Diagram Of Organ Of Corti

The inner ear is housed in a maze of temporal bone passageways called the bony labyrinth, which is lined by a system of fleshy tubes called the membranous labyrinth (fig. 16.11). Between the bony and membranous labyrinths is a cushion of fluid called perilymph (PER-ih-limf), similar to cerebrospinal fluid. Within the membranous labyrinth is a fluid called endolymph, similar to intracel-lular fluid.

The labyrinths begin with a chamber called the vestibule, which contains organs of equilibrium to be discussed later. The organ of hearing is lee-uh), a coiled tube that arises from the anterior side of the vestibule. In other vertebrates, the cochlea is straight or slightly curved. In most mammals, however, it assumes the form of a snail-like spiral, which allows a longer cochlea to fit in a compact space. In humans, the spiral is about 9 mm wide at the base and 5 mm high. Its apex points anterolaterally. The cochlea winds for about 2.5 coils around an axis of spongy bone called the modiolus26 (mo-DY-oh-lus). The modiolus is shaped like a screw; its threads form a spiral platform that supports the fleshy tube of the cochlea.

A vertical section cuts through the cochlea about five times (fig. 16.12a). A single cross section looks like

23ot = ear + itis = inflammation 24myringo = eardrum + tomy = cutting

25cochlea = snail 26modiolus = hub

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

16. Sense Organs

Text

600 Part Three Integration and Control

600 Part Three Integration and Control

Inner Ear Bony Labyrinth
Figure 16.11 Anatomy of the Inner Ear. (a) The membranous labyrinth and its nerves. (b) Relationship of the perilymph (blue) and endolymph (yellow) to the labyrinth.

figure 16.12b. It is important to realize that the structures seen in cross section actually have the form of spiral strips winding around the modiolus from base to apex.

The cochlea has three fluid-filled chambers separated by membranes. The superior one is called the scala27 vestibuli (SCAY-la vess-TIB-you-lye) and the inferior one is the scala tympani. These are filled with perilymph and communicate with each other through a narrow channel at the apex of the cochlea. The scala vestibuli begins near the oval window and spirals to the apex; from there, the scala tympani spirals back down to the base and ends at the round window (see fig. 16.10). The round window is covered by a membrane called the secondary tympanic membrane.

The middle chamber is a triangular space, the cochlear duct (scala media). It is separated from the scala vestibuli above by a thin vestibular membrane and from the scala tympani below by a much thicker basilar membrane. Unlike those chambers, it is filled with endolymph rather than perilymph. Within the cochlear duct, supported on the basilar membrane, is the organ of Corti28 (COR-tee), a thick epithelium with associated structures (fig. 16.12c). It is the transducer that converts vibrations into nerve impulses, so we must pay particular attention to its structural details.

The organ of Corti has an epithelium composed of hair cells and supporting cells. Hair cells are named for

28Alfonso Corti (1 822-88), Italian anatomist

Saladin: Anatomy & I 16. Sense Organs I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 16 Sense Organs 601

Oval window-

Spiral ganglion

Vestibular membrane

Cochlear duct

Tectorial membrane

Organ of Corti

Basilar membrane

Oval window-

Spiral ganglion

Vestibular membrane

Cochlear duct

Tectorial membrane

Organ of Corti

Corti Organ

Hairs (stereocilia) Inner hair cell

Fibers of cochlear nerve

Figure 16.12 Anatomy of the Cochlea. (a) Vertical section. The apex of the cochlea faces downward and anterolaterally in anatomical position. (b) Detail of one section through the cochlea. (c) Detail of the organ of Corti.

Hairs (stereocilia) Inner hair cell

Fibers of cochlear nerve

Figure 16.12 Anatomy of the Cochlea. (a) Vertical section. The apex of the cochlea faces downward and anterolaterally in anatomical position. (b) Detail of one section through the cochlea. (c) Detail of the organ of Corti.

the long, stiff microvilli called stereocilia29 on their apical surfaces. (Stereocilia should not be confused with true cilia. They do not have an axoneme of microtubules as seen in cilia, and they do not move by themselves.) Resting on top of the stereocilia is a gelatinous tectorial30 membrane.

The organ of Corti has four rows of hair cells spiral-ing along its length (fig. 16.13). About 3,500 of these, called inner hair cells (IHCs), are arranged in a row on the medial side of the basilar membrane (facing the modiolus). Each of these has a cluster of 50 to 60 stereocilia, graded from short to tall. Another 20,000 outer hair cells (OHCs) are neatly arranged in three rows across from the inner hair cells. Each outer hair cell has about 100 stereocilia arranged in the form of a V, with their tips embedded in the tectorial membrane. All that we hear comes from the IHCs, which supply 90% to 95% of the sensory fibers of the cochlear nerve. The function of the OHCs is to adjust

Stereoscopic Cochlea

29 stereo = solid

30tect = roof Figure 16.13 Apical Surfaces of the Cochlear Hair Cells (SEM).

Saladin: Anatomy & I 16. Sense Organs I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

602 Part Three Integration and Control the response of the cochlea to different frequencies and enable the IHCs to work with greater precision. We will see shortly how this is done. Hair cells are not neurons, but synapse with nerve fibers at their base—the OHCs with both sensory and motor neurons and the IHCs with sensory neurons only.

Was this article helpful?

0 0
How To Become A Bee Keeping Pro

How To Become A Bee Keeping Pro

Companies that have beekeeping stuff deal with all the equipment that is required for this business, like attire for bee keeping which is essential from head to torso, full body suits and just head gear. Along with this equipment they also sell journals and books on beekeeping to help people to understand this field better. Some of the better known beekeeping companies have been in the business for more than a hundred years.

Get My Free Ebook


Responses

  • dora
    What is corti fung N do?
    6 months ago

Post a comment