![]() However, there are five major neuron forms. Given the sheer number of neurons, there are thousands of different types, much like there are thousands of species of living organisms on Earth. Neurons vary in structure, function, and genetic makeup. These cells have highly developed dendritic trees which allow them to receive thousands of signals. For instance, Purkinje cells are a special type of neuron found in a part of the brain called the cerebellum. How many they have generally depends on their role. Neurons can have more than one set of dendrites, known as dendritic trees. Like antennae, dendrites receive and process signals from the axons of other neurons. Dendritesĭendrites are fibrous roots that branch out from the cell body. Myelin helps axons to conduct an electrical signal. Many axons are insulated with a fatty substance called myelin. It joins the cell body at a specialized junction called the axon hillock. AxonĪn axon is a long, tail-like structure. It’s enclosed by a membrane that both protects it and allows it to interact with its immediate surroundings. Like other cell bodies, a neuron’s soma contains a nucleus and specialized organelles. The cell body contains genetic information, maintains the neuron’s structure, and provides energy to drive activities. Cell bodyĪlso known as a soma, the cell body is the core section of the neuron. However, nearly all neurons have three essential parts: a cell body, an axon, and dendrites. However, because the envelope contains lipids, it makes the virus more susceptible to inactivation by environmental agents, such as detergents that disrupt lipids.Neurons vary in size, shape, and structure depending on their role and location. Most enveloped viruses depend on their envelopes to infect cells. ![]() These receptor molecules allow host cells to recognize and bind the virions, which may result in easier uptake of the virion into the cell. The proteins in the envelope can include glycoproteins, which act as receptor molecules. For example, they have better protection from the host's immune system, enzymes and certain chemicals. The viral envelope can give a virus some advantages over other capsid-only viruses. Varicella zoster virus causes chicken pox and shingles. The influenza virus, HIV, and the varicella zoster virus ( Figure below) are enveloped viruses.Īn enveloped virus. However, the lipid membrane itself and any carbohydrates present come entirely from the host cell. This membrane is studded with proteins coded for by both the viral genome and the host genome. In this way the virus gains an outer lipid bilayer known as a viral envelope. The virus can use either the outer membrane of the host cell, or an internal membrane such as the nuclear membrane or endoplasmic reticulum. Some viruses are able to surround (envelop) themselves in a portion of the cell membrane of their host. The envelope which surrounds the capsid is typically made from portions of the host cell membranes (phospholipids and proteins). The capsid encloses the genetic material of the virus. They make it easier for the virus to infect the cells.ĭiagram of a Cytomegalovirus. The envelope may also have receptor molecules that can bind with host cells. It surrounds the capsid and helps protect the virus from the host’s immune system. The envelope is made from portions of the host’s cell membrane. Some viruses have an envelope of phospholipids and proteins. Virally coded proteins will self-assemble to form a capsid. The capsid of the virus shown in Figure below is icosahedral. The shape of the capsid serves as one basis for classification of viruses. ![]() The capsid is made from the proteins that are encoded by viral genes within their genome. The shape of the capsid may vary from one type of virus to another. A virus particle consists of DNA or RNA within a protective protein coat called a capsid.
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