Neurophysiology AP obj

Describe the physiological process involved in the conduction (propagation) of an action potential, including the types and locations of the ion channels involved.

when a graded potential (dendrites) reaches threshold and triggers an action potential at axon hillock then down axon. as voltage gated Na+ ions flood into cell, this segmant of the membrane depolarizes. at the peak of action potential, the influx of sodium gates in the adjacent segment of the membrane to open down the axon. at the same time gated K+ channels are opening and Na+ channels are closing, repolarizing and refractory period down the axon. this cycle continues along the length of the axonal membrane from trigger zone to axon terminals

Describe the role of the sodium-potassium ATPase pump in maintaining the resting membrane potential.

- Pump uses energy to maintain/restore gradients to resting conditions - Every pump moves 2 K + in 3 Na + out -uses atp- energy

list the major ion channels of neurons and describe them as leak (leakage or passive) or voltage-gated channels, mechanically gated channels, or ligand-gated (chemically-gated) channels, and identify where they typically are located on a neuron.

-chemically gated channels: open and close in response to a binding of neurotransmitter (like acetylcholine) located: on the dendrites and cell body of neuron -voltage gated channels: open and close in change of membrane potential located: axon hillock -mechanically gated channels: open and close in response to physical deformation (like pressure) of receptors located: axon

Define and describe depolarization, repolarization, hyperpolarization, and threshold.

-depolarization: after graded potential where sodium ion channels open and sodium goes into the cell making the ICF more positive and hits threshold. -threshold: where voltage hits -55mV and fires action potential -repolarization: sodium channels close and it hits +30mV, potassium ion channels open to get back to resting state, AP stops rising -hyperpolarization: potassium leaves cell which makes ICF more negative than resting state -90mV, sodium potassium pump helps restore gradient to resting conditions: every pump moves 2 K+ in 3 Na+ out

Distinguish between absolute and relative refractory periods and compare the physiological basis of each.

During the absolute refractory period, a second stimulus (no matter how strong) will not excite the neuron. During the relative refractory period, a stronger than normal stimulus is needed to elicit neuronal excitation.

Compare and contrast graded potentials and action potentials, with particular attention to their locations in the neuron and the ions and ion channels involved in each.

compare: graded potentials help start action potentials contrast: graded potentials are depolarization and hyperpolarization, located in dendrites and cell body, chemically (or ligand) gated channels, amplitude is small, Na, K ions, no refractory period action potentials: all or nothing amplitude, large amplitude, absolute and relative refractory period, located axon hillock and axon, voltage gated and mechanically gated channels

Explain the role of myelin in saltatory conduction.

myelin sheath increases axonal conduction velocity. The propagation of electrical impulses along axons is highly accelerated by the myelin sheath and produces saltating or "jumping" action potentials across internodes, from one node of Ranvier to the next.

Explain how axon diameter and myelination affect conduction velocity.

myelination: By acting as an electrical insulator, myelin greatly speeds up action potential conduction -• Unmyelinated slow (1m/s), continuous propagation• Myelinated fast (5m/s), saltatory propagation- Saltare = leaping axon diameter: Larger diameter axons have a higher conduction velocity, which means they are able to send signals faster. This is because there is less resistance facing the ion flow.

Label a voltage-versus-time diagram of an action potential with the ions involved in each phase, the direction of their movement across the membrane, and the terms depolarize, repolarize, and hyperpolarize.

stage 1 of action potential: Resting stateNo ions move through voltage-gated channels.-70mv stage 2 of action potential: Depolarization is caused by Na+ flowing into the cell. stage 3 of action potential: Repolarization is caused by K+ flowing out of the cell.+30 mv stage 4 of action potential: hyperpolarization is caused by K+ continuing to leave the cell.-90mv

Describe the physiological basis of the resting membrane potential (RMP) in a neuron including the ion channels involved, the relative ion concentrations, and the electrochemical gradient.

the resting membrane potential is where the cell is at rest at -70mV. The sodium and potassium ion channels are closed. There are an increase of potassium ions inside cell where it is negative. There are an increase of sodium ions outside cell where it is positive. The leak channels are open which ions pass through to maintain membrane potential. The electrochemical gradient is the sum of all chemical and electrical forces.

Compare action potential conduction (propagation) in an unmyelinated versus a myelinated axon.

unmyelinated axon conduction velocities range from about 0.5 to 10 m/s, myelinated axons can conduct at velocities up to 150 m/s.

Explain the impact of absolute and relative refractory periods on the activity of a neuron.

The absolute refractory period starts immediately after the initiation of the action potential and lasts until after the peak of the action potential, located beginning of axon. The relative refractory period (RRP) occurs during the hyperpolarization phase. The neuron membrane is more negatively-charged than when at resting state; K+ ion channels are only just starting to close, located end of neuron

Describe the importance of voltage-gated channels in the conduction (propagation) of an action potential.

They control the sodium exchange between the extracellular and intracellular spaces, and are essential for the initiation and firing of action potentials and repolarization of the membrane, necessary for returning the membrane to a negative resting potential