psy 131 ch 4 auditory system midterm 2

What did von Békésy observe regarding a pure tone played to the ear? What is a traveling wave (pp. 66-67)?

A pure tone on the basilar membrane we see a characteristic motion of wave from base to apex until it hits the spot where it resonates the most and then diminishes. This pattern of wave is called a traveling wave.

What is an auditory filter? In what way does the basilar membrane perform a spectral analysis of an incoming sound (pp. 65-66, Figs. 4.5, 4.6 and 4.7)?

An auditory filter refers to the areas of basilar membrane that behave like an array of tuned resonators and band-pass filters. When complex sounds enter the ear, frequencies are separated by the membrane like a spectral analysis.

What is transduction, at least in terms of what happens to acoustic vibrations in the cochlea? By what means is this task accomplished (p. 68)?

Converting the mechanical vibrations of the basilar membrane into electrical activity in the auditory nerve. This is accomplished by the inner hair cells.

What causes motion of the stereocilia (inner hair cells on the Organ of Corti)? What is the effect of this motion? What are tip links? What is depolarization, and what process does it cause? What is the relationship between the magnitude of basilar membrane movement, the opening of tip links, the electrical charge in the inner hair cell, the amount of neurotransmitter released by depolarization, and the resulting activity in the auditory nerve (pp. 68-71, Figs. 4.10, 4.11 and 4.12)?

Movement of the basilar membrane moves the stereocilia. This causes them to move side to side. Tip links connect the stereocilia together and also are ion channels for the membrane. Opening them causes depolarization. The more movement of the basilar membrane the more the tip links open. This causes more action potentials.

What are the three conceptual divisions of the peripheral auditory system (pp. 59-60, Fig. 4.1)?

Outer ear, middle ear, inner ear.

What are the relative patterns of response to high and low frequency pure tones on the basilar membrane? Does a particular place on the basilar membrane respond to a range of frequencies or to one frequency only (pp. 67-68, Figs. 4.8 and 4.9)?

Places on the basilar membrane respond to a range of frequencies rather than one frequency only.

What is the role of the basilar membrane? What is a characteristic frequency, and how does it relate to location on the basilar membrane (p. 64)?

The basilar membrane separates out the frequency components of a sound. Each part of the membrane has a characteristic frequency to which it is most sensitive.

What is the cochlea, and how is it structured from base to apex? What are the scala vestibuli, scala media, scala tympani and helicotrema? (pp. 61-62, Figs. 4.2 and 4.3)?

The cochlea is water-filled compartment where transduction occurs. It is widest at the base and thinnest at the apex. The cochlea is separated into 3 compartments by 2 membranes inside. The 3 compartments are the scala vestibuli, scala media, and scala tympani. The helicotrema is a small opening that connects the scala vestibuli and the scala tympani.

What is the ear canal (external auditory meatus)? What effect does the ear canal have on sound waves and, in turn, on perception (p. 60)?

The tube between the concha and the ear drum. It has resonant properties like an organ pipe that has resonant properties. Can act as a broadly tuned band-pass filter.

What is the Organ of Corti, and how is it structured from tectorial membrane to stereocilia to inner and outer hair cells? What are the basic functions of the inner and outer hair cells (pp. 63-64, Fig. 4.4)?

The organ of Corti is inside the cochlea and contains rows of hair cells and various supporting cells and nerve endings. It sits between the basilar membrane and the tectorial membrane. Inner hair cells are closer to auditory nerves than outer hair cells. Stereocilia sits on top of hair cells. Outer hair cells change the mechanical properties of the basilar membrane. The inner hair cells are responsible for converting the vibration of the basilar membrane into electrical activity.

What is the pinna? What effect does the pinna have on sound waves and, in turn, on perception (pp. 59-60)?

The pinna is the external part of the ear. They cause spectral modifications (filtering) to sounds that depend on direction. Good for locating sound sources.

What is the eardrum? What are the ossicles and what is their function in the middle ear (pp. 60-61)? What does the author mean when he writes that the middle ear "...acts as an impedance-matching transformer (p. 61)?"

Thin membrane that vibrates to pressure changes in ear canal. The ossicles are the three bones that transmit pressure variations in an air-filled compartment into pressure variations in a water-filled compartment. Water has a higher impedance than air. This entails that sound pressure would have a hard time going directly from air to water. The ossicles increase pressure of the sound waves so that they move through the water-filled compartment.

What is the main function of sensory systems (p. 59)?

To get information about the outside world to the brain.