The causes of strokes can be broken down into three main categories: 1) hemorrhage, 2) embolic, 3) thrombotic. Intracerebral hemorrhage occurs when a blood vessel breaks, releasing blood directly into the brain tissue. This can happen from a weakness in the vessel wall, when the blood pressure is too high, or when a person’s blood is not able to clot, for example, when they are placed on “blood thinners.” The resulting blood clot forms a mass and can squeeze surrounding brain, rapidly leading to death or severe brain damage. Often, by the time the patient reaches medical care, it is too late to reverse the damage and many neurosurgeons believe surgery is not worthwhile.
Embolic strokes occur when a blood clot or piece of cholesterol plaque breaks off a heart valve or inside of a blood vessel and flows upstream to becomes lodged in a smaller vessel. This prevents blood from nourishing to the tissue supplied by the vessel. The size of the stroke depends upon where along the vessel it is blocked. Disease that damages the heart valves or the lining of the heart chambers are common causes for emboli.
Thrombotic strokes occur commonly in the carotid and vertebral arteries that supply the brain. Vessel disease, like arteriolosclerosis can narrow the inside of the vessel, slowing blood like a kink in a hose and eventually resulting in a clot that stops flow entirely. There is a narrow window of time that, if this the cause of the stroke is diagnosed and the proper facilities are available, drugs called “clot busters” may help dissolve the blockage and restore flow.
More hospitals are establishing stroke teams, a group of specialized doctors and nurses who can provide the expertise to diagnose and treat stroke as rapidly as possible.
Monday, March 29, 2010
Saturday, March 27, 2010
3/27/2010
In my last blog I mentioned preprogrammed motor activity, so I thought this might be a good time to expand on that concept. There is a vast literature on motor control – the physiology of how we execute movements - and the brain pathways involved in even simple tasks are complex.
Think back to when you learned how to ride a bike. Initially there were several things you needed to learn; how to balance, how to peddle, how to turn, how to stop, and how to shift gears. To help balance, you may initially have used trainer wheels. But as you progressed, the trainer wheels came off and you became more confident. Part of this learning process was that repetitive movements like peddling were becoming programmed into your nervous system so that you didn’t have to think about them and you could focus on more important tasks, such as where to turn.
Another example is shooting baskets. The first time you threw a basketball at a hoop you probably didn’t come close to hitting it, much less sinking the shot. The weight of the ball was new and you had no concept of the forces needed to send it in the right trajectory. As you practiced, your nervous system learned to make numerous calculations extremely rapidly and your accuracy improved. Some of these calculations went from the conscious to the unconscious level. In addition your nervous system transitioned from linear processing to parallel processing. In parallel processing a process is broken down into several component tasks which are solved simultaneously and then made whole again.
Think back to when you learned how to ride a bike. Initially there were several things you needed to learn; how to balance, how to peddle, how to turn, how to stop, and how to shift gears. To help balance, you may initially have used trainer wheels. But as you progressed, the trainer wheels came off and you became more confident. Part of this learning process was that repetitive movements like peddling were becoming programmed into your nervous system so that you didn’t have to think about them and you could focus on more important tasks, such as where to turn.
Another example is shooting baskets. The first time you threw a basketball at a hoop you probably didn’t come close to hitting it, much less sinking the shot. The weight of the ball was new and you had no concept of the forces needed to send it in the right trajectory. As you practiced, your nervous system learned to make numerous calculations extremely rapidly and your accuracy improved. Some of these calculations went from the conscious to the unconscious level. In addition your nervous system transitioned from linear processing to parallel processing. In parallel processing a process is broken down into several component tasks which are solved simultaneously and then made whole again.
Friday, March 26, 2010
3/26/2010
A comment to the 3/22/ post asked. “… An "expert" said that when you are driving and receiving information through the phone, your brain goes into something he called sensory overload. Your peripheral vision is severely reduced and you basically are looking straight ahead. I can understand this when actually holding a cell phone to your ear. They did not make a distinction between hands free devices and holding a phone however. So my question is this.....would it be different if you were hands free and talking on the phone or would you still be overloaded. And if this is the case, how does this relate to talking to a passenger? Is that the same dynamic or different? Explain sensory overload.”
Sensory overload is a condition where the senses are strained and to the point it becomes difficult to focus on the task at hand. We commonly experience this situation if, say, we’re talking on the phone and our spouse asks us a question. It’s impossible to carry on the phone conversation and answer, so we pause the conversation long enough to take care of our spouse. Okay, you say, but that’s not the same as driving and talking. Well, yes it is. Can you type a letter while carrying on a conversation? No you can’t. And it doesn’t make any difference if you’re holding the phone or not – concentrating on the conversation at hand detracts from paying attention to driving.
