Stimulation of medial portion of vasomotor centre results in
Correct Answer: Decreased cardiac output
Description: Ans. d). Decreased cardiac output. (Ref. Ganong Physiology 23rd/Chapter 33)Inflation of the lungs causes vasodilation and a decrease in blood pressure. This response is mediated via vagal afferents from the lungs that inhibit vasomotor discharge. Pain usually causes a rise in blood pressure via afferent impulses in the reticular formation converging in the RVLM.VASOMOTOR CONTROL# Spinal reflex activity affects blood pressure, but the main control of blood pressure is exerted by groups of neurons in the medulla oblongata that are sometimes called the vasomotor area / center.# Neurons that mediate increased sympathetic discharge to blood vessels and the heart project directly to sympathetic preganglionic neurons in the intermediolateral gray column (IML) of the spinal cord.# On each side, the cell bodies of these neurons are located near the pial surface of the medulla in the rostral ventrolateral medulla (RVLM). They contain PNMT, but it appears that the excitatory transmitter they secrete is glutamate rather than epinephrine.# When vasoconstrictor discharge increases, arteriolar constriction also increases and blood pressure rises.# Venoconstriction and a decrease in the stores of blood in the venous reservoirs usually accompany these changes, although changes in the capacitance vessels do not always parallel changes in the resistance vessels. Heart rate and stroke volume are increased because of activity in the sympathetic nerves to the heart, and cardiac output is increased.# Control of heart activity bx vasomotor center:# Lateral portions of vasomotor center transmit excitatory impulses through sympathetic fibers and increases heart rate and contractility.# Medial portion of vasomotor center- Lies in apposition to dorsal motor nuclei of vagus nerves- Transmits parasympathetic impulses through the vagus nerves to the heart to decrease heart rate. Vasomotor center can also decrease heart rate.Factors Affecting the Activity of the Vasomotor Area in the MedullaDirect stimulationCO2 and hypoxiaExcitatory inputsFrom cortex via hypothalamus.From pain pathways and muscles.From carotid and aortic chemoreceptorsInhibitory inputsFrom cortex via hypothalamus.From lungs.From carotid, aortic, and cardiopulmonary baroreceptors.
Category:
Physiology
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