PRESS-NEWS.org - Press Release Distribution
PRESS RELEASES DISTRIBUTION

Neurobiology -- tuning of timing in auditory axons

2015-08-26
(Press-News.org) This news release is available in German.

An LMU team has shown that the axons of auditory neurons in the brainstem which respond to low and high-frequency sounds differ in their morphology, and that these variations correlate with differences in the speed of signal conduction. As a rule, the axons (i.e. signal-transmitting fibers) of the neurons in the central nervous systems of vertebrates are ensheathed in layers of myelin, which serves as a form of insulation that improves their electrical conduction properties. In fact, the fat-rich myelin coating largely consists of the cell membranes of so-called glia cells, which wrap themselves around the axon. Along the axons, the myelin sheath is regularly interrupted by structures referred to as the nodes of Ranvier, and its insulating effect ensures that action potentials can be built up (i.e. signal transmission can occur) only at these sites. In other words, the action potentials in myelinized axons propagate in a saltatory fashion, jumping from node to node across the intervening insulated stretches or 'internodes'. It has generally been assumed that the speed of conduction of action potentials along such axons increases with axon diameter and with the distance between successive nodes of Ranvier. A new study done by a team of researchers led by LMU neurobiologist Professor Benedikt Grothe, in collaboration with colleagues based at University College London, has now overturned this idea ­- which is cited in most neurobiology textbooks. "Our findings clearly refute the conventional notion that the speed of signal transmission in the myelinized axon of vertebrate neurons always increases in proportion to the length of the internodes," says Grothe. The new results appear in the latest issue of the online journal Nature Communications.

Our sense of hearing is dependent on the conversion of incoming mechanical oscillations into electrical impulses by the sensory hair cells in the inner ear. The impulses are then relayed by other neurons for further processing, which itself depends on the structural characteristics of the signal-transmitting axons. Since both ears encode a given acoustic stimulus in the same way, the decisive cues for sound localization arise from the fact that a given sound both arrives earlier at, and is perceived as louder by the 'ipsilateral ear' (the one closer to the sound source) than the stimulus that reaches the 'contralateral' ear. Hence, precise communication of the timing difference between the responses of the two ears to a given sound to higher processing centers is crucial for accurate localization of the sound source. For this reason, the brain must be capable of encoding minimal differences between the arrival times of signals at the two ears. This computation requires a complex set of interactions between the several different nerve cells that relay this information, in the form of action potentials, from the inner ear to auditory neurons in the brainstem.

Grothe and his colleagues have unexpectedly discovered that structural adaptations relating to the nodes of Ranvier and the intervening internodes in the auditory neurons in the mammalian brainstem play a critical role in tuning the rate and precision of signal propagation via these pathways.

Precise modeling of axonal geometry

"Our investigation revealed structural differences in the pattern of myelinization of their axons. The axons that are most sensitive to low-frequency tones are larger in diameter than those that respond to high-frequency sounds but ­- surprisingly ­- their internode regions are actually shorter," Grothe explains. In addition, computer simulations carried out by the researchers indicated that these variations in axon morphology should act to tune the speed of signal conduction. Subsequent electrophysiological measurements then confirmed that axons that react to low-frequency tones transmit signals faster and with greater fidelity.

"Our findings also contradict the widespread assumption that axons which serve the same function must be structurally identical, and that the length of their internodes is always proportional to the axon diameter," Grothe points out. "Instead, it looks as if there are systematic structural differences between them that depend on the site of origin of the signals and the nature of their target circuits." (Nature Communications 2015)

INFORMATION:



ELSE PRESS RELEASES FROM THIS DATE:

Rehabilitation improves the prognosis of serious heart disease

2015-08-26
Rehabilitation is recommended for many patients following a hospital stay for acute heart disease. In a recent original article in Deutsches Ärzteblatt International (Dtsch Arztebl int 112: 527-34) Axel Schlitt et al. show that this improves prognosis for heart disease and can thus reduce patient mortality. More than 1900 patients in Saxony-Anhalt were contacted and asked to fill out a questionnaire. They had spent time in the hospital for serious cardiovascular disease an average of 11 years earlier. The authors used the data to analyze how many of the patients who ...

Routine surgery

2015-08-26
Cholecystectomy and treatment for inguinal, femoral, umbilical, or abdominal hernia are common surgeries and are considered routine in Germany. In an original article in the current edition of Deutsches Ärzteblatt International (Dtsch Arztebl Int 112: 535-43), Ulrike Nimptsch and Thomas Mansky show that fewer than 0.5% of patients die as a result of such surgeries. However, in those who do die risks are frequently apparent even before surgery. Between 2009 and 2013, 731 000 cholecystectomies and 1 023 000 herniotomies took place in Germany. Over 2400 of the patients ...

The fear of trying new foods may have negative dietary implications

2015-08-26
This news release is available in Spanish. The behaviour involving rejection of new foodstuffs is a typical phase in infant development, above all in 2- to 3-year-olds and which subsides around the age of 5. The children who go through dietary neophobia also display signs of anguish and anxiety and this behaviour may even turn into a habit in adulthood. In her PhD thesis the researcher of the UPV/EHU's Faculty of Psychology Edurne Maiz conducted a study on 831 schoolchildren between the ages of 8 and 16. In the study she used questionnaires on infant neophobia -adapted ...

The missing link

The missing link
2015-08-26
University of Alberta paleontologists have discovered a new species of lizard, named Gueragama sulamericana, in the municipality of Cruzeiro do Oeste in Southern Brazil in the rock outcrops of a Late Cretaceous desert, dated approximately 80 million years ago. "The roughly 1700 species of iguanas are almost without exception restricted to the New World, primarily the Southern United States down to the tip of South America," says Michael Caldwell, biological sciences professor from the University of Alberta and one of the study's authors. Oddly however, iguanas closest ...

