The Brain’s Inner Workings Part I: Structure and Function

The Brain’s Inner Workings Part I: Structure and Function


The National Institute of Mental Health, or NIMH, has the mission of supporting research on mental illness including schizophrenia, depression, anxiety and panic disorders. The key to helping those who suffer from mental illness is to first understand normal brain function. This knowledge can then be applied to help treat or prevent mental illness. This is a challenge because it involves understanding the neural pathways and molecular mechanisms subserving behaviours like winning at chess. Now we are well on track to unlocking the mysteries of some of those special abilities. Progress in brain research has been due both to the increasing number of scientists interested in studying the brain and to unprecedented technological innovations. These new tools give us a window to the brain. The cerebral cortex is the outermost covering of the brain, which has evolved in humans further than in any other species and what is most responsible for making humans human. It is also the structure most associated with higher mental functions. With its multiple folds, ridges and grooves the cortex is made up of two similar looking hemispheres joined at the middle by an extensive bundle of nerve fibres, which cross from side to side. One of the keys to understanding the brain is to recognise that nerve cells are highly interconnected. Any given nerve cell may make thousands of connections with other nerve cells. The orange looking surface in this image is the cerebral cortex. Since the size of the brain is limited by the space within the skull the only way to increase the amount of cortical tissue is to fold it. With a specialized method we can look deep into the cortex and see individual cells. Here they appear black and have braches coming from them. As magnification increases we see greater detail in the network of the branches. These are dendrites, which are the appendages of neurons, which will receive synaptic connections from other cells. Connections are made with another specialized process called an axon. The place where communication occurs between an axon and a dendrite is called a synapse. Synapses are the communicational links between neurons. Remember, thousands can occur along a single dendrite. Understanding how neuronal communication occurs at the synapse is one key to understanding the most interesting questions like how memories are stored and how learning occurs. Indeed scientists now believe that disruptions of normal activity occurring at synapses are involved in several of the disorders we call “mental illness”. Our current understanding of how synapses work is represented in this computer animation. As we dive deeper into the cell’s own structure down into a single axon terminal at a synapse we see small round objects, which are the synaptic vesicles. They are like tiny balloons: miniature containers filled with chemical neurotransmitters. When an electrical impulse reaches the nerve terminal, proteins in the watery soup orchestrate the movement of these vesicles toward the membrane forming one side of the synapse. The visualization is slowed down here but in real time this process happens in less than a thousandth of a second. As the transmitter filled vesicles touch the inside of the nerve terminal membrane their own membrane fuses with it. When this happens the inside of the vesicle opens into the synaptic cleft and transmitter molecules diffuse across this tiny space to reach their target receptors on the other side. This causes electrical conduction to occur completing the propagation of the neuronal message across the cleft. The processes of neural conduction and neural transmission occur by the billions throughout the human brain. It is this complex interplay of chemical, electrical and physical events which underlies the rich tapestry of everyday experiences: the sights we see, the sounds we hear, the feelings we experience, the activities we initiate and the ideas we ponder. Even slight errors or variations in any of these neural events can lead to the kind of abnormalities which underline most of brain disorders including mental illness. By understanding the intricacies of neural activities and how they are related to cognitive and behavioural processes we’re on the threshold of providing specific treatments and ultimately cures and preventions in our mission to ensure the mental health of the nation.

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