Lab Report- Neurophysiology of Nerve Impulses

Topics: Action potential, Neuron, Membrane potential Pages: 6 (1755 words) Published: March 13, 2013
Neurons (also known as neurons, nerve cells and nerve fibers) are electrically excitable and the most important cells in the nervous system that functions to process and transmit information. Neurons have a large number of extensions called dendrites. They often look likes branches or spikes extending out from the cell body. It is primarily the surfaces of the dendrites that receive chemical messages from other neurons. One extension is different from all the others, and is called the axon. Although in some neurons, it is hard to distinguish from the dendrites, in others it is easily distinguished by its length. The purpose of the axon is to transmit an electro-chemical signal to other neurons, sometimes over a considerable distance. Longer axons are usually covered with a myelin sheath, a series of fatty cells which have wrapped around an axon many times. They serve a similar function as the insulation around electrical wire. At the very end of the axon is the axon ending. It is there that the electro-chemical signal that has travelled the length of the axon is converted into a chemical message that travels to the next neuron. (Dr. C. George Boeree, 2009). Axons are what make up nerves. A nerve is a bundle of neurons fibers or processes wrapped in connective tissue that extends to and/or from the CNS and visceral organs or structures of the body periphery (Marieb & Mitchell, 2009). In this experiment we will work with a nerve The action potential we will see on this experiment reflects the cumulative action potentials of all the neurons in the nerve, called a compound nerve action potential. Although an action potential follows the all-or none law within a single neuron, it does not necessarily follows the all-or-none law within an entire nerve. When you electrically stimulate a nerve at a given voltage, the stimulus may result in depolarization of most of the neurons but not necessarily all of them. To achieve depolarization of all of the neurons, a higher stimulus voltage may be needed ( Marieb & Mitchell, 2009).

Sypnapses in the body all begin with the resting membrane potential. This is the natural state of a nerve before it is presented with a stimulus (Martini, Nath & Bartholomew, 2012). Resting membrane potential is important because it is necessary in order for a synapse to occur (Marieb & Mitchell, 2009). This resting state stands at -70mV because of three factors. First the ionic composition of the extracellular and intracellular fluid varies in their charge. The Extracellular fluid has a negative charge because of the Na+ ion that exist, just as the intracellular fluid has a negative charge because of K+ ions and negatively charged proteins (Martini, Nath & Bartholomew, 2012). Second the cells have an uneven distribution because of the existence of sodium and potassium leak channels. This allows the creation of an electrochemical gradient, which ultimately is the force that guides the conduction of an action potential. The electrochemical gradient is created by sodium-potassium pump which is responsible for exchanging 3 Na+ ions out while bringing in 2 K+ ions (Martini, Nath & Bartholomew, 2012). Third, the resting membrane potential varies in permeability based on the type of ion. Membranes are more easily permeable by K+ ions because of their size, which is responsible for the negative charge during the resting state (Martini, Nath & Bartholomew, 2012)

Without a resting potential, we would not have a threshold to conduct an action potential. When a stimulus is presented, it requires a certain excitability, or depolarization level of at least 10mV to 15mV (Martini, Nath & Bartholomew, 2012). The action potential depends on the threshold stimulus because of the “all or none” principle. This states that if a stimulus does not break the required threshold level, no action potential will occur (Martini, Nath & Bartholomew, 2012). However, if a threshold does uphold this principle, an...
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