Essay BIOS252 Week 3 PowerPhys4 Lab Report 2

b. What phenomena must take place for the small postsynaptic potentials to reach threshold and produce action potentials?

This stage is called repolarisation. The K+ channels then close, the sodium-potassium pump restarts, restoring the normal distribution of ions either side of the cell surface membrane and thus restoring the resting potential. In response to this the Na+ channels in that area would open up, allowing Na+ ions to flood into the cell and thus reducing the resting potential of the cells. If the resting potential of the cell drops to the threshold level, then an action potential has been generated and an impulse will be fired.

Once a presynaptic neuron is passive, an electrical current is spread along the length of the axon (Schiff, 2012). This is known as action potential (Pinel, 2011). Action potential happens once an abundant amount of depolarisation reaches the limit through the entry of sodium, by means of voltage gated sodium channels

3. A nerve is a bundle of axons, and some nerves are less sensitive to lidocaine. If a nerve, rather than an axon, had been used in the lidocaine experiment, the responses recorded at R1 and R2 would be the sum of all the action potentials (called a compound action potential). Would the response at R2 after lidocaine application necessarily be zero? Why or why not?

What effect will opening more of these channels have on the excitability of a neuron?

-It is harder to generate a second action potential during the relative refractory period because a greater stimulus is required because voltage-gated K+ channels that oppose depolarization are open during this time.

1. Number the events in the action potential in the order in which they occur.

a. Yes the amplitude of action potential in the median giant axon vary with the stimulus voltage in an earthworm. From the experiment, we saw that as the amplitude of stimulus voltage increases,

2. If the depolarization that reaches the axon is large and suprathreshold, the result in the axon is You correctly answered: c. action potentials at higher frequency.

Activation of a sensory neuron: The generated action potential is then carried to the spinal cord by the sensory neuron.

The synchronized bursts from a sufficient number of neurons result in a so-called spike discharge on the EEG. At the level of single neurons, epileptiform activity consists of sustained neuronal depolarization resulting in a burst of action potentials, a plateau-like depolarization associated with completion of the action potential burst, and then a rapid repolarization followed by hyperpolarization. This sequence is called the paroxysmal depolarizing shift. The bursting activity resulting from the relatively prolonged depolarization of the neuronal membrane is due to influx of extracellular Ca++, which leads to the opening of voltage-dependent Na+ channels, influx of Na+, and generation of repetitive action potentials. The subsequent hyperpolarizing after potential is mediated by GABA receptors and Cl− influx, or by K+ efflux, depending on the cell type.

Depolarization in membrane potential triggers an action potential because nearby axonal membranes will be depolarized to values near or above threshold voltage.

Neurons and impulses form the basis on of life on earth. Neurons are specialized cells that communicate with one another, muscles, and organs through electrical synapses. The neuron consists of a soma, axon, and dendrites. The axon within the nerve cell has the ability to generate an action potential. The purpose of this study is to understand the basic neurophysiology of excitable cells and understand the monophasic and biphasic action potentials. Monophasic is when there is a single phase to the nerve impulse. In this study, the sciatic nerve from a euthanized Rana Catesbelana frog was used. Our results demonstrate that that the response increased as stimulus increased. In addition, the action potential rate decreased with duration. This

Excitatory Postsynaptic Potentials (EPSPs): EPSPs increase the postsynaptic neuron’s likelihood to generate an action potential by generating a local depolarization. EPSPs result from excitatory stimuli, such as an excitatory neurotransmitter (Glutamate) released by the presynaptic neuron. Excitatory stimuli will bind and open ligand-gated Na+ channels, allowing Na+ ions to move inside a cell down their concentration gradient. The influx of Na+ ions will cause a local depolarization at the postsynaptic membrane, which if summated can reach threshold and fire an action potential.

The compound action potential adds up all the action potentials that each individual neuron experiences in the sciatic nerve. Different stimulus amplitudes cause different neurons to fire an action potential; this is due to the fact that each neuron has a different threshold potential, or the minimum voltage the neuron needs to fire an action potential. The individual neuron action potential is an ‘all-or-nothing’ event, but the CAP, as a summation of different individual neurons, is not. The CAP amplitude will increase with larger stimulus potentials because more neurons with higher individual thresholds will be recruited. For this frog sciatic nerve, there are three fiber types, A, B, and C. A fibers are further divided, in the order of decreasing diameter, into α, β, γ, and δ fibers. There is an inverse relationship between the diameter of the nerve fiber and the threshold potential: the larger the diameter, the lower the threshold. Thus, as the largest fibers, the Aα neurons will be the first to be stimulated at a low stimulus potential, and the Aδ neuron fibers will be the last to be recruited. Because the sciatic nerve is mostly composed of A fibers, the recruitment of A-subtype nerve fibers are more readily distinguishable from the data. The minimum potential required to stimulate the Aα fibers was between 75 mV and 80 mV. Once the stimulus potential reached 90 mV, Aβ neurons were recruited and contributed to the increase in amplitude of the CAP. At a stimulus