1. Starting at the dendrite of the never explain how an action potential is gene
ID: 59920 • Letter: 1
Question
1. Starting at the dendrite of the never explain how an action potential is generated which leads to muscle contraction. Discuss ion movement, neurotransmitters, action potential, and sliding filament theory while commenting on optimal length.
2. Determine the differences between “restrictive pulmonary” and “obstructive pulmonary” diseases. Describe how Vital capacity, inspiratory capacity, tidal volume, functional residual capacity, residual volume, expiratory reserve volume, and total lung capacity will be affected by both types of diseases.
3. Dr. Ferguson is going to climb Mount Everest where the barometric pressure is 252 mm Hg at the summit. Assuming that CO2 production in the body will be constant describe a) the partial pressures oxygen, nitrogen, and carbon dioxide b) contrast these values to the partial pressures at sea level, c) explain the differences in gas exchange at sea level vs Mount Everest, d) explain how altitude will affect exercise capacity, and d) should Dr. Ferguson climb Mount Everest?
Explanation / Answer
1.
Synapse is the junction between axon of one neuron and dendrite of another neuron. These neurons communicate with the help of chemical mediators called as “neurotransmitters.” The neuron above the synapse is called as “presynaptic neurone,” and the neurone below the synapse is called as “post synaptic neurone.”
The junction between the nerve terminal (axonal terminal) and the muscle fibre is called as “myoneural junction” or “neuromuscular junction.” At this site, the nerve does not contain myelin sheath and gets expanded, which contains the stores of acetyl choline (Ach), which act as a neurotransmitter at neuromuscular junction.
Excitation of the nervous tissue releases acetylcholine from the synaptic vesicles that attaches to the receptor site of the muscle (motor end plate) by passing through the synaptic cleft. Thus, simple release of neurotransmitter at the neuromuscular junction cannot fire action potentials, the chemical has to bind to motor end plate receptor site.
During the resting state, the muscle cell is polarised. The interior of the cell is negatively charged, and it contains high concentrations of K+ ions. The exterior of the cell is positively charged, and it contains high concentrations of sodium ions. The resting membrane potential of a neuron is, -95mV (millivolts).
The binding of ACh to the muscle fibers causes change in membrane potential by changing the ion permeability across the membrane. If the membrane potential reach threshold potential (the minimum potential difference to elicit a response), then the action potential is generated. The fast sodium channels open after reaching the threshold potential causing depolarization of the membrane.
Action potential propagation on the muscle fibers occur through sarcolemma. Electrophysiological events of impulse conduction are given below:
1. Depolarization: It is the influx of sodium ions, and the membrane potential moves towards positive side, when the membrane potential becomes more positive inside i.e., approximately, +35 to +45mV, the process of depolarisation stops by the closure of sodium channels. This phase is followed by repolarisation.
2. Repolarization: It is the efflux of potassium ions, and the membrane potential moves to the negative side (restoring the resting membrane potential of sarcolemma). When it reaches normal resting membrane potential, the cell enters into the resting stage.
3. Refractory period: During refractory period, the nerve fibre does not respond to the stimuli because the sodium channels are in closed state (depolarisation ends by the closure of sodium channels, without depolarization, the impulse cannot be transmitted).
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