PKU, a genetic disorder discussed earlier, causes a reduction in myelin and abnormalities in white matter cortical and subcortical structures. To understand how this works, let’s consider an example. The myelin sheath is crucial for the normal operation of the neurons within the nervous system: the loss of the insulation it provides can be detrimental to normal function. These gaps in the myelin sheath are known as the Nodes of Ranvier. The myelin sheath is not continuous and there are small gaps that occur down the length of the axon. In some axons, glial cells form a fatty substance known as the myelin sheath, which coats the axon and acts as an insulator, increasing the speed at which the signal travels. The terminal buttons contain synaptic vesicles that house neurotransmitters, the chemical messengers of the nervous system.Īxons range in length from a fraction of an inch to several feet. These signals are transmitted electrically across the soma and down a major extension from the soma known as the axon, which ends at multiple terminal buttons. The neuron is a small information processor, and dendrites serve as input sites where signals are received from other neurons. The soma has branching extensions known as dendrites. The nucleus of the neuron is located in the soma, or cell body. This membrane allows smaller molecules and molecules without an electrical charge to pass through it, while stopping larger or highly charged molecules.įigure 3.8 This illustration shows a prototypical neuron, which is being myelinated by a glial cell. A neuron’s outer surface is made up of a semipermeable membrane. Like all cells, neurons consist of several different parts, each serving a specialized function ( Figure 3.8). Neurons are the central building blocks of the nervous system, 100 billion strong at birth. This section briefly describes the structure and function of neurons. Neurons, on the other hand, serve as interconnected information processors that are essential for all of the tasks of the nervous system. This is important because it suggests that human brains are more similar to other primate brains than previously thought (Azevedo et al, 2009 Herculano-Houzel, 2012 Herculano-Houzel, 2009). For years, researchers believed that there were many more glial cells than neurons however, more recent work from Suzanna Herculano-Houzel's laboratory has called this long-standing assumption into question and has provided important evidence that there may be a nearly 1:1 ratio of glia cells to neurons. Glial cells provide scaffolding on which the nervous system is built, help neurons line up closely with each other to allow neuronal communication, provide insulation to neurons, transport nutrients and waste products, and mediate immune responses. Glial cells are traditionally thought to play a supportive role to neurons, both physically and metabolically. The nervous system is composed of two basic cell types: glial cells (also known as glia) and neurons. Learning how the body's cells and organs function can help us understand the biological basis of human psychology. Psychologists striving to understand the human mind may study the nervous system. Explain how drugs act as agonists or antagonists for a given neurotransmitter system.Describe how neurons communicate with each other.By the end of this section, you will be able to:
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