The carries oxygen-poor venous blood from above the diaphragm from areas of the upper body and extremities into the right atrium. The carries oxygen-poor venous blood of the coronary circulation into the right atrium. The carries oxygen-poor venous blood from below the diaphragm from the areas of the lower body and extremities into the right atrium.

Superior vena cava

Explanation:

Of the two vena cava, the superior vena cava is the large vein without valves that is responsible for conveying de-oxygenated blood from the upper extremities and body (neck, chest, arm and head) above the diaphragm to the right artrium.

Although the superior vena cava is a large vein, it also short; it is about 2 cm wide and 7 cm long.

When there is an obstruction of the superior vena cava, it can result to the enlargement of the veins and could lead to chest pain and breathlessness.

what are the options?

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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