Basic science

Introduction

The human brain is a very powerful organ. It controls all parts of the body and allows us to think, feel, move our arms and legs and it helps us stay healthy.

The brain looks like a pink sponge and consists of a mass of nerve cells. It is protected by the skull. An adult's brain weighs about 1.5 kilograms. Large animals such as whales and elephants have larger brains in absolute terms, but when measured using the encephalization quotient which compensates for body size, the human brain is almost twice as large as the brain of the bottlenose dolphin, and three times as large as the brain of a chimpanzee. Much of the expansion comes from the part of the brain called the cerebral cortex, especially the frontal lobes, which are associated with executive functions such as self-control, planning, reasoning, and abstract thought. The portion of the cerebral cortex devoted to vision is also greatly enlarged in humans.

 The adult human brain weighs on average about 3 lb (1.5 kg) with a size of around 1130 cubic centimeters (cm3) in women and 1260 cm3 in men, although there is substantial individual variation. Men's brains are on average 100g heavier than a woman's, even when corrected for body size differences The brain is very soft, having a consistency similar to soft gelatin or firm tofu. Despite being referred to as "grey matter", the live cortex is pinkish-beige in color and slightly off-white in the interior.

My main focus of presenting this paper is based on the human brain. Human brain is a very complicated organ. My effort in presenting this paper is try to understand the functions and features of the brain. Thus, in way I somehow learnt so many things about the brain. Brain which is one of the main organs in our body is very complicated to understand. It does many complicated work which we are not aware of. In my presentation I tried to understand some of these complicated things.

                                                                                                         

                                                          

Brain Structures and their Functions

The nervous system is our body's decision and communication center. The central nervous system (CNS) is made of the brain and the spinal cord and the peripheral nervous system (PNS) is made of nerves. Together they control every part of your daily life, from breathing and blinking to helping you memorize facts for a test. Nerves reach from our brain to our face, ears, eyes, nose, and spinal cord... and from the spinal cord to the rest of our body. Sensory nerves gather information from the environment; send that information to the spinal cord, which then speed the message to the brain. The brain then makes sense of that message and fires off a response. Motor neurons deliver the instructions from the brain to the rest of your body. The spinal cord, made of a bundle of nerves running up and down the spine, is similar to a superhighway, speeding messages to and from the brain at every second.

The brain is made of three main parts: the forebrain, midbrain, and hindbrain. The forebrain consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system). The midbrain consists of the tectum and tegmentum. The hindbrain is made of the cerebellum, Pons and medulla. Often the midbrain, Pons, and medulla are referred to together as the brainstem.

The Cerebrum: The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. Here is a visual representation of the cortex:

What does each of these lobes do?

Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving

Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli

Occipital Lobe- associated with visual processing

Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech

Note that the cerebral cortex is highly wrinkled. Essentially this makes the brain more efficient, because it can increase the surface area of the brain and the amount of neurons within it. We will discuss the relevance of the degree of cortical folding later. A deep furrow divides the cerebrum into two halves, known as the left and right hemispheres. The two hemispheres look mostly symmetrical yet it has been shown that each side functions slightly different than the other. Sometimes the right hemisphere is associated with creativity and the left hemisphere is associated with logic abilities. The corpus callosum is a bundle of axons which connects these two hemispheres.

Nerve cells make up the gray surface of the cerebrum which is a little thicker than our thumb.  White nerve fibers underneath carry signals between the nerve cells and the other parts of the brain and body.

The neocortex occupies the bulk of the cerebrum. This is a six-layered structure of the cerebral cortex which is only found in mammals. It is thought that the neocortex is a recently evolved structure, and is associated with "higher" information processing by more fully evolved animals (such as humans, dolphins, etc).

The Cerebellum: The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance.

The cerebellum is assumed to be much older than the cerebrum, evolutionarily. In other words, animals which scientists assume to have evolved prior to humans, for example reptiles, do have developed cerebellums. However, reptiles do not have neocortex. 

 Limbic System: The limbic system, often referred to as the "emotional brain", is found buried within the cerebrum. Like the cerebellum, evolutionarily the structure is rather old.

This system contains the thalamus, hypothalamus, amygdala, and hippocampus.

