Introduction:

The nervous system is at a microscopic level, but controls the entire body. There are many components that make up the nervous system. Neurons are called the functional unit of the nervous system. Normally people wouldn't think that there is electricity involved in the body processes, but the neurons conduct electrical impulses. The nervous system is broken down into two main categories. The central nervous system, (CNS), and the peripheral nervous system, (PNS), includes all of the nerves in the body. The CNS is the brain and the spinal cord, while the PNS is the nerves coming off of the brain and spinal cord. Without the nervous system our bodies wouldn't maintain homeostasis. These tiny cells are sending messages at rapid passes all throughout the body.



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Concept #1: Structure and classifications of neurons

The neuron is the functional unit of the nervous system. The neurons are the cells that conduct electrical impulses and respond to chemical and physical stimuli. There are supporting cells which help the neurons complete their jobs. Glial cells are much more abudant throughout the body and are able to divide by mitosis unlike neurons. The cell body is a part of the neuron which contains the nucleus. Dendrites branch off of the neuron help to receive the impulses. The axon is the part of the neuron that conducts the impulses, or action potentials. Action potentials originate in the axon hillock, which is located near the cell body. Myelin helps to protect the axon, by insulating it. The unmyelinated regions of the neuron are slower then the myelinated regions. In the PNS, Schwann cells make the wrap around the cell membrane. Oligodendrocytes forms the insulating cover in the CNS. There are gaps between each millimeter of Schwann cells on the axon of a neuron. These gaps are called the nodes of Ranvier. There are many classifications of neurons. Their function and structure decide what class the neuron falls in. Sensory neurons conduct impulses from sensory receptors into the CNS, while motor neurons conduct impulses out of the CNS. Somatic motor neurons and autonomic motor neurons are the two kinds of motor neurons. Voluntary control is used by the somatic motor neurons, while the autonomic motor neurons are involuntary. The sympathetic and parasympathetic are the two divisions of the autonomic nervous system. The structural neurons are based on how many processes come out from the cell body. Most people would think that the nervous system is just made up of nerves. Nerves are actually a bundle of axons outside of the CNS.


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Concept #2: Electrical activity of axons and action potentials

Every cell the body has a voltage charge, and when the charge is more negatively charged inside the cell than outside the cell, it's called a resting membrane potential. The membrane catches negatively charged molecules, and only lets out a certain amount of positively charged molecules. Potassium ions (Na+) is more concentrated within the cell, and sodium ions (K+) is more concentrated outside the cell. There are pumps that help to maintain the membrane potential. When the voltage changes and more positive charges flow into the cell, depolarization occurs. Voltage-regulated channels open in response to the stimulus of depolarization. When the charge is going back to the resting membrane potential, it's called repolarization. The opening of sodium channels and outward diffusion of sodium causes the cell to go back to it's resting membrane potential. Hyperpolarization happens when cell becomes more negative then the resting membrane potential. There are different channels that allow different molecules to go in and out of the cell. While all of the chemicals are in motion in and out of the cell, and action potential can be formed. The opening of voltage-regulated channels makes an action potential. Action potentials are used in many systems throughout the body. Without an action potential, messages would never get sent by cells. There are chemicals that send a message to part of the axon, and thus changes the chemical levels. When the permeability changes it is then going to allow for different chemicals to go in and out of the axon membrane. The molecules potassium and sodium are diffusing from the membrane, an action potential, or nerve impulse is made. Action potentials are considered an all or none event. All of these processes are vital in order for the nervous system to function properly.



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Concept #3: The autonomic nervous system

The autonomic nervous system is divided up into two divisions, the sympathetic and parasympathetic. The sympathetic division is known as the "fight or flight" part of the body. In emergencies when intense physical activity is needed the sympathetic system helps the body. When an emergency happens and the sympathetic system is activated, the blood pressure will increase, blood gluclose levels increases, and blood is directed to the skeletal muscles. The parasympathetic system is pretty much opposite of the sympathetic system. Dialation of visceral blood vessels, slowing of the heart, and increased activity to the digestive tract are some of the jobs the parasympathetic system does. The nerves of the autonomic nervous system can be either inhibitory or excitatory. Both the sympathetic and the parasympathetic systems release neurotransmitters. Acetylcholine (ACh) is a neurotransmistter shared by both systems. Norepinephrine is the main neurotransmitter released by the sympathetic system. Most of the visceral organs are involved with both systems. The activity of both systems can either be antagonistic, complementary, or cooperative. The autonomic nervous system involves involuntary controls of cardiac muscle, smooth muscle, and glands. Without the proper function of the autonomic system, our bodies would not maintain homeostasis.

