Exercise 3: Neurophysiology of Nerve Impulses

c. If the frequency of action potentials in this presynaptic cell (#10a) increases, what happens to the number of action potentials in the postsynaptic cell?

1. Exceeding the threshold depolarization at the trigger zone DECREASES the likelihood of generation of action potential.

What is a voltage-gated sodium ion channel? What is it made of? What is its function?

13. Understand the transportation of potassium and sodium across plasma membranes. (p. 10 bottom right, p. 20 bottom right, p. 21 diagram)

Resting potentials require ions as they play a vital role in the process. In the surface membrane of a cell there are protein carriers. These actively pump Na+ ions out of the cytoplasm to the outside of the cell. At the

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

What was the smallest voltage required to produce the maximum (largest) CAP? What proportion of the nerve fibers were excited to produce this maximal response?

2. Explain why increasing extracellular K_ causes the membrane potential to change to a less negative value. How well did the results compare with your prediction? _______________________________________________________________________

Both electrical and chemical forces combine to determine the resting membrane potential of the cell. Although the resting membrane potential of most cells is normally negative, the selective permeability of the membrane allows certain ions in and out, causing the neuronal membrane voltage to become depolarized (more positive), or hyperpolarized (more negative). Key ions involved in muscle membrane potential are sodium, potassium, and chloride, which move via passive or active diffusion through ion channels and transporter pumps (Baierlein et al. 2011). The Nernst equation predicts the membrane voltage based on the assumption that the membrane is only permeable to one type of ion. In this investigation, we are seeking to understand the basis for how different ions interact to produce the membrane potential of DEM, DEL1, and DEL2 crayfish muscle

Explain why a change in extracellular Na+ did not alter the membrane potential in the resting neuron. ___

Differences in the electrical charge on each side of the cell membrane produce a resting potential which means that the neurons will have a resting potential of 70 millivolts.

When a membrane is excited depolarization begins. When the membrane depolarizes the resting membrane potential of -70 mV becomes less negative. When the membrane potential reaches 0 mV, indicating there is no charge difference across the membrane. the sodium ion channels start to close and potassium ion channels open. By the time the sodium ion channels finally close. The membrane potential has reached +35 mV. The opening of the potassium channels allows K+ to flow out of the cell down its electrochemical gradient ( ion of like charge are repelled from each other). The flow of K+ out of the cell causes the membrane potential to move in a negative direction. This is referred to as repolarization. ( Marieb & Mitchell, 2009). As the transmembrane potential comes back down towards its resting potential level and the potassium channels begins to close, the trasmembrane potential level goes just below -90mV, causing a brief period of hyperpolarization (Martini, Nath & Bartholomew, 2012). Finally, as the potassium channels close, the membrane turns back to its resting potential until it is excited or inhibited again.

The extracellular Na+ did not alter the membrane potential in the resting neuron because the Na+ channels were mostly closed.

Hence, this would allow for an influx of sodium into the cell down its electrochemical gradient. It would also allow for the flow of potassium outward, as it has a 140mM concentration inside the cell and wants to shift down its concentration gradient to 5.4mM. Therefore, this great driving force for the influx of sodium and efflux of potassium helps to explain the findings at this point. As Table 1 shows, the findings within this figure are statistically supported. The fact that there is not significant difference between the findings of this experiment and the calculated Nernst at the 10, 20 and 40mM of potassium is an indicator that sodium is the largest determinant of the resting membrane potential. However, some findings defy the expectations, as the last two concentrations elicit a resting membrane potential significantly more negative than expected. This can be explained by the fact that at this point, each muscle at their respective muscle groups has been protruded many

Whenever the balance is altered, the process of transmitting electrical signals, which is called action potential initiates by carrying information across a neuron’s axon; which is called resting membrane potential. This process occurs as uneven ions distribution flow across cell membrane, creating electrical potential. As a result, the duration of active potential can be as fast as 1 ms. Similarly, the average resting membrane is between -40 mV and -80 mV. Since the membrane from inside is more negatively charged than the outside, it reflected on the negative average voltage readings of the resting membrane.