Question

The transport of ions across cell membranes is a key part of the processes of generation and conduction of action potentials in neurons.

1. a) Why do ions require an integral membrane protein in order to pass across neuronal cell membranes?

2. Briefly discuss the specific ion channels and transporters that are involved in the generation and conduction of a neuronal action potential, and indicate whether the protein is involved in facilitated diffusion or active transport of ions.

3. How does myelination of the axon of a neuron affect the transport of ions across the membrane and the conduction of an action potential?

Answer 1

a. IOns neede an integral membrane proteins because the ions are charged particles and they can't pass through the membrane which is hydrophobic made of phospho lipids.

b. The nerve membrane has number of transporters, channels and pumps present. There are Na gated channels. K gated channels which are the channels through which facilitated diffusion occurs. The Na-K pumps are active transport pumps which carry 3 Na ions out and 2 K ions into the cell by spending 1 ATP molecule in one turn of the pump.

Soon after the stimulus, it is Na gated channels which open to allow the Na ions. The Na ions diffuse in to the axon. This reverses the polarity making inside +vely charged and outside negatively charged. The potential difference now existing across the nerve membrane is action potential. Mean while the K gated channels open outside to let the K ions out and regain the -ve charge internally. The Na ions which are mroe inside are taken out and K ions which are now more out side are brought in by Na-K pumps which are active transport pumps. These pumps restore the Na and K levels inside and out side the axon. Once the action potential is generated it spreads till it reaches the end of the neuron.

c.The myelin sheath is made of lipid membrane which is an insulator. Because the myelin shaeath is insulator, it does not allow the flow of ions or electric potential to passs through. Due to this the potential difference or the action potential jumps from one node of Raranvier to another. This increases the speed of the conduction of action potential.

Nodes of Ranvier are the regions where there is no myelin sheath covering the axon.