Neurons and AP

Question 1

what are the causes of resting membrane potential?

Answer 1

1. selective permeability: continous potassium efflux out of the cell, accumulation of +ve charges on the outer surface of the cell membrane.
2. sodium-potassium pump: Which extrudes 3 sodium ions out of the cell in exchange for 2 potassium ions intruded into the cell, accumulation of +ve charges out of the cell

Question 2

What is the RMP?

Answer 2

The potential difference between the outter and inner surfaces of the cell membrane during rest.

Question 3

How is the magnitiude of the nernest equation determined?

Answer 3

By the ratio of the concentrations of that specific ion on the two sides of the membrane

Question 4

What happens when the Ci/Co ratio inceases?

Answer 4

the greater tendency for the ion to diffuse in one direction and the greater the nerst potential required to prevent additional net diffusion

Question 5

What forms the ion selectivity filter in voltage-gated structure?

Answer 5

formed by the P loop between the S5 and S6 segments.

Question 6

Where is the activity gate of voltage gated sodium channel ionized?

Answer 6

At the intracellular end of the s6 segments

Question 7

What is the structure of the a-subunit of a voltage-gated sodium channel?

Answer 7

composed of four homologous domains, each contains six transmembrane segments
4 voltage-sensing modules composed of s1 to s4 segments
S5 to S6 segments form a pore doman and a p loop between them

Question 8

What is the nernest potential?

Answer 8

the membrane potential level that exactly opposes the net diffusion of that ion through the membrane. its the potential inside the membrane while potential in the extracellular fluid outside the membrane remains at zero potential.

Question 9

What is the absolute refractory period?

Answer 9

It occupies all the depolarization phase and initial 1/3 of the repolarization phase
The nerve cannot generate new action potential whatever was the strength of the new stimulus

Question 10

What is the relative refractory period?

Answer 10

it occupies the late 2/3 of the repolarization phase
Another stimulus can generate a new action potential if the strength of the new stimulus was supra-threshold

Question 11

What causes the absolute refractory period?

Answer 11

Caused by innervation of the na+ channels so there is a delay before another action potential can occur in the same piece of membrane

Question 12

What causes the relative refractory period?

Answer 12

Vooltage gated potassium channels do not close quickly, causing extra potassium conductance, so the membrane is at a higher threshold and will require a greater stimulus to cause action potentials fire.

Question 13

What is the communication between neurons called?

Answer 13

Action potential

Question 14

What is the communication within neurons called?

Answer 14

local potential

Question 15

What is local potential?

Answer 15

Induced by small depolarizing or hyperpolarizing currents to induce excitability or inhibitory effects on the excitable tissue membrane.

Question 16

Why does local potential occur?

Answer 16

Due to changs in the membrane ionic conduction through non voltage-gated channels.

Question 17

What are the characteristic features of the local potential?

Answer 17

1. Its magnitude is proportionate to the strength of the stiulus = gradd response (amplitude modulated)
2. It decays with distance from the initial state= decremental conduction
3. It is localized to the area of stimulation = not propogated
4. It is not followed by refractory period
5. Local potentials could be induced by subthreshold stimulation of the excitable membranes of the nerve and muscl fibers
6. Are important in short distance signaling
7. Are importats physiological responses in sensory receptors, synapses and neuro muscular junctions