Due MIDNIGHT: Respond/Critique two discussion posts.

Part II: Respond to at least 2 classmates’ posts to 
discuss/ theorize other conditions that might affect or influence the topic that was discussed (i.e. NMJ, muscle contraction, etc). Please choose from the list of diseases, disorders, toxins and drugs located in the Course Information folder.

                                    Due – 11:59PM

 

Respond to the two entries I’ve provided.

 

There is also an attachment with an example response to a different entry for comparason.

 

Thanks.

The action potential of a neuron begins when voltage-gated channels open due to reaching their threshhold value (McKinley 2013). Once this occurs, the charges between the inside and outside of the neuron plus the traveling of chemicals is able to be exchanged. For example, if there is a substantial amount of Na+ within the cell, the opening of the channels allows some of the chemical to flow out and exhange with the substantial amount of K+ outside the cell. Once this occurs, the membrane potential of the neuron is switched.

The next part in the system is the propagation of the axon. The process is a two part system dealing with depolarization, which is a positive change across the membrane potential, and repolarization, which is returning a neuron to the resting potential it was first at. Depolarization begins with the opening of voltage-gated Na+ channels along the axon. Once one of these is open, the rest of the channels begin to follow the pattern and begin opening up rapidly for very short bursts of time. The channels open to allow the outflow of Na+ into the axon to continue depolarizing the cell by depleting it of the positive charge within.

Repolarization occurs after the depolarization of the axon is finished. The event begins to return to the axon’s resting potential by opening the K+ channels on the outside of the Na+ channels and allowing them to dispurse and switch places. This event however only occurs towards the end of the depolarization process (McKinley 2013). Once the places are switched and the channels have finished exchanging, the hyperpolarization period occurs. This is when the axon is slighty above the negative potential it needs to be at (McKinley 2013). This last step is the final conclusion in putting the action potential propagation back into the RMP or resting membrane potential it ends up at so that the potential is allowed to occur again.

Multiple Sclerosis is an autoimmune disease that causes the neurons of a cell to progressively demylenate themselves or lose the mylenation that helps shield them and to transport action potentials. The oligodendrocytes are the creators of the mylein that aids with the action potential but when these are removed, the abilities associated with motor coordination and sensory information processing is impaired. (McKinley 2013). The disease usually occurs between the ages of 18 and 40 (McKinley 2013).

 

           “An action potential is generated within the initial segment and propagated along an axon of the neuron” (McKinley, 2013). Most action potentials are located along the sarcolemma of muscle cells. When action potential is propagated along the plasma membrane it is called the all or none law (McKinley, 2013).  This means that the axon is decreasing intensity and only the subthreshold value is being reached (McKinley, 2013).  Action potential happens because voltage-gated channels respond to a voltage change (McKinley, 2013). The minimum voltage change is called the threshold value and any voltage below that is called subthreshold value. There are three steps when action potential occurs. The three major events of action potential are depolarization, repolarization, and hyperpolarization.  

            In action potential there is a propagation called a nerve signal (McKinley, 2013). An unstimulated axon usually has a resting membrane potential of -70 mV, also known as membrane voltage. The graded potentials then reach the axon hillock and are added to one another (McKinley, 2013). Then the first step of action potential occurs. This is called depolarization. Depolarization causes a positive charge in the membrane potential (McKinley, 2013). It occurs in the threshold (-55 mV) and voltage-gated Na+ channels open (McKinley, 2013). The Na+ enters quickly and reverses the polarity from negative to positive (+30 mV) and causes the depolarization (McKinley, 2013).

            The next event that occurs in action potential is repolarization. Repolarization involves returning a neuron to its RMP, or resting membrane potential (McKinley, 2013). It then goes through voltage-gated K+ channels, which are located in the plasma membrane (McKinley, 2013). Repolarization usually occurs because the voltage-gated Na+ channels close and the voltage-gated K+ channels open. So K+ finally exits the cell and goes in the IF and returns the neuron to its RMP (-70 mV) (McKinley, 2013). The propagation of repolarization occurs when voltage-gated K+ channels open along the length of the axon (McKinley, 2013). Finally polarity is reversed from positive to negative (-70 mV) and causes the repolarization (McKinley, 2013).

            The final event in action potential is hyperpolarization. Hyperpolarization is when everything returns to the resting membrane potential. This usually happens when the voltage-gated K+ channels stay open longer than needed (McKinley, 2013). The time reaches the membrane potential. During this time, the membrane potential is less than the resting membrane potential, therefore this makes everything return to normal (-70 mV) and causes hyperpolarization (McKinley, 2013). After that the “voltage-gated K+ channels close and the plasma membrane returns to resting conditions by activity of Na+/K+ pumps” (McKinley, 2013).

               Multiple sclerosis is a disease that affects the brain and spinal cord (WebMD, 2012). It results in loss of muscle control, vision, balance, and sensation (WebMD, 2012). Multiple sclerosis affects the nerves of the brain and spinal cord (WebMD, 2012). These are usually damaged by one’s own immune system, which a condition called autoimmune disease (WebMD, 2012). Multiple sclerosis affects the action potential events because the neurons are not able to send message to the brain to function properly (WebMD, 2012). Therefore, the action potential events cannot occur properly as they should.

            All of these events sum up what action potential is and what it does. First, it depolarizes by opening Na+ channels and reversing the polarity to negative to positive (McKinley, 2013). Then, it repolarizes by closing Na+ channels and opening K+ channels and reversing back to positive to negative (McKinley, 2013). And lastly, it hyperpolarizes by reaching the resting membrane potential and returning back to normal (McKinley, 2013). These are all the events of action potential.

 

Works Cited

Mckinley, Michael P., Valerie D. O’Loughlin, and Theresa S. Bidle. Anatomy & Physiology. New York: McGraw-Hill, 2013. 459-65. Print.

WebMD. What Is Multiple Sclerosis? N.p.: Richard Senelick, 2012. Web. 15 Nov. 2013.

EXAMPLE of RESPONSE:

“I think you did a great job of explaining muscle contraction and relaxation and connecting it to rigor mortis. I like the way you broke things down into events and steps. The sequential steps really helped me understand what I was reading. I think your report was well executed with an introduction and conclusion. In adding to your comments on ACh within the process of contraction, I want to highlight Parkinson’s disease. Parkinson’s is a disease stimulated by the degeneration of nerve cells that control movement (Web MD, 2013). The cells of the brain that control movement require a balance of dopamine and ACh, which are both involved in the transmission of nerve signals and therefore the instigation of the muscle contraction process. With the disease, cells that produce dopamine begin to degenerate, throwing off the balance causing muscle rigidity, tremors, and alterations in gait and speech (Web MD, 2013). Although medicine can be given to help with the symptoms of Parkinson’s disease, there is no cure (Web MD, 2013).

Web MD. (2013, April 03). Parkinson’s disease health center. Retrieved from

http://www.webmd.com/parkinsons-disease/

”

            You did a wonderful job explaining all the steps of muscle contraction! It helped me to clearly understand all the steps. I really liked how you describe ATP production, which was also really helpful. One thing that you might be able to change would be dividing up the steps in a different way. Although you put in all the steps, it was kind of confusing when trying to keep up which ones went first. One disorder that you might could add is muscular dystrophy. Muscular Dystrophy is a genetic disorder that destroys how the muscle functions (Answers Corporation). The muscle is destroyed by this disorder and is replaced with fat and connective tissue (Answers Corporation). It causes muscle weakness and affects to the nervous system as well (Answers Corporation). Over all you did an excellent job. Keep up the good work!

These are responses classmates posted. Just to give you general idea. They are not long responses.