View a light-microscopic slide of an axon hillock of a sensory neuron.At the distal-most end of the axon and its collaterales are small branches whose tips are button-shaped cytoplasmic enlargements called terminal boutons or nerve endings.ĭiagrammatic representation of the initial segment of a neuron, emphasizing the areas in which the action potential is initiated. The area under the axolemma in this region has material that stains darkly when viewed by EM.
In many cases, this region is the anatomical location for the initiation of the action potential. The region between the axon hillock and the beginning of the myelin sheath is known as the initial segment. The neurofilaments in the axon hillock become clustered together as fascicles.
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This area is free of ribosomes and most other cell organelles, with the exception of cytoskeletal elements and organelles that are being transported down the axon. The cone-shaped region of the cell body where the axon originates is termed the axon hillock. For instance, an average spinal motor neuron with a moderate-sized dendritic tree, receives 10,000 contacts, with 2,000 of these on the soma and 8,000 on the dendrites. Dendrites may consist of a single twig-like extension from the soma or a multi-branched network capable of receiving inputs from thousands of other cells. Information is received by the dendrite through an array of receptors on dendrite surface that react to transmitters released from the axon terminals of other neurons.
View an EM slide of a dendrite and a spine. View a light-microscopic slide of a dendrite with spines. The dendritic spines often contain microfilaments which is the cytoskeletal element responsible for changes in spine shape observed in some examples of synaptic plasticity.ĭiagrammatic representation of the neuron dendrite, emphasizing the areas of contact by other afferent inputs to the neuron. The shape and extent of the "dendritic tree" of an individual neuron is indicative of the quantity and variety of information received and processed by that neuron. Rough endoplasmic reticulum and ribosomes are present in large but not small dendrites. Mitochondria are often arranged longitudinally. In addition, microtubules in dendrites have their positive ends toward the cell soma. The microtubule associated proteins (MAPs) in the dendrite have a higher molecular weight than those found in the axon. Dendrites contain numerous orderly arrays of microtubules and fewer neurofilaments (see below). The dendritic processes and spines of neurons are essentially expansions of cytoplasm containing most of the organelles found in the cell body. Spines provide a tremendous increase in the surface area available for synaptic contacts. The dendritic processes may branch extensively and are often covered with projections known as dendritic spines. The membrane of the neuron functions as a receptive surface over its entire extent however, specific inputs (termed afferents) from other cells are received primarily on the surface of the cell body and on the surface of the specialized processes known as dendrites. Place cursor over image to identify organelles. Many of these cell inclusions are responsible for the expression of genetic information controlling the synthesis of cellular proteins involved in energy production, growth, and replacement of materials lost by attrition.ĭiagrammatic representation of the neuron cell body or perikaryon emphasizing the endoplasmic reticulum, Golgi apparatus and cytoskeleton. Embedded within the neuronal cytoplasm are the organelles common to other cells, the nucleus, nucleolus, endoplasmic reticulum, Golgi apparatus, mitochondria, ribosomes, lysosomes, endosomes, and peroxisomes. As described in Chapter 6, it also acts as a receptive area for synaptic inputs from other cells. The interior of the soma consists of cytoplasm, a gel within a microtrabecular lattice formed by the microtubules and associated proteins that make up the cytoskeleton.Įnergy producing metabolism and the synthesis of the macromolecules used by the cell to maintain its structure and execute its function are the principal activities of the neuronal soma. The cell body is the metabolic center of the neuron. The region of the neuron containing the nucleus is known as the cell body, soma, or perikaryon (Figure 8.2). Tap on the parts of the Model Neuron to view structures.Īfter reviewing the Model Neuron above, learn more about the function of each structure by tapping from the list below.Ĭlick the identified structures on the model neuron to move to the related section.
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