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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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The basilar papilla of the northern leopard frog as seen from the round window. A Light microscopy image with definition of the x and y directions; the z direction points into the image plane. B Indication of important structures in panel A. E endolymphatic space (white), Ep epithelium (blue), N nerve fibers (yellow), TM tympanic membrane (red).
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Fig2: The basilar papilla of the northern leopard frog as seen from the round window. A Light microscopy image with definition of the x and y directions; the z direction points into the image plane. B Indication of important structures in panel A. E endolymphatic space (white), Ep epithelium (blue), N nerve fibers (yellow), TM tympanic membrane (red).

Mentions: An example of an individual measurement image is given in Figure 2A, with the important anatomical features indicated in Figure 2B. The TM occludes approximately half of the BP’s lumen. It has a free edge (at the top in Fig. 2), and an approximately semicircular area, when viewed from the round-window side. The free edge is firmly attached on both sides to the lumen boundary, and thick compared to the rest of the TM (personal observation from scanning electron microscopy). The TM thickness, i.e., the extent along the viewing direction (z direction, Fig. 2), is approximately 50 μm (Schoffelen et al. 2007). The sensory epithelium is located under the curved perimeter of the TM (Fig. 2B).FIG. 2


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)

The basilar papilla of the northern leopard frog as seen from the round window. A Light microscopy image with definition of the x and y directions; the z direction points into the image plane. B Indication of important structures in panel A. E endolymphatic space (white), Ep epithelium (blue), N nerve fibers (yellow), TM tympanic membrane (red).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2717376&req=5

Fig2: The basilar papilla of the northern leopard frog as seen from the round window. A Light microscopy image with definition of the x and y directions; the z direction points into the image plane. B Indication of important structures in panel A. E endolymphatic space (white), Ep epithelium (blue), N nerve fibers (yellow), TM tympanic membrane (red).
Mentions: An example of an individual measurement image is given in Figure 2A, with the important anatomical features indicated in Figure 2B. The TM occludes approximately half of the BP’s lumen. It has a free edge (at the top in Fig. 2), and an approximately semicircular area, when viewed from the round-window side. The free edge is firmly attached on both sides to the lumen boundary, and thick compared to the rest of the TM (personal observation from scanning electron microscopy). The TM thickness, i.e., the extent along the viewing direction (z direction, Fig. 2), is approximately 50 μm (Schoffelen et al. 2007). The sensory epithelium is located under the curved perimeter of the TM (Fig. 2B).FIG. 2

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