Know The Hardware - II (Nervous System)

Synapse

Synapses are specialized junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands. Synapses define the circuits in which the neurons of the central nervous system interconnect. They are thus crucial to the biological computations that underlie perception and thought. They also provide the means through which the nervous system connects to and controls the other systems of the body.

Anatomy and Structure

At a classical synapse, a mushroom-shaped bud projects from each of two cells and the caps of these buds press flat against one another. At this interface, the membranes of the two cells flank each other across a slender gap, the narrowness of which enables signaling molecules known as neurotransmitters to pass rapidly from one cell to the other by diffusion. This gap is sometimes called the synaptic cleft.

Synapses are asymmetric both in structure and in how they operate. Only the so-called pre-synaptic neuron secretes the neurotransmitter, which binds to receptors facing into the synapse from the post-synaptic cell. The pre-synaptic nerve terminal generally buds from the tip of an axon, while the post-synaptic target surface typically appears on a dendrite, a cell body or another part of a cell.

 

Signalling across the Synapse

The release of neurotransmitter is triggered by the arrival of a nerve impulse (or action potential) and occurs through an unusually rapid process of cellular secretion: Within the pre-synaptic nerve terminal, vesicles containing neurotransmitter sit "docked" and ready at the synaptic membrane. The arriving action potential produces an influx of calcium ions through voltage-dependent, calcium-selective ion channels, at which point the vesicles fuse with the membrane and release their contents to the outside. Receptors on the opposite side of the synaptic gap bind neurotransmitter molecules and respond by opening nearby ion channels in the post-synaptic cell membrane, causing ions to rush in or out and changing the local transmembrane potential of the cell.

 

Synaptic strength

The amount of current, or more strictly the change in transmembrane potential, depends on the "strength" of the synapse, which is subject to biological regulation. One regulatory mechanism involves the simple coincidence of action potentials in the synaptically linked cells. Because the coincidence of sensory stimuli (the sound of a bell and the smell of meat, for example, in the experiments by Pavlov) can give rise to associative learning or conditioning, neuroscientists have hypothesized that synaptic strengthening through coincident activity in two neurons might underlie learning and memory. This is known as the Hebbian theory.

 

Integration of synaptic inputs

Generally, if an excitatory synapse is strong, an action potential in the pre-synaptic neuron will trigger another in the post-synaptic cell; whereas at a weak synapse the excitatory post-synaptic potential ("EPSP") will not reach the threshold for action potential initiation. In the brain, however, each neuron typically connects or "synapses" to many others, and likewise each receives synaptic "inputs" from many others. When action potentials "fire" simultaneously in several neurons that weakly synapse on a single cell, they may initiate an impulse in that cell even though the synapses are weak. In this way the output of a neuron may depend on the input of many others, each of which may have a different degree of influence, depending on the strength of its synapse with that neuron. Complex input/output relationships form the basis of transistor-based computations in computers, and so are thought to figure similarly in neural circuits.

 

Detailed properties and regulation

Following fusion of the synaptic vesicles and release of transmitter molecules into the synaptic cleft, the neurotransmitter is rapidly cleared from the space for recycling by specialized membrane proteins in the post-synaptic membrane. This "re-uptake" prevents "desensitization" of the post-synaptic receptors and ensures that succeeding action potentials will elicit the same size EPSP. The necessity of re-uptake and the phenomenon of desensitization in receptors and ion channels means that the strength of a synapse may in effect diminish as a train of action potentials arrive in rapid succession--a phenomenon that gives rise to the so-called frequency dependence of synapses. The nervous system exploits this property for computational purposes, and apparently tunes its synapses through such means as phosphorylation of the proteins involved. The size, number and replenishment rate of vesicles also are subject to regulation, as are many other elements of synaptic transmission. The drugs known as selective serotonin re-uptake inhibitors or SSRIs affect certain synapses by inhibiting the re-uptake of of the neurotransmitter serotonin.

