Question

a) Explain what factors, structures, and ion channels contribute to establishing and maintaining the resting membrane potential. Draw a cell and show all relevant contributors to the resting membrane potential with explanations of how they contribute to establish and maintain the resting membrane potential.

b)  What cells have a resting membrane potential? Is it only nerve and muscle (excitable) cells?

Answer 1

Ansa)

The potential difference across the membrane at rest is called as resting membrane potential and the membrane is said to be polarized. Resting membrane potential is about -70 mV where negative sign indicates that inside of cell is negative with respect to the outside of the cell. Resting membrane potential is ranges from -60 to -85 mV depending upon cell type.

The resting membrane potential is maintained by active transport and passive diffusion of ions. Sodium ion and chloride ion are present outside the cell while potassium ion phosphate ion and negative charge proteins are present inside the cell which makes more negative inside cell as compared to outside of cell.

The resting membrane potential is maintained by the active transport of Ions against their electrochemical gradient by Sodium Potassium pump . these are protein Carriers located in the cell surface membrane. They are driven by energy supplied by ATP and coupled the removal of three sodium ions from the axon with the uptake of two potassium ion. The active movement of these ions is opposed by passive diffusion of the ions. The rate of diffusion is determined by the permeability of the axon membrane of the ions. At rest potassium ions have a membrane permeability greater than and that of sodium ions. Therefore potassium ions loss from axon is greater than sodium ion gain . this leads to a net loss of positive ions from the axon, the production of negative charge within the axon. Along with these ions there are many organic anions ,negatively charged proteins, PO₄^3-ions present within the axoplasm, which also contribute to axoplasn negativity. Mainly due to active transport and diffusion process positive charges more outside and negative charges more inside.

Fig: showing neuron axon at resting .

Ansb) All cells of body have a resting membrane potential not only excitable cells. Resting membrane is the potential difference which exist across the cell surface membrane at rest or in absence of stimuli.So resting membrane potential is potential difference across membrane when cell is non excited so there is no difference either cell is excitable or not.

Difference between excitable and non excitable cell lies in terms of depolarisation not in terms of resting membrane potential. Excitable cells get excited in presence of stimuli ie depolarisation. While non excitable cell do not get excited on recieving stimulus.