Rewrite the textbooks (on what neurons can do)

Rewrite the textbooks

From the February 17 2011 Eureka news alert

Image via Wikipedia (Click on Image to Enlarge)

 

Neurons are complicated, but the basic functional concept is that synapses transmit electrical signals to the dendrites and cell body (input), and axons carry signals away (output). In one of many surprise findings, Northwestern University scientists have discovered that axons can operate in reverse: they can send signals to the cell body, too.

It also turns out axons can talk to each other. Before sending signals in reverse, axons can perform their own neural computations without any involvement from the cell body or dendrites. This is contrary to typical neuronal communication where an axon of one neuron is in contact with another neuron’s dendrite or cell body, not its axon. And, unlike the computations performed in dendrites, the computations occurring in axons are thousands of times slower, potentially creating a means for neurons to compute fast things in dendrites and slow things in axons.

A deeper understanding of how a normal neuron works is critical to scientists who study neurological diseases, such as epilepsy, autism, Alzheimer’s disease and schizophrenia.

The findings are published in the February issue of the journal Nature Neuroscience.***

“We have discovered a number of things fundamental to how neurons work that are contrary to the information you find in neuroscience textbooks,” said Nelson Spruston, senior author of the paper and professor of neurobiology and physiology in the Weinberg College of Arts and Sciences. “Signals can travel from the end of the axon toward the cell body, when it typically is the other way around. We were amazed to see this.”

He and his colleagues first discovered individual nerve cells can fire off signals even in the absence of electrical stimulations in the cell body or dendrites. It’s not always stimulus in, immediate action potential out. (Action potentials are the fundamental electrical signaling elements used by neurons; they are very brief changes in the membrane voltage of the neuron.)

Similar to our working memory when we memorize a telephone number for later use, the nerve cell can store and integrate stimuli over a long period of time, from tens of seconds to minutes. (That’s a very long time for neurons.) Then, when the neuron reaches a threshold, it fires off a long series of signals, or action potentials, even in the absence of stimuli. The researchers call this persistent firing, and it all seems to be happening in the axon.

Spruston and his team stimulated a neuron for one to two minutes, providing a stimulus every 10 seconds. The neuron fired during this time but, when the stimulation was stopped, the neuron continued to fire for a minute.

“It’s very unusual to think that a neuron could fire continually without stimuli,” Spruston said. “This is something new — that a neuron can integrate information over a long time period, longer than the typical operational speed of neurons, which is milliseconds to a second.”

This unique neuronal function might be relevant to normal process, such as memory, but it also could be relevant to disease. The persistent firing of these inhibitory neurons might counteract hyperactive states in the brain, such as preventing the runaway excitation that happens during epileptic seizures.

Spruston credits the discovery of the persistent firing in normal individual neurons to the astute observation of Mark Sheffield, a graduate student in his lab. Sheffield is first author of the paper.

The researchers think that others have seen this persistent firing behavior in neurons but dismissed it as something wrong with the signal recording. When Sheffield saw the firing in the neurons he was studying, he waited until it stopped. Then he stimulated the neuron over a period of time, stopped the stimulation and then watched as the neuron fired later.

“This cellular memory is a novelty,” Spruston said. “The neuron is responding to the history of what happened to it in the minute or so before.”

Spruston and Sheffield found that the cellular memory is stored in the axon and the action potential is generated farther down the axon than they would have expected. Instead of being near the cell body it occurs toward the end of the axon.

Their studies of individual neurons (from the hippocampus and neocortex of mice) led to experiments with multiple neurons, which resulted in perhaps the biggest surprise of all. The researchers found that one axon can talk to another. They stimulated one neuron, and detected the persistent firing in the other unstimulated neuron. No dendrites or cell bodies were involved in this communication.

“The axons are talking to each other, but it’s a complete mystery as to how it works,” Spruston said. “The next big question is: how widespread is this behavior? Is this an oddity or does in happen in lots of neurons? We don’t think it’s rare, so it’s important for us to understand under what conditions it occurs and how this happens.”

###

The title of the paper is “Slow Integration Leads to Persistent Action Potential Firing in Distal Axons of Coupled Interneurons***.” In addition to Spruston and Sheffield, other authors of the paper are Tyler K. Best and William L. Kath, from Northwestern, and Brett D. Mensh, from Harvard Medical School.

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Stretching before a run does not prevent injury

Stretching before a run does not prevent injury
However, runners who typically stretch should continue, or risk injury

This image was originally posted to Flickr by SteelCityHobbies at http://flickr.com/photos/94767754@N00/1394011566.

From the February 18 2011 Eureka news alert

Stretching before a run neither prevents nor causes injury, according to a study presented today at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS).

