Spiral Organ Organ of Corti

The sensory hair cells are located on the basilar membrane, with their "hairs" (actually stereocilia) projecting into the endolymph of the cochlear duct. These hair cells are arranged to form one row of inner cells, which extends the length of the basilar membrane, and multiple rows of outer hair cells: three rows in the basal turn, four in the middle turn, and five in the apical turn of the cochlea (fig. 10.21).

The stereocilia of the outer hair cells are embedded in a gelatinous tectorial membrane (tectum = roof, covering), which overhangs the hair cells within the cochlear duct (fig. 10.22). The

Malleus Incus Oval

Malleus Incus Oval

Cochlear Duct Frequency

Figure 10.20 The effect of sounds of different frequency on the basilar membrane. The cochlea is shown "unwound" in this diagram. Sounds of low frequency cause pressure waves of perilymph to pass through the helicotrema. Sounds of higher frequency cause pressure waves to "shortcut" through the cochlear duct. This causes displacement of the basilar membrane, which is central to the transduction of sound waves into nerve impulses. Maximum displacement of the basilar membrane occurs closer to its base as the sound frequency is increased. (The frequency of sound waves is measured in hertz [Hz], or cycles per second.)

Figure 10.20 The effect of sounds of different frequency on the basilar membrane. The cochlea is shown "unwound" in this diagram. Sounds of low frequency cause pressure waves of perilymph to pass through the helicotrema. Sounds of higher frequency cause pressure waves to "shortcut" through the cochlear duct. This causes displacement of the basilar membrane, which is central to the transduction of sound waves into nerve impulses. Maximum displacement of the basilar membrane occurs closer to its base as the sound frequency is increased. (The frequency of sound waves is measured in hertz [Hz], or cycles per second.)

Outer hair cells

■ Figure 10.21 A scanning electron micrograph of the hair cells of the spiral organ (organ of Corti).

association of the basilar membrane, hair cells with sensory fibers, and tectorial membrane forms a functional unit called the spiral organ, or organ of Corti (fig. 10.22). When the cochlear duct is displaced by pressure waves of perilymph, a shearing force is created between the basilar membrane and the tectorial membrane. This causes the stereocilia to move and bend. Such movement causes ion channels in the membrane to open, which in turn depolarizes the hair cells. Each depolarized hair cell then releases a transmitter chemical, believed to be glutamate, that stimulates an associated sensory neuron.

The greater the displacement of the basilar membrane and the bending of the stereocilia, the greater the amount of transmitter released by the hair cell, and therefore the greater the generator potential produced in the sensory neuron. In other

Vestibulocochlear nerve

Cortis Organ Frequency

Scala tympani 1

Spiral organ (of Corti)

Scala tympani 1

Spiral organ (of Corti)

Tectorial membrane Inner hair cell \ Outer hair cells

Tectorial membrane Inner hair cell \ Outer hair cells

Tectorial Membrane

Basilar

Nerve fibers membrane

(b) Vestibulocochlear nerve

Basilar

Nerve fibers membrane

■ Figure 10.22 The spiral organ (organ of Corti). This functional unit of hearing is depicted (a) within the cochlear duct and (b) isolated to show greater detail.

words, a greater bending of the stereocilia will increase the frequency of action potentials produced by the fibers of the cochlear nerve that are stimulated by the hair cells. Experiments suggest that the stereocilia need bend only 0.3 nanometers to be detected at the threshold of hearing! A greater bending will result in a higher frequency of action potentials, which will be perceived as a louder sound.

As mentioned earlier, traveling waves in the basilar membrane reach a peak in different regions, depending on the pitch of the sound. High-pitched sounds produce a peak displacement closer to the base, while sounds of lower pitch cause peak displacement further toward the apex (see fig. 10.20). Those neurons that originate in hair cells located where the displacement is greatest will be stimulated more than neurons that originate in other regions. This mechanism provides a neural code for pitch discrimination.

There is evidence that the outer hair cells shorten and stiffen in the peak stimulated region of the basilar membrane, and thereby contribute to pitch discrimination. This active response of the hair cells may serve to more sharply tune the frequency response of the basilar membrane. Lateral inhibition by neurons in the CNS accentuates the response of the spiral organ to different frequencies of sound, and thereby serves to sharpen pitch discrimination.

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Responses

  • petra weckman
    What is the action potential is generated by the hair cells of the spiral organ of Corti.?
    7 years ago
  • asmait
    Are the hair cells of the spiral organ of corti covered with perilymph?
    7 years ago
  • huriyyah
    What triggers bending of hairs of the hair cells in the spiral organ of corti?
    7 years ago
  • zewdi
    What is the gelatinous membrane over the hair cells of the spiral organ of corti?
    7 years ago
  • BARBARA
    How sounds of different frequencies affect the human body"?
    7 years ago
  • kari
    Which part of the spiral organ of corti control high pitched sounds?
    7 years ago
  • enrico
    Is it true that the base of the spiral organ responds to low frequencies of sound.?
    7 years ago
  • veli pokka
    Where do the high & low frequency sounds cause depolarization in the cochlear duct?
    7 years ago
  • Darcy
    Which part of the spiral organ responds to low pitched sounds?
    7 years ago
  • john
    What causes the hairs of the spiral organ to move?
    7 years ago
  • cosimo
    How is the organ of corti stimulated by sound waves?
    7 years ago
  • sm
    How frequency effects cells?
    7 years ago
  • Claudio
    What is the spiral organ Where is it located?
    6 years ago
  • KALLE
    Which part of the spiral organ responds to low pitch sounds?
    6 years ago
  • Maria Pia
    How inner and outer hair cells innervate low frequency neurons?
    6 years ago
  • Gabriele
    Where are the sensory hair cells of the cochlear duct located?
    6 years ago
  • Fikru
    Is the spiral organ associated with hearing?
    6 years ago
  • alcide longo
    Does the base of the spiral organ respond to low frequencies of sound?
    2 years ago
  • heli
    Which of the following stimulates the hair cells found within the spiral organ of Corti?
    2 years ago
  • hagosa brhane
    What are the main part of physiology of spiral organ?
    2 years ago
  • Mary
    What happens when the hair cells of the spiral organ bend?
    2 years ago
  • mattalic
    Which structure inside the spiral organ allows us to differentiate sounds of different pitch?
    6 months ago
  • BRAYDEN
    Which of the following structures in the cochlea corresponds to the location of the spiral organ?
    6 months ago
  • Vihtori
    What is spiral organ anatomy?
    3 months ago

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