Question

Neurophysiology is based on a reductionist approach. The model of the action potential we have studied was developed from animal studies. The first researchers started with a squid neuron, and actually just cut off the axon and threw away the rest of the cell. Never mind about the squid's brain.

While this approach has yielded some impressive results, reductionism and mechanism (treating the brain like a machine) may have some limitations. Do dogs have feelings? How about earthworms? How about Jenning's protozoa? How about a computer? What does this tell us about human mind? Are we nothing more than a machine?

describe how action potentials are generates, how they propagete along axons (both myelinated and unmyelinated ), and how the membrans of the axon returns to restimg potential.

Answer 1

Transmission of nerve impulses involves 3 basic processes as

A) Maintaining Membrane potential

B) Generating Action potential

C) Propagating Action potential

The non-stimulated neuron is called Resting neuron and a stimulated neuron is called active neuron. The membrane potential of a resting neuron is the Resting potential, whereas the membrane potential of active neuron is called Action potential. In resting potential, the membrane is negative inside and positive outside and the opposite state in Action potential.

The resting potential is maintained by Sodium- potassium pump. At this state, more sodium ions will be outside the cell than potassium ions inside the cell. Sodium- potassium pump transports two potassium ions inside and three sodium ions out to maintain the resting potential.

The charge of the membrane of neurons can change by the neurotransmitter molecules or by environmental stimuli. The signals are transmitted through the neuron via an action potential, by the sudden depolarization and polarization of membranes. The action potential is transmitted down the axon as the membrane of the axon depolarizes and repolarizes. When neuron is stimulated, the sodium potassium pump stops, and sodium gates open widely. As a result, heavy influx of Na+ occurs. This completely reverse the resting potential, which is called Depolarization, the beginning of generation of action potential.

Immediately after depolarization, the sodium potassium pump resumes functioning and sodium gates close. This regains the resting potential state of membranes, which is called Repolarization. Depolarization and the following Repolarization is together called an action potential. Transmission of impulses is accomplished by propagating action potential. The action potential excites the subsequent resting potentials in series during which a local electric current is set up. Current flows from resting area to the depolarized area. As a result, the action potential gets shifted and impulse is transmitted.

As the action potential get transmitted down the membrane, ions may displace as they cross the membrane and exit the cell. The presence of myelin acts as an insulator to make this escape impossible, and so helps to preserve the action potential. The space between Myelin sheath, The nodes of Ranvier, also helps push the signal strong. The positive charges gather near this unsheathed area, waiting to swarm inside when the channels open.