Autonomic Nervous System Overview

These are proteins on cell surfaces that are stimulated by various catecholamines like epinephrine, norepinephrine, and dopamine. They play a role in the sympathetic nervous system, influencing heart rate, blood pressure, and other functions.

These receptors are found in vascular smooth muscles and pupillary radial muscles. Their activation leads to constriction of blood vessels and dilation of pupils.

The ANS controls involuntary bodily functions like heart rate, digestion, and breathing, operating without conscious effort.

The ANS has two divisions: the sympathetic and parasympathetic nervous systems.

These receptors are further divided into ß1 and ß2 subtypes. ß1 receptors are found in the heart, increasing heart rate and contractility. ß2 receptors are found in bronchial muscles, relaxing them and causing bronchodilation.

After being released at the synapse, about 50-80% of norepinephrine is actively transported back into the nerve ending. This process helps to regulate the amount of norepinephrine available between nerve cells.

The sympathetic nervous system prepares the body for 'fight-or-flight' responses, increasing heart rate, blood pressure, and alertness.

The remaining norepinephrine not re-uptaken is broken down by enzymes in the body. Two main enzymes are involved: catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO).

The parasympathetic nervous system conserves energy and promotes relaxation, slowing heart rate, lowering blood pressure, and aiding digestion.

Sympathetic nerve fibers originate in the spinal cord between segments T1 and L2, then travel through the sympathetic chain.

Parasympathetic fibers leave the brain through cranial nerves III, VII, IX, and X, and the spinal cord through the 4th sacral nerves.

Both divisions of the ANS use a two-neuron pathway: the first neuron originates in the CNS, the second neuron innervates the target organ.

The sympathetic and parasympathetic systems have antagonistic actions, maintaining a balance for optimal bodily function.

The sympathetic nervous system stimulates radial muscles in the eye, causing pupil dilation (mydriasis). It also stimulates the ciliary muscle, relaxing it and allowing for far vision.

The parasympathetic nervous system stimulates the circular muscle in the eye, causing pupil constriction (miosis). It also stimulates the ciliary muscle, contracting it and allowing for near vision.

The sympathetic nervous system stimulates salivary glands to produce thick, viscous saliva.

The parasympathetic nervous system stimulates salivary glands to produce watery saliva.

The sympathetic nervous system constricts blood vessels in the skin, GIT, and internal organs, but dilates blood vessels in skeletal muscles. It also stimulates the release of adrenaline from the adrenal medulla.

The parasympathetic nervous system dilates blood vessels in the skin, GIT, and internal organs. It constricts skeletal muscle blood vessels.

The sympathetic nervous system increases heart rate and contractility, stimulates the SA and AV nodes, and dilates coronary vessels.

The parasympathetic nervous system decreases heart rate and contractility, inhibits the SA and AV nodes, and constricts coronary vessels.

The sympathetic nervous system increases heart rate, strengthens heart contractions, and dilates coronary vessels for increased blood flow.

The parasympathetic nervous system slows heart rate, weakens heart contractions, and constricts coronary vessels to reduce blood flow.

The sympathetic nervous system dilates the pupil, allowing more light into the eye for better vision in dim conditions.

The parasympathetic nervous system constricts the pupil, reducing the amount of light entering the eye for better vision in bright conditions.

The sympathetic nervous system stimulates thicker saliva production, making it more viscous and less watery.

The parasympathetic nervous system stimulates watery saliva production, making it thinner and more abundant.

The sympathetic nervous system decreases secretion of tears from the lacrimal glands.

The parasympathetic nervous system increases secretion of tears from the lacrimal glands.

A branch of the autonomic nervous system that controls involuntary bodily functions like digestion, heart rate, and breathing, generally promoting rest and recovery.

The tenth cranial nerve, a major component of the parasympathetic nervous system, responsible for controlling many vital organs in the chest and abdomen.

The vagus nerve slows heart rate and reduces the force of heart contractions, promoting a resting state.

The vagus nerve constricts bronchioles, increases mucus production, and dilates blood vessels in the lungs, promoting airway relaxation and air retention.

The vagus nerve stimulates contractions of the esophagus, stomach, and small intestine, relaxes sphincters, and increases secretions, promoting digestion and nutrient absorption.

A branch of the parasympathetic nervous system originating from the sacral region of the spinal cord, responsible for controlling bladder, bowel, and sexual functions.

Receptors located on cell membranes that respond to acetylcholine, a neurotransmitter of the parasympathetic nervous system.

Nicotinic receptors are found in autonomic ganglia, motor end plates, adrenal medulla, and the CNS. Muscarinic receptors are found in effector organs receiving parasympathetic and some sympathetic postganglionic fibers.