09+Nervous+System

Nervous System Chapters 7 & 9

//Chapters 7 and 9 cover everything from the basic synaptic activity to the neural control of the involuntary effectors. These two chapters are two thirds of the nervous system sections in the book, so the extent of the topic covered is extensive but very interesting. Chapter 7 is mostly a review of things for me, such as the neurons and supporting cells, electrical activity in axons, the synapse, acetylcholine as a neurotransmitter, monoamines as neurotransmitters, a few other types of neurotransmitters, and the synaptic integration. Chapter 9 was a bit more concise as far as topics are concerned only containing three different sections. Of all the material in these two chapters the three topics that I found to be the most interesting were all from chapter 9 and included neural control of involuntary effectors, divisions of the autonomic nervous system, and the functions of the autonomic nervous system. All three of these topics are from the 9th chapter of the book, and I found these three to be the most interesting because they were some of the things that I was learning for the first time. //
 * __Content Summary __**

//The first of my topics was the neural control of involuntary effectors. First of all there are two different types of autonomic neurons discussed in this section, and those are the preganglionic and the postganglionic autonomic neurons. The difference between these two all depends on the location for starters. The postganglionic neurons are located outside of the CNS, whereas the preganglionic autonomic neurons are located either in the brain of in the spinal cord. Autonomic innervations is specific to only a few types of muscle. These special few include smooth muscle, cardiac muscle, and a few glands. Involuntary effectors are independent of their innervations and become hypersensitive whenever the two are separated. The autonomic nerves can have only two separate effects on their target organs. These two possibilities are either an excitatory response or effect, or the other option is an inhibitory effect. // Source (Physiology Book)

//The divisions of the autonomic nervous system are split into two sections, the preganglionic neurons of the sympathetic division and the preganglionic neurons of the parasympathetic division. Starting with the preganglionic neurons of the sympathetic division, they are located between the lumbar and thoracic levels of the spinal cord. These specific neurons often synapse with the postganglionic neurons that originate outside of the spinal cord. These postganglionic neurons are located in the double chain of sympathetic ganglia, also known as the paravertebral. Some of these preganglionic neurons innervate the adrenal medulla, and this secretes epinephrine to blood in the response of stimulation. Preganglionic parasympathetic fibers originate in the sacral level of the spinal cord and also in the brain. Parasympathetic fibers have direct ties with the cranial nerves III, VII, IX, and X. The long preganglionic fibers of the cranial nerve X, also known as the vagus nerve, synapse at ganglia located in the direct vicinity of the target organ. After that, the short preganglionic fibers innervate the effector cells. The vagus nerve plays a large role in delivering innervations to the heart, lungs, esophagus, stomach, liver, small intestine, and the upper half of the large intestine. // Source(Physiology Book)

//The next topic that I chose was the functions of the autonomic nervous system. The complexity and diverseness of this system has many more functions that I will explain here. The topics I cover here will just brush on the main aspects of the functions. One common topic when talking about the autonomic system will be the fight or flight dilemma. The sympathetic division of the autonomic nervous system triggers this reaction in the body, all this through adrenergic effects. Some of the adrenergic effects on the body’s organs include the heart, vasoconstriction of the viscera and the skin, bronchodilation, and glycogenolysis in the liver. The parasympathetic system often responds to signals antagonistically through cholinergic effects. All the nerve fibers of the preganglionic autonomic system are cholinergic. Inhibitory effects on the cholinergic parasympathetic nerves are caused by atropine, and promoted by a drug known as muscarine. There are a few organs that are innervated by both the sympathetic and the parasympathetic divisions. These organs can accept the innervations as synergistic, antagonistic or complimentary actions. // Source(Physiology Book)

[|__Autonomic Nervous System__]



//Anyone that is going into the nursing field should have a very good grasp on how the muscles work, even if that is not their expertise. My ultimate goal however is to become a nurse anesthetist, and this is where I believe that the greater the understanding of the neural control on the muscles you have, the better it is for you in the long run. Dealing with anesthesia, there really is not one instance that you can be wrong and get away with it. One simple mistake could cause someone’s life to be in jeopardy, and that is the last place that anyone wants to be. Just simply knowing how all the muscles work and were they are located could save you a lot of trouble. The motor neurons that control the muscles cannot be afforded to be damaged during something that is supposed to be a simple procedure, but is taken for granted and a mistake takes that away from someone. //
 * __Application __**

//It all starts in the presynaptic neuron, where action potentials conducted by axon reach the axon terminals, which then opens voltage-gated Ca2+ channels. Then there is a release of the excitatory neurotransmitter. The neurotransmitters then bind to receptor proteins on the postsynaptic membrane. Receptor proteins have specificity for their neurotransmitter, which is the ligand of the receptor protein. Ion channels open in the postsynaptic membrane when the neurotransmitter ligand binds to its receptor protein. Means the gates open in response to the binding of a chemical ligand to its receptor in the postsynaptic membrane, they are called ligand-regulated gates (located in the dendrites and cell body). A graded change in the membrane potential is produced when the chemically regulated channels are opened. The opening of specific channels produces a graded depolarization. This is where the inside of the postsynaptic membrane becomes less negative. The name of this typeis called excitatory postsynaptic potential (EPSP) because the membrane potential moves toward the threshold required for action potentials. When the ligand-gated channels are open, there is an inward diffusion of Na+ that causes depolarization (EPSP). From there, there is a localized, decremental conduction of EPSP. The EPSP then causes the opening of voltage-gated Na+ and then K+ channels in the axon hillock. This then results in the conduction of action potential. //
 * __Essential Questions __**

//Neurotransmitter molecules within the presynaptic neuron endings are contained within many small, membrane-enclosed synaptic vesicles. When the neurotransmitter is ready to be released into the synaptic cleft, the vesicle membrane must fuse with the axon membrane in the process of exocytosis. Action potentials that stimulate the entry of Ca2+ into the axon terminal through voltage-gated Ca2+ channels triggers exocytosis of synaptic vesicles, and the release of neurotransmitter molecules into the synaptic cleft. Therefore, when the voltage-gated Ca2+ channels open, Ca2+ binds to the sensor protein in the cytoplasm. Then Ca2+-protein complex stimulates fusion and exocytosis of the neurotransmitter. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">In some instances, when CI- enters the cell through specific channels, a graded hyperpolarization is produced. This is where the inside of the postsynaptic membrane becomes more negative. Inhibitory postsynaptic potential (IPSP) is what refers to hyperpolarization because the membrane potential moves father from the threshold depolarization required to produce action potentials. // <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Source (Physiology Book)

<span style="color: #da2323; font-family: Verdana,Geneva,sans-serif; font-size: 200%;">[|__Neurons & the Nervous System__]