Tag Archives: synapse

Brain 101 redux

Many of my early posts on Neurons Firing were about the brain. In fact, they are catalogued on a separate page, Brain 101. In wanting to better understand what the brain looks like, how it feels, and how it works, I even did a mini-dissection of a small sheep brain. And last year, in a Frontiers In Science elective at my school, I had the opportunity to participate in a dissection of a brain that still had the eyes attached. 

I still haven’t found my “ideal” brain book – a book with pictures of a human brain, shown by parts of the brain, pictured at actual size but also enlarged to better see what is there, with explanations of each part, and essays similar to those written by Lewis Thomas in books such as The Lives of a Cell. (V.S. Ramachandran would be a perfect author for such a book!) Meanwhile, I enjoy these projects created by sixth graders at my school as part of their Science class.

brainstem1

nervoussystem1

partsofbrain1

entire2

The Aging Brain (Aaron Nelson)

Aaron Nelson began his Learning & the Brain session by telling a tale on himself regarding memory. If you’ve ever left home on a car trip and wondered if you turned off the coffee pot or the stove or some other gadget, Nelson’s tale of forgetting his child’s blanket and returning home only to discover that he had left the keys to their other car in that car, which was parked in the driveway and running, will resonate! He went on to describe the components of memory, which consist of “multiple memory systems” as explained by Larry Squire and his memory schema. Scroll to the third page and notice that  the diagram, which references long term memory, shows memory as residing in multiple areas of the brain.

The bulk of Nelson’s talk focused on how the brain and memory change with age. Did you know that “memory starts to decline between 25 and 30 years of age in normal situations.” He explained a bit about what scientists think happens in the brain in terms of aging and memory, further explained the concept of “cognitive reserve”, and then discussed ways to optimize memory. No doubt one reason his talk was well attended is that every last attendee had an aging brain, and a number most likely also have parents who are well ahead in the aging arena!

I took a lot of notes and was persuaded by the practical nature of Aaron’s talk to then purchase his book, The Harvard Medical School Guide to Achieving Optimal Memory.

Of particular interest was Aaron’s description of Yakov Stern and his study of cognitive reserve. SharpBrains has an informative interview with Dr Stern entitled Build Your Cognitive Reserve. I referenced cognitive reserve, or the brain-reserve hypothesis in my prior post on Ken Kosik’s talk.

As with many of the books I read, an entry or two about Aaron Nelson’s book will eventually wind up posted here. Meanwhile, I leave you with this teaser from his book:

Obtain regular exercise
Put out the cigarettes
Take vitamins
Involve yourself with others
Maintain healthful nutrition
Aim for a good night’s sleep
Learn something new
Moderate alcohol intake
Engage in life!
Manage stress
Organize your thinking, organize your life
Routinely take precautions to protect your brain
Yes you can! Maintain a positive attitude

(and a promise to myself to stop buying books until I’ve read all the ones waiting for me!)

The Adult Brain & Memory (Ken Kosik)

The theme of November’s Learning & the Brain conference was Using Emotions Research to Enhance Learning. As with last April, when I believe it was first introduced, there was an Adult Learning strand. Saturday morning I had the pleasure of presiding over the Adult Brains & Memory session, which featured two talks:

My Dad has Alzheimer’s, and hearing about what is going on within his brain is something that I can listen to over and over again, hence my second time as an audience member for a talk by Ken Kosik. In the cozy environment of MIT’s Brain & Cognitive Sciences auditorium, Kosik took us from the statistics on aging through the neurofibrillary tangles and amyloid plaques of Alzheimer’s to MCI (mild cognitive impairment) to studies and practicalities of hedging against Alzheimer’s, to adult brain plasticity, to wondering just where memories go. In my May 23rd post of this year you can read more about what Ken shares regarding Alzheimer’s.

In this recent talk, I did pick up some new information, and was reminded of some old. Being a teacher, and having very definite opinions about professional development formats, I especially enjoyed Ken’s three-point proof that Education protects against Alzheimer’s.

