Sympathetic and Parasympathetic Nervous Systems Explained PDF
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This document provides an overview of the sympathetic and parasympathetic nervous systems, detailing their functions, effects, and receptors. It clarifies the roles of each system and contrasts their actions. It is well-organized for ease of understanding.
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Sympathetic and Parasympathetic Nervous Systems Explained The autonomic nervous system (ANS) is divided into the sympathetic and parasympathetic systems, each with distinct roles in regulating involuntary body functions. Here's an overview of their differences and their receptors: Sympathetic Nerv...
Sympathetic and Parasympathetic Nervous Systems Explained The autonomic nervous system (ANS) is divided into the sympathetic and parasympathetic systems, each with distinct roles in regulating involuntary body functions. Here's an overview of their differences and their receptors: Sympathetic Nervous System (SNS) Function: Prepares the body for "fight or flight" responses. Activates during stress, danger, or vigorous activity. Effects: Increases heart rate and force of contraction. Dilates bronchioles in the lungs. Dilates pupils. Inhibits digestion. Stimulates the release of glucose from the liver. Constricts blood vessels in non-essential organs and dilates them in muscles. Receptors: Adrenergic Receptors: Respond to adrenaline (epinephrine) and noradrenaline (norepinephrine). ○ Alpha Receptors: Alpha-1: Found in blood vessels; causes vasoconstriction. Alpha-2: Found in the CNS and on the presynaptic nerve terminals; modulates neurotransmitter release. ○ Beta Receptors: Beta-1: Found in the heart; increases heart rate and force of contraction. Beta-2: Found in the lungs and skeletal muscle blood vessels; causes bronchodilation and vasodilation. Parasympathetic Nervous System (PNS) Function: Promotes "rest and digest" activities. Activates during restful periods and promotes the conservation of energy. Effects: Decreases heart rate. Constricts bronchioles in the lungs. Constricts pupils. Stimulates digestion and peristalsis. Promotes the storage of glucose in the liver. Dilates blood vessels in the gastrointestinal tract. Receptors: Cholinergic Receptors: Respond to acetylcholine. ○ Muscarinic Receptors: M1: Found in the CNS and gastric parietal cells; involved in cognitive function and gastric acid secretion. M2: Found in the heart; decreases heart rate. M3: Found in smooth muscles and glands; causes smooth muscle contraction and glandular secretion. M4 and M5: Found in the CNS; involved in various central nervous system functions. Nicotinic Receptors: Found in the autonomic ganglia (both SNS and PNS) and the neuromuscular junction; involved in the transmission of nerve impulses to muscles. Key Differences: 1. Origin: ○ Sympathetic: Thoracolumbar region (T1-L2) of the spinal cord. ○ Parasympathetic: Craniosacral region (brainstem nuclei of cranial nerves III, VII, IX, X, and sacral spinal cord segments S2-S4). 2. Neurotransmitters: ○ Sympathetic: Uses norepinephrine (noradrenaline) primarily for postganglionic neurons. ○ Parasympathetic: Uses acetylcholine for both preganglionic and postganglionic neurons. 3. Responses: ○ Sympathetic: Typically generates widespread and longer-lasting effects due to the adrenal medulla releasing adrenaline into the bloodstream. ○ Parasympathetic: Usually generates more localized and shorter-lasting effects.