More than 70 million people worldwide run recreationally or competitively, and recently there has been controversy regarding whether runners should stretch before running, or not at all. This study included 2,729 runners who run 10 or more miles per week. Of these runners, 1,366 were randomized to a stretch group, and 1,363 were randomized to a non-stretch group before running. Runners in the stretch group stretched their quadriceps, hamstrings, and gastrocnemius/soleus muscle groups. The entire routine took 3 to 5 minutes and was performed immediately before running.

The study found that stretching before running neither prevents nor causes injury. In fact, the most significant risk factors for injury included the following:

• history of chronic injury or injury in the past four months;
• higher body mass index (BMI); and
• switching pre-run stretching routines (runners who normally stretch stopping and those who did stretch starting to stretch before running).

“But, the more mileage run or the heavier and older the runner was, the more likely he or she was likely to get injured,”

“As a runner myself, I thought stretching before a run would help to prevent injury,” said Daniel Pereles, MD, study author and orthopaedic surgeon from Montgomery Orthopedics outside Washington, DC. “However, we found that the risk for injury was the same for men and women, whether or not they were high or low mileage runners, and across all age groups. But, the more mileage run or the heavier and older the runner was, the more likely he or she was likely to get injured, and previous injury within four months predisposed to even further injury,” he added.

Runners who typically stretch as part of their pre-run routine and were randomized not to stretch during the study period were far more likely to have an injury. “Although all runners switching routines were more likely to experience an injury than those who did not switch, the group that stopped stretching had more reported injuries, implying that an immediate shift in a regimen may be more important than the regimen itself,” he added.

The most common injuries sustained were groin pulls, foot/ankle injuries, and knee injuries. There was no significant difference in injury rates between the runners who stretched and the runners who didn’t for any specific injury location or diagnosis.

Carbohydrates: How carbs fit into a healthy diet

Image via Wikipedia

Carbohydrates: How carbs fit into a healthy diet

By Mayo Clinic staff

Carbohydrates often get a bad rap, especially when it comes to weight gain. But carbohydrates aren’t all bad. Because of their numerous health benefits, carbohydrates have a rightful place in your diet. In fact, your body needs carbohydrates to function well. But some carbohydrates may be better for you than others. Understand more about carbohydrates and how to choose healthy carbohydrates.

Understanding carbohydrates

Carbohydrates are a type of macronutrient found in many foods and beverages. Most carbohydrates are naturally occurring in plant-based foods, such as grains. Food manufacturers also add carbohydrates to processed foods in the form of starch or added sugar. The most basic carbohydrate is a sugar molecule, which joins together one or two units of carbon, hydrogen and oxygen. Other carbohydrates contain three or more units of the carbon-hydrogen-oxygen trio.

Common sources of naturally occurring carbohydrates include:

• Fruits
• Vegetables
• Milk
• Nuts
• Grains
• Seeds
• Legumes

Types of carbohydrates

There are three main types of carbohydrates:

• Sugar. Sugar is the simplest forms of carbohydrates. Sugar occurs naturally in some foods, including fruits, vegetables, milk and milk products. Sugars include fruit sugar (fructose), table sugar (sucrose) and milk sugar (lactose).
• Starch. Starch is made of sugar units bonded together. Starch occurs naturally in vegetables, grains, and cooked dry beans and peas.
• Fiber. Fiber also is made of sugar units bonded together. Fruits, vegetables, whole grains, and cooked dry beans and peas are among foods that are naturally rich in fiber.

More carbohydrate terms: Net carbs and glycemic index

You may see terms such as “low carb” or “net carbs” on some products, or promoted by some diet programs. But the Food and Drug Administration doesn’t regulate these terms, so there’s no standard meaning. Net carbs is typically used to mean the amount of carbohydrates in a product excluding fiber or excluding both fiber and sugar alcohols.

You’ve probably also have heard talk about the glycemic index. The glycemic index classifies carbohydrate-containing foods according to their potential to raise your blood sugar level. Many healthy foods, such as whole grains, legumes, vegetables, fruits and low-fat dairy products, are naturally low on the glycemic index. Weight-loss diets based on the glycemic index typically restrict foods with a relatively high glycemic index ranking, such as potatoes and corn. However, there also are health benefits from these foods, so you don’t necessarily have to eliminate them from your diet.

How many carbohydrates do you need?

The 2010 Dietary Guidelines for Americans recommends that carbohydrates make up 45 to 65 percent of your total daily calories. So, if you get 2,000 calories a day, between 900 and 1,300 calories should be from carbohydrates. That translates to between 225 and 325 grams of carbohydrates a day.

You can find the carbohydrate content of packaged foods by reading the Nutrition Facts label. The Nutrition Facts label shows total carbohydrates, which includes starches, fiber, sugar alcohols, and naturally occurring and added sugars. It may also list total fiber, soluble fiber and sugar separately. You may also be able to find nutrient calculators online or find information on a manufacturer’s website.

