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/
Scientists learn more about how gene linked to autism affects brain
19.06.2018 | Cincinnati Children's Hospital Medical Center
Overdosing on Calcium
19.06.2018 | Albert-Ludwigs-Universität Freiburg im Breisgau
Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...
Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.
Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...
The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.
Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.
An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.
Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...
Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for...
13.06.2018 | Event News
08.06.2018 | Event News
05.06.2018 | Event News
19.06.2018 | Physics and Astronomy
19.06.2018 | Life Sciences
19.06.2018 | Physics and Astronomy