Neural Signalling

What is are neurons? + main parts

Neurons (nerve cells) are cells in the nervous system that carry electrical impulses. There are 85 billion in a human, and they have 3 main parts: the dendrites (short branched around cell body), axon (long nerve fiber), and cell body (nucleus).

What is membrane potential? Resting potential for a neuron?

Membrane potential can be found by placing electrodes inside and outside the living cells. It is usually between 10-100 mV, and it is due to the imbalance between the net change inside and outside. Typically, the inside is more negative than the outside. The resting potential for a neuron is -70 mV.

What is resting potential and how does the sodium/potassium pump work?

There is more k+ inside and more Na+ outside, so the sodium/potassium pump actively pumps 3 Na+ out and 2 K+ in to maintain resting potential. The ions leak back by facilitated diffusion. Side note: Negatively charged proteins inside also add to charge imbalance.

How do nerve impulses of action potential work?

• Action potential is a sudden change in membrane potential

• Depolarization is a change from negative to positive (Na + ions in)

• Repolarization is a change from positive back to negative (K+ ions in)

what is the depolarization step of action potential?

The stimulus arrives and the sodium channels open (Na+ enters by facilitated diffusion), the extra positive changes raise the membrane potential to 30 mV.

What is the repolarization step of action potential?

The sodium gates close and the potassium gates open, the potassium diffuses out by facilitated diffusion, and the positive changes lead back to resting potential. The ions then reverse, so the sodium potassium pump restores the imbalance.

Action potentials are…

• All or nothing (reaches threshold or doesn’t)

• Stereotypical (look the same regardless of stimulus)

What does stronger stimulus mean?

Greater frequency of action potentials.

What does it mean that axon potentials propogate down the nerve fiber?

That ion movements that depolarize one part of fiber trigger depoliza