Home sweet microbe: Dust in your house can predict geographic region, gender of occupants

Home sweet microbe: Dust in your house can predict geographic region, gender of occupants
2015-08-26
The humble dust collecting in the average American household harbors a teeming menagerie of bacteria and fungi, and as researchers from the University of Colorado Boulder and North Carolina State University have discovered, it may be able to predict not only the geographic region of a given home, but the gender ratio of the occupants and the presence of a pet as well. The new findings, which were published today in the journal Proceedings of the Royal Society B, highlight the impressive amount of microbial diversity in the average household and the degree to which these ...

Police professionals are better observers than ordinary civilians

2015-08-26
Dutch research shows that trained detectives of specialized observation teams are much better at registering details of a drug deal than ordinary civilians. Previous legal-psychological research revealed no relevant differences in observation skills between police professionals and civilians. The findings have been published in Legal and Criminological Psychology. Judges and juries often assume that police officers' statements are more reliable than those of regular eyewitnesses. Because of this assumption, police officers' statements typically carry more weight in legal ...

Few gay teenage boys get tested for HIV

2015-08-26
Only one in five gay and bisexual teen boys have been tested for HIV HIV infections are on the rise for young men who have sex with men Text messages, online program can identify nearby confidential testing sites Testing in schools would 'normalize' the process. CHICAGO --- Young men who have sex with men have the highest risk for HIV infection, but only one in five has ever been tested for HIV, a much lower rate than testing for non-adolescents, reports a new national Northwestern Medicine study conducted in partnership with the Center for Innovative Public ...

Foes can become friends on the coral reef

Foes can become friends on the coral reef
2015-08-26
On the coral reef, knowing who's your friend and who's your enemy can sometimes be a little complicated. Take seaweed, for instance. Normally it's the enemy of coral, secreting toxic chemicals, blocking the sunlight, and damaging coral with its rough surfaces. But when hordes of hungry crown-of-thorns sea stars invade the reef, everything changes, reports a study to be published August 25 in the journal Proceedings of the Royal Society B. Seaweeds appear to protect coral from the marauding sea stars, giving new meaning to the proverb: "The enemy of my enemy is my friend." ...

Chocolate physics: How modeling could improve 'mouthfeel'

2015-08-26
Lecithin is an ingredient that you've probably never heard of, but one that plays a vital role in the production of chocolate and many other foods. It's never been clear how this ingredient works on a molecular level, and confectioners have relied on observational methods - essentially trial and error - to perfect their recipes. Now, scientists have shown how the field of molecular dynamics (simulation on a molecular level) could be a valuable tool in understanding chocolate conching - the part of the chocolate-making process where aromatic sensation, texture and 'mouthfeel' ...

New cardiovascular disease death rates show stark inequalities between European countries

2015-08-26
Diseases of the heart and blood vessels are the most common cause of death in Europe, resulting in over four million deaths a year (45% of all deaths) according to the latest available figures published today (Wednesday) in the European Heart Journal [1]. Although deaths from cardiovascular disease (CVD) are declining in most of Europe, there are large inequalities between European countries, with higher death rates seen in Eastern Europe. These high death rates correspond to the lower life expectancy also found in these countries, indicating the impact of CVD on inequalities ...

LAST 30 PRESS RELEASES:

Signs identified that precede sudden arrhythmic death syndrome in young people

Discovery of bacteria's defence against viruses becomes a piece of the puzzle against resistance

Pre-eclampsia is associated with earlier onset and higher incidence of cardiovascular risk factors

Warwick astronomers discover doomed pair of spiralling stars on our cosmic doorstep

Soil conditions significantly increase rainfall in world’s megastorm hotspots

NK cells complexed with bispecific antibody yield high response rates in patients with lymphoma

Planetary health diet and mediterranean diet associated with similar survival and sustainability benefits

Singapore launches national standard to validate antimicrobial disinfectant products

Molecular stool test could improve detection of tuberculosis in adults with HIV

Suspected fibrocartilaginous embolus in Asian small-clawed otter (Aonyx cinereus)

Enhancing heat transfer using the turbulent flow of viscoelastic fluids

Exercise as an anti-ageing intervention to avoid detrimental impact of mental fatigue

UMass Amherst Nursing Professor Emerita honored as ‘Living Legend’

New guidelines aim to improve cystic fibrosis screening

Picky eaters by day, buffet by night: Butterfly, moth diets sync to plant aromas

Pennington Biomedical’s Dr. Leanne Redman honored with the E. V. McCollum Award from the American Society for Nutrition

CCNY physicists uncover electronic interactions mediated via spin waves

Researchers’ 3D-printing formula may transform future of foam

Nurture more important than nature for robotic hand

Drug-delivering aptamers target leukemia stem cells for one-two knockout punch

New study finds that over 95% of sponsored influencer posts on Twitter were not disclosed

New sea grant report helps great lakes fish farmers navigate aquaculture regulations

Strain “trick” improves perovskite solar cells’ efficiency

How GPS helps older drivers stay on the roads

Estrogen and progesterone stimulate the body to make opioids

Dancing with the cells – how acoustically levitating a diamond led to a breakthrough in biotech automation

Machine learning helps construct an evolutionary timeline of bacteria

Cellular regulator of mRNA vaccine revealed... offering new therapeutic options

Animal behavioral diversity at risk in the face of declining biodiversity

Finding their way: GPS ignites independence in older adult drivers

[Press-News.org] Neurobiology -- tuning of timing in auditory axons