Module 1 The Nervous System

Lesson 1.1.6

1.1.6 page 4

Read

The Inner Ear

inner ear: one of the three regions of the ear that is located deepest in the head and consists of a fluid filled chamber which contains the semicircular canals, the utricle, the saccule, and the cochlea

cochlea: contains the organ of Corti, which functions to convert the mechanical energy of sound waves into a nerve impulse

auditory nerve: a nerve composed of sensory fibres from the organ of Corti, the vestibular apparatus which conducts impulses to the temporal lobe of the cerebrum

round window: a membrane-covered opening between the chamber of the middle ear and the inner ear located below the oval window; functions in dissipating sound waves in the inner ear

Sound has been collected, transmitted, and amplified, but you haven’t heard anything yet. The inner ear is responsible for converting mechanical stimulation to a nerve impulse to be communicated to the brain. The inner ear also converts mechanical stimulation into information on balance to be interpreted by the brain.

Read page 420 and study Figure 12.20 Can you determine which structures make up the inner ear? The inner ear is composed of two organs: one for hearing and one for balance. Note the structures for hearing which include the oval window, cochlea, round window, and auditory nerve. Note also the utricle, saccule, and semi-circular canals which function in balance. You may wish to record the information in summary notes, a concept map, or as additions to your diagram or table. Store your work in your course folder.

The Structures and Functions of the Inner Ear

Structure	Function(s)
Oval window
Cochlea
Round window
Auditory nerve

Read

Organ of Corti

Special parts of the inner ear must be functional in order to facilitate hearing. From your study so far, you have not encountered the mechanoreceptors of these parts and how they function in hearing. Mechanoreceptors are specialized receptor cells that detect a stimulus such as pressure or vibration.

As you study these parts of the inner ear, you will discover why people can lose their range of hearing as they age.

organ of Corti: contains hair cells that detect vibrations in the fluid of the inner ear and intiates a nerve impulse that is transmitted to the auditory nerve

Read the section on the inner ear and the organ of Corti on pages 420 and 421. Study Figure 12.21 on page 420 which shows a cross section of the cochlea and the location of the organ of Corti (blown up on the far left of the figure). The receptors for sound waves are located inside the organ of Corti. Make summary notes or summarize the functions of the structures of the organ of Corti in a table similar to the following. File your work in your course folder.

The Structures and Functions of the Organ of Corti

Structure	Function(s)
Basilar membrane
Hair cells
Tectorial membrane
Auditory nerve
Sensory neurons

basilar membrane: one of two parallel membranes that comprise the organ of Corti in the inner ear (the other being the tectorial membrane); hair cells are attached to it.

hair cells: sensory mechanoreceptors attached to the basilar membrane in the organ of Corti within the inner ear

tectorial membrane: one of two parallel membranes (the other being the basilar membrane) that is found in the organ of Corti; during the transmission of sound waves, the basilar membrane vibrates and causes the sensory hairs to flex against the tectorial membrane

sensory neurons: nerve cells that are stimulated by hair cells in the organ of Corti to conduct messages toward the temporal lobe of the brain