moving on to nervous tissue and nervous tissue is made up of two types of cells neurons and neuroglia neurons form the complex processing networks within the brain and spinal cord and connect all of the regions of the body to the brain and spinal cord as well neurons provide most of the unique functions of the nervous system including ining sensing thinking remembering controlling muscular activity and regulating glandular secretions so a neuron or a nerve cell which we have up on the slide here is an electrically excitable cell this means that it can respond to a stimulus and convert it into an action potential which is the electrical impulse that the nervous system uses to communicate a stimulus is any change in the environment that is strong enough to initiate an action potential so an action potential which we'll speak about in more detail in the next module is an electrical signal that propagates or travels along the surface of the membrane of a neuron it begins and travels due to the movement of ions such as sodium and potassium between the interstitial fluid and the inside of a neuron through specific ion channels in its plasma membrane some neurons are tiny and propagate an action potential over short distances like less than one mm other neurons are some of the longest cells in the body for example the neurons that allow you to move your toes extend from the lumber regions in your spinal cord so just above your waist all the way down to the muscles in your feet so looking at the parts that make Upp a neuron and most neurons have three parts a cell body dendrites and an axon so the cell body or Soma is this part here and it contains a nucleus surrounded by cytoplasm which includes all of the typical organal such as lomes mitochondria and a GOI complex neuronal cell bodies also contain free ribosomes and prominent clusters of rough endoplasmic micul which we call nissle bodies proteins produced by the nissle bodies are used to replace the cellular components of a neuron as material for the growth of a neuron as well as to regenerate damaged axons in the peripheral nervous system dendroides are the receiving or the input portion of a neuron they're all of these little extensions here the plasma membrane of dendroides contain numerous recepto sites for binding chemical Messengers from other cells and the dendroides are usually quite short they're tapered and they're highly branched the single axon of a neuron propagates the action potential or the nerve impulse towards another neuron a muscle or a gland and axon is this thin long cylindrical projection here the axon Ends by dividing into many fine processes called axon terminals at the tip of an axon terminal they swell into these bulb shaped structures called synaptic end bulbs others will exhibit a string of swollen bumps called varicosities both synaptic end bulbs and varicosities will contain tiny membrane enclosed sacks called synaptic vesicles that store a chemical called a neurotransmitter a neurotransmitter is a chemical that is released from a synaptic vesicle that either excites or inhibits a another neuron a muscle fiber or a gland many neurons contain two or even three types of neurotransmitters with each different neurotransmitter having a different effect on that prooptic cell or the Snell that it connects with the site of communication between two neurons or between a neuron and an fecta cell whether that be a muscle or a gland is called a syapse so a syapse would be like this part here before it connects with the next cell the next muscle or the next gland so that is the basic structure of a neuron however neurons display great diversity in both their shape and their size as well as the pattern of branching of their dendrites both structural and functional features are used to classify a neuron so structurally neurons are classified according to the number of processes extending from the cell body so if this is our cell body here multi-polar neurons have several dendrites and one axon so multiple extensions coming off that cell body most neurons in the brain and the spinal cord are multi-polar neurons as are all of our motor neurons neurons bipolar neurons have one dendrite and one axon emerging from that cell body by means two so one dendrite and one axon they are found in the retina of the eye the inner ear and the olfactory or the smell area of the brain unipolar neurons have dendrites and one axon that are fused together to form one continuous process that emerges from the cell body so our cell body here and only one extension out of that cell body uni means one the dendrites of most of our uni pool neurons function as sensory receptors that detect a sensory stimulus such as touch pressure pain or thermal stimuli