  • Brain-reserve hypothesis – If you start out strong, you’ll decline less.
  • Brain-battering hypothesis – Better-educated people take better care of themselves, and therefore may be better protected. Lesser educated people have more stroke, myocardial infection, diabetes, depression and earlier mortality.
  • Diagnostic bias – Highly schooled patients score higher on dementia screening and tests of cognitive ability.

Kosik also pointed out some very salient features to keep in mind. Perhaps the most protective factor against Alzheimer’s is having friends, social networks, and being connected.

While all rules do not apply to everyone – each of us is, after all, an individual – the rules are based on statistics, and we can use these generalizations to guide us in our decision making in terms of preventive care and general health care.

Dealing with the aging brain and how it can impact our lives is at the very heart of what Ken Kosik studies. To that end, in addition to his long list of impressive credentials, he is the Executive Director of the Center for Cognitive Fitness and Innovative Therapies at Santa Barbara, California, part of whose mission is:

…we believe that every person has the ability to age gracefully and live a full active life even with a diagnosis of Alzheimer’s. The key is integrating all the tools you need to thrive under one roof.

(Next post: Aaron Nelson’s talk)

Norepinephrine

Norepinephrine is both a hormone and a neurotransmitter. When released as a hormone in response to excitement, which can include both positive and negative stimuli, norepinephrine also helps in cementing memories caused by the excitement.Norepinephrine’s role in responding to excitement may sound similar to Epinephrine, which I wrote about in my previous post. It turns out that norepinephrine is epinephrine that has reached the brain.

When released as a neurotransmitter, norepinephrine helps carry messages across synapses. It also plays a role in retrieving memories, according to this Science Daily 2004 article about research at the University of Pennsylvania Medical Center. Norepinephrine is also useful in telling the brain to shake, rattle, and roll in an attempt to make the brain alert and focused. However, too high levels can be a cause of aggression. Serotonin, dopamine, and endorphin, working as a trio, can help balance high levels of norepinephrine and somewhat control the aggressive behavior.

You can tinker with a 3D model of norepinephrine at the 3Dchem site, which focuses on chemistry, structures and 3D molecules and is maintained by Dr Karl Harrison from the Department of Chemistry at the University of Oxford. Folks with Parkinson’s have a decrease in production of norepinephrine. Marilee Sprenger, citing Wurtman & Suffes, 1996, notes that “Norepinephrine and dopamine, sometimes called the alertness chemicals, are produced when tyrosine reaches the brain. Tyrosine is found in protein.” That’s certainly a plug for having proteins in the diet. There will be more on what makes for a “really good brain diet” in a future post.

Epinephrine aka Adrenaline

I’ve always liked the way these two words conjure up mental images. Epinephrine brings to mind the Epi Pen, a potentially lifesaving device for people who deal with certain types of allergies. Adrenaline brings to mind the Road Runner of cartoon fame, cruising along at break neck speed.

Those images help explain epinephrine’s function, both as a hormone and neurotransmitter, to get the body revved up in response to a perceived threat or excitement. This response is known as “fight or flight” because adrenaline is released when the body perceives an event to which it needs to respond by “fight or flight”.

While not all excitement is negative, the body prepares itself just in case. Adrenaline is released in the adrenal glands (located above the kidneys and not in the brain) in reaction to a message begun in the amygdala. The amygdala does not waste time figuring out if something is a threat or not; instead it responds rapidly with the aim of protecting you if necessary. The signal goes from the amygdala to the hypothalamus to the pituitary gland (all of which are located in the brain) and then to the adrenal glands located mid-body. The adrenal glands then release adrenaline.Thus, your hands might get clammy before making a presentation or performing, and you might wish you could be invisible, but hopefully you are simply excited and not overly threatened, and you manage to go on with the show!

[9/23/08 – For a delightful look at adrenaline, please skoot on over to this post on 1000 Awesome Things: #934 Adrenaline. I came upon this post thanks to the blog cross-referencing feature of WordPress.]

