Where are the vasomotor centers of the cardiovascular centers located? List the

Question

Where are the vasomotor centers of the cardiovascular centers located? List the two major types of sensory neurons that communicate with the vasomotor center, and state two places you would find each. For each, briefly explain one stimulus that would cause them to encourage vasoconstriction. What division/s of the ANS control/s blood vessel constriction? Name the neurotransmitter that is used at most vessels, and describe it's effect on those vessels (cause constriction or dilation); do the same for the neurotransmitter that is used at some vessels that lead to skeletal muscle and the brain. What is vasomotor tone?

Explanation / Answer

The vasomotor center is the center of autonomic control of blood pressure. It is located bilaterally in the reticular substance of the medulla oblongata and lower third of the pons.

The two major type of sensory nerves that communicate with the vasomotor center are carotid sinus nerve which is a branch of Cranial nerves IX (Glossopharyngeal nerve) and X Vagus nerve.

Carotid sinus nerves can be found around the walls of the carotid sinuses near the bifurcation of the common carotid arteries. Vagus nerves can be found near the bifurcation of common carotid arteries and along the aortic arch.

Levels of oxygen in the blood can act as a stimulus to initiate vasoconstriction via vagus nerve. The change in arterial pressure stimuates the carotid sinus nerve to encourage vasoconstriction.

The stimulation of the sympathetic nervous system (a division of Autonomous Nervous System) causes blood vessel constriction.

The neurotransmitters used at most blood vessels are norepinephrine (NE) released by sympathetic nervous system causing vasoconstriction while the parasympathetic nervous system releases acetylcholine (ACh) causing vasodilation.

The neurotransmitter that is used at some vessels that lead to skeletal muscle and the brain is acetylcholine. In the brain, acetylcholine functions both as a neurotransmitter and as a neuromodulator.

Neurons emanating from the vasoconstrictor region of vasomotor center are always active. This ongoing activity produces an ongoinf repetitive firing of sympathetic vasoconstrictor fibres that sustains a partial state of vascular smooth muscle contraction referred to as vasomotor tone. The vasomotor tone is an essential determinant of blood pressure. A decrease in vasomotor tone lowers the mean arterial pressure and may cause an intense vasoplegia with arterial vascular resistance below than 800 dyn/s/cm leading to a lack of tissue oxygenation.  

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