Awesome Anatomy

The brain is the fundamental core of the nervous system and is by far the most intricate, complicated and powerful part of the human body. It is responsible for both the lower order functions (such as digesting and breathing) and the higher order functions (such as thinking and inventing). It is at the root of most characteristics that set us apart from simpler forms of animals (language, rationality, mathematics, etc.).

On average, the adult human brain weighs around three pounds and is responsible for the consumption of up to twenty percent of an adult’s total energy (in newborns it consumes as much as sixty percent!) Mankind’s interest in unlocking the mysteries of the brain could be seen even thousands of years ago when Herophilus, the first known anatomist, posited that the brain was the seat of intelligence (Aristotle, on the other hand, posited that the brain’s function was to cool blood). But for however long it has been studied, the brain has only truly begun to be understood in recent years, thanks to advancing technologies and research techniques. One interesting piece of information to emerge is that, contrary to the commonly held belief, humans do use their entire brains and not the ten percent that had previously been suggested. All sectors of the brain perform some function, and many of them will be performed in parallel.


Parts of the Brain



The human brain is an extremely complex organ composed of interdependent parts with each having its own specific functions and properties. However, all of these individual parts can be grouped into three fundamental segments: the hindbrain, the midbrain and the forebrain.

The hindbrain is the part located at the upper section of the spinal cord. It includes the brain stem and the cerebellum. The hindbrain is responsible for monitoring the vital functions of a body, like its heart rate and respiration. The hindbrain (by means of the cerebellum) is the coordinator of motion and is also responsible for muscle memory as seen in the seemingly reflex manner in which a pro golfer swings a club or an encoder types without looking at the keyboard.



The midbrain is the topmost section of the brain stem. It is associated with some, but not all, reflex actions, as well as with certain voluntary movements. The midbrain, for example, is part of the reason why an eye is able to move.

The forebrain is made up of the cerebrum, the hypothalamus, the thalamus, the basal ganglia and the hippocampus. It is the most advanced and the largest section of the brain, located in its uppermost part. It is from the forebrain that the “higher order” activities such as reasoning, remembering and thinking are derived.


Lobes of the Brain

Just as the different parts of the brain can be categorized according to their location (the forebrain, the midbrain and the hindbrain), so too can the brain be examined based on its lobes. The human brain is divided into two hemispheres, and within each of these hemispheres are found four lobes or sections: the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe. These lobes perform their own specific functions.

The frontal lobes of each hemisphere are located just behind the forehead. Among other things, they are partially responsible for language, motor function, judgment, problem solving, impulse control, reasoning, memory and the ability to plan and fulfill plans. Behind the frontal lobes lie the parietal lobes. These lobes are the least understood among the four, but are the principal integrators of sensory information such as taste, pain and temperature. They are also responsible for reading and arithmetic. The occipital lobes lie in the back and are related to visual processing, so much so that injury to an occipital lobe could cause blindness. Lastly, the temporal lobes are found under the parietal lobe and are responsible for memory, hearing, perception and recognition.


The Neuron



The neuron is the fundamental cell that comprises the nervous system of an organism. It is referred to as a nerve cell, and is what allows an organism to monitor its external environment as well as its internal operations. The neuron is also responsible for determining the appropriate response to the data gathered from the outer and inner signals, as well as for controlling the body as demanded by the chosen response.

In the human brain there are around 100 billion neurons, each containing pieces of information that need to be transmitted from one neuron to another in order for the body to function properly. It is through this transmission of information that neurons communicate with each other. Communication between neurons is vital, since without it no degree of information contained in any one neuron would be worth anything. This communication is made possible by the synapses that are located in between neurons and that act as connectors when fueled by special chemicals known as neurotransmitters.


Although there are a number of specialized neuron types, certain components are universally present. All neurons have dendrites, the receptors of information from other neurons. All have somas, containers of nuclei and the organelles required for proper function. Also, all have axons, transmitters of information to other neurons.

Neurons are often categorized by their functional role in the nervious system. Sensory neurons transmit information from the sensory organs to the brain. Motor neurons transmit information from the brain to muscles, directing muscle movement. Visceral neurons connect internal organs to the central nervous system. Somatic neurons connect skin and muscle to the central nervous system.