Dopamine

Dopamine functions both as a neurotransmitter and a hormone. It helps control physical movement and also helps regulate information flow to the higher levels of the brain, thus having low levels of dopamine may impact working memory and ability to focus. You might know someone who takes Ritalin. Well, that is a drug which is sometimes prescribed for people who have difficulty focusing because it counters the low levels of dopamine.

When tripled up with serotonin and endorphin, dopamine balances out high levels of norepinephrine, which can cause aggression. These three neurotransmitters also release into the brain when stimulated by exercise (think of a runner’s high, for instance), listening to music you like, smelling smells you enjoy (like freshly baked cookies), and receiving positive feedback, so you can understand why dopamine, serotonin and endorphin are thought of as the “feel good” chemicals. :-)

There is a down side, though, to having naturally produced “feel good” chemicals in the brain. External elements often influence us and how we feel, and some of these elements can have negative effects on the body, such as too much alcohol or indulgence in other types of drugs. This is where addiction comes in to the story, as you can read in this University of Texas at Austin article.

From the Surfari wiki (which I co-authored with a colleague): Did you know that your brain is about 80 percent water? To keep it alert, it is good to drink water throughout the day. Another type of food that feeds your brain is protein. Protein provides amino acids, which help produce dopamine and norepinephrine. Sources of protein include yogurt and cheese (hey, this sounds like dairy products!), animal foods (chicken, meat, fish and eggs), and for those of you who prefer vegetarian foods (beans, lentils, nuts and seeds).

In Parkinson’s’ disease there are decreased quantities of dopamine which result in physical movements that are constant and jerky. An insufficient quantity of dopamine is also associated with Schizophrenia. The pharmaceutical L-dopa can sometimes help neurons to continue producing dopamine.

Acetylcholine

The chemical acetylcholine (ACh) is produced in an area just above the brain stem and is present throughout the brain. It is involved in voluntary and involuntary muscle movement, as well as in the formation of long-term memory. At night, when memory consolidation takes place, there are higher levels of acetylcholine present, and it turns out that many of our dreams are caused by this chemical. Most importantly, acetylcholine assists with communication from neuron to neuron.

So how do you make sure your brain is producing adequate amounts of acetylcholine? Choline is one of the ingredients that goes into producing acetylcholine and is found in eggs, salmon, liver, soy and lean beef. These foods all help raise choline levels because they contain lecithin, which has been connected to having a positive impact on memory recall. Hmm, it looks like not all fats are bad for your health and what you eat actually can make a difference to your brain’s health!

What happens if there are not proper quantities of acetylcholine? Apparently this is what happens to patients with Parkinson’s and Alzheimer’s diseases. Aricept is a drug that is possibly slowing the breakdown of acetylcholine in Alzheimer’s patients and you can see a video of how it is believed to work at the Aricept site.

Neurotransmitters

I imagine neurotransmitters as the grease that keeps the brain functioning much the same way that a well-oiled machine runs smoothly. Without neurotransmitters, communication between neurons does not happen. It is the neurotransmitters that carry nerve impulses across synapses from one neuron to the next.

When a neuron initially fires, it sends an electrical signal down its axon to the pre-synaptic terminal (also known as the end of the neuron and the end of the axon). The neurotransmitter’s task is to convert that electrical signal to a chemical signal and transmit it across the synapse to the dendrites of a nearby neuron. The nearby neuron’s dendrites contain receptors to receive that transmission, which convert the chemical signal into a new electrical signal.

For a visual explanation of how this process works visit the Mind Project’s Flash animation Introduction to Synapses. A consortium of educational institutions, the folks at The Mind Project are creating “curriculum materials that provide students with a challenging yet accessible introduction to the cognitive sciences (the study of the mind and brain).”

Back in 1921, Otto Loewi discovered the first neurotransmitter, Acetylcholine, and there are now some 50 or so known neurotransmitters. Over the next several posts we will explore some of the ones that just roll off the tongue (!): Acetylcholine, Dopamine, Epinephrine, Endorphin, Norepinephrine, Serotonin, Cortisol and Melatonin. Meanwhile you can check out some neurotransmitter tidbits at Neuroscience for Kids – Neurotransmitters.