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Application:

The nervous system is an important system for me and my family. My Dad was driving to work one day with his friend, when they were hit by a semi going the wrong way on a one way. The doctors airlifted him and his friend, Terry, to Sioux Falls, where we were told he wouldn't make it through the night. He had received a traumatic brain injury, plus many more injuries from the accident. Luckily, he woke up from his coma, and went through rehabilitation. Because of his brain injury, today he is has disabilities. While learning about the nervous system, alot of his disabilities start to make more sense to me. He has temperature sensitivities, appetite and food aren't the same, and numbness on parts of his body. All of those disabilities are coming from his nervous system. It was so difficult for me and my family to understand why he was having these problems, but when the accident happened, injuries to his brain affected the rest of his body. As a nurse I need to understand that the nervous system controls all of the body. If I see a patient who has multiple sclerosis, I need to be able to explain that the myelin sheaths become hardened. Also understand the central nervous system, and the peripheral nervous system are essential for a health care worker.

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Essential question:

1. Neurotransmitters are molecules that are released from one neuron and received by another neuron. The synpatic cleft is the area between the two neurons where the neurotranmitters are. Postsynaptic cell is the cell that is receiving the neurotransmitters, while the presynaptic cell is the one releasing them. Once the neurotransmitter is released by the presynaptic cell, it goes through the synaptic cleft and binds to a receptor protein that is a part of the postsynaptic cell. The ligand is a receptor protein that binds a small molecule, the neurotransmitter, and forms a complex with the larger molecule, which is the receptor. There are ion channels which are located on the postsynaptic cell. When the neurotransmitter ligand binds to the receptor, the gate opens up. The ligand-regulated gates are also chemically regulated because of the binding of the chemical ligand to the receptor protein. The ligand-regulated channel, and the voltage-regulated channel, are the two main kinds of gated ion channels. Potassium and sodium are the two voltage-gated channels that will open up. Voltage-regulated channels open up when depolarization occurs. Depolarization happens when the cell becomes more positive then negative. If the cell is able to open up the gates to allow sodium or calcium in, the cell has an excitatory postsynaptic potential. The dendrite of the cell is the part of the cell that receives messages from another cell, and have the ligand gated channels. The dendrite sends the message to the axon hillock where the action potential is initiated. The action potential runs down the axon and releases a neurotransmitter. Excitatory postsynaptic potentials are produced in the dendrites. Action potentials are first made at the axon hillock where there are alot of voltage-gated channels. The total amount of the depolarization produced by the excitatory postsynaptic potentials determine if the axon will fire an action potential.

2. The resting membrane potential is when the cell is more negative outside then it is inside. -70mV is the resting membrane potential for a neuron. Potassium is more concentrated in the cell, while sodium is more concentrated outside the cell. The sodium/potassium pumps are way that the cell brings in sodium or out, and potassium in or out. When depolarization is occuring sodium comes into the cell, it causes the cell to become more positive. Potassium then goes out of the cell. Thereshold, -50mV, is the membrane potential the cell must meet in order for an action potential to occur. If the cell reaches the threshold, an action potential happens. After the action potential the cell goes through repolarization to return it it's resting membrane potential. Hyperpolarization, <-70mV, happens when the cell becomes more negative then the resting membrane potential. The voltage-gated channels help to regulate the amount of potassium ions, and calcium ions that go into the cell. In order for the neurotransmitter in the vesicle to be released, the vesicle membrane must join with the axon membrane, this process is called exocytosis. The release of the neurotransmitters into the synpatic cleft is stimulated by the action potentials of the entry of calcium ions through the voltage-gated channels.

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References from top to bottom:

http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/8679.jpg

http://www.youtube.com/watch?v=i-NgGKSNiNw

http://wikieducator.org/images/b/bd/Neuron.jpg

http://www.youtube.com/watch?v=YP_P6bYvEjE

http://internal.psychology.illinois.edu/~etaylor4/action_potential.jpg

http://griffithbiomed.wikispaces.com/file/view/F02_16.gif/35948433/F02_16.gif

http://www.youtube.com/watch?v=tCLJlvhyUrY

http://www.clipartheaven.com/clipart/health_&_medical/cartoons/nurse_04.gif

http://encefalus.com/wp-content/uploads/2010/07/neuron_action_potential.jpg

http://www.anselm.edu/homepage/jpitocch/genbio/synapse.JPG