Anatomy Week Three

So In this week of class we really got into the structure and diversity of neurons.  We learned that nervous tissue contains two types of cells, and these are neurons and neuroglia.  The neurons carry out a lot of the unique functions of the system like the sensing, thinking, remembering, controlling muscle activity, and the regulation of glandular secretions.  They also have the property of electrical excitability.  Electrical excitability is the ability to produce action potentials or impulses in response to stimuli.  Once these action potentials arise, they propagate from one point to the next along the neuron.  The neuroglia are responsible for supporting, nourishing, protecting the neurons, and maintaining homeostasis in the interstitial fluid that bathes them.  

The neurons have three main parts that comprise them structurally.  They have a cell body, dendrites, and an axon.  the cell body is what contains the nucleus and is surrounded by cytoplasm.  In the cytoplasm are the typical organelles such as mitochondria, lysosomes, and the Golgi apparatus complex.  Neurons, however, cannot divide though because they lack the centrioles that are essential in mitosis.  What makes them really stand out is the fact that they contain very prominent clusters of endoplasmic reticulum that are called Nissl bodies.  This is where the protein synthesis occurs in the neuron.  The Nissl bodies are what produce newly synthesized proteins that are used to replace cellular components as material for growth for new neurons, and to regenerate damaged axons.  

There are two types of extensions that come off the neuron, and these are multiple dendrites and a single axon.  The dendrites are the portions of the neuron that receive the messages or input.  These structures are usually short, tapering, and highly branched.  They kind of form a tree like array of these processes that extend from the cell body.

The axon extends from the cell body as well, and is usually kind of the opposite end of the dendrites.  This is where the neuron propagates nerve impulses toward another neuron, muscle fiber, or gland cell.  The axon itself looks like a long, thin, cylindrical projection that joins the cell body at a cone-shaped elevation called the axon hillock.  Sometimes small branches, called axon collaterals, form at right angles to the axon.  All the axons end by dividing into many fine processes called the axon terminals.  These form little bulb-like structures called synaptic end bulbs.  These are the sites of the communication between the neuron and another neuron or an effector cell.  

The structures of the neurons are extremely important, because are where the physiological aspects of the Central and Peripheral nervous system take place.  There are millions of neurons in the body, and they are constantly sending messages to one another or to receptor cells to eventually have your body do something, like move your arm, or even to blink.  It it constantly happening in your body, and sometimes you can control it, and with some things you have no control and these neurons are constantly sending messages to do things you have no control over!