The deceiving thing about driving is that much of the brain’s motor activity is automatic in that the visual information coming into our brain elicits a preprogrammed response, like turning through a curve in the road. This lulls us into believing we can do other things while driving. (I’ve seen drivers putting on makeup while driving 60 mph on the freeway). But the truth is the brain really can only really concentrate on one task at a time. The more you try to multitask, the poorer your performance in any of the tasks.
Driving requires constant vigilance. The more that vigilance that is distracted, the longer the reaction time to an unplanned event and the less we are aware of what’s going on around us. This holds true regardless of whether the conversation is on the phone or with the passenger next to us.
Sensory overload is a condition where the senses are strained and to the point it becomes difficult to focus on the task at hand. We commonly experience this situation if, say, we’re talking on the phone and our spouse asks us a question. It’s impossible to carry on the phone conversation and answer, so we pause the conversation long enough to take care of our spouse. Okay, you say, but that’s not the same as driving and talking. Well, yes it is. Can you type a letter while carrying on a conversation? No you can’t. And it doesn’t make any difference if you’re holding the phone or not – concentrating on the conversation at hand detracts from paying attention to driving.
The deceiving thing about driving is that much of the brain’s motor activity is automatic in that the visual information coming into our brain elicits a preprogrammed response, like turning through a curve in the road. This lulls us into believing we can do other things while driving. (I’ve seen drivers putting on makeup while driving 60 mph on the freeway). But the truth is the brain really can only really concentrate on one task at a time. The more you try to multitask, the poorer your performance in any of the tasks.
Driving requires constant vigilance. The more that vigilance that is distracted, the longer the reaction time to an unplanned event and the less we are aware of what’s going on around us. This holds true regardless of whether the conversation is on the phone or with the passenger next to us.
Thursday, March 25, 2010
3/25/2010
Having just mentioned the Blood Brain Barrier, it’s a good time to discuss Multiple Sclerosis. MS is an autoimmune disease. Auto immune diseases are strange in that the same immune system that guards our body against infections for some reason turns against certain our own body and attacks them in the same manner.
When this occurs in the brain to cause MS, lymph cells attack the blood brain barrier to break it down, allowing other immune system components into the brain where they attack the myelin, the insulation on neurons. When this happens, the myelin becomes damaged to the point the nerves no longer can transmit information. The name multiple sclerosis refers to the multiple scars (known as plaques) that form as a result of the immune attack. Although myelin also coats peripheral nerves, they are seldom involved in the disease.
Neuroscientists know a great deal about MS, but they do not know what causes or triggers this autoimmunity. Some believe it results from a prior infection as if an immune response against the infection gets confused and attacks the BBB and myelin instead. Genetics does not play a strong role in this disease. The frustrating aspect about this disease is it is intermittent, meaning a person may have one or two attacks and no others. Another person may have attacks one after another in a very progressive course. Once the diagnosis is made, there is no way to predict what will happen. The good news is that there are at least five-modifying treatments that are approved for treatment and have various degrees of efficacy.
When this occurs in the brain to cause MS, lymph cells attack the blood brain barrier to break it down, allowing other immune system components into the brain where they attack the myelin, the insulation on neurons. When this happens, the myelin becomes damaged to the point the nerves no longer can transmit information. The name multiple sclerosis refers to the multiple scars (known as plaques) that form as a result of the immune attack. Although myelin also coats peripheral nerves, they are seldom involved in the disease.
Neuroscientists know a great deal about MS, but they do not know what causes or triggers this autoimmunity. Some believe it results from a prior infection as if an immune response against the infection gets confused and attacks the BBB and myelin instead. Genetics does not play a strong role in this disease. The frustrating aspect about this disease is it is intermittent, meaning a person may have one or two attacks and no others. Another person may have attacks one after another in a very progressive course. Once the diagnosis is made, there is no way to predict what will happen. The good news is that there are at least five-modifying treatments that are approved for treatment and have various degrees of efficacy.
Tuesday, March 23, 2010
3/23/2010
Because I’ve blogged about drugs lately, it’s a good time to mention the Blood Brain Barrier. If we swallow a pill, it is digested and enters the blood stream. The drug passes from our blood into all tissues, but not necessarily into the brain. This is because of a special barrier, the Blood Brain Barrier, which is fairly selective about what can and cannot reach brain tissue. The barrier is actually made up of tightly packed brain connective tissue called astrocytes that surround the blood vessels.
The good news is that the BBB acts very effectively to protect the brain from common bacterial infections. The bad news is that when brain infections do occur, the BBB may block drugs meant to fight the infecting agent. In addition, this barrier makes it more difficult to deliver wanted drugs to specific brain regions. This is especially problematic when treating brain tumors with chemotherapy. There are various chemical ways of temporarily opening the BBB to enhance drug delivery. Also, since the brain actively takes up glucose and other molecules, some drugs have been attached to these molecules to enhance their delivery. Finally, small tubes can be placed into tumor beds and attached to reservoirs that have been implanted just under the scalp so that drugs can be injected directly into the desired location.
