Question

1) What is hearing?

2) What is the pathway for hearing?

3) What are the two vestibular systems?

4) Explain how the two vestibular systems detect changes in movement.

Answer 1

Ans(1). Hearing is the ability to percieve sounds by detecting vibrations, changes in the pressure of the sorrounding medium, through time, through an organ such as ear.

Ans-(2). The external ear or ear pinna makes sound waves into unidirectional waves and directs to auditory canal. The sound reaches the tympanic membrane and causes it's vibration. The handle of malleus articulates with the tympanic membrane and the malleus also has articulating facet for incus. It articulates with the stapes via its lenticular process. The stapes impacts into the oval window and causes it to move in and out with sounds. There is a round window located below the oval window that moves out when oval window moves in.

The sound waves now reaches the inner ear. They are sent up the scala vestibuli to the apex of cochlear duct. Now it continues down the spiral shaped cochlear organ in the scala tympani. The scala vestibuli and scala media are separated by reissner's membrane. Scala media and scala tympani below are separated by the basilar membrane.

When these waves moves up and down the perilymph in the scala vestibuli and scala tympani, the vibrations move the basilar membrane. The organ of corti lies on the basilar membrane and converts vibrations into electrochemical signals. There are stereocilia that lie on organ of corti and their tips go into gel like layer called tectorial membrane. When vibrations move basilar membrane, these hair cells bend and pottasium channels open. The influx of pottasium causes generation of local current and action potential is then sent to vestibulocochlear nerve which sends the signal to nuclei in the brainstem which are cochlear nuclei.

The information from cochlear nerve passes to ventral and dorsal cochlear nuclei. The three major outputs to these nuclei are to the superior olivary complex. The other half of the information is sent to the contralateral superior olivary complex. The second order neurons are sent via the lateral leminiscus to the inferior colliculus which recieves connections from the superior olivary complex. The majority of these connections will ultimately terminate in the auditory cortex.

Ans-(3). The vestibular system consists of two otolith organs( saccule and utricle) and three semicircular canals which sense angular acceleration in three planes.

Ans-(4). The vestibular system provides us with our subjective sense of movement and orientation in space. The two otolith organs sense linear acceleration ( gravity and translational movement). The utricle detects movement in horizontal plane and saccule in the vertical the thrplane.While semicircular canals sense angular acceleration in three planes. The receptor cells of otolith organs and semicircular canals sends signals through the vestibular nerve fibres to the neural structures that control eye movements, posture and balance.