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Tuning of the tectorial membrane in the basilar papilla of the northern leopard frog.

Schoffelen RL, Segenhout JM, van Dijk P - J. Assoc. Res. Otolaryngol. (2009)

Bottom Line: Our results are comparable to those of neural-tuning curves in the same and a similar species.Also, they are in agreement with the response of an associated structure-the contact membrane-in a closely related species.Our data provides evidence for a mechanical basis for the frequency selectivity of the frog's BP.

View Article: PubMed Central - PubMed

Affiliation: Department of Otorhinolaryngology/Head and Neck Surgery, University Medical Center Groningen, 9700RB, Groningen, The Netherlands. r.l.m.schoffelen@med.umcg.nl

ABSTRACT
The basilar papilla (BP) in the frog inner ear is a relatively simple auditory receptor. Its hair cells are embedded in a stiff support structure, with the stereovilli connecting to a flexible tectorial membrane (TM). Acoustic energy passing the papilla presumably causes displacement of the TM, which in turn deflects the stereovilli and stimulates the hair cells. Auditory neurons that contact the BP's hair cells are known to have nearly identical characteristic frequencies and frequency selectivity. In this paper, we present optical measurements of the mechanical response of the TM. Results were obtained from five specimens. The TM displacement was essentially in phase across the membrane, with the largest amplitudes occurring near the hair cells. The response was tuned to a frequency near 2 kHz. The phase accumulated over at least 270 degrees across the measured frequencies. The tuning quality Q(10dB) values were calculated; the average Q(10dB) was 2.0 +/- 0.8 (standard deviation). Our results are comparable to those of neural-tuning curves in the same and a similar species. Also, they are in agreement with the response of an associated structure-the contact membrane-in a closely related species. Our data provides evidence for a mechanical basis for the frequency selectivity of the frog's BP.

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Frog ear anatomy and orientation in the measurement setup. A Schematic cross-section of the frog ear (adapted from Wever 1985). On the right, the air-filled middle ear is displayed with the tympanic membrane and the columella. On the left, the fluid-filled inner ear is shown, with the perilymphatic fluid in white and the endolymphatic fluid in gray. The tectorial membranes of both the AP and the BP are indicated in red. The oval window is covered by the footplate (F) of the columella and the operculum (Op). B Schematic of the preparation and its orientation in the experimental setup. The preparation is rotated approximately 90° relative to panel A. The arrow indicates the microscope’s viewing direction; the green dashed line indicates the line of sight. The stimulator (S), placed against the operculum, is indicated in blue on the left. The dashed gray outline indicates the area detailed in panel C. C Cross-section of the frog’s BP anatomy (based on Frishkopf and Flock 1974; R. catesbeiana). The arrow again indicates the viewing direction. Labels: AP amphibian papilla, BP basilar papilla, CM contact membrane (purple), E endolymph, Ep epithelium (blue), F columella footplate, MM middle-ear muscles, N nerve fibers (yellow), O microscope objective, Op operculum, P perilymph, S stimulator (blue), Sacc sacculus, TM tectorial membrane (red).
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Fig1: Frog ear anatomy and orientation in the measurement setup. A Schematic cross-section of the frog ear (adapted from Wever 1985). On the right, the air-filled middle ear is displayed with the tympanic membrane and the columella. On the left, the fluid-filled inner ear is shown, with the perilymphatic fluid in white and the endolymphatic fluid in gray. The tectorial membranes of both the AP and the BP are indicated in red. The oval window is covered by the footplate (F) of the columella and the operculum (Op). B Schematic of the preparation and its orientation in the experimental setup. The preparation is rotated approximately 90° relative to panel A. The arrow indicates the microscope’s viewing direction; the green dashed line indicates the line of sight. The stimulator (S), placed against the operculum, is indicated in blue on the left. The dashed gray outline indicates the area detailed in panel C. C Cross-section of the frog’s BP anatomy (based on Frishkopf and Flock 1974; R. catesbeiana). The arrow again indicates the viewing direction. Labels: AP amphibian papilla, BP basilar papilla, CM contact membrane (purple), E endolymph, Ep epithelium (blue), F columella footplate, MM middle-ear muscles, N nerve fibers (yellow), O microscope objective, Op operculum, P perilymph, S stimulator (blue), Sacc sacculus, TM tectorial membrane (red).

Mentions: The anuran inner ear provides us with an opportunity to study a variation of the vertebrate auditory receptor that is a lot less complex than the mammalian cochlea. The anatomy of the frog inner ear (Fig. 1) differs significantly from that of the mammalian inner ear. It contains two auditory end organs, the amphibian papilla (AP) and the basilar papilla. Both the AP and the BP have hair cells as their mechano-electrical transducers. However, they lack a basilar membrane as the flexible substrate for these cells. Instead, the hair cells are set in limbic tissue (Wever 1985), with the stereovilli protruding into the endolymphatic space and connecting to the overlying TM.FIG. 1


Tuning of the tectorial membrane in the basilar papilla of the northern leopard frog.

