![]() Some sources describe a fourth type of neuron, called an anaxonic neuron. Some cutting edge research suggests that certain neurons in the CNS do not conform to the standard model of “one, and only one” axon. With the exception of the unipolar sensory ganglion cells, and the two specific bipolar cells mentioned above, all other neurons are multipolar. They have one axon and two or more dendrites (usually many more). Multipolar neurons are all of the neurons that are not unipolar or bipolar. They are found mainly in the olfactory epithelium (where smell stimuli are sensed), and as part of the retina. The axon projects from the dendrite endings, past the cell body in a ganglion, and into the central nervous system.īipolar cells have two processes, which extend from each end of the cell body, opposite to each other. Sensory reception is a peripheral function (those dendrites are in the periphery, perhaps in the skin) so the cell body is in the periphery, though closer to the CNS in a ganglion. Secondly, the cell bodies of unipolar neurons are always found in ganglia. First, their dendrites are receiving sensory information, sometimes directly from the stimulus itself. Unipolar cells are exclusively sensory neurons and have two unique characteristics. At one end of the axon are dendrites, and at the other end, the axon forms synaptic connections with a target. Human unipolar cells have an axon that emerges from the cell body, but it splits so that the axon can extend along a very long distance. Invertebrate unipolar cells do not have dendrites. True unipolar cells are only found in invertebrate animals, so the unipolar cells in humans are more appropriately called “pseudo-unipolar” cells. Unipolar cells have only one process emerging from the cell. Neurons are broadly divided into four main types based on the number and placement of axons: (1) unipolar, (2) bipolar, (3) multipolar, and (4) pseudounipolar (Credit: Figure 16.5, Opentext Concepts of Biology, CC BY 4.0. Because information flows through the neuron from dendrites or cell bodies toward the axon, these names are based on the neuron’s polarity. Using the standard model of neurons, one of these processes is the axon, and the rest are dendrites. ![]() The first way to classify them is by the number of processes attached to the cell body. They can be classified by many different criteria. And there are many different types of neurons. There are many neurons in the nervous system-a number in the trillions. This gives the neuron a polarity, meaning that information flows in this one direction. Information flows through a neuron from the dendrites, across the cell body, and down the axon. The dendrites are usually highly branched processes, providing locations for other neurons to communicate with the cell body. ![]() The other processes of the neuron are dendrites, which receive information from other neurons at specialized areas of contact called synapses. It is the axon that propagates the nerve impulse, which is communicated to one or more cells. That single axon can branch repeatedly to communicate with many target cells. ![]() Neurons are usually described as having one, and only one, axon-a fiber that emerges from the cell body and projects to target cells. But what makes neurons special is that they have many extensions of their cell membranes, which are generally referred to as processes. The cell body contains the nucleus and most of the major organelles. The main part of a neuron is the cell body, which is also known as the soma (soma = “body”). Neurons are important, but without glial support, they would not be able to perform their functions. Ongoing research pursues an expanded role that glial cells might play in signaling, but neurons are still considered the basis of this function. Glial cells, or glia, are known to play a supporting role for nervous tissue. They are electrically active and release chemical signals to target cells. They are responsible for the computation and communication that the nervous system provides. Neurons are the primary type of cell that most anyone associates with the nervous system. Nervous tissue is composed of two types of cells, neurons and glial cells. This Neuroscience section is composed of excerpts from that chapter to highlight just the key concepts that are most relevant to a study of sensation and perception. If you have yet to take a neuroscience class, you will want to read-thoroughly-the very excellent Chapter 12 from the OpenStax Anatomy and Physiology textbook. Make sure that you’re familiar with each of these concepts-t his introductory section recaps background vocabulary to support other learning goals.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |