) b) ______(“little sac”) Signaling mechanism of Vestibular sacs Receptive organ located on the “floor” of and on “wall” of when head is in upright position - ______move within ______upon head movement; - crystals slightly bend ______also located within gelatinous mass; - this ______of action potentials in bipolar vestibular sensory . Otoconia: Calcium carbonate crystals Gelatinous mass

Cilia

Hair cells

Vestibular

Vestibular 2. Semicircular canals: 3 ring structures; each filled with fluid, separated by a membrane. Signaling mechanism of Semicircular canals -head movement induces movement of ______but ______of slightly bends cupula (endolymph movement is initially slower than head mvmt); - cupula bending slightly moves the cilia of hair cells; - this bending changes rate of action potentials in bipolar vestibular sensory neurons; - when head movement stops: endolymph movement ______, again bending the cupula but in reverse direction on hair cells which changes rate of APs; - detects “acceleration” in all 3 planes

semicircular Ampulla Cross- canal section Cross- section

Perilymph Membrane Cupula Hair Endolymph cells

Vestibular Ganglion

3. Vestibular pathway to the nervous system: - vestibular bipolar sensory cell bodies located in ______, which looks like a nodule (______) on the vestibular nerve; - from vestibular neurons get together with axons of the (auditory) and give rise to ______= VIII cranial nerve; - vestibular axons within ______in medulla, and in ; - vestibular neurons send axons to cerebellum, , medulla and ; - medullary responses to vestibular stimulation involved in ______(nausea, emesis); - responsible for controlling ______for keeping head upright; - controls eye movement; compensates for sudden head movement = ______.

Chap. 8- 4 out of the “vestibule” . . .

. . . and entering the brain () I. AUDITORY (ACOUSTIC) STIMULUS - waves of energy = sound waves - propagates through: (air), (water), and (metals)

1 cycle Intensity (loudness): measured on a logarithmic scale ; very sensitive & wide range - range: 0 - 160+ dB (>140 dB = painful) Frequency: Normal range (humans): ______- cps = cycles per seconds = ______- frequency = ______- ex., women’s voice higher pitch than men’s - range gets considerably narrower with age Complexity: addition of gives rise to ______waves - most sounds are complex waves that can be analyzed with into their component simple waves. II. EAR A. a. (external ear) b.

Hammer (middle Anvil Stirrup}ear bones)

Oval window Auditory nerve

Bone

Vestibule Tympanic Round membrane Pinna window (connects with throat)

B. a. (______) b. Ossicles 1. ______2. ______3. ______C. = COCHLEA C. COCHLEA a. b. c. Endolymph d. - contains 1. (top) 2. (bottom) 3. Hair cells

Tectorial Cilia of Inner membrane hair cell Outer (rigid) hair cells Deiter’s cells

Cochlear Axons of auditory nerve duct Basilar membrane - mobile Organ of Corti

Cochlear nerve Spiral ganglion Bone Membrane surrounding cochlea Slice through cochlea Signaling mechanism for hearing: - sound waves produce movement of basilar membrane; - movement of basilar membrane induce movement of cilia of hair cells; - cilia movement increase or decrease polarization of hair cells, which increase or decrease neurotransmitter release onto terminals of bipolar auditory neurons; - this increases or decreases action potentials in bipolar auditory neruons.

- it is the inner hair cells that provide the auditory signal to the brain; - the outer hair cells are believed to control the “tightness” of the basilar membrane, and therefore provide some modulation of hearing. D. CODING OF FREQUENCY:

Pitch (frequency) perception: 1. ______a. Different spots on basilar membrane vibrate to different frequencies (Fig. A above) b. Works for moderate to high frequencies, 100-200 to 20,000 Hz; - near oval window: very high frequencies (20,000 Hz) - near round window: moderate frequencies (100-200 Hz) 2. ______a. Frequency of sound waves over a large portion of basilar membrane = frequency of action potentials b. Works for low frequency sounds (below about 100-200 Hz)

Chap. 8- 8 E. CODING OF INTENSITY (LOUDNESS): Determined by action potential frequency; ex. soft sound = , loud sound = F. CODING OF : Based on: 1. : ex., click sound generated to the left arrives at left ear first 2. : ex., continuous sound waves will reach each ear at slightly different phases of the oscillating sound waves - these mechanisms work best with sounds of moderate frequencies 3. : ex., sound generated to the left are sensed slightly louder on the left side - this mechanism works best with sounds of high frequencies

Note. Low frequencies (______) are nearly impossible to localize (that’s why you need only one “sub-woofer” in a home-theater system) G. AUDITORY SYSTEM PATHWAY Spiral ganglion - contains bipolar neurons - receive information from hair cells - send their axons to brain via VIII nerve (auditory component of vestibulocochear nerve)

Lateral fissure

Auditory cortex Forebrain : Medial geniculate body

Midbrain

Dorsal Trapezoid Medulla body

Auditory nerve Superior (VIII nerve) olivary complex Frequency organization kept throughout auditory system all the way to