By, Dr. Shamanthakamani Narendran, M.D. THE BRAIN & FIVE SENSES By, Dr. Shamanthakamani Narendran, M.D.

THE BRAIN The adult human brain weighs an average of 1.4 kg, or about 2 percent of the total body weight.  Despite this relatively small mass, the brain contains approximately 100 billion neurons. Functioning as a unit, these neurons make up the most complex and highly organized structure on Earth. 

THE BRAIN The brain is responsible for many of the qualities that make each individual unique-thoughts, feelings, emotions, talents, memories, and the ability to process information. Much of the brain is dedicated to running the body, the brain is responsible for maintaining Homeostasis by controlling and integrating the various systems that make up the body.

The brain has three main parts: The brain is the main switching unit of the central nervous system; It is the place to which impulses flow and from which impulses originate. The spinal cord provides the link between the brain and the rest of the body. The brain has three main parts: The cerebrum The cerebellum The brain stem

The Brain is a highly organized ORGAN that contains approximately 100 billion neurons and has a MASS of 1.4 Kilograms. The Brain is Protected by a BONY Covering called the SKULL. The Brain is also WRAPPED in THREE LAYERS of CONNECTIVE TISSUE known as the MENINGES.

Connective Tissue connects one tissue to another. The INNER most layer, which covers and is bound to the surface of the brain, is called PIA MATER. It is a FIBEROUS LAYER made up of many Blood Vessels which carry FOOD and OXYGEN to the Brain. The OUTER Layer, called the DURA MATER, is composed of Thick Connective Tissue.

The ARACHNOID is the THIN, elastic, weblike layer between the PIA MATER and the DURA MATER. Between the Pia Mater and the Arachnoid is a space filled with CEREBROSPINAL FLUID.

Cerebrospinal Fluid separates the middle and inner Meninges and fills four interconnected VENTRICLES, or Cavities in the Brain. Within the Ventricles, Cerebrospinal Fluid acts as a Transport Medium for substances that are important to Brain Function.

The Cerebrospinal Fluid is a clear liquid that PROTECTS the Brain from mechanical injury by acting as a Shock Absorber. In order for the Brain to perform its functions, it must have a constant supply of Food and Oxygen. If the Oxygen supply to the brain is cut off even for a few minutes, the brain will usually suffer enormous damage. Such damage may result in DEATH.

PARTS OF THE BRAIN THE CEREBRUM

THE CEREBRUM IS THE CONTROL CENTER OF THE BRAIN. The LARGEST and most PROMINENT part of the Human Brain is the CEREBRUM. 85% OF THE WEIGHT OF A HUMAN BRAIN. The Cerebrum is responsible for all the VOLUNTARY (CONSCIOUS) ACTIVITIES OF THE BODY. It is the site of INTELLIGENCE, LEARNING AND JUDGMENT.

IT FUNCTIONS IN LANGUAGE, CONSCIOUS THOUGHT, MEMORY, PERSONALITY DEVELOPMENT, VISION, AND OTHER SENSATIONS. The Cerebrum takes up most of the space in the cavity that houses the Brain. (SKULL) The CEREBRUM IS DIVIDED INTO TWO HEMISPHERES, THE LEFT AND RIGHT CEREBRAL HEMISPHERES.

There is a DEEP GROVE that separates the Two Hemispheres. The Hemispheres are Connected in a region known as the CORPUS CALLOSUM. The right and left cerebral hemispheres are linked by a bundle of neurons called A TRACT tells each half of the brain what the other half is doing.

The MOST Obvious FEATURE on the surface of each hemisphere are NUMEROUS FOLDS. These FOLDS and the GROOVES INCREASE the Surface Area of the Cerebrum. The Ridges are called GYRI, and the grooves are called SULCUS. The Cerebrum, which looks like a wrinkled mushroom, is positioned over the rest of the brain.

It contains thick layers of Unmyelinated Neurons, which look GRAY It contains thick layers of Unmyelinated Neurons, which look GRAY. ("GRAY MATTER") The increased surface area permits the large number of neurons to fit easily within the confines of the Skull.

Each Hemisphere of the Cerebrum is divided into Four regions called LOBES. These LOBES are named for the SKULL BONES that cover them, FRONTAL, PARIETAL, TEMPORAL, AND OCCIPITAL LOBES.

The RIGHT hemisphere is associated with creativity and artistic ability. The LEFT hemisphere is associated with analytical and mathematical ability.

Sometimes blood vessels in the brain are blocked by blood clots, causing a disorder called A STROKE. During a Stroke, circulation to an area in the brain is blocked and the brain tissue dies. A severe Stroke in one side of the brain may cause PARALYSIS of the other side of the body.

