The human nervous system consists of several parts. The main structures are the brain and the spinal cord. The system includes nerves that sense external and internal stimuli and then relay the information to the central processing unit — the brain.
The brain is the portion of the vertebrate central nervous system that constitutes the organ of thought and neural coordination. It includes all the higher nervous centers, receiving stimuli from the sense organs and interpreting and correlating them to formulate the motor impulses. It is made up of neuronal cells, supporting and nutritive structures, and is enclosed within the skull. The brain is continuous with the spinal cord through the foramen magnum – the opening in the skull through which the spinal cord passes to become the medulla oblongata.
The knowledge we have of brain structure, function and interrelativity has been substantially accelerated over the last century. This is largely due to advances in nuclear medicine technological advances in noninvasive methods of studying and viewing brain structure and the actual ability to visually measure live neural activity in relation to activity. The scope of this paper is to discuss brain scanning and to then discuss some of the structures and functions of the brain whose discovery this technology has made possible.
X-ray machines have been the chief mechanical tools for internal observations of the human body since Wilhelm Roentgen discovered X-rays in 1901. The development of computers made it possible for better and more accurate techniques to be applied to scan the human body. These methods employ various scanners like the CT (computerized tomography), PET (positron emission tomography), MRI (magnetic resonance imaging) and SPECT (single photon emission computed tomography).
The CT is an acronym for computerized tomography. This method of scanning involves computer-enhanced X rays of brain structures, shot from many angles and then combined by the computer to render a clear image of a horizontal slice of the brain. Doctors and scientists are able to view the three dimensional format on a computer screen.
MRI stands for magnetic resonance imaging. This scan uses magnetic fields, radio waves and computer enhancement to provide much better images of brain structure and function than CT scans. Once called nuclear magnetic resonance imaging, the “nuclear” was dropped off because of fears that people would think there was something radioactive involved, which there is not. MRI is a way of getting pictures of various parts of the body without the use of X rays, unlike regular X ray pictures and CT scans. An MRI scanner consists of a large and very strong magnet in which the patient lies. A radio wave antenna is used to send signals to the body and then receive signals back. These “radio wave signals” are actually a varying or changing magnetic field that is much weaker than the steady, strong magnetic field of the main magnet. These returning signals are converted into pictures by a computer attached to the scanner. Pictures of almost any part of your body can be obtained at almost any particular angle.
PET stands for positron emission tomography, and it is much more complicated than the CT scan. A PET scans is a medical imaging technique that provides images of biochemical function over time. This enables researchers to map which areas of the brain become active to specific stimuli. PET machines bombard the subject with doses of positrons: the anti-matter equivalents of the electrons. As the positrons enter the body, they encounter electrons that are escaping from radioactive elements that have been injected into the bloodstream. When the positrons and the electrons collide, they give off energy that is recorded by a computer. The result of this scan is a detailed 3-D picture of the brain.
The SPECT, which is the short form for Single Photon Emission Computed Tomography, is a device that resembles the PET. The SPECT equipment is a brand new addition to the family of body scanners. However, it uses radiation that is less harmful, and the tracers that are injected into the patient are non-radioactive isotopes of Lithium, Carbon and Phosphorus. The system is also much faster, which permits quicker diagnoses.
Traditional surgical procedures, along with fiber optic cameras and sensors create an image of the brain that is fascinating. All of the technological methods discussed above have given us a much greater understanding of the human brain, its structure and functions. We now know that the brain is divided into three main sections, namely, the forebrain, midbrain and hindbrain.
The forebrain is the largest and most complex region of the brain, encompassing a variety of structures including the cerebral cortex, thalamus, hypothalamus, limbic system and cerebrum. It is the forebrain that attains the highest set of integrating and organization of the nervous system — the cerebral cortex.
The cerebral cortex is the wrinkled looking outer layer of the cerebrum, and, when fully grown, it completely covers the brain structures. From every nerve cell (neuron), fibers pass to other neurons, both of the cortex and of the other brain parts. Trillions of lines of communication, called synaptic connections, connect one region of gray matter with another, and these in turn with distant organs. By such means the brain is in communication with the lungs, heart and other bodily organs, with the specialized cells that serve as the receptors of touch, taste, smell, vision, hearing and with the muscles.
The thalamus also serves as an integrating center. It also serves as a relay station for incoming sensory information to the cortex. Many impulses going from one area of the cerebral cortex to another travel by way of synapses in the thalamus.
The hypothalamus serves to control vital autonomic regulatory centers, rather, “need conditions” of tissues. Such conditions can include hunger, thirst and temperature. The centers arouse and sustain internal and external responses until the need condition is corrected and thus are the basis of drives.
The limbic system is a group of subcortical structures (as the hypothalamus, parts of the thalamus, the hippocampus and the amygdala) of the brain whose role is producing emotion and motivated behavior. Rage, fear, sexual response and other instances of intense arousal originate from various points in the limbic system.
The cerebrum is the largest structure of the forebrain and is most of what we see when we look at the brain. The cerebrum is divided in two cerebral hemispheres (left and right), by a deep cleft called the longitudinal fissure. The two hemispheres are connected and are constantly communicating with each other via a sickle-shaped connecting fiber tract called the corpus callosum. The cerebrum controls voluntary movements, sensations, learning, remembering, thinking, emotion and consciousness.
The midbrain is the segment of the brainstem that lies between the hindbrain and the forebrain. The midbrain is a link between the structures above and below it, and acts as a conduction and switching center, coordinating reflex responses to sights and sounds such as bright flash and sudden noise. It coordinates nearly all sensory input and initiates motor responses. A portion of the reticular formation is located in the midbrain.
The reticular formation is a dense group of fibers that carry stimulation related to sleep and arousal through the brainstem, awakening the brain to consciousness and keeping it alert. It also serves to direct the traffic of messages in the nervous system, monitor and reject stimuli, muscle reflexes, bodily movements and also contributes to the highest mental processes of focusing attention, introspection and forms of reasoning.
The hindbrain is the posterior division of the brain including the cerebellum, the pons and the medulla oblongata.
The medulla oblongata attaches to the spinal cord and it controls several unconscious but essential functions like breathing, heart and blood vessel activity, maintaining muscle tone, swallowing, vomiting and digestion.
The pons is a bridge that connects the brainstem with the cerebellum. It is also involved with sleep and arousal. The pons takes part in many of the activities above, sharing responsibility with the medulla. The most important functions of the pons and medulla are data transfer of sensory information and motor impulses.
The cerebellum is involved with the more complex functions of the brain and sometimes is even referred to as “the brain within the brain.” The cerebellum acts as a control and coordination center for movement. The cerebellum stores things we have learned such as how to write, move, run and jump. The brain can recall this information as needed, much like a computer program. The cerebellum coordinates movement and maintains equilibrium. It assists in the execution of commands for muscular movements. Fine motor skills and hand-eye coordination originate from this part of the brain. The cerebellum is one of the first brain structures affected by alcohol.
Mankind has long sought to explore the mysteries of the consciousness and the brain. We have steadfastly plodded on in our efforts to understand just what we are, what it is that makes us like we are, what makes us do what we do and to learn the reasons why. Abraham Maslow was right. I believe this human need for “self-actualization” has manifested itself in the creation of wonderfully helpful and much safer methods for us to advance our knowledge of ourselves. This will continue to be responsible for future technological advances that will, in turn, assist us in biomedical advances.
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