It is hoped that nanotechnology will also provide innovative methods for delivering drugs to the targeted areas.
The good news is that the BBB acts very effectively to protect the brain from common bacterial infections. The bad news is that when brain infections do occur, the BBB may block drugs meant to fight the infecting agent. In addition, this barrier makes it more difficult to deliver wanted drugs to specific brain regions. This is especially problematic when treating brain tumors with chemotherapy. There are various chemical ways of temporarily opening the BBB to enhance drug delivery. Also, since the brain actively takes up glucose and other molecules, some drugs have been attached to these molecules to enhance their delivery. Finally, small tubes can be placed into tumor beds and attached to reservoirs that have been implanted just under the scalp so that drugs can be injected directly into the desired location.
It is hoped that nanotechnology will also provide innovative methods for delivering drugs to the targeted areas.
Monday, March 22, 2010
3/22/2010
Got a great question after my 3/21 post, check it out. She asks, “… how do you see this technological age affecting young people? Are we creating a generation of people that have a difficult time doing one thing at a time? Can the brain really multitask all that well?”
First, let’s define what I’m talking about. To me an example of multitasking is a student in class who is Tweeting, text messaging, and trying to listen at the same time. The effects of this type of multitasking are not good. Some of the negative effects are: 1) it’s promoting an excessive need to “stay connected” at the expense of other activities, 2) reliance on electronic communication at the expense of direct interaction can result in the poor development of social skills and increased isolation. 3) It can also result in poor development of executive functioning characterized by an inability to focus on any task. More simply put, regardless of what a multitasker might think, it results in a person who is less competent, less efficient, and socially less skilled. So yes, this kind of multitasking can definitely cause cognitive problems.
First, let’s define what I’m talking about. To me an example of multitasking is a student in class who is Tweeting, text messaging, and trying to listen at the same time. The effects of this type of multitasking are not good. Some of the negative effects are: 1) it’s promoting an excessive need to “stay connected” at the expense of other activities, 2) reliance on electronic communication at the expense of direct interaction can result in the poor development of social skills and increased isolation. 3) It can also result in poor development of executive functioning characterized by an inability to focus on any task. More simply put, regardless of what a multitasker might think, it results in a person who is less competent, less efficient, and socially less skilled. So yes, this kind of multitasking can definitely cause cognitive problems.
Sunday, March 21, 2010
3/21/2010
Recently, I’ve seen a lot of television ads for Aricept, so I thought the Alzheimer’s drugs would be a good topic to write about. Neurons communicate with one another by sending impulses across synapses and the synapses do this with chemicals (that are called neurotransmitters). There are a variety of neurotransmitters in different regions of the brain, one of them being acetylcholine, which is used the hippocampus (a region important in memory storage and retrieval).
Acetylcholine is destroyed by the enzyme cholinesterase. Aricept works by blocking the action of cholinesterase (thus is called a cholinesterase inhibitor). In doing so, it raises brain levels of acetylcholine. The idea is that increasing brain levels of this crucial neurotransmitter will benefit memory and behavior. But because the underlying cause for the loss of neurons continues, the effect of a drug like Aricept only postpones the worsening by about 6 to 12 months. These drugs do not reverse the eventual course of the disease.
Other anti-alzheimer drugs are Exelon and Razadyne. Because of varying side effects and possible interactions with other medications, doctors may try different cholinesterase inhibitors until the most effective one is found for the individual. Namenda regulates glutamate, another neurotransmitter which plays a key role in processing information.
When you take a pill it is adsorbed from your gut and then goes everywhere in the body rather than exclusively to the target, like the brain. Acetylcholine is necessary not only for some brain regions, but also in various nerves that control the heart, gut, bladder, and a variety of other function. This is why the undesirable side-effects of anticholinesterase inhibitors are so wide spread.
Acetylcholine is destroyed by the enzyme cholinesterase. Aricept works by blocking the action of cholinesterase (thus is called a cholinesterase inhibitor). In doing so, it raises brain levels of acetylcholine. The idea is that increasing brain levels of this crucial neurotransmitter will benefit memory and behavior. But because the underlying cause for the loss of neurons continues, the effect of a drug like Aricept only postpones the worsening by about 6 to 12 months. These drugs do not reverse the eventual course of the disease.
Other anti-alzheimer drugs are Exelon and Razadyne. Because of varying side effects and possible interactions with other medications, doctors may try different cholinesterase inhibitors until the most effective one is found for the individual. Namenda regulates glutamate, another neurotransmitter which plays a key role in processing information.
When you take a pill it is adsorbed from your gut and then goes everywhere in the body rather than exclusively to the target, like the brain. Acetylcholine is necessary not only for some brain regions, but also in various nerves that control the heart, gut, bladder, and a variety of other function. This is why the undesirable side-effects of anticholinesterase inhibitors are so wide spread.
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