Brain Stem: Underneath the limbic system is the brain stem. This structure is responsible for basic vital life functions such as breathing, heartbeat, and blood pressure. Scientists say that this is the "simplest" part of human brains because animals' entire brains, such as reptiles resemble our brain stem.

The living brain is very soft, having a consistency similar to soft gelatin or soft tofu. Despite being referred to as grey matter, the live cortex is pinkish-beige in color and slightly off-white in the interior.

General features of brain

The human brain has many properties that are common to all vertebrate brains, including a basic division into three parts called the forebrain, midbrain, and hindbrain, each with fluid-filled ventricles at their core, and a set of generic vertebrate brain structures including the medulla oblongata, Pons, cerebellum, optic tectum, thalamus, hypothalamus, basal ganglia, olfactory bulb, and many others.

As a mammalian brain, the human brain has special features that are common to all mammalian brains, most notably a six-layered cerebral cortex and a set of structures associated with it, including the hippocampus and amygdala. All vertebrates have a forebrain whose upper surface is covered with a layer of neural tissue called the pallium, but in all except mammals the pallium has a relatively simple three-layered cell structure. In mammals it has a much more complex six-layered cell structure, and is given a different name, the cerebral cortex. The hippocampus and amygdala also originate from the pallium, but are much more complex in mammals than in other vertebrates.

As a primates (monkey) brain, the human brain has a much larger cerebral cortex, in proportion to body size, than most mammals, and a very highly developed visual system. The shape of the brain within the skull is also altered somewhat as a consequence of the upright position in which primates hold their heads. As a hominid brain, the human brain is substantially enlarged even in comparison to the brain of a generic monkey. The sequence of evolution from Australopithecus (four million years ago) to Homo sapiens (modern man) was marked by a steady increase in brain size, particularly in the frontal lobes, which are associated with a variety of high-level cognitive functions.  

Humans and other primates have some differences in gene sequence, and genes are differentially expressed in many brain regions. The functional differences between the human brain and the brains of other animals also arise from many gene–environment interactions.

Cerebral cortex: The cerebral hemispheres form the largest part of the human brain and are situated above most other brain structures. They are covered with a cortical layer with a convoluted topography. Underneath the cerebrum lies the brainstem, resembling a stalk on which the cerebrum is attached. At the rear of the brain, beneath the cerebrum and behind the brainstem, is the cerebellum, a structure with a horizontally furrowed surface that makes it look different from any other brain area. The same structures are present in other mammals, although the cerebellum is not so large relative to the rest of the brain. As a rule, the smaller the cerebrum, the less convoluted the cortex. The cortex of a rat or mouse is almost completely smooth. The cortex of a dolphin or whale, on the other hand, is more convoluted than the cortex of a human.

The cerebral cortex is essentially a sheet of neural tissue, folded in a way that allows a large surface area to fit within the confines of the skull. Each cerebral hemisphere, in fact, has a total surface area of about 1.3 square feet (0.12 m2). Anatomists call each cortical fold asulcus, and the smooth area between folds a gyrus.

The four lobes of the cerebral cortex

The cerebral cortex is nearly symmetrical, with left and right hemispheres that are approximate mirror images of each other. Anatomists conventionally divide each hemisphere into four "lobes", the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. This division into lobes does not actually arise from the structure of the cortex itself, though: the lobes are named after the bones of the skull that overlie them, the frontal bone, parietal bone, temporal bone, and occipital bone. The borders between lobes are placed beneath the sutures that link the skull bones together. There is one exception: the border between the frontal and parietal lobes is shifted backward from the corresponding suture, to the central sulcus, a deep fold that marks the line where the primary somatosensory cortex and primary motor cortex come together.

Because of the arbitrary way most of the borders between lobes are demarcated, they have little functional significance. With the exception of the occipital lobe, a small area that is entirely dedicated to vision, each of the lobes contains a variety of brain areas that have minimal functional relationship. The parietal lobe, for example, contains areas involved in somatosensation, hearing, language, attention, and spatial cognition. In spite of this heterogeneity, the division into lobes is convenient for reference.