Know The Hardware - I (Nervous System)

Neuron

Neurons (also called nerve cells) are the primary cells of the nervous system. They are found in the brain, the spinal cord, in the peripheral nerves and ganglia.  The neuron is the basic unit of information processing and the building block of the brain. Working together with other neurons and cells throughout the body, it allows us to think, feel, move and breathe. Neuron is an excitable cell that receives some sort of stimuli (often signal from other neurons) and responds by either sending the signal or not. In a way, a neuron is a digital circuit (either on or off) The difference is that it can fire at various rates and thus pass on processed information to other neurons.

Structure of Neuron:

Neurons have a quasi-amoeboid shape, consisting of a single long projection called an axon and shorter, typically branching projections called dendrites.

Soma:

The soma is the part of the neuron that contains the nucleus. The soma is also called cell body. The soma is the part of neuron where all the information is collected by the dendrites converge and merge. The soma, in effect calculates the sum of these informing signals (Works as Logic Gate with previous experiences) and decides whether or not to fire (more accurately, if incoming signals result in voltage that is above the certain threshold, the neuron will fire). If it triggers it sends its own signal, the neuron will then pass it on to other neurons.

Dendrites:

A branched extension of a neuron, the dendrite is a sensing or listening, part of the neuron that receives signals typically from other neurons. It conducts these signals towards the soma or the cell body. A single neuron can have as many as 2000 connections to other neurons, all coming in through its dendritic branches.

Nucleus:

Like all other cells in the body that contain nuclei the nucleus of the neuron holds the genetic code used to create protein needed by the cell.

Axon:

The axon is a filament like extension to the cell that it carries an electro-chemical signal away from the soma. From one cell type to another, the axons can vary greatly in length. (Some are very short, while others can be almost as long as person is tall). Some axons for example stretch from the base of the brain down to the tips of the toes. When neuron decides to fire, the axon’s job is to carry the signal generated at the cell body to both nearby and far away neurons to which the neuron is connected to.

Myelin Sheath:

A myelin sheath is fatty, insulating cover that surrounds portion of the axon. In addition to protecting the axon, the myelin sheath increases the speed and strength of signals transmitted down the axon. Axons that are  very long need myelin sheaths to do their jobs well, Not all neurons have myelin sheath.

Synaptic End Bulbs (Axon Terminal Buttons):

Synaptic end bulbs are the structures at the tip of the axon branches where electrical signal carried by the axon can cause the release of neurotransmitters. These neurotransmitters are received by other neurons, muscle cells and gland cells.

 

