![]() ![]() In animals exhibiting bilateral symmetry such as (c) planarians, neurons cluster into an anterior brain that processes information. In (b) echinoderms, nerve cells are bundled into fibers called nerves. In (a) cnidarians, nerve cells form a decentralized nerve net. Nervous systems vary in structure and complexity. Nervous systems throughout the animal kingdom vary in structure and complexity, as illustrated by the variety of animals shown below: The information below was adapted from OpenStax Biology 35.1 The material in the nervous system can also be classified based on whether it contains white matter (myelinated axons) and gray matter (uunmyelinated axons and cell bodies). It would be combinations of interneurons in your brain that would allow you to draw the conclusion that things that looked like hot coals weren’t good to pick up, and, hopefully, retain that information for future reference. Interneurons are the most numerous class of neurons and are involved in processing information, both in simple reflex circuits (like those triggered by hot objects) and in more complex circuits in the brain. Some of these interneurons would signal to the motor neurons controlling your finger muscles (causing you to let go), while others would transmit the signal up the spinal cord to neurons in the brain, where it would be perceived as pain. For instance, if you picked up a hot coal, the signal from the sensory neurons in your fingertips would travel to interneurons in your spinal cord. They receive information from other neurons (either sensory neurons or interneurons) and transmit information to other neurons (either motor neurons or interneurons). Interneuons, which are found only in the CNS, connect one neuron to another.For instance, if you picked up a hot coal, it motor neurons innervating the muscles in your fingers would cause your hand to let go. Efferent neurons (also called motor neurons) get information from other neurons and convey commands to your muscles, organs and glands.For instance, if you picked up a hot coal, sensory neurons with endings in your fingertips would convey the information to your CNS that it was really hot Afferent neurons (also called sensory neurons) get information about what’s going on inside and outside of the body and bring that information into the CNS so it can be processed.There are three different classes of neurons that make up the nervous system: Nerves in the peripheral nervous system (PNS) carry information to and from neurons in the the central nervous system (CNS), where information is integrated and processed. Nerves are bundles of nervous tissue, often containing hundreds to thousands of axons wrapped in connective tissue. The nervous system is made up of neurons, specialized cells that can receive and transmit chemical or electrical signals, and glia, cells that provide support functions for the neurons by playing an information processing role that is complementary to neurons. A nervous system is an organism’s control center: it processes sensory information from outside (and inside) the body and controls all behaviors: from eating to sleeping to finding a mate. Even fundamental functions, like breathing and regulation of body temperature, are controlled by the nervous system. The visual system is processing what is seen on the page the motor system controls the click of the mouse and (if you’re lucky) the prefrontal cortex maintains your attention. ![]() All Khan Academy content is available for free at When you’re reading this website, your nervous system is performing several functions simultaneously. The information below was adapted from OpenStax Biology 35.0 and Khan Academy Overview of neuron structure and function.
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