Schoffelen RL, Segenhout JM, van Dijk P - J. Assoc. Res. Otolaryngol. (2009)

Frog ear anatomy and orientation in the measurement setup. A Schematic cross-section of the frog ear (adapted from Wever 1985). On the right, the air-filled middle ear is displayed with the tympanic membrane and the columella. On the left, the fluid-filled inner ear is shown, with the perilymphatic fluid in white and the endolymphatic fluid in gray. The tectorial membranes of both the AP and the BP are indicated in red. The oval window is covered by the footplate (F) of the columella and the operculum (Op). B Schematic of the preparation and its orientation in the experimental setup. The preparation is rotated approximately 90° relative to panel A. The arrow indicates the microscope’s viewing direction; the green dashed line indicates the line of sight. The stimulator (S), placed against the operculum, is indicated in blue on the left. The dashed gray outline indicates the area detailed in panel C. C Cross-section of the frog’s BP anatomy (based on Frishkopf and Flock 1974; R. catesbeiana). The arrow again indicates the viewing direction. Labels: AP amphibian papilla, BP basilar papilla, CM contact membrane (purple), E endolymph, Ep epithelium (blue), F columella footplate, MM middle-ear muscles, N nerve fibers (yellow), O microscope objective, Op operculum, P perilymph, S stimulator (blue), Sacc sacculus, TM tectorial membrane (red).
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Fig1: Frog ear anatomy and orientation in the measurement setup. A Schematic cross-section of the frog ear (adapted from Wever 1985). On the right, the air-filled middle ear is displayed with the tympanic membrane and the columella. On the left, the fluid-filled inner ear is shown, with the perilymphatic fluid in white and the endolymphatic fluid in gray. The tectorial membranes of both the AP and the BP are indicated in red. The oval window is covered by the footplate (F) of the columella and the operculum (Op). B Schematic of the preparation and its orientation in the experimental setup. The preparation is rotated approximately 90° relative to panel A. The arrow indicates the microscope’s viewing direction; the green dashed line indicates the line of sight. The stimulator (S), placed against the operculum, is indicated in blue on the left. The dashed gray outline indicates the area detailed in panel C. C Cross-section of the frog’s BP anatomy (based on Frishkopf and Flock 1974; R. catesbeiana). The arrow again indicates the viewing direction. Labels: AP amphibian papilla, BP basilar papilla, CM contact membrane (purple), E endolymph, Ep epithelium (blue), F columella footplate, MM middle-ear muscles, N nerve fibers (yellow), O microscope objective, Op operculum, P perilymph, S stimulator (blue), Sacc sacculus, TM tectorial membrane (red).
Mentions: The anuran inner ear provides us with an opportunity to study a variation of the vertebrate auditory receptor that is a lot less complex than the mammalian cochlea. The anatomy of the frog inner ear (Fig. 1) differs significantly from that of the mammalian inner ear. It contains two auditory end organs, the amphibian papilla (AP) and the basilar papilla. Both the AP and the BP have hair cells as their mechano-electrical transducers. However, they lack a basilar membrane as the flexible substrate for these cells. Instead, the hair cells are set in limbic tissue (Wever 1985), with the stereovilli protruding into the endolymphatic space and connecting to the overlying TM.FIG. 1

Bottom Line: Our results are comparable to those of neural-tuning curves in the same and a similar species.Also, they are in agreement with the response of an associated structure-the contact membrane-in a closely related species.Our data provides evidence for a mechanical basis for the frequency selectivity of the frog's BP.

View Article: PubMed Central - PubMed

Affiliation: Department of Otorhinolaryngology/Head and Neck Surgery, University Medical Center Groningen, 9700RB, Groningen, The Netherlands. r.l.m.schoffelen@med.umcg.nl

ABSTRACT
The basilar papilla (BP) in the frog inner ear is a relatively simple auditory receptor. Its hair cells are embedded in a stiff support structure, with the stereovilli connecting to a flexible tectorial membrane (TM). Acoustic energy passing the papilla presumably causes displacement of the TM, which in turn deflects the stereovilli and stimulates the hair cells. Auditory neurons that contact the BP's hair cells are known to have nearly identical characteristic frequencies and frequency selectivity. In this paper, we present optical measurements of the mechanical response of the TM. Results were obtained from five specimens. The TM displacement was essentially in phase across the membrane, with the largest amplitudes occurring near the hair cells. The response was tuned to a frequency near 2 kHz. The phase accumulated over at least 270 degrees across the measured frequencies. The tuning quality Q(10dB) values were calculated; the average Q(10dB) was 2.0 +/- 0.8 (standard deviation). Our results are comparable to those of neural-tuning curves in the same and a similar species. Also, they are in agreement with the response of an associated structure-the contact membrane-in a closely related species. Our data provides evidence for a mechanical basis for the frequency selectivity of the frog's BP.

Show MeSH
Related in: MedlinePlus