Sunday, August 12, 2012

Getting to the heart of a stroke - Part II

Based on a talk at the HOPE stroke support group July 2012

The word ‘stroke’ is derived from the Greek word apoplexia which means “to strike”. The first written descriptions of sudden paralysis appeared in the writings of Hippocrates, the father of modern medicine. Before the word stroke became popular, the term apoplexy was commonly used to describe this disease.

From a structural standpoint, the brain can be thought of as a house with three levels. The first floor or the lowest level is called the hindbrain. The second floor or the middle level is called the midbrain and the top floor is the forebrain. The hindbrain or the lowest part of the brain controls vital bodily functions such as breathing, heart rate and digestion. This part of the brain is connected to the spinal cord and controls many bodily functions that does not need approval from the higher centers in the brain. There is a certain amount of autonomy that is given to this part of the brain. The midbrain controls posture, movement and reflex eye movements. The midbrain is a small structure that connects the forebrain and the hindbrain. The forebrain is the largest part of the brain and most of it taken up by what is called the cerebral cortex. Of all the earthly creatures, humans have the largest cerebral cortex. The cerebral cortex fills most of the space under the skull and is divided into two halves that are interconnected. Although the two halves of the brain appear similar, they have very different functions. The right brain controls the left side of the body and the left brain controls the right side of the body. 

The cerebral cortex is a very complex data processing center. Internal data from the body is channeled through the midbrain and external data from the outside world is channeled through the sense organs.

There are two main types of brain tissue, called grey and white matter. The grey matter consists of nerve cells. White matter consists of nerve fibres that interconnect different areas of the brain. White matter also connected different parts of the body to the brain.

Individual brain cells are called neurons. Neurons are basic building blocks of the nervous system. The human brain is estimated to have over 100 billion neurons. Depending on the location within the brain and the spinal cord, individual neurons serve different functions.

If I were a neuron what would I look like and how would I communicate with other neurons? My hair would be magnified and individual hairs would extend outwards like the branches of a large tree making my body look very tiny in relation to the length of each individual hair. These individual branches would serve as receiving stations for information from other neurons.

My head and body would appear like a large rounded structure containing all the material required for keeping the neuron alive. This rounded structure or the body of the neuron is like a fortress sealed off from the outside world. Inside this fortress is a self contained city. The main wealth of this city is the genetic material stored in the center. Just like the brain regulates functions of the body, the genetic material stored in the cell regulates the function of the cell. Since this “city cell” is sealed off from direct outside contact, it also has its own food factory and power plant. The food factory produces everything that the cell needs such as proteins, and other products. Some of these are also exported out of the “city cell” via specialized packaging plants. All this requires power. This power is generated in a small power plant within the cell called the mitochondria. Raw materials for power generation come from the oxygen in the air we breathe in and glucose or sugar in the food we eat.

My arms and legs would appear very thin and elongated, appearing tens, hundreds and sometimes thousands of times the size of my head and body. Just as my hair would serve as a receiving station getting input from outside, my very long arms and legs would be the output stations that send information out from the “city cell”.

How do individual neurons communicate? Rather than transfer information through direct physical contact, neurons use electricity and chemicals to do this. If I need to communicate something to someone far away, it is far quicker to use my cell phone and transmit that information via airwaves rather than physically conveying that information. A small portion of the body of the neurons have tiny gates that control movement of charged particles in and out. This movement of charged particles generates electricity. Just as power lines transmit electricity, a long thin structure attached to the neuron carries this generated electricity. This electricity travels as far as the power line can take it.  There are electrically operated storage bins at the end of the power line. When electrical impulses arrive here, these storage bins open and chemicals are released. These chemicals are taken are taken up via receiving stations on other neurons. Broadly speaking, these chemicals either tell the neuron to fire off more electricity or turn off and go silent.

Neurons are interconnected. Each neuron is connected to thousands of other neurons. Tens of billions of neurons in the human brain make trillions of connections. Imagine looking at the earth from a spaceship high above. At nighttime, the earth would have light and dark areas representing large well lit cities and the poorly lit countryside respectively. Now imagine lights turning on and off in different parts of the world. Different parts of the brain control different bodily functions. As different bodily functions are carried out, interconnected neurons in parts of the brain generate electrical impulses appearing like lights going on and off. Brain function is essentially a coordinated electrochemical activity.

Human beings have the distinct capability to think and act as opposed to animals that act instinctively. For example when a dog runs, it cannot think of itself as a dog that is running. It identifies itself completely with the act of running. It acts on instinct and impulse. When human beings act, thinking goes on in the background either consciously or unconsciously. The physical brain has an invisible friend called the mind. The mind is a medium which allows us to think. Just as the physical brain can be seen as a house with three levels, the mind can also be seen as a house with three rooms.

The three rooms of the mind are the conscious mind, the subconscious mind and the latent mind. Just as the physical brain has billions of interconnected neurons, the basic building blocks of the mind are thoughts. Thoughts travel freely in and out of the different rooms of the mind. When we are able to perceive thoughts in a conscious waking state we are seeing the conscious mind. The subconscious mind is active in sleep. The mind also has latent thoughts, desires and impulses that manifest when the timing and environment are appropriate.

We are born with a set number of brain cells. Brain cells grow and form new connections with other cells but we are not able to generate new brain cells. Once brain cells die, they cannot be replaced. In the mind, there is a completely different scenario. We don’t come into the world with a set number of thoughts. As we grow, we process a huge amount of sensory data everyday. New thoughts are generated constantly. Thoughts can never die, they can only be made dormant. When we consciously think of something this is instantly registered and stored in a part of the mind called the latent mind.

Without the brain the mind cannot express itself and without the mind, the brain is simply a collection of switches controlling the flow of electrical activity. The mind adds flavor and color to the bland electrical impulses in the brain. In this way, we feel pleasure and pain. The flavor and color that is added by the mind comes from our sense of individuality or ego. Just as the taste of food may be ruined by adding too much of a certain type of flavor, our sense of happiness will ultimately be ruined with a strong flavor of ego.

Neurons in the brain subsist on a diet of oxygen and glucose. Thoughts in the brain subsist on a diet of sensory impulses. When a certain type of sensory impulse appeals to us and we want more of it, we use expend valuable neuronal energy in deriving more pleasure. Once “neuronal fatigue” sets in, we sense unhappiness and we go after something else. This cycle can go on endlessly. A spider spins a perfect web with a single purpose of catching its prey. After a spider has trapped its prey, it has the ability to easily escape its own web without getting entangled in it. Human beings weave thought patterns that attempt to “trap” happiness. These thought patterns ultimately lead to conditioned thinking. Unlike a spider, it is very hard for human beings to escape from conditioned thought patterns, especially the ones that lead to a state of unhappiness. Collectively, these thought patterns lead to our present state of mind. However, using the power of concentrated positive thought, we also have the ability to spin a perfect web of neuronal activity that leads to a lasting state of bliss and happiness.