Physiology Exam 2

Why is it important that another action potential cannot be generated during the rising phase of an action potential?

It's important because if the another action potential occurred during the rising phase of an action potential, there would be too much excitatory stimulation in a cell and could lead to cell death.

Differentiate among a graded potential, the threshold potential, and an action potential?

-Graded potentials- are local changes in the membrane potential. They occur in varying grades or degrees of magnitude or strength. The stronger a triggering event, the larger the resultant graded potential. -threshold potential- -50-(-55) mV depending on the neuron, needs to hit threshold to get an action potential -Action potentials are brief, rapid, large (100mv) changes in membrane potential. The potential actually reverses- inside of the excitable cell transiently becomes more positive than the outside. Marked changes in the membrane permeability and ion movement lead to an action potential. Includes voltage gated Na+ and K+ channels. Changes in permeability and ion movement during an action potential.

Describe two types of graded potential change

-excitatory and inhibitory bc a graded potential can either be positive (depolarized) or negative (hyperpolarized)

Describe the forces that maintain the distribution of K+ and Na+ across the cell membrane in a neuron at rest?

1. passive leak channels, membrane is 100x more permeable to potassium than sodium. Potassium is able to diffuse from high conc. to low conc. (ICF-ECF), while sodium can still diffuse outside to inside, but it is much slower due to the fewer amounts of channels. This alone can lead to potassium in the cell continually decreasing, while sodium inside the cell continually increasing slowly BUT sodium potassium pump is able to use energy to oppose the rate of the channels. It pumps three sodium ions out while pumping two potassium into the cell. Potassium does not need as much help as sodium. Sodium potassium pump is also a carrier mediated protein, meaning it changes conformation so that it can expose itself to ICF and ECF. It uses ATP changed to ADP along with a phosphate group.

How do myelin and the nodes of Ranvier speed neural impulse transmission along an axon?

AP's can only be generated where there are many channels, local current can flow between node and adjacent resting node, bringing this node to threshold. -no channels in the myelinated sections, there the action potential can jump from node to node making it 50x faster. -when the axon is myelinated, the fiber diameter also influences the velocity of action potential propagation. When fiber diameter increases, the resistance to local current decreases. Thus, the larger the fiber diameter, the faster action potentials can be propagated. (less traffic) -AP faster at myelin due to the distance between opposite charges. Negative inside, positive outside, therefore less of an opposite attraction.

How does exocytosis and endocytosis play a role in the transport process?

Active transport-requires energy

Describe the parts of a typical neuron?

Axon, axon hillock, dendrities, nucleus, cell body, schwann cells, myelin sheath

What is the role of graded potentials?

Graded potentials are local changes in the membrane potential. They occur in varying grades or degrees of magnitude or strength. The stronger a triggering event, the larger the resultant graded potential. They degrade over time. A) entire membrane at resting potential B) Triggering event opens ion channels, most commonly permitting net Na+ entry, Inward movement of Na+ depolarizes membrane, producing a graded potential. C) Current flows between the active and adjacent inactive areas, depolarization spreads by local current flow to adjacent inactive areas, away from point of origin

Why does the voltage "undershoot"?

Hyper polarization due to the slow closing potassium channels/ leak channels which take a long time to close, which means potassium is leaving the cell at a slow rate.

What happens when humans drink salt water?

Hypertonic solution because causes us to become dehydrated

If a person has an abnormally low concentration of proteins in his/her plasma, edema (accumulation of fluid in the tissues) will occur. Why?

If theres a low conc. of proteins in plasma, the solution is hypotonic, therefore the cells will absorb water from the plasma membrane and cause accumulation of fluid in the tissues.

What events occur at the peak of the action potential?

Inactivation gate of sodium closes, and the activation sodium gate is open. The potassium activation gate is also open. This is why there is an absolute refractory period and action potentials only travels in one direction.

What factors impact establishing the resting membrane potential?

K+ tends to drive membrane potential to the equilibrium potential for K+ (-90mV) whereas Na+ tends to drive membrane potential to the equilibrium potential for Na+ (+60mV) K+ exerts the dominant effect of resting potential because the membrane is more permeable to K+. as a result, the resting potential of -70mV is closer to Equil K+ than Equil Na+ Inside of the cell is more negative than the outside due to the nee negatively charged intracellular proteins A- that cannot cross the membrane.

What causes the carrier to change shape to facilitate diffusion, active transport? Try to understand the concept of all types of transport.

Passive transport: facilitated diffusion (goes through channel), carrier mediated (changes conformation) Active transport- low to high conc. Carrier changes shape-1. Carrier protein takes conformation in which solute binding site is exposed to the region of higher concentration. 2. Solute molecule binds to carrier protein 3. Carrier protein changes conformation so that binding site is exposed to region of lower concentration 4. Transported solute is released and carrier protein returns to conformation in step 1.

Why is the sodium-potassium pump necessary after an action potential has been generated?

Sodium potassium pump is necessary to get the membrane potential back to its resting state of -70mV.

How does an axon generate and transmit a neural impulse?

Voltage gated sodium channel opens when the axon hillock

What prevents action potentials from spreading in both directions along an axon?

because after the firing, the voltage gated sodium channels are inactivated and it don't allow for additional influx of sodium therefore The action potential moves in only one direction because when one region of an axon is depolarized • The region of the axon in front of it is resting and ready to depolarize o So the action potential can spread in this direction • The region of the axon behind has just finished depolarizing so it is still REFRACTORY. o So the action potential cannot spread in this direction.

Why do action potentials only reach a certain height, "all or none"

change in voltage during an action potential results from ion movements down the conc. and electrical gradients. These gradients are not effected by the strength of the depolarizing triggering event -once the voltage change hits -50mV threshold of an action potential, the action potential will fire. it is all or none because it cannot produce a half life of an action potential.

What do you understand about refractory period?

refractory period is the time when a action potential can may or may not fire depending on if it's absolute refractory or relative refractory. Absolute refractory period means an Action potential cannot fire do the sodium channels that are inactivated. If an action potential is to fire during the relative refractory period, it must be a strong stimulus. The strong stimulus must be able to offset the extra negativity in the cell during hyper polarization.

After a long day, you soak in the tub for several minutes to relax. As you dry off, you notice that your fingers and toes are very wrinkled. What has happened?

the cells become hypotonic, filled with water, therefore more surface area on your fingertips to compensate for the water filled in the cells.