Now, reporting on rat experiments in the October 22 issue of Nature, a Johns Hopkins team says it has for what is believed to be the first time managed to measure and record the elusive electrical activity of the type II neurons in the snail-shell-like structure called the cochlea.
And it turns out the cells do indeed carry signals from the ear to the brain, and the sounds they likely respond to would need to be loud, such as sirens or alarms that might be even be described as painful or traumatic.
The researchers say they’ve also discovered that these sensory cells get the job done by responding to glutamate released from sensory hair cells of the inner ear. Glutamate is a workhorse neurotransmitter throughout the nervous system and it excites the cochlear neurons to carry acoustic information to the brain.
“No one thought recording them was even possible,” says Paul A. Fuchs, Ph.D., the John E. Bordley Professor of Otolaryngology–Head and Neck Surgery and co-director of the Center for Sensory Biology in the Johns Hopkins University School of Medicine, and a co-author of the report. “We knew the type II neurons were there and now at last we know something about what they do and how they do it.”
Working with week-old rats, neuroscience graduate student Catherine Weisz removed live, soft tissue from the fragile cochlea and, guided by a powerful microscope, touched electrodes to the tiny type II nerve endings beneath the sensory hair cells. Different types of stimuli were used to activate sensory hair cells, allowing Weisz to record and analyze the resulting signals in type II fibers.
Results showed that, unlike type I neurons which are electrically activated by the quietest sounds we hear, and which saturate as sounds get louder, each type II neuron would need to be hit hard by a very loud sound to produce excitation, Fuchs says.
The cell bodies of both type I and type II neurons sprout long filaments, or axons that head to the brain, and some others that connect to sensory hair cells. Unlike the big type I neurons, each of which make one little sprout that touches one sensory hair cell in one spot, the type II cells have projections that contact dozens of hair cells over a relatively great distance.
“Somewhat counter-intuitively, the type II cell that contacts many hair cells receives surprisingly little synaptic input,” Fuchs says. “In fact, all of its many contacts put together yield less input than that provided by the one single hair cell touching a type I neuron.”
Fuchs and his team postulate that the two systems may serve different functional roles. “There’s a distinct difference between analyzing sound to extract meaning — Is that a cat meowing, a baby crying or a man singing? — versus the startle reflex triggered by a thunderclap or other sudden loud sound.” Type II afferents may play a role in such reflexive withdrawals from potential trauma.”
This study was supported by the National Institute on Deafness and Other Communication Disorders, and a grant from the Blaustein Pain Foundation of Johns Hopkins.
Authors on the paper are Fuchs, Weisz and Elisabeth Glowatzki, all of the Center for Hearing and Balance and the Center for Sensory Biology, Johns Hopkins University School of Medicine.
On the Web:
Paul Fuchs: http://neuroscience.jhu.edu/PaulFuchs.php
Elisabeth Glowatzki: http://neuroscience.jhu.edu/ElisabethGlowatzki.phpCenter for Sensory Biology: http://www.hopkinsmedicine.org/institute_basic_biomedical_sciences/
Center for Hearing and Balance: http://ww2.jhu.edu/chb/
Neutrons produce first direct 3D maps of water during cell membrane fusion
21.09.2018 | DOE/Oak Ridge National Laboratory
Narcolepsy, scientists unmask the culprit of an enigmatic disease
20.09.2018 | Universitätsspital Bern
The building blocks of matter in our universe were formed in the first 10 microseconds of its existence, according to the currently accepted scientific picture. After the Big Bang about 13.7 billion years ago, matter consisted mainly of quarks and gluons, two types of elementary particles whose interactions are governed by quantum chromodynamics (QCD), the theory of strong interaction. In the early universe, these particles moved (nearly) freely in a quark-gluon plasma.
This is a joint press release of University Muenster and Heidelberg as well as the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.
Then, in a phase transition, they combined and formed hadrons, among them the building blocks of atomic nuclei, protons and neutrons. In the current issue of...
Thin-film solar cells made of crystalline silicon are inexpensive and achieve efficiencies of a good 14 percent. However, they could do even better if their shiny surfaces reflected less light. A team led by Prof. Christiane Becker from the Helmholtz-Zentrum Berlin (HZB) has now patented a sophisticated new solution to this problem.
"It is not enough simply to bring more light into the cell," says Christiane Becker. Such surface structures can even ultimately reduce the efficiency by...
A study in the journal Bulletin of Marine Science describes a new, blood-red species of octocoral found in Panama. The species in the genus Thesea was discovered in the threatened low-light reef environment on Hannibal Bank, 60 kilometers off mainland Pacific Panama, by researchers at the Smithsonian Tropical Research Institute in Panama (STRI) and the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica.
Scientists established the new species, Thesea dalioi, by comparing its physical traits, such as branch thickness and the bright red colony color, with the...
Scientists have succeeded in observing the first long-distance transfer of information in a magnetic group of materials known as antiferromagnets.
An international team of researchers has mapped Nemo's genome, providing the research community with an invaluable resource to decode the response of fish to...
21.09.2018 | Event News
03.09.2018 | Event News
27.08.2018 | Event News
21.09.2018 | Physics and Astronomy
21.09.2018 | Life Sciences
21.09.2018 | Event News