Question

Paragraph les 9. List and draw the 3 classes of neurons based on their structure a. b. C. 10. What are the 2 main functions of neurons? a. b. 11. Why is there a resting membrane potential across the cell membrane? 12. What causes an action potential? 13 Explain what is happening to Nat and K during these phases a. Resting state b. Depolarization c. Repolarization 14 What restores the ion (Na , K) distribution after an action potential? 5 Describe saltatory conduction

Answer 1

9. ANS:

10. ANS: Neuron main function:
-Receive the information from the surroundings,
-process it,
-interpret it and then
-respond to it accordingly
Depending on the functions neurons are of three types:
1) Sensory Neurons transmits impulse from sense organs to CNS
2) Motor Neurons carries impulses from brain and spinal cord to effector organs.
3) Mixed Neurons contains both sensory and motor neurons.

11. ANS: Resting membrane potential is established and maintained in neurons with the help of ion channels and some leakage through the membrane. They are responsible for pumping 3Na ions out of the cell and 2K in the cell against the concentration gradient with the help of transmembrane ATPase. In resting condition the membrane bears positive charge outside while negative charge inside while concentration of Na is high inside than outside. Na K ATPase help pump these ions against concentration gradient and maintain resting potential. Moreover, negativity on inside does not mean more negative ions inside cell but less positive charge as compared to outside.

12. ANS: An action potential occurs when a neuron sends information down an axon, away from the cell body. A cell in resting condition will have negative potential (-70mV). At such conditions, there will be more Na+ ions on the outside and more K+ in the cytosol. When a neuron is stimulated, the stimulus causes sodium channels to open. sodium ions rush into the neuron. Inside of the cell becomes more positive as sodium ions rush in. It is called depolarization.

Following depolarization K+ channels open, causing K+ ions to rush out of the cell reversing the depolarization. Simultaneously, Na+ ion channels start to close. This causes the action potential to go back toward -70 mV (a repolarization). As the K+ ion channels open longer, it causes the membrane potential to go past -70mV - called hyperpolarization. Eventually, the resting membrane potential is restored.

An action potential moves down an axon in only one direction and never backward because when one region of an axon is depolarized the proceeding region is resting and ready to depolarize so that the action potential can spread in this direction. The preceding region of the axon is still in refractory phase (hyperpolarized), so the action potential cannot spread backwards.

15. ANS: An action potential transfer from one node of Ranvier to another through myelinated axons is called as an action potential. Generally Ranvier nodes unmyelinated portions exchange ions and increase the action potential unlike the normal circuit. This phenomenon increases the conduction velocity of the action potentials.

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