The Cerebrum consists of TWO SURFACES The FOLDED OUTER SURFACE is called the CEREBRAL CORTEX and consists of GRAY MATTER (UNMYELINATED NEURONS). The INNER SURFACE is called the CEREBRAL MEDULLA, which is made up of bundles of MYELINATED AXONS. THE WHITE MATTER. The Myelin gives the White Matter its White Color.

THE CEREBELLUM The CEREBELLUM is the SECOND LARGEST part of the Brain, and is located at the back of the Skull. It coordinates muscle movements.

The Cerebellum coordinates and balances the actions of Muscles so that the body can move gracefully and efficiently. The Cerebellum CONTROLS BALANCE, POSTURE, and COORDINATION. The Cerebellum receives sensory impulses from muscles, tendons, joints, eyes, and ears, as well as input from other brain centers.

It processes information about position and controls posture by keeping skeletal muscles in a constant state of partial contraction. The Cerebellum Coordinates rapid and ongoing movements. This is a small CAULIFLOWER SHAPED Structure.

A Major part of learning how to perform physical activities seems to be related to training the Cerebellum to coordinate the proper muscles. Because the function of the Cerebellum is INVOLUNTARY (not under conscious control), learning a completely new physical activity can be very difficult.

The BRAIN STEM CONNECTS the BRAIN to the SPINAL CORD.

The brain stem, which maintains life support systems, consist of the diencephalon,  medulla oblongata, pons, and the midbrain. The Brain Stem Controls Vital Body Processes. The Brain stem not only coordinates and integrates all INCOMING INFORMATION; it also serves as the place of entry or exit for ten of the Twelve Cranial Nerves.

The Upper Brain Stem, the Diencephalon, contains important relay centers for information entering an exiting the brain. The Lower Brain Stem consists of the MEDULLA OBLONGATA, PONS, AND MIDBRAIN. The Lowest Part of the Brain Stem is the Medulla Oblongata (Sometimes just called the Medulla).

The Medulla contains WHITE MATER that conducts impulses between the Spinal Cord and Brain. The MEDULLA controls involuntary functions that include, breathing, blood pressure, heart rate, digestion, swallowing, and coughing. Another important part of the Medulla is a GROUP of CELLS known as THE RETICULAR ACTIVATING SYSTEM or RETICULAR FORMATION (RAS).

The Reticular Activation System (RAS) actually helps to alert, or awaken, the upper parts of the Brain, including the Cerebral Cortex. Such actions keep the Brain alert and conscious. The RAS also helps to control respiration and circulation and serves as a filtering system for incoming sensory signals. For example, we awaken to the sound of an alarm clock, to a bright light flash, or to a painful pinch because activity in the RAS that arouses the Cerebral Cortex.

Just above the Medulla, the brainstem enlarges to form the PONS Just above the Medulla, the brainstem enlarges to form the PONS. PONS mean BRIDGE, and this area of the brain stem contains mostly white matter that provides a link between the cerebral cortex and the cerebellum. Above the PONS and continuous with it is the MIDBRAIN, the smallest division of the lower brain stem.

DIENCEPHALON THE THALAMUS AND HYPOTHALAMUS The Thalamus and Hypothalamus are found in the part of the brain between the Brain Stem and Cerebrum. The Thalamus, which is composed of Gray Matter, serves as a SWITCHING STATION FOR SENSORY INPUT. With the Exception of SMELL, each Sense Channels its Sensory Nerves through the Thalamus.

The Thalamus passes information to the proper region of the Cerebrum for further processing. Immediately Below the Thalamus is the Hypothalamus, which is the CONTROL CENTER for hunger, thirst, fatigue, anger, and body temperature. Parts of the Diencephalon and the Cerebrum are included in an important group of connected Brain Centers called the LIMBIC SYSTEM.

The Limbic System includes the Thalamus, the Hypothalamus, some deeper parts of the Cerebral Cortex, and centers in the Temporal Lobes. The Limbic system plays an important role in emotions, memory, and motivation, among other things.

BRAIN GROWTH IN FETUS

SENSORY SYSTEMS Human experience is effected by both internal and external stimuli.  Humans are able to distinguish among many different types of stimuli by means of a highly developed system of SENSE ORGANS.  Sensory Systems represent an integration of the functions of the Peripheral Nervous System and the Central Nervous System.

The Sensory Division of the Peripheral Nervous System gathers information about the Body's Internal Conditions and External Environment. Sensory Systems translate light, sound, temperature, and other aspects of the Environment to Electrical Signals and transmit these signals, in the form of Action Potentials, to the Central Nervous System, where they are Interpreted.