Adult human brain weighs up to 1.5 kg. Human brain has Neurons, Glial Cells and blood Vessels. There are near 200 billion Neurons with 125 Trillion Synapses alone in Cerebral Cortex. Cerebrum forms the largest part of the human brain and is above other brain structures. It is covered with Cerebral Cortex. Underneath Cerebrum is Brainstem a stalk on which Cerebrum is attached. Behind Brainstem at the rear of Brain is Cerebellum. Cerebellum is a furrowed surface structure, the Cerebellar Cortex that makes it different from any other brain region. Living Brain is very soft and has consistency like that of Gelatin or Tofu. Although being referred as Grey Matter its live Cortex is Pinkish in color and Off-White from inside. Human brain like all the other vertebrates has division into three parts i.e.

• Forebrain

• Midbrain

• Hindbrain

Each of these parts has fluid filled Ventricles at their core. Also these parts give generic vertebrate structures which are as follows.

• Medulla Oblongata

• Pons

• Cerebellum

• Optic Tectum

• Thalamus

• Hypothalamus

• Basal Ganglia

• Olfactory Bulb

CEREBRAL CORTEX

The dominant part of the human Brain is Cerebral Cortex which overshadows every other part of the Brain. It is a sheet of folded tissues that allows it to cover a large surface area in the Skull. The damage to Cerebral Cortex can lead to permanent state of Coma. It has two parts which are Symmetrical, Right and Left Hemispheres. Each of these hemispheres is divided into four Lobes i.e.

• Frontal Lobe

• Parietal Lobe

• Occipital Lobe

• Temporal Lobe

FUNCTIONAL DIVISION

Cortex is also divided into three regions according to their functioning which are as follows.

• Primary Sensory Areas; receives signals from sensory nerves by way of relay nuclei in Thalamus. It controls Visual Area of Occipital Lobe, Auditory Area in Temporal Lobe and Insular Cortex.

• Primary Motor Cortex; sends Axons to Motor Neurons in Brainstem and Spinal Cord. They occupy the rear of Frontal Lobe.

• Association Areas; rest of the Cortex that receive input from Sensory areas in lower part of brain responsible for complex functions like Perception, Thought, and Decision making.

BLOOD SUPPLY

Brain is dependent for its blood supply on two sets of branches from Dorsal Aorta. Internal Carotid Arteries branches of Common Carotid Arteries supply blood to the Brain. They arise in the neck at the point where Carotid Arteries branch out. Internal Carotid Arteries branch to form major Cerebral Arteries. Right and left Vertebral Arteries at level of Pons form Basilar Artery. Conjoining the two main sources of Cerebral Blood Vascular Supply through the circle of Willis proves useful if by any chance one of the major arteries is cut off.

CLINICAL SIGNIFICANCE

• Absence of Brain Activity is the definition of Death. Injuries to the brain sometimes cause Deficit in Intelligence, Memory, Personality and Movement. Stroke which is the rupturing of Blood vessels in Brain is one of the main causes of death from brain damage. Other problems of brain classified as diseases are as follows.

• Neurodegenerative Diseases for example Alzheimer, Parkinson, Huntington and Motor Neuron diseases. They are caused by gradual death of Neurons resulting in lacking of control, memory and Intellect. One of the most common Motor Neuron Disease is Amyotrophic Lateral Sclerosis (ALS).

• Mental Disorders for example Clinical Depression, Schizophrenia, Bipolar Disorder and Posttraumatic Stress Disorder.

• Congenital Disorders like Tay - Sachs disease, Fragile X Syndrome and Down syndrome. They are all connected to Genetic and Chromosomal errors.