THE NERVOUS SYSTEM
The brain is a member of the nervous system family. The nervous system controls all your conscious and automatic actions and sensations in all parts of your body like your thoughts, feelings, memories, heartbeat, blood pressure, body temperature, breathing rate and senses.
There are two parts of the nervous system - central and peripheral(pehr-if-er-ul). The central nervous system is composed of the brain and the spinal cord. The branching web of nerves to all the different parts of your body is the peripheral system. The nervous system is controlled by the brain and is connected to the spinal (spy-nuhl) cord and the huge network of nerves that run from the spinal cord to all the different parts of the body. (Show me the diagram!) Your nerves are like electrical wires which picks up signals. Signals or messages flows from these nerves to the spinal cord, then to the brain and back again. These signals are called nerve impulses.The brain is the control center. It receives and sorts out millions of signals it receives from all the different parts of your body. The brain sorts out information with amazing speed. Incredibly, it also sorts out important information and ordinary information. For example, it tells you not to pay attention to a bird singing so you can drop the hot skewer you just picked up.The nervous system also controls your breathing, heartbeat, body temperature, and the actions of your stomach and intestines.
As you look at your computer screen, electrical signals or nerve impulses are sent to your brain so you can do many different actions. Your nervous system is telling your finger to move the mouse, move your eye muscles so you can focus on the words, recognize words and sentences, form new ideas and store what you just learned in your brain and makes you remember.
THE HUMAN BRAIN
Your brain is wrapped by layers of lining called the meninges(me-nin-jeez). The topmost layer is called the dura mater. Sandwiched between the brain and the meninges is brain fluid called the cerebrospinal (see-reeh-bro-spy-nahl) fluid. (Show me the diagram!) This brain fluid acts as a shock absorber. For extra protection, the brain's house is a strong bony box called skull. (Show me the diagram!) Like your skin, the germs can attack the meninges. If this happens the person gets very sick and this condition is called meningitis(men-ihn-jhitis).
The brain is grayish pink in color, feels like tofu and would you believe only weighs three pounds, approximately the weight of 6 video cassettes. It makes up only 2% of your body size but uses up 20% of the energy your body produces. Energy is from blood sugar or glucose (glue-coz). Arteries which run to all parts of your brain carry the blood that delivers the food and oxygen to your brain.
There are three main parts of the brain: (Show me the diagram!)
The cerebrum is the largest part of the brain. It looks like a wrinkled giant walnut. (Show me the diagram!) The cerebrum (sehr-e-bruhm) is divided into two halves. Each half is called a hemisphere (he-miss-fear). The left side is the left hemisphere and the right side is the right hemisphere. The halves or hemispheres are connected to each other by a wide material called the corpus (kohr-pus) callosum (kahl-oh-sum). Each hemisphere has an inside layer called the white matter (Show me the diagram!) and an outside layer of gray matter called the cerebral cortex (kohr-teks). Different parts of the cortex do different jobs. The cortex controls your voluntary actions like running and walking. It is also responsonsible for body sensations like pain, learning, and emotions. These areas can be mapped on the surface of the cerebrum. (Show me the diagram!) If your brain is injured and your speech center is damaged, you may not be able to talk clearly. If your motor area is damaged, you may not be able to walk as well as you did before or you can be paralyzed.
It is weird but the right side of your brain is connected to the left side of your body. The left side of the brain is connected to the right side of your body. This is because the nerves connecting the brain and the spinal cord cross to the opposite side. If you are right handed, you depend on your left hemisphere or left brain. So, you are probably good at solving problems, math, and language. If you are left handed, you are probably good in music, drawing and singing.
If you turn the brain upside down, there are twelve pairs of nerves called cranial nerves that come out from the brain itself. (Show me the diagram!). These nerves have names and also do very important jobs. For example, the olfactory nerve is the nerve for smell, and the optic nerve is the nerve for vision.
The cerebellum (ser-e-bell-um) is the second largest part of your brain. (Show me the diagram!) It is below the cerebrum and sort of looks like a ball of yarn. It's main job is to coordinate your movements, posture and keeping your balance. Damage or injury to the part of this brain will make your movements jerky and uncoordinated.
The brains stem is on the top of the spinal cord (Show me the diagram!). The brain stem deals with very very important functions that keep us alive. It automatically controls our breathing, heartbeat, blood pressure, and circulation. If this does not happen automatically, can you imagine what would happen if you forget to breathe? What a catastrophe that would be!!!
The thalamus is reponsible for relaying sensory messages to the cerebrum.
The hypothalamus is located at the base of the brain. It controls many body functions like body temperature, appetite, thirst, and sleeping. It also regulates a gland in our body called the pituitary gland. The pituitary gland is the master of all the other glands in our body because it helps the other glands to produce their hormones. It also produces growth hormones which makes us grow tall and helps the kidneys regulate the water we drink.
The Spinal Cord
Your spinal cord is a long tube that begins from the bottom of the brain and snakes down to your lower back. (Show me the diagram!) There are nerves called the spinal nerves that come out of the spinal cord. It looks like a tree branch with twigs branching from the sides. These nerves carry electrical signals or messages up and down the spinal cord to your brain where the messages are sorted out. The spinal cord connects the brain to the rest of the body. Just like the brain, the spinal cord is also wrapped by the meninges for protection. It is inside a tunnel of bones stacked up on its other called the vertebrae or backbones. (Show me the diagram!)
If you look at the brain under the microscope, you see a mess of bundles of nerve cells which looks like long knotted pieces of thread. These bundles of nerves are your electrical cables. There are 100 billion of these nerve cells called neurons (Show me the diagram!). They also have an important job to do. These neurons carry and send the electrical signals from the peripheral nerves to the brain and back again. They can send a message from your arm to your head in 5 microseconds.
The neuron is composed of a cell body , dendrites and the axon. The cell body looks like a blob and has an eye called the nucleus. Coming out of the cell body are fingers called the dendrites and a long leg. A single nerve cell can have 50,000 dendrite branches and can communicate with 250,000 other nerve cells.
The long leg connected to the cell body is the axon and looks like a string of sausages.The axon can be over three feet long. The axon carries nerve impulses from the cell body to the dendrite of the next neuron. The neurons do not really connect ot each other. When the messages reach the feet of the axon which are called the axon terminals , the nerve impulse has to cross a gap so it can reach the dendrite of the next cell. As the messages or nerve impulses arrive at the gap, a chemical called neurotransmitter is released. This chemical acts like a bridge so the message is passed to the next neuron. So the nerve impulses are like playing a game of relay. Some nerves are covered by a lining called myelin sheath. The sheath around the axon insulates the axon to speed up the passage of nerve impulses. Top speed in covered nerves nerves can reach 395 feet per second!
When you are born, you already have your whole package of neurons with you. The bad news is that the human brain cannot make new neurons. When they get damaged they die, period. The good news is that everytime you learn something new, new nerve connections are made. So the funny thing is the more tangled your brain, the smarter you are!