Depression Chapter 4


Your Brain Is Electric

PART 1

How Your Brain Transmits Information

Information, in the form of electrical impulses, travels along neural pathways composed of interconnected neurons. Neuron cells are composed of three basic elements: the cell body, the axon, and the dendrite. Axons are long fibers, sometimes branched, which extend out of the cell body and transmit electrical impulses to the next neuron. Dendrites are highly branched fibers that receive signals from the axons of other neurons. The place where axons and dendrites join is called a synapse. For every neuron, there are between 1,000 and 10,000 synapses. Axons and dendrites don't actually touch at the synapse: there's a microscopic space in between where information is transferred.
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PART 2

Synapses and Neurotransmitters

When the cell body receives enough stimulation—when you touch a very hot object, for instance—it generates an electrical impulse that is transmitted to the end of the axon. These impulses travel across the neurons at an amazing rate of speed: less than 1/5,000 of a second. The impulse causes the axon to release chemicals called neurotransmitters into the synapse between the axon and the adjoining dendrite. Neurotransmitters are chemical messengers, carrying information from one neuron to another. READ MORE

The neurotransmitters diffuse across the synapse and bind to special molecules, called receptors, on the dendrite. This, in turn, stimulates or inhibits an electrical response in the receiving neuron's dendrites. Once the neurotransmitter releases from the receptor site on the dendrite, it floats back into the synapse. It may then be broken down by a chemical called monoamine oxidase, or it may be taken back in by the neuron that originally released it. The latter case is called reuptake. LESS
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PART 3

The Embryonic Brain

Depression can occur at any point during your lifetime. To understand it better, it helps to start at the beginning, with the development of your nervous system. READ MORE

The nervous system begins to develop at the embryonic stage (the earliest stages of growth), when the brain and then the spinal cord start to develop. The nervous system consists of two subsystems. The brain and the spinal cord together make up the central nervous system (CNS). The second subsystem is the peripheral nervous system (PNS), which consists of the neurons that process all signals coming from the environment and communicate the state of the body to the brain. It is the link between the outside world and the CNS, and develops at a later stage.

Early on, three distinct areas of the brain appear: the forebrain, midbrain, and hindbrain. Each produces its own set of structures that control how we function. The cerebral cortex––the most prominent feature when we think of a human brain––derives from the forebrain. By the end of the second trimester it is the primary visible structure. LESS
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PART 4

Adolescent Development

The brain undergoes a number of changes during adolescence that are important for understanding adolescent moods and behavior. One major change is surprising. You would expect that all parts of the brain would grow during adolescence, but in fact a large reduction in the number of synapses takes place. It’s thought that this large reduction is related to active restructuring of neural connections so that connections with very little activity are pruned out. These changes, according to this theory, create a more efficient and less energy-consuming brain. READ MORE

A second change in the brain during adolescence is myelination. In myelination, a layer of myelin forms around the axons, which allows the nerve impulses to travel faster. Throughout adolescence, myelination continues for the long-distance neural connections in the frontal, parietal, and temporal areas of the brain. This encourages the development of more advanced functions of the brain, such as planning and decision-making, by helping different areas of the brain to work together and by increasing the speed of information processing.

New neurons continue to develop in the brain during adolescence (new neurons grow in other stages of life as well, including adulthood). This process is called neurogenesis. LESS
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