Pharmacology, Disorders & Control of Homeostasis

Sympathetic agonist

A drug that mimics the effects of norepinephrine or otherwise activates sympathetic receptors.

Sympathetic antagonist

A drug that blocks sympathetic receptors and prevents or reduces the effects of sympathetic neurotransmitters.

Adrenergic agonist

Drug that activates an adrenergic receptor and mimics sympathetic stimulation.

Adrenergic antagonist

Drug that blocks an adrenergic receptor and reduces sympathetic effects.

Alpha-1 (α1) antagonists

Drugs that block α1 receptors, causing relaxation of smooth muscle.

α1 antagonists and blood pressure

Blocking α1 receptors relaxes vascular smooth muscle and lowers blood pressure.

α1 antagonists and prostate

Blocking α1 receptors can relax smooth muscle of the prostate.

Clinical uses of α1 antagonists

Used to treat hypertension and symptoms associated with an enlarged prostate.

Alpha-2 (α2) agonists

Drugs that activate α2 receptors and decrease sympathetic nervous system output.

Effect of α2 agonists

Reduce sympathetic activity.

Clinical uses of α2 agonists

May be used to treat hypertension and symptoms of opiate withdrawal.

Beta blockers

Drugs that block beta-adrenergic receptors and reduce sympathetic effects.

Effect of beta blockers on the heart

Decrease heart rate and force of cardiac contraction.

Clinical use of beta blockers

Can be used to reduce cardiac activity and blood pressure.

Beta-2 (β2) agonists

Drugs that activate β2 receptors and relax bronchiolar smooth muscle.

Effect of β2 agonists

Cause bronchodilation.

Clinical use of β2 agonists

Commonly used to treat asthma by opening the airways.

Muscarinic agonists

Drugs that activate muscarinic receptors and mimic parasympathetic effects.

Effect of muscarinic agonists on digestive system

Increase activity of the gastrointestinal tract.

Effect of muscarinic agonists on urinary system

Increase activity of the urinary bladder.

Muscarinic antagonists

Drugs that block muscarinic receptors and therefore block or reduce parasympathetic effects.

Atropine

Muscarinic antagonist that can increase a very slow heart rate and dilate the pupils.

Atropine effect on heart

Blocks parasympathetic effects and can increase a very slow heart rate.

Atropine effect on pupils

Blocks parasympathetic effects and causes pupil dilation.

Scopolamine

Muscarinic antagonist used to treat motion sickness, nausea, and hypersalivation.

Anticholinergic drug

A drug that blocks the effects of acetylcholine.

Common anticholinergic side effects

Dry mouth, constipation, urinary retention, and blurred vision.

Why anticholinergic drugs cause dry mouth

Blocking parasympathetic activity decreases salivary secretion.

Why anticholinergic drugs cause constipation

Blocking parasympathetic activity decreases digestive activity.

Why anticholinergic drugs cause urinary retention

Blocking parasympathetic activity interferes with normal bladder emptying.

Why anticholinergic drugs cause blurred vision

Blocking parasympathetic activity interferes with normal eye responses.

Postural orthostatic tachycardia syndrome (POTS)

Disorder characterized by tachycardia when a person stands.

POTS cardiovascular changes

Standing is associated with an increased heart rate and vasodilation that can cause a drop in blood pressure.

Possible POTS symptoms

May include lightheadedness, fainting, weakness, and fatigue associated with standing.

Cause of POTS

The cause is unknown.

Possible autonomic explanation for POTS

May involve excessive sympathetic nervous system activity or excessive sensitivity to sympathetic stimulation.

POTS treatment approaches

Treatment may include changes in diet and exercise as well as drugs that block certain autonomic receptors.

Main brain regions controlling autonomic function

Hypothalamus and reticular formation of the brainstem.

Hypothalamus and ANS

The hypothalamus plays an important role in controlling autonomic activity and maintaining homeostasis.

Reticular formation and ANS

Contains autonomic centers that regulate activity of sympathetic and parasympathetic preganglionic neurons.

Autonomic centers in the brainstem

Regulate activity of preganglionic sympathetic and parasympathetic neurons.

Relationship between hypothalamus and reticular formation

Hypothalamic signals influence autonomic centers within the reticular formation.

Reticular formation without hypothalamic input

Autonomic centers in the reticular formation can continue functioning even if circuits connecting them with the hypothalamus are severed.

Amygdala and autonomic control

Provides emotional information that can influence autonomic responses through the hypothalamus.

Cerebral cortex and autonomic control

Can provide input related to thoughts and emotions that influences hypothalamic autonomic responses.

Emotion-to-ANS pathway

Emotional input from the amygdala and cerebral cortex → hypothalamus → reticular formation → autonomic nervous system.

Emotional sympathetic response

Emotions can activate hypothalamic and brainstem pathways that produce sympathetic responses.

Examples of autonomic responses to emotion

Changes such as increased heart rate, sweating, and other sympathetic signs can accompany strong emotions.

Overall control of autonomic homeostasis

Higher brain centers and brainstem autonomic centers adjust sympathetic and parasympathetic activity to maintain homeostasis.