which of the following is the main fucntion of chchlea aamplifies the sound bconverts the sound to electrical signal cbothaa and b dnone of these
Answers
Answer:
The key structure in the vertebrate auditory and vestibular systems is the hair cell. The hair cell first appeared in fish as part of a long, thin array along the side of the body, sensing movements in the water. In higher vertebrates the internal fluid of the inner ear (not external fluid as in fish) bathes the hair cells, but these cells still sense movements in the surrounding fluid. Several specializations make human hair cells responsive to various forms of mechanical stimulation. Hair cells in the Organ of Corti in the cochlea of the ear respond to sound. Hair cells in the cristae ampullares in the semicircular ducts respond to angular acceleration (rotation of the head). Hair cells in the maculae of the saccule and the utricle respond to linear acceleration (gravity). (See the chapter on Vestibular System: Structure and Function). The fluid, termed endolymph, which surrounds the hair cells is rich in potassium. This actively maintained ionic imbalance provides an energy store, which is used to trigger neural action potentials when the hair cells are moved. Tight junctions between hair cells and the nearby supporting cells form a barrier between endolymph and perilymph that maintains the ionic imbalance.
Figure 12.1 illustrates the process of mechanical transduction at the tips of the hair cell cilia. Cilia emerge from the apical surface of hair cells. These cilia increase in length along a consistent axis. There are tiny thread-like connections from the tip of each cilium to a non-specific cation channel on the side of the taller neighboring cilium. The tip links function like a string connected to a hinged hatch. When the cilia are bent toward the tallest one, the channels are opened, much like a trap door. Opening these channels allows an influx of potassium, which in turns opens calcium channels that initiates the receptor potential. This mechanism transduces mechanical energy into neural impulses. An inward K+ current depolarizes the cell, and opens voltage-dependent calcium channels. This in turn causes neurotransmitter release at the basal end of the hair cell, eliciting an action potential in the dendrites of the VIIIth cranial nerve.
Press the "play" button to see the mechanical-to-electrical transduction. Hair cells normally have a small influx of K+ at rest, so there is some baseline activity in the afferent neurons. Bending the cilia toward the tallest one opens the potassium channels and increases afferent activity. Bending the cilia in the opposite direction closes the channels and decreases afferent activity. Bending the cilia to the side has no effect on spontaneous neural activity.
12.2 Sound: Intensity, Frequency, Outer and Middle Ear Mechanisms, Impedance Matching by Area and Lever Ratios
The auditory system changes a wide range of weak mechanical signals into a complex series of electrical signals in the central nervous system. Sound is a series of pressure changes in the air. Sounds often vary in frequency and intensity over time. Humans can detect sounds that cause movements only slightly greater than those of Brownian movement. Obviously, if we heard that ceaseless (except at absolute zero) motion of air molecules we would have no silence.