Brain Imaging



The practice of brain imaging is improving steadily thanks to the rapidly advancing technologies available to today’s neuroscientists and to the field of medicine in general. Brain imaging allows for a glimpse into the internal functions, properties and capacities of the living brain, all of which could only be assumed or hypothesized until the last few decades.

One benefit provided by brain imaging is the greater understanding of specific brain areas, of how these areas interact and of how they operate. Another advantage is the capacity to determine which areas are adversely influenced by brain disorders, thus providing doctors with the relevant information needed to properly and effectively treat the disorders.


There are a number of methods that fall under the category of brain imaging. Some examples include Computed Axial Tomography (known as a CAT scan, which shows structure but not function), Magnetic Resonance Imaging (known as an MRI, which provides a detailed view of different angles of the brain), Functional Magnetic Resonance Imaging (known as a functional MRI, which shows both anatomy and function), and Positron Emission Tomography (known as a PET, which shows brain activity).

Chemicals in the Brain

Most chemicals found in the brain are neurotransmitters, chemicals used to relay, amplify, and modulate the electrical signals passed between neurons and other cells.

The neurotransmitters found in the brain consist primarily of small-molecule transmitters (a class of about ten molecules), and more than fifty neuroactive peptides or proteins. Some fatty acids may also be neurotransmitters, as are several single ions like synaptically-released zinc.

Though the chemicals in the brain vary, their effect is determined by the receptor they go to, not by the chemicals themselves.

The small-molecule neurotransmitter molecules are generally packaged in vesicles, and their release is triggered by synaptic depolarization which causes calcium ion channels to open and release the neurotransmitter; the whole process is called exocytosis. Neurotransmitters released in this way diffuse across the synaptic divide to bind to receptors. Peptides are synthesized in the neuron's soma and transmitted through the axon to the synaptic divide; otherwise, the mechanism of release is similar.

Neurotransmitters are often removed from the synaptic divide by a process called reuptake or uptake; this clears the channel so that the neuron is no longer stimulated or inhibited. With acetylcholine and some other neurotransmitters, the mechanism is digestion by an enzyme instead, or dissolution by proteases. Most neuroactive drugs take advantage of these removal mechanisms to affect the brain.




A list of common neurotransmitters:

Derived from amino acids
aspartate
glutamate (Glu)
γ-aminobutyric acid (GABA)
glycine (Gly)

Biogenic amines
acetylcholine (Ach)

Monoamines (in order of synthesis)

-from phenylalanine and tyrosine:
dopamine (DA)
norepinephrine or noradrenaline (NE)
epinephrine or adrenaline (Epi)

-from tryptophan:
serotonin (5-hydroxytryptamine, 5HT)
melatonin (Mel)

-from histidine:
histamine (H)

Polypeptides (or neuropeptides)

bombesin
gastrin releasing peptide (GRP)

Gastrins

gastrin
cholecystokinin (CCK)

Neurohypophyseals

vasopressin
oxytocin
neurophysin I
neurophysin II

Neuropeptide Y

neuropeptide Y (NY)
pancreatic polypeptide (PP)
peptide YY (PYY)

Opioids

corticotropin (adrenocorticotropic hormone, ACTH)
Beta-lipotropin
dynorphin
endorphin
enkephaline
leumorphin

Secretins

secretin
motilin
glucagon
vasoactive intestinal peptide (VIP)
growth hormone-releasing factor (GRF)

Somatostatins

somatostatin

Tachykinins

neurokinin A
neurokinin B
neuropeptide A
neuropeptide gamma
substance P

Other neurotransmitters

nitric oxide (NO) no receptor
carbon monoxide (CO)
anandamide

Besides neurotransmitting chemicals, many other chemicals found in the brain function as precursors or building blocks to neurotransmitters. Additionally, the cerebrospinal fluid of the brain which provides protection, nutrition and buoyancy to the brain is a clear fluid that contains traces of glucose and various proteins. And of course, the brain's neuron and glial cells have unique cellular and chemical structures as well.