Topography

Many of the brain areas have their own complex internal structures. In a number of cases, brain areas are organized into "topographic maps", where adjoining bits of the cortex correspond to adjoining parts of the body, or of some more abstract entity. A simple example of this type of correspondence is the primary motor cortex, a strip of tissue running along the anterior edge of the central sulcus. Motor areas innervating each part of the body arise from a distinct zone, with neighboring body parts represented by neighboring zones. Electrical stimulation of the cortex at any point causes a muscle-contraction in the represented body part. This "somatotopic" representation is not evenly distributed, however. The head, for example, is represented by a region about three times as large as the zone for the entire back and trunk. The size of any zone correlates to the precision of motor control and sensory discrimination possible. The areas for the lips, fingers, and tongue are particularly large, considering the proportional size of their represented body parts.

In visual areas, the maps are retinotopic—that is, they reflect the topography of the retina, the layer of light-activated neurons lining the back of the eye. The visual circuitry in the human cerebral cortex contains several dozen distinct retinotopic maps, each devoted to analyzing the visual input stream in a particular way. The primary visual cortex, which is the main recipient of direct input from the visual part of the thalamus, contains many neurons that are most easily activated by edges with a particular orientation moving across a particular point in the visual field. Visual areas farther downstream extract features such as color, motion, and shape.

In auditory areas, the primary map is tonotopic. Sounds are parsed according to frequency (i.e., high pitch vs. low pitch) by subcortical auditory areas, and this parsing is reflected by the primary auditory zone of the cortex. As with the visual system, there are a number of tonotopic cortical maps, each devoted to analyzing sound in a particular way.

Within a topographic map there can sometimes be finer levels of spatial structure. In the primary visual cortex, for example, where the main organization is retinotopic and the main responses are to moving edges, cells that respond to different edge-orientations are spatially segregated from one another.

Lateralization

Each hemisphere of the brain interacts primarily with one half of the body, but for reasons that are unclear, the connections are crossed: the left side of the brain interacts with the right side of the body, and vice versa. Motor connections from the brain to the spinal cord, and sensory connections from the spinal cord to the brain, both cross the midline at the level of the brainstem. Visual input follows a more complex rule: the optic nerves from the two eyes come together at a point called the optic chiasm, and half of the fibers from each nerve split off to join the other. The result is that connections from the left half of the retina, in both eyes, go to the left side of the brain, whereas connections from the right half of the retina go to the right side of the brain. Because each half of the retina receives light coming from the opposite half of the visual field, the functional consequence is that visual input from the left side of the world goes to the right side of the brain, and vice versa. Thus, the right side of the brain receives somatosensory input from the left side of the body, and visual input from the left side of the visual field—an arrangement that presumably is helpful for visuomotor coordination.

My personal experience

Through this course I learnt so many things for my life. When I was studying basic science I realized that there was something which I had studied already in my high school days but I had forgotten it. This way the study of basic science refreshed my mind. I came to know so many things about physics, chemistry and biology which I use in my daily life. There are some important things around me which I just ignore but they are very important for my life. I felt that there are so many miracles taking place in my life and around my life which I just bypass. In our body there are so many organs which work day and night to keep us healthy. We do not think much about all these things but when some organs stop functioning then we realize that there is something wrong with us.

Similarly when we talk about nature we see that they also work quietly in order to maintain the stability in the environment. Thus, the study of basic science was really very amazing and wonderful for me. Subject was very interesting which kept me focused on some amazing things. Some of the things which were taught in the class were really new for me therefore these things were a kind of new findings for my life. As a religious some of the things which I should know, basic science provided some of those things. In a way basic science gave a taste of scientific world. In other words I can say that it has developed a kind of curiosity in me to know about the scientific world.

When we talk about the human brain this is another very complicated organ. By studying about the human brain I could learn so many things. In human brain many activities take place all the times but we are not aware of that. These organs quietly complete their work without our knowledge. All these function takes place in our body system but still we are not aware about all these things.

Thus, I can say that this course was very important for me. This course gave me an opportunity to learn many things about the science world. I am sure it will help me a lot in my life. The study of science has brought a kind of awareness in my life. And the feelings of awareness certainly bring changes in my life.