The brain is the center of the nervous system located in the head and protected by the skull. It contains billions of neurons that communicate through long fibers called axons. While protected, the human brain is susceptible to damage from head injuries, strokes, diseases, and disorders. The cerebral cortex is divided into left and right hemispheres, each with four lobes - frontal, parietal, occipital, and temporal. Each hemisphere primarily interacts with the opposite side of the body through crossed connections in the brain and spinal cord.

1. THE BRAIN

2. The brain is the center of the nervous system in all vertebrate and most invertebrate animals.Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates the brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing, balance, taste, and smell.

3. HUMAN BRAIN SHARK BRAIN

4. Brains can be extremely complex. The cerebral cortex of the human brain contains roughly 15–33 billion neurons, perhaps more, depending on gender and age,linked with up to 10,000 synaptic connections each. Each cubic millimeter of cerebral cortex contains roughly one billion synapses.These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body and target them to specific recipient cells. Structure of a typical chemical synapse

5. In spite of the fact that it is protected by the thick bones of the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood-brain barrier, the delicate nature of the human brain makes it susceptible to many types of damage and disease. The most common forms of physical damage are closed head injuries such as a blow to the head, a stroke, or poisoning by a wide variety of chemicals that can act as neurotoxins. Infection of the brain is rare because of the barriers that protect it, but is very serious when it occurs. The human brain is also susceptible to degenerative disorders, such as Parkinson's disease, multiple sclerosis, and Alzheimer's disease. A number of psychiatric conditions, such as schizophrenia and depression, are widely thought to be caused at least partially by brain dysfunctions, although the nature of such brain anomalies is not well understood.

6. Cortical divisions Four lobes Outwardly, the cerebral cortex is nearly symmetrical, with left and right hemispheres. Anatomists conventionally divide each hemisphere into four "lobes", the: Frontal lobe Parietal lobe Occipital lobe Temporal lobe This categorization does not actually arise from the structure of the cortex itself: the lobes are named after the bones of the skull that overlie them. There is one exception: the border between the frontal and parietal lobes is shifted backward to the central sulcus, a deep fold that marks the line where the primary somatosensory cortex and primary motor cortex come together. Although the division of the cortex into hemispheres and lobes is very general and perhaps lack the precision of specifying by brain coordinates (e.g. Talairach space) or through the region of specific brain cytoarchitecture (e.g. Brodmann areas, or deep brain structures), it is nevertheless useful for discussing general brain anatomy or the locating the lesions in a general area of the brain.

8. 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 brainstem levels. 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. Lateralization of brainfunction

9. INSTITUTO TECNOLOGICO DE EDUCACION AVANZADA EnglishTeacher: Gina Leroux Team: Investigation:Nathalie& Wendy Pictures: Alejandra & Isui Realization PPS: Grecia December 2010