Carbohydrates and your health

Despite their bad rap, carbohydrates are vital to your health for a number of reasons.

Providing energy
Your body uses carbohydrates as its main fuel source. Sugars and starches are broken down into simple sugars during digestion. They’re then absorbed into your bloodstream, where they’re known as blood sugar (glucose). From there, the glucose enters your body’s cells with the help of insulin. Some of this glucose is used by your body for energy, fueling all of your activities, whether it’s going for a jog or simply breathing. Extra glucose is stored in your liver, muscles and other cells for later use or is converted to fat.

Protecting against disease
Some evidence shows that whole grains and dietary fiber from whole foods helps reduce your risk of cardiovascular diseases. Fiber may also protect against obesity and type 2 diabetes. Fiber is also essential for optimal digestive health.

Controlling weight
Evidence shows that eating plenty of vegetables, fruits and whole grains can help you control your weight. Their bulk and fiber content aids weight control by helping you feel full on fewer calories. Contrary to what some weight-loss diets claim, very few studies show that a diet rich in healthy carbohydrates leads to weight gain or obesity.

Choosing carbohydrates wisely

Carbohydrates are an essential part of a healthy diet, and they also provide many important nutrients. Still, not all carbs are created equal. Here’s how to make healthy carbohydrates work in a balanced diet:

• Emphasize fiber-rich fruits and vegetables. Aim for whole fresh, frozen and canned fruits and vegetables without added sugar. They’re better options than are fruit juices and dried fruits, which are concentrated sources of natural sugar and therefore have more calories. Also, whole fruits and vegetables add fiber, water and bulk, and help you feel fuller on fewer calories.
• Choose whole grains. All types of grains are good sources of carbohydrates. They’re also rich in vitamins and minerals and naturally low in fat. But whole grains are healthier choices than are refined grains. Whole grains are better sources of fiber and other important nutrients, such as selenium, potassium and magnesium. Refined grains go through a process that strips out certain parts of the grain — along with some of the nutrients and fiber.
• Stick to low-fat dairy products. Milk, cheese, yogurt and other dairy products are good sources of calcium and protein, plus many other vitamins and minerals. Choose the low-fat versions, though, to help limit calories and saturated fat. And beware of dairy products that have added sugar.
• Don’t forget beans and legumes. Legumes — beans, peas and lentils — are among the most versatile and nutritious foods available. Legumes are typically low in fat, contain no cholesterol, and are high in folate, potassium, iron and magnesium. They also have beneficial fats, and soluble and insoluble fiber. Because they’re a good source of protein, legumes can be a healthy substitute for meat, which has more saturated fat and cholesterol.
• Limit added sugars. Added sugar probably isn’t harmful in small amounts. But there’s no health advantage to consuming any amount of added sugar. In fact, too much added sugar, and in some cases naturally occurring sugar, can lead to such health problems as tooth decay, poor nutrition and weight gain.

So choose your carbohydrates wisely. Limit foods with added sugars and refined grains, such as sugary drinks, desserts and candy, which are packed with calories but low in nutrition. Instead, go for whole grains and fruits and vegetables.

From the Mayo Clinic patient handout

Carbohydrates aren’t bad, but some may be healthier than others. See why carbs are important for your health and which ones to choose.

By Mayo Clinic staffCarbohydrates often get a bad rap, especially when it comes to weight gain. But carbohydrates aren’t all bad. Because of their numerous health benefits, carbohydrates have a rightful place in your diet. In fact, your body needs carbohydrates to function well. But some carbohydrates may be better for you than others. Understand more about carbohydrates and how to choose healthy carbohydrates.

Understanding carbohydrates

Carbohydrates are a type of macronutrient found in many foods and beverages. Most carbohydrates are naturally occurring in plant-based foods, such as grains. Food manufacturers also add carbohydrates to processed foods in the form of starch or added sugar. The most basic carbohydrate is a sugar molecule, which joins together one or two units of carbon, hydrogen and oxygen. Other carbohydrates contain three or more units of the carbon-hydrogen-oxygen trio.

Common sources of naturally occurring carbohydrates include:

• Fruits
• Vegetables
• Milk
• Nuts
• Grains
• Seeds
• Legumes

Types of carbohydrates

There are three main types of carbohydrates:

• Sugar. Sugar is the simplest forms of carbohydrates. Sugar occurs naturally in some foods, including fruits, vegetables, milk and milk products. Sugars include fruit sugar (fructose), table sugar (sucrose) and milk sugar (lactose).
• Starch. Starch is made of sugar units bonded together. Starch occurs naturally in vegetables, grains, and cooked dry beans and peas.
• Fiber. Fiber also is made of sugar units bonded together. Fruits, vegetables, whole grains, and cooked dry beans and peas are among foods that are naturally rich in fiber.

