Question

A. Draw graphs showing the effect on action potentials in a cell following effective doses of each of the listed neurotoxins Assume that the cell is normally brought to threshold by an electrical stimulus applied to it, so that any abnormality is due to the toxin. Precise values for voltage and duration are not important, just a general trend in how the action potential may be different from normal 1. puffer fish poison (blocks voltage-gated sodium channel activation) (25 Points) 2. tetraethylammonium (blocks voltage-gated potassium channels) (25 Points) Multiple sclerosis (MS) is one of the better known diseases resulting from demyelination of axons (in MS, only CNS axons are affected). Some of the earliest symptoms of the disease are difficulty in focusing the eyes, such as in reading, and difficulty in maintaining balance, and frequently not being able to make adjustments in posture to avoid falling. How do these symptoms "fit" with what you know about nerve impulses and myelin sheaths? (25 Points) Explain the processes that lead to the exocytosis of neurotransmitter from a presynaptic cell. Which components are recycled? Which ion is important in triggering exocytosis? (25 Points)

Answer 1

1)Myelin sheath is a fatty material coating which covers and insulate the nerves and enabling them to move quickly to conduct the impulse transmission   between the brain and the different parts of the body .due to it contains may proteins which are targeted by the immune system. The destruction of this myelin sheath cause the obstruct in the transmission of the impulse due to which the signals aren’t relayed to the further targeted part. Nerve cells are coated with sections of myelin, and the tiny spaces between the sections are called nodes( node of Ranvier). As the brain sends messages through the nerves of the spinal cord, the impulses jump from node to node. The myelin sheath prevents these impulses from escaping from the nerve at the wrong point. Upon destruction of the myelin sheath the it affects the impulse transmission and due to which messages do not get through quickly and clearly from the brain to the correct body part. The more sheath is destroyed, the slower and less efficient the nerve impulses are. Thus the impairment of the correct signalling affect the communication with nerves from other areas of CNS .The symptoms like dizziness and loss in vision problems are arises due to the same .

2)The Ca2+ ions are responsible for triggering exocytosis.

Mostly all components SNARE proteins, the clatherin coat got merged in the plasma membrane, only the neurotransmitter is expelled from the cell

Process of exocytosis

It follows the five steps-

a) Vesicle trafficking –the neurotransmitter is loaded in the vesicles and is transported through the cytoplasm towards the part of the cell from which it will be kept out.

b) Vesicle tethering – the vesicle aligned to the plasma membrane and pulled towards the [art of the cell from which it will be out.

c) Vesicle docking –the vesicle comes in contact with the cell membrane, where it merge with the proteins in cells

d) Vesicle priming –here the neurotransmitter are released, and it involves the chemical preparation s for the last step of the exocytosis. Also the SNARE proteins they got intact with the plasma membrane proteins (synaptobrevin) which holds them tighter at this stage the calcium ion starts moving in from the plasma membrane

e) Vesicle fusion- the proteins forming the walls merge with the cell membrane and breach , pushing the vesicle contents out of the cell. And thus the size of plasma membrane size increases.

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