Facts About Human Brain

1.  Avearge weight of human brain at the time of the birth is about 350-400g (about 4/5 lbs), while in adults the average weight of the brain is 1300-1400g (about 3 lbs).
2. Average dimensions of the adult brain: Width = 140 mm/5.5 in, Length = 167 mm/6.5 in, Height = 93 mm/3.6 in.
3.  A living brain is so soft you could cut it with a table knife. There are no pain receptors in the brain, so the brain can feel no pain.
4. Total surface area of the cerebral cortex is 2,500 sq. cm or 2.69 sq.ft.
5. The composition of the brain is  77-78% water, 10-12% lipids, 8% protein, 1% carbs, 2% soluble organics, 1% inorganic salt.
6. The breakdown of intracranial contents by volume (1,700 ml, 100%): brain = 1,400 ml (80%); blood = 150 ml (10%); cerebrospinal fluid = 150 ml (10%).
7. The cerebellum contains half of all the neurons in the brain but comprises only 10% of the brain.
8. The cerebral cortex is about 85% of the brain.
9. Percentage of total cerebral cortex volume = frontal lobe 41%, temporal lobe 22%, parietal lobe 19%, occipital lobe 18%.
10. There are about 100 billion neurons in the human brain, the same number of stars in our galaxy.
11. It  is not he number of neurons that determines inteligence but the number of connections between the neurons. These connections are called synapses. As you use more of the brain the number of synapses increases i.e. number of connections of neurons increases. Humans continue to make new neurons throughout life in response to mental activity. Every time you recall a memory or have a new thought, you are creating a new connection in your brain.
12. The left hemisphere of the brain has 186 million more neurons than the right hemisphere.
13. There are about 100,000 miles of blood vessels in the brain. 750-1000ml of blood flow through the brain every minute. In that minute the brain will consume 46cm3 (1/5 cups) of oxygen from that blood. Thus the brain uses 25% of the body oxygen and blood supply, but is only 3% of body weight. Of that oxygen consumed, 6% will be used by the brain's white matter and 94% by the grey matter.
14. While awake, the energy used by the brain is enough to light a 25 watt bulb.
15. The brain can stay alive for 4 to 6 minutes without oxygen. After that cells begin die. No oxygen for 5 to 10 minutes will result in permanent brain damage.
16. The slowest speed at which information travels between neurons is 416 km/h or 260 mph, thats as "slow" as todays supercar's top speed (the Bugatti EB 16.4 Veyron clocked at 253 mph).
17. 10 seconds is the amount of time until unconsciousness after the loss of blood supply to the brain.
18. Time until reflex loss after loss of blood supply to the brain, 40-110 seconds.
19. During early pregnancy the rate of neuron growth is 250,000 neurons a minute.
20. More electrical impulses are generated in one day by a single human brain than by all the telephones in the world.
21. The brain is a muscle. The more you use it, the stronger and bigger it gets.  Researchers at the institute of neurology at University College London scanned the brains of 18 London cab (Taxi) drivers. They discovered that the part of the brain that stores mental maps of the capital had grown in size. The longer the cabbie had been driving the bigger the increase in the brain size.
22. How much does human brain think? 70,000 is the number of thoughts that it is estimated the human brain produces on an average day.
23. After age 30, the brain shrinks a quarter of a percent (0.25%) in mass each year.
24. Alcohol interferes with brain processes by weakening connections between neurons.
25. Differences in brain weight and size do not equal differences in mental ability. Albert Einsteins brain weighed 1,230 grams (2.71 lbs), significantly lesss than the human average of 1,300g to 1,400g (3 lbs).
26. 89.06 is the percentage of people who report normally writing with their right hand, 10.6% with their left hand  0.34% with either hand.
27.  The Hypothalamus part of the brain regulates body temperature much like a thermostat. The hypothalamus knows what temperature your body should be (about 98.6 Fahrenheit or 37 Celsius), and if your body is too hot, the hypothalamus tells it to sweat. If you’re too cold, the hypothalamus makes you start shivering. Shivering and sweating helps get your body’s temperature back to normal.
28.  There are two different schools of thought as to why we dream: the physiological school, and the psychological school. While many theories have been proposed, not single consensus has emerged as to why we dream. Some researchers suggest that dreams serve no real purpose, while other believe that dreaming is essential to mental, emotional and physical well-being. One theory for dreaming suggests dreams serve to clean up clutter from the mind.
29.  Memories triggered by scent have a stronger emotional connection, therefore appear more intense than other memory triggers.
30.  Each time we blink, our brain kicks in and keeps things illuminated so the whole world doesn’t go dark each time we blink (about 20,000 times a day).
31. Laughing at a joke is no simple task as it requires activity in five different areas of the brain.
32.  Altitude makes the brain see strange visions – Many religions involve special visions that occurred at great heights. Similar phenomena are reported by mountain climbers, but they don’t think it’s very mystical. Many of the effects are attributable to the reduced supply of oxygen to the brain. At 8,000ft or higher, some mountaineers report perceiving unseen companions, seeing light emanating from themselves or others, seeing a second body like their own, and suddenly feeling emotions such as fear. Oxygen deprivation is likely to interfere with brain regions active in visual and face processing, and in emotional events.
33. Reading aloud and talking often to a young child promotes brain development.
34. The capacity for such emotions as joy, happiness, fear, and shyness are already developed at birth. The specific type of nurturing a child receives shapes how these emotions are developed.
35. The left side of your brain (left hemisphere) controls the right side of your body; and, the right side of your brain (right hemisphere) controls the left side of your body.
36. Children who learn two languages before the age of five alters the brain structure and adults have a much denser gray matter.
37. A study of one million students in New York showed that students who ate lunches that did not include artificial flavors, preservatives, and dyes did 14% better on IQ tests than students who ate lunches with these additives.
38. For years, scientists believed that tinnitus was due to a function within the mechanics of the ear, but newer evidence shows that it is actually a function of the brain.

