The activities of all the organs and systems of the human body are controlled by a dominant organ - the brain. As the body's master organ, the human brain is the center of consciousness, emotion, learning, reason, and skill; it is likewise a repository of memories. The intricateness of the human brain and its power to direct influence over every process of the body make even the most advanced computer an insignificancy when compared to it.
The human brain - that compact mass of puckered grey and white matter protected first and foremost by the skull - is one amazing electrical and chemical machine. Millions of fragments of information are received, processed and sent out by this super machine every second, and this is true even during sleep. It does not, however, work alone; it counts on the body's sense organs for information from the outside world. The complexity of the structure of the human brain is such that to describe it, in detail, as an electrical and chemical machine is quite a task.
The brain structure, in a nutshell:
Among all the organs of the body, the brain is the one that is best protected. Weighing about 1400 grams (49 ounces), the brain is secured by 3 layers of protection, each one carefully arranged. The first layer is the hard, bony helmet known as the skull. The second layer consists of three strong fibrous membranes known as the meninges, which further envelop and protect the brain's delicate tissues. Lastly, a cushion of cerebrospinal fluid circulates between the middle (arachnoid mater) and inner (pia mater) meninges, buffering the brain, especially when the head is knocked from side to side or from back to front.
The human brain is made up of 3 main parts:
1. Cerebrum - interprets messages from the sense organs and controls such higher functions as the ability to speak, reason, and remember. This activity takes place largely in the cortex, the outer grey layer of the cerebrum.
2. Cerebellum - orchestrates balance and muscle coordination.
3. Brain stem - links the brain with the spinal cord and helps to regulate the vital functions of the body, including breathing, heartbeat, sneezing, coughing, swallowing, and blinking.
Several more crucial structures are located deep within the brain:
- Thalamus - relays sensory nerve impulses to the cerebral cortex.
- Hypothalamus - secretes the chemical corticoliberin, which helps to control the body's metabolism and to regulate appetite and sex drive.
- Pituitary gland - secretes different kinds of chemical substances (hormones) and activates other glands throughout the body.
- Basal ganglia - relay outgoing impulses from the cerebral cortex and are associated with the ability to move rapidly and smoothly.
The human brain needs the nerves as a means of communicating with the rest of the body. Through the spinal cord and the vast network of branching nerves that make up the peripheral nervous system, nerve impulses pass back and forth - like current in an electrical circuit - between the brain and every part of the body. These crucial messages, apart from keeping people alive, enable them to think, feel, remember, and do actions as simple as flicking a switch, or as complex as writing a science article.
It is estimated that the human brain has about 100 billion nerve cells, called neurons. Bundles of neurons make up a nerve, which may be likened to a telephone cable. Through a complex electrochemical process, messages flash from neuron to neuron. This means that the chemicals in the brain cause electrical signals. Neurons that carry messages from the central nervous system (the brain and the spinal cord) to muscles and other tissues, causing them to move and react, are called motor neurons; those that carry messages to the central nervous system, on the other hand, are called sensory neurons. Both motor and sensory neurons may be contained in a single nerve.
To get a message from one neuron to another, chemical transporters are required. These brain chemicals, called neurotransmitters, constantly cross the gaps (synapses) between neurons, carrying instructions and sensations to and from the central nervous system. Again, these messages travel from one part of the body to another like electrical currents in wires, albeit much slower. All these enable you to move your muscles, feel the things that are happening in your environment, and keep some of the events you experience as memories.
As previously mentioned, certain chemical substances (neurotransmitters) are secreted in the brain, which allow transmission of information from one neuron to another. Some of these are listed below.
- Dopamine - This neurotransmitter is produced by the nerve cells in the basal ganglia; it enables nerve cells to send messages to one another and to muscle fibers. When there is a deficiency of this chemical substance, messages between nerve cells and muscle fibers may become confused, causing the tremor and other symptoms characteristic of Parkinson's disease.
- Serotonin - This neurotransmitter allows brain cells to communicate with each other and is involved in emotion. A shortage of this chemical substance can lead to depression.
- Endorphin - This neurotransmitter, a special protein compound found mainly in the pituitary gland, produces effects similar to those of morphine and other opiates; that is, it relieves pain, slows down breathing, and alters mood.
- Acetylcholine - This neurotransmitter functions in muscle stimulation. A lower than normal concentration of this chemical substance in the brain has been cited as one of the possible causes of Alzheimer's disease.
The human brain, again, can be compared to a computer, and the nerves to electrical wiring; together with the chemical substances that are the neurotransmitters, the brain is concededly an astounding electrical and chemical machine that works ceaselessly to keep us alive.