Sympathetic neurons stimulate vasoconstriction in the gi tract, while sympathetic neurons stimulate vasodilation in arterioles supplying skeletal muscles. which mechanism explains these opposite effects?

It is because of the different neurotransmitters and their receptors.

Sympathetic stimulation of arterioles in skeletal muscle is mediated by epinephrine acting on its β-adrenergic receptors.  

Sympathetic stimulation   of vasoconstriction occurs as a result of activation of α-1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons.

Sympathetic neuron stimulates vasoconstriction in the GI tract, while the sympathetic neuron stimulates vasodilation in arterioles due to the presence of different receptor.

Further Explanation:

The “Somatic Nervous System” controls the voluntary function of the sensory organs and skeletal muscle. It contains both efferent (motor neuron) and afferent (sensory neuron) nerve that connects the “Central Nervous System” to the body muscles and tissues. This allows the body to perform a complex movement.It has two important divisions, namely, sympathetic and parasympathetic. They work in opposition. The sympathetic system helps to produce the excitatory response at the time of physical activity.

The sympathetic system of the ANS helps in stimulating the activity of the adrenal gland that releases epinephrine and nor epinephrine. These hormones increase the blood flow within the body by stimulating the heart rate and increase the rate of breathing by binding the adrenergic receptor on the peripheral tissue. Sympathetic neurons perform vasoconstriction in the gastrointestinal tract and perform vasodilation in skeletal muscle; both functions are different. The presence of beta-2 adrenergic receptors present in skeletal muscle that stimulates vasodilation. The presence of the alpha-1 receptor in the gastrointestinal tract stimulates vasoconstriction. Thus, sympathetic neuron performs two different functions at two different places.

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Answer Details:

Grade: High School

Subjects: Biology

Chapter: Central Nervous System

Keywords:

Central nervous system, physical activity, sympathetic neuron, parasympathetic neuron hormone, gastrointestinal tract, vasodilation, vasoconstriction, skeletal muscle.

this would be called the responsiveness