Neuron Development

Neurons grow like wildfire before birth! The developing brain generates between 50 and 100 thousand new cells per second from the fifth through twentieth weeks of gestation. These brain cells migrate to different locations in the brain and begin to differentiate, although many more neurons than are needed are produced.

Eventually about 75 percent of these cells will die in the normal development of the brain and nervous system. This process – programmed cell death – is known as apoptosis. Of those cell connections present at birth, some 40 percent will be pruned, just like weeding a garden to dispose of what is not needed.

Birth to Age 3
It might surprise you to know that a three year old has about twice as many connections as an adult, but who has more “intelligence”? From birth through about age three there are vast numbers of connections and collections being recorded in the brain, but there is no understanding or organizing of this wiring. The brain does not yet have the ability to distinguish what is important.

Ages 3 to 12
From age three through twelve the brain begins to realize, as a result of collecting too much, that it has recorded events in more than one place, resulting in dense sets of synapses. At this point it begins to prune the excessive synapses in an attempt to get organized and eliminate what is not necessary.

Ages 12 to 19
The teenage years consist of more aggressive pruning as the brain begins to specialize and build an identity. While the brain does a ton of learning in the early years, the bulk of learning takes place after the frenzy of forming synapses has stabilized and the duplicated synapses have been pruned.

Adulthood
Adulthood ushers in a bit of a pruning plateau, where some connections are diminished and others are enhanced. These are the years of using the brain as life experiences fine-tune the neural connections!

For more on brain development, check out J. Madeleine Nash’s article, Fertile Minds, in TIME.

Neurons

As noted previously, the Cerebellum takes up just ten percent of the brain’s mass but contains about half of the brain’s neurons. That is a huge amount of processing power contained in a relatively small portion of the brain; kind of a heady responsibility for the Cerebellum!

One possible reason that the Cerebellum contains this large quantity of neurons is that the Cerebellum does a lot of communicating with many areas of the brain in its diverse role as coordinator of muscle movement, maintainer of bodily equilibrium, handler of cognitive patterns such as speaking, automator of certain repetitive tasks, and responder to novelty. Whew, a busy schedule, to say the least! Since the neurons are the pathways that let all of this communication take place, it makes perfect sense to have so many in the Cerebellum.

There are about one hundred billion neurons in the brain. Essentially they all deal with the same thing – facilitating communication within the brain by sending impulses between neurons and thus throughout the brain. This sending of impulses is assisted by neurotransmitters.

neuron-chat-21.jpgSo how do neurons communicate with each other? First it helps to have an idea of what a neuron looks like. Think of the nucleus, which is surrounded by the cell body (called the soma), as a circle in the center of an octopus. The dendrites of the nucleus are like the tentacles of the octopus, extending out from all around the cell. Imagine one dendrite, called the axon, stretched out longer than the rest and at the other end of this axon are many axon terminals that look like spindly fingers. And now imagine that there are billions of these neurons within the brain.

A typical neuron “chat” takes place extremely fast. The dendrites extend from the perimeter of the cell body, with the nucleus in the center. The cell either fires or not, and the fired message shoots down the axon to the pre-synaptic terminal, which is the end of the neuron and the end of the axon. The pre-synaptic terminal is right next to, but does not touch, the dendrites of the next neuron. Simplified, the dendrites receive signals, and the axon and its terminals send signals.

At the end of each axon terminal are neurotransmitters. The neurotransmitters float across the synapse, which is the space between neurons, and communicate with the next neuron. Each neuron synapses onto many different neurons. On any given neuron some synapses will tell it NOT to fire while other synapses will tell it TO fire. The sum total of all the synapses’ influences will determine whether the neuron fires or not.

For a more detailed description of this process along with a wonderful set of Flash movies that clearly animate and visually explain neurons firing, please visit The Consortium on Mind/Brain Science Instruction’s article Neurons, synapses, and neurotransmission: An introduction and scroll to the bottom of the screen for the Flash animations.