The effects of the sympathetic and parasympathetic autonomic divisions differ because______________ .
The effects of the sympathetic and parasympathetic autonomic divisions differ because______________ .
In bilateral animals, the nervous system is classified into the central nervous system and the peripheral nervous system. The nerves that reside outside the brain and spinal cord comprise the peripheral nervous system.
The peripheral nervous system is further classified into the autonomic nervous system and the somatic nervous system. The involuntary physiologic responses is conducted by the autonomic nervous system, which is classified into three branches namely sympathetic, parasympathetic, and enteric nervous system.
In the body, the homeostatic activity is controlled by the parasympathetic division. It keeps the body at rest and is found to be responsible for the digestive function of the body. On the other hand, the sympathetic nerve is responsible for the body's fight and flight response. It controls the response of the body when a threat is either perceived or encountered.
In simpler words, with the sympathetic branch, everything increases (heart rate, blood pressure), and blood flow to the skin gets elevated. But, the blood supply to the digestive tract decreases. On the other hand, the parasympathetic division is associated with decreasing activity in blood flow, blood pressure, and heart rate, where activities digestion and waste elimination are found to be normal.
The nerve fibers that are located above the ganglia refer to the preganglionic neurons. In the parasympathetic nervous system, at both the sites of ganglia and effector organs, acetylcholine acts as a neurotransmitter. Whereas, in the case of the sympathetic nervous system, the ganglia have the neurotransmitter as acetylcholine and nicotinic type of acetylcholine receptors, but the effector organ accommodates the neurotransmitter noradrenaline. This condition states that the release of neurotransmitters at the postsynaptic neuron is found to be different for both sympathetic and parasympathetic neurons. This causes differences in the physiological effects caused by these two divisions, opposing each other in most of the cases.
Some of the effects induced by parasympathetic and sympathetic division in effector regions are given below.
| Affected structure | Parasympathetic | Sympathetic |
| Pupil | Constricts | Dilates |
| Salivation | stimulates | Inhibits |
| Heart rate | Slows | Increases |
| Bronchi | Constricts | Dilates |
| Digestion | Stimulates | Inhibits |
| Gall bladder and Bile duct | contraction | Relaxation |
| Bladder | Contraction | Inhibition |
| Uterus | Relaxation | Vaginal contraction |
| Urinary system | Increased urine output | Relaxation |
| Penis | Erection | Ejaculation |
| Nasal and lacrimal glands | Secretion | vasoconstriction |
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