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About the Brain
- Ever wonder about all the bumps and folds on the brain’s surface? If we flattened the brain’s cerebral cortex, the total surface area would be about 2.5 sq ft!
- According to Ray Boyd (Jonathan Lipnicki) in Jerry Maguire, the human head weighs 8 pounds. However, the adult human brain weighs only about 3 pounds—about 2% of the total body weight.
- An elephant brain weighs over 13 lbs. A cat’s brain weighs about 1.06 oz.
- The average human brain (in mm) is 140 x 167 x 93 (in inches: 5.5 x 6.6 x 3.7)
- The weight of an adult human cerebellum is 150 g (5.3 oz).
- Human brains have about 100 billion neurons. Brains of octopi have about 300 million neurons.
- Unconsciousness will occur after 8-10 seconds after loss of blood supply to the brain.
- Cerebrospinal fluid is normally clear and colorless. The total volume of cerebrospinal fluid (CSF) is 125-150 ml. A total of 400-500 ml of cerebrospinal fluid (CSF) is produced every day.
- There are 12 pairs of cranial nerves, 31 pairs of spinal nerves, and about 13,500,00 neurons in the human spinal cord (which is 45 cm long in men and 43 cm long in women).
- Gray matter encompasses the parts of the brain and spinal cord that are composed primarily of groups of neuron cell bodies. During the adolescent years, we observe a decline in gray matter volume as unused neural pathways and connections are “pruned.”
- White matter, as opposed to gray matter, is mainly made up of myelinated nerve fibers (myelin is a fatty substance sheathing nerve cell axons, insulating and protecting the nerve, and speeding up nerve impulse transmission).
- Cerebral Spinal Fluid (CSF) circulates both inside and outside the brain. The differences in pressure between the inside and outside maintain equilibrium and cushion the brain in the skull.
Lobes
- The Frontal Lobe is located in the front part of the cerebrum, beneath the forehead. Higher cognitive processes occur in this area of the brain—such as reasoning, decision-making, and judgment. This area of the brain contains the prefrontal cortex.
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- The Parietal Lobe is located on the top part of the cerebrum (just behind the central sulcus). Spatial orientation and map interpretation take place in the parietal lobe, as does processing of sensory information from the body.
- The Occipital Lobe is located at the rear of the brain, just above the cerebellum. This area is concerned with vision and houses the visual cortex.
- The Temporal Lobes are located on either side of the head, roughly below the temples. Hearing, language, memory storage, and emotion are some of the temporal lobes’ responsibilities.
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Cerebellum
- The cerebellum is a structure in the brain located just above the brain stem. The cerebellum helps organize the brain’s skilled, repetitive movements, and coordinates balance. Recent research suggests the cerebellum, in conjunction with the cerebrum, may play a role in higher cognitive processes.
Brain Stem
- The brain stem is a much older (in evolutionary terms) anatomical region, connecting the brain to the spinal cord. Basic survival functions—such as breathing, heart rate, digestive processes, and sleep—are controlled by the brainstem. To illustrate the importance of this structure, let us examine the sad life of Mike, the almost-headless chicken. Although the majority of Mike’s head was chopped off in an unfortunate accident, he was still in possession of his brain stem, and he lived for another year and a half before he choked on a piece of corn and passed away.
Hemispheres
- The Left hemisphere of the brain controls the right side of the body. This hemisphere is generally involved with sequential analysis—the systematic, logical interpretation of information—and houses the control centers for language, mathematics, abstraction, and logical reasoning.
- The Right hemisphere controls the left side of the body and is responsible for holistic functioning—the integration of multi-sensory input into a comprehensive whole. The right hemisphere also controls spatial abilities, face recognition, and visual imagery.
- Processes such as memory and attention reside in both hemispheres. For example, memory for language is more likely to be localized to the left hemisphere, whereas memory for spatial information is more likely found in the right hemisphere.
- Sometimes hemispheric functions are flipped (more often in left-handed individuals or women).
- The crossed nature of brain-body control (the left hemisphere’s control of the right side of the body and vice versa) is one of those curious facts that has no particular explanation. It just happens to be the case. Damage or disease in the left hemisphere shows up in the right side of the body and right hemisphere damage in the left side of the body.
Our fMRI (functional magnetic resonance imaging) machine utilizes a large, powerful magnet to “scan” human brains and transfer the information into visual format. Visual outputs are based upon statistical analysis of oxygen usage by different anatomical functions. The metallic content of oxygenated blood—carried to the brain via arterial pathways—differs from that of deoxygenated blood—“used” blood, or that which is carried from the brain via veins. These differences allow intense magnetic fields to differentiate between the two types of blood, and interpolate which brain structures were activated. A continuous series of high-speed digital images maps activity, and the resulting images provide an idea of occurrences over time inside a human brain. Researchers are able to examine these images, interpret the results, and draw conclusions about function and purpose of various anatomical brain structures.
(Adapted from The Dana Sourcebook of Brain Science, 3rd Ed.)
- 1489: Leonardo da Vinci sketches the human brain.
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- 1543: Artists in the painter Titian’s studio sketched detailed drawings of the brains of cadavers. This sketch appeared in a book by Dutch anatomist Andreas Vesalius, which revolutionized the study of anatomy.
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- 1861: French surgeon Paul Broca identified the speech center in the brain through autopsies.
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- 1911: Santiago Ramon y Cajal’s drawings and staining methods advanced those of Camillo Golgi for visualizing neurons, dendrites, and axons. Cajal promoted the “neuron theory,” the fundamental principle of modern neuroscience, which holds that neurons are the basic unit of the central nervous system. More important, Cajal realized that neurons communicate across a small gap, or synapse.
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- 1929: Electroencephalogram (EEG) introduced; measures and records minute wavelike electrical signals produced by neurons as they “fire.”
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- 1973: First computed tomography (CT) camera; produces a composite image of the brain with a scanner that revolves around the skull, taking thousands of x-rays.
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- 1975: First positron emission tomography (PET) camera; uses the principle that blood is rushed to busy areas of the brain to deliver oxygen and nutrients to the neurons. Patients are injected with radioactive glucose, then scanned for the rays emitted as the solution metabolizes, highlighting neuronal activity.
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- 1977: First magnetic resonance imaging (MRI) camera; produces images by subjecting the patient’s head to a strong magnetic field, followed by several pulses of radio waves, producing three-dimensional computer-generated images.
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- 1992: Functional magnetic resonance imaging (fMRI) introduced; used to map brain activity by detecting variation sin the response of hydrogen atoms when oxygen is present in the blood.
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At times during prenatal brain development, as many as 250,000 neurons are added every minute! At birth, humans possess nearly all the neurons they will have in a lifetime. The first two years of a human’s life are characterized by the most dramatic changes in the brain; by age 2, the brain is about 80% the adult size. The processes of dendritic spreading (the development of new connections between brain cells) and myelination (the coating of neural axons for faster signal transfer) of neurons are exhibited until about age 11. Neural synapses connect brain cells and allow for cellular communication. About twice as many connections are made as will be used in the adult brain. During the “pruning” phase of brain development—described as “use it or lose it”—the unused connections die off, strengthening more relevant connections and tailoring to the individual’s needs. In adolescence, the prefrontal cortex finishes its development. The relatively late maturation of the prefrontal cortex allows the individual to acquire the skills necessary to become a functioning member of society. Humans do not need these processes earlier in life—the cognitive and social demands of a five-year-old, for example, are significantly simpler than those of a 16- or 17-year-old.
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