More carbohydrate terms: Net carbs and glycemic index

You may see terms such as “low carb” or “net carbs” on some products, or promoted by some diet programs. But the Food and Drug Administration doesn’t regulate these terms, so there’s no standard meaning. Net carbs is typically used to mean the amount of carbohydrates in a product excluding fiber or excluding both fiber and sugar alcohols.

You’ve probably also have heard talk about the glycemic index. The glycemic index classifies carbohydrate-containing foods according to their potential to raise your blood sugar level. Many healthy foods, such as whole grains, legumes, vegetables, fruits and low-fat dairy products, are naturally low on the glycemic index. Weight-loss diets based on the glycemic index typically restrict foods with a relatively high glycemic index ranking, such as potatoes and corn. However, there also are health benefits from these foods, so you don’t necessarily have to eliminate them from your diet.

How many carbohydrates do you need?

The 2010 Dietary Guidelines for Americans recommends that carbohydrates make up 45 to 65 percent of your total daily calories. So, if you get 2,000 calories a day, between 900 and 1,300 calories should be from carbohydrates. That translates to between 225 and 325 grams of carbohydrates a day.

You can find the carbohydrate content of packaged foods by reading the Nutrition Facts label. The Nutrition Facts label shows total carbohydrates, which includes starches, fiber, sugar alcohols, and naturally occurring and added sugars. It may also list total fiber, soluble fiber and sugar separately. You may also be able to find nutrient calculators online or find information on a manufacturer’s website.

Carbohydrates and your health

Despite their bad rap, carbohydrates are vital to your health for a number of reasons.

Providing energy
Your body uses carbohydrates as its main fuel source. Sugars and starches are broken down into simple sugars during digestion. They’re then absorbed into your bloodstream, where they’re known as blood sugar (glucose). From there, the glucose enters your body’s cells with the help of insulin. Some of this glucose is used by your body for energy, fueling all of your activities, whether it’s going for a jog or simply breathing. Extra glucose is stored in your liver, muscles and other cells for later use or is converted to fat.

Protecting against disease
Some evidence shows that whole grains and dietary fiber from whole foods helps reduce your risk of cardiovascular diseases. Fiber may also protect against obesity and type 2 diabetes. Fiber is also essential for optimal digestive health.

Controlling weight
Evidence shows that eating plenty of vegetables, fruits and whole grains can help you control your weight. Their bulk and fiber content aids weight control by helping you feel full on fewer calories. Contrary to what some weight-loss diets claim, very few studies show that a diet rich in healthy carbohydrates leads to weight gain or obesity.

Choosing carbohydrates wisely

Carbohydrates are an essential part of a healthy diet, and they also provide many important nutrients. Still, not all carbs are created equal. Here’s how to make healthy carbohydrates work in a balanced diet:

• Emphasize fiber-rich fruits and vegetables. Aim for whole fresh, frozen and canned fruits and vegetables without added sugar. They’re better options than are fruit juices and dried fruits, which are concentrated sources of natural sugar and therefore have more calories. Also, whole fruits and vegetables add fiber, water and bulk, and help you feel fuller on fewer calories.
• Choose whole grains. All types of grains are good sources of carbohydrates. They’re also rich in vitamins and minerals and naturally low in fat. But whole grains are healthier choices than are refined grains. Whole grains are better sources of fiber and other important nutrients, such as selenium, potassium and magnesium. Refined grains go through a process that strips out certain parts of the grain — along with some of the nutrients and fiber.
• Stick to low-fat dairy products. Milk, cheese, yogurt and other dairy products are good sources of calcium and protein, plus many other vitamins and minerals. Choose the low-fat versions, though, to help limit calories and saturated fat. And beware of dairy products that have added sugar.
• Don’t forget beans and legumes. Legumes — beans, peas and lentils — are among the most versatile and nutritious foods available. Legumes are typically low in fat, contain no cholesterol, and are high in folate, potassium, iron and magnesium. They also have beneficial fats, and soluble and insoluble fiber. Because they’re a good source of protein, legumes can be a healthy substitute for meat, which has more saturated fat and cholesterol.
• Limit added sugars. Added sugar probably isn’t harmful in small amounts. But there’s no health advantage to consuming any amount of added sugar. In fact, too much added sugar, and in some cases naturally occurring sugar, can lead to such health problems as tooth decay, poor nutrition and weight gain.

So choose your carbohydrates wisely. Limit foods with added sugars and refined grains, such as sugary drinks, desserts and candy, which are packed with calories but low in nutrition. Instead, go for whole grains and fruits and vegetables.

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