Format

Send to

Choose Destination
See comment in PubMed Commons below
J Basic Clin Physiol Pharmacol. 2001;12(2 Suppl):91-9.

The pathway for the transmission of external sounds into the fetal inner ear.

Author information

  • 1Department of Physiology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel. sohmer@md2.huji.ac.il

Abstract

After at least 20 weeks gestation, the human fetus in utero is able to hear and respond to external and internal (maternal) sounds. The external sounds are attenuated by maternal tissues and fluids - higher frequencies by about 20 dB, and lower frequencies are only slightly reduced. The sounds in the amniotic fluid, which completely envelops the fetus, then reach the fetal inner ear by bone conduction. The sound pressure in the amniotic fluid induces skull vibrations which are transmitted directly into the contents of the cranial cavity (brain and CSF) and from there, presumably by fluid channels connecting them, into the cochlear fluids. A further stage of conductive attenuation is probably involved in this transmission. Since the fetus in utero receives oxygen by placental diffusion (less efficient than pulmonary diffusion), the fetal inner ear is hypoxic compared to that following birth (pulmonary oxygen diffusion). This leads to a reduction in the magnitude of the endocochlear potential, to a depression of cochlear transduction and amplification, and thus to an additional sensorineural component of threshold elevation in the fetus. Upon birth, these conductive and sensorineural attenuations are removed.

PMID:
11605684
[PubMed - indexed for MEDLINE]
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Loading ...
    Write to the Help Desk