Imbalances of the ANS (Autonomic Nervous System)

Imbalances of the ANS

Because of its widespread effects, imbalances of the ANS and part of the PNS can cause a variety of out-comes. These include hypertension, autonomic dysreflexia, and Raynaud’s disease. Autonomic disor-ders often cause the smooth muscles to be overcon-trolled or undercontrolled. Hypertension is commonly referred to as high blood pressure and may be caused by overactive sympathetic vasoconstrictor responses due to continuous stressors. It is a serious condition because it causes the heart to work harder than nor-mal leading to heart disease and may harm the walls of the arteries. Treatments for hypertension may include adrenergic receptor-blocking drugs, which counteract sympathetic nervous system effects on the cardiovas-cular structures.

Autonomic dysreflexia occurs due to uncontrolled activation of autonomic neurons. This life-threaten-ing disorder is common in quadriplegics and those who have spinal cord injuries above the T₆ level within one year after injury. Triggers for autonomic dysreflexia include overfilling of the urinary blad-der or another visceral organ or painful skin stimuli. The arterial blood pressure then becomes danger-ously high and may cause a blood vessel of the brain to rupture, which precipitates a stroke. Symptoms of autonomic dysreflexia include flushing of the face, headache, cold and clammy skin below the area of the injury, and sweating above the area of the injury. This disorder’s actual mechanism of action is not fully understood.

Raynaud’s disease is often caused by exposure to emotional stress or cold temperatures and is an exaggerated response of vasoconstrictive activities. The patient experiences intermittent attacks, with the skin of the fingers and toes becoming pale at first and eventually cyanotic and painful. The disease may be an uncomfortable condition or can cause severe con-striction of the blood vessels, leading to ischemia and gangrene (death of tissue). Adrenergic blockers and other vasodilators are often used for treatment. If the disease is extremely severe, preganglionic sympathetic fibers that serve the affected regions are surgically sev-ered (sympathectomy). Dilation of the involved vessels can then occur and adequate blood flow to the region is reestablished.

1. Explain the effects of sympathomimetic drugs.

2. Differentiate between sympathetic tone and parasympathetic tone.

3. Explain how the sympathetic nervous system may be linked to hypertension