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Amir Mishreky 20766906 Kin 255L Section 001 1. Median Nerve Stimulation at wrist

Latency of the motor response

Median nerve Stimulation at the elbow

Latency of the motor response

Stimulation at the elbow took double the time (10ms) for a response compared to the wrist (5ms), the response is the beginning of the M wave. This is due to the longer distance the electrical signal must travel from the elbow towards the thumb compared to the distance the electrical signal has to travel from the wrist to the thumb

2a) An electrical stimulus applied to the median nerve causes an action potential because of the depolarization that occurs on the cell(neuron) membrane. The ion channels on the neuron are voltage gated, so when we manually apply the stimulus, and depolarization occurs, the voltage gated ion channels allow Na+ to enter the cell which results in an action potential to be propagated down the cell. b) The latency of the M wave is the time between the onset of stimulus and the first response of the muscle that the motoneuron stimulated synapses onto, this is seen through EMG. What this translates to in the Nervous System is the time it takes for the electrical stimulus to cause an action potential in the motoneuron, and then that action potential must be propagated down the axon and synapse on the muscle it innervates. c) No, the M-wave is not a reflex. because a reflex is defined as an automatic and immediate response to a stimulus. With a reflex, the body responds to a physiological change, triggering receptor potentials then action potentials that will be processed in the spinal cord and responded to by a motoneuron. To produce an M-wave on the other hand, an external stimulus evokes the motoneuron directly, without the contributions of the afferent neuron entering the dorsal horn of the spinal cord and producing an output, there is no CNS processing which is a vital characteristic of a reflex. The only reason there is response to this electrical stimulus is the depolarization of the neuron opening Na channels leading to an action potential, but since there is no control from the spinal cord or the CNS at all, the M wave is not a reflex.

3. Distance (proximal to distance site) = 0.25m Average proximal latency= 10+10+10+10+9+10/5 =9.8ms = 0.0098s Average distal latency = 5msec = 0.005s

Conduction velocity = distance/ (proximal latency – distal latency) = 0.25/ (0.0098s – 0.005s) = 52.08 m/s Therefore, the nerve conduction velocity is 52.08 m/s

4. The Normative nerve conduction values for a 19-year-old male are 46-65 m/s. If a participant had a slower conduction velocity, there could be damage to the stimulated nerve, its hard to diagnose the damage to the nerve, but for median nerve conduction velocity tests, a slower than norm result could mean the participant could be suffering from carpel tunnel syndrome, which would prevent the nerve from functioning properly and potentially slow down conduction velocity, that would be a biological explanation. A procedural explanation could be that we did not control for the temperature where we completed the tests, if the room was colder than what the normative values were tested at, then that may be the reason we get a slower nerve conduction velocity 5a. As the diameter of the axon increases, it will result in less resistance. Therefore, the signal will propagate quicker due to the ease of ions flowing in and through the axon reaching the axon terminal quicker. This results in an increases nerve conduction velocity. If the diameter of the axon decreases, there is more resistance for the ions to flow in, this could make the nerve conduction velocity slower.

b) Myelin acts as an axon insulator which prevents ion leakage, they also forms Nodes of Ranvier which are areas in the axon between the myelinated segments that that the signal can “jump” and go to the next myelinated segment, both of these characteristics of myelin result in faster conduction velocity. Therefore, if an axon was demyelinated it would allow for ion leakage and no segments of the axon would be “jumped” as they were because of the nodes of Ranvier. Due to the unmyelinated nerve lacking these two important characteristics, it will ultimately result in a decrease neuron conduction velocity.

c) As axon length increases, it takes longer for the action potential to travel the distance of towards the axon terminal, therefore conduction speed is slower. A shorter axon means the action potential has less distance to travel which means that the conduction speed will be quicker. This means that there is an indirect relation between axon length and conduction velocity.

6a) When one’s skin temperature decreases it will result in a decreased Sodium (Na+) permeability into the nerve. The slower influx means that the whole process of excitation of that neuron. Also, as the temperature decreases, resistance to conduction of impulses increases (indirect relation). The more resistance to the conduction of impulses, the longer the latency. Therefore, a decrease in temperature will result in slower conduction velocity because of the reasons stated. If the temperature is increased, nerve resistance decreases and there is less resistance to the conduction of impulses, so the nerve conduction velocity will increase.

6b) When a person gets older, nerve conduction velocity can decrease, this is due to degeneration of the nerve causing a smaller diameter, demyelination, and less nerve fibres, (some of these are discussed in question 5a and 5b) which will result in slower conduction velocity, because the signal will not be

propagated down the axon as quickly as when a person is younger and their axons have a larger diameter and are myelinated.

7) Guillain-Barre Syndrome is a disease in which the immune system attacks parts of the peripheral nervous system. The first symptoms of this disease could be tingling or weakness in the legs. Other symptoms include unstable walking, and difficulty with facial movements. This disease causes the immune system attacks the PNS, the nerves become damaged due to damage of the myelin. This results in a loss of insulation and the nerve begins to lose its ability to send signals, which affects the nerve conduction velocity.

References Axon diameter and Myelination. (n.d.). Retrieved from https://ilearn.med.monash.edu.au/physiology/action-potentials/axon-diameter.html.

Dhavalikar, M., Narkeesh, A., & Gupta, N. (2009). Effect of Skin Temperature on Nerve Conduction Velocity and Reliability of Temperature Correction Formula in Indian Females. Journal of Exercise Science and Physiotherapy, 24-29. Mayo Clinic Staff. (2018, May 18). Guillain-Barre syndrome. Retrieved from Mayo Clinic. Nerve Conduction Velocity (NCV). (n.d.). Retrieved from https://www.sehat.com/tests-andprocedures/1805/ncv.htm.

Palve, S., & Palve, S. (2018). Impact of Aging on Nerve Conduction Velocities and Late Responses in Healthy Individuals. Journal of Neurosciences in Rural Practise, 112-116....