As you already know, sympathetic involves the adrenergic receptors. Let’s look at the three adrenergic receptors.
Alpha Adrenergic Receptors stimulated by norepinephrine causes…
- Vasoconstriction. This causes an increase in blood pressure. If a person is in shock, you’d see this utilized.
- Stimulates sweat & salivary glands (this is not the opposite of parasympathetic)
- Decreases intra-ocular pressure (again, not the opposite of parasympathetic)
So these last two effects are not competing with the parasympathetic effects.
Beta 1 Adrenergic Receptors stimulated by norepinephrine…
Increases heart rate and the force of contraction. If a person is in shock, you’d see this utilized.
Beta 2 Adrenergic Receptors stimulated by norepinephrine causes…
Bronchodilation (useful for asthma) and can also relax smooth muscle. One potential use is to relax the uterus in case of premature labor.