Human Nervemuscle Interaction Essay Example | Topics and Well Written Essays - 1500 words

Human Nervemuscle Interaction - Essay Example When the threshold potential or firing level was reached, an action potential was created causing Na++ influx. This in turn made the inside of the cell more positive causing it to be depolarized. This action potential was propagated along the entire length of the nerve by salutatory conduction. As the nerve nears its termination, it loses its myelin sheath and divides into terminal buttons. The action potential caused the voltage-gated Ca++ channels to open resulting in Ca++ influx. The Ca++ then triggered the synaptic vesicles containing the neurotransmitter (in this case, acetylcholine (AcH)) to fuse with the plasma membrane causing it to release its contents to the neuromuscular (NMJ) junction. The AcH then fused with the nicotinic receptors on the motor end plate of the muscle consequential in the opening of Na++ channels. This created an end plate potential until it reached its threshold potential and brought about the potential to be conducted away in both directions along the muscle fiber. The potential traversed down the T- tubules and reached the sarcoplasmic reticulum. The end plate potential caused a conformational change in the dihydropyridine receptor (DHPR) which initiated the ryanodine receptor (RYR) to release the Ca++ (Berne, et.al, 2006). The Ca++ then binds with the Troponin C, causing exposure of the active site in the actin. The myosin head then attached to the active site, and with ATP, performed a "power stroke" causing shortening and contraction of the muscle. This is the contraction seen when the thumb moves towards the palm (abduction). However, the contraction seen as a response to the electric stimulation is not tetanic, meaning it is not sustained; therefore a relaxation period occurs as well. In order for the muscle contraction to stop, the Ca++ attached to the Troponin C must be sequestered back to the sarcoplasmic reticulum. This is done by the Ca++ -Mg++ ATPase. Only when there is cessation of the interaction between actin and m yosin can muscle relaxation occur. Consequently, in order for repolarization of the motor end plate, the AcH that has attached to the nicotinic acetylcholine receptors on the motor end plate is broken down by acetylcholinesterase, which hydrolysis Ach to acetate and choline. Re-uptake of these products then occurs by the pre-synaptic neuron for synthesis of new AcH. 2.) The normal nerve conduction velocity for myelinated nerves is 50-60 m/s, depending on the diameter of the nerve and as to its myelination. The greater the diameter size, the faster the conduction velocity. Similarly, myelinated neurons are also faster conductors than unmyelinated neurons. Our results yielded a NCV of 44 m/s which is not within the range but is near the accepted values. Latency or time that the impulse took to travel within the axon is expected to be longer from the elbow compared to the wrist due to the increased distance from the thumb. However, if we are to consider the fiber type of the ulnar nerve, which is an -motor neuron, the NCV that we got was significantly less than the known conduction velocity of 70-120 m/s. Several factors can affect the NCV such as age and temperature. The conduction velocity decreases significantly with decrease temperature and the distal latencies become correspondingly prolonged. (DeLisa, 2005). The standard temperature used in l aboratories is 32oC. It was also found out that the conduction ve