Similarities and Dissimilarities Between the Brain and a Computer

What are the similarities between the brain and the computer?

1. Both use electrical signals to send messages. The brain uses chemicals to transmit information; the computer uses electricity.
2. Both transmit information. A computer uses switches that are either on or off ("binary"). Neurons in the brain are either on or off by either firing an action potential or not firing an action potential.
3. Both have a memory that can grow. Computer memory grows by adding computer chips. Memories in the brain grow by stronger synaptic connections.
4. Both can adapt and learn. It is much easier and faster for the brain to learn new things. Computer is to be programmed.
5. Both have evolved over time. Computers have evolved much faster than the human brain.
6. Both need energy. The brain needs nutrients like oxygen and sugar for power; the computer needs electricity to keep working.
7. Both can be damaged. It is easier to fix a computer - just get new parts. There are no new or used parts for the brain. Both a computer and a brain can get "sick" - a computer can get a "virus" and there are many diseases that affect the brain. The brain has "built-in back up systems" in some cases. If one pathway in the brain is damaged, there is often another pathway that will take over this function of the damaged pathway.
8. Both can change and be modified. The brain is always changing and being modified. There is no "off" for the brain - even when an animal is sleeping, its brain is still active and working. The computer only changes when new hardware or software is added or something is saved in memory. There IS an "off" for a computer. When the power to a computer is turned off, signals are not transmitted.
9. Both can do math and other logical tasks. The computer is faster at doing logical things and computations. However, the brain is better at interpreting the outside world and coming up with new ideas. The brain is capable of imagination.
10. Both can do multitasking. Number of programs can be run simultaneously. A brain also does some multitasking using the autonomic nervous system. For example, the brain controls breathing, heart rate and blood pressure at the same time it performs a mental task.
11. Both brains and computers are studied by scientists. Scientists understand how computers work. There are thousands of neuroscientists studying the brain. Nevertheless, there is still much more to learn about the brain..

What are the differences between the brain and the computer?

1. Brains are analogue; computers are digital.
2. The brain uses content-addressable memory. In computers, information in memory is accessed by polling its precise memory address. This is known as byte-addressable memory.
3. The brain is a massively parallel machine; computers are modular and serial
4. Processing speed is not fixed in the brain; there is no system clock
5. No hardware/software distinction can be made with respect to the brain or mind
6. Synapses are far more complex than electrical logic gates
7. Unlike computers, processing and memory are performed by the same components in the brain
8. The brain is a self-organizing system
9. The brain is much, much bigger than any [current] computer. Accurate biological models of the brain would have to include some 225,000,000,000,000,000 (225 million billion) interactions between cell types, neurotransmitters, neuromodulators, axonal branches and dendritic spines, and that doesn't include the influences of dendritic geometry, or the approximately 1 trillion glial cells which may or may not be important for neural information processing. Because the brain is nonlinear, and because it is so much larger than all current computers, it seems likely that it functions in a completely different fashion.

Introduction:

There is a ultra super computer, which has billions of individual pieces, trillions of connections, and weighs only about 1.4 kilograms, and it works on electrochemical energy. It is far better than your laptop or palmtop, because it is at your service, at every instant and at any place, where you are. Yes, I am talking of the human brain, a mass of white-pink tissue that allows you to ride a bike, read a book, laugh at a joke, and remember your friend's phone number. It controls your emotions, appetite, sleep, heart rate, and breathing. But what is a use of this super computer,  if you don’t have its operating manual. If you don’t have knowledge of its operating system, then you can’t use this computer optimally. This blog is to understand the hardware, operating system, softwares and programs, applications, viruses and antiviruses of the super computer called the BRAIN. Now TRAIN YOUR BRAIN