Autonomic Nervous System (ANS)

• The autonomic nervous system (ANS) regulates unconscious bodily functions necessary for survival.
• Functions controlled include heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal.
• The ANS is also known as the visceral nervous system.
• It's the main mechanism controlling the fight-or-flight response.

Divisions of the ANS

• The ANS consists of three divisions: the sympathetic nervous system (SNS), the parasympathetic nervous system (PNS), and the enteric nervous system (ENS).

Sympathetic Nervous System (SNS)

• The SNS is responsible for the "fight or flight" response, preparing the body for action.

Parasympathetic Nervous System (PNS)

• The PNS is known as the "rest and digest" system, and it promotes relaxation and energy conservation.

Enteric Nervous System (ENS)

• The ENS is an independent network of neurons within the digestive system.
• The ENS regulates gut motility, secretion, and absorption.

Comparison of SNS and PNS

• Primary Role: The SNS is for fight or flight, while the PNS is for rest and digest.
• Heart Rate: The SNS increases heart rate, and the PNS decreases it.
• Blood Pressure: The SNS increases blood pressure, and the PNS decreases it.
• Digestion: The SNS inhibits digestion, and the PNS stimulates it.
• Pupil Size: The SNS dilates pupils, and the PNS constricts them.
• Bronchial Muscles: The SNS relaxes bronchial muscles, and the PNS constricts them.
• Neurotransmitter: The SNS primarily uses norepinephrine (sometimes acetylcholine), and the PNS uses acetylcholine.
• Location of Ganglia: The SNS has ganglia near the spinal cord, and the PNS has ganglia near or within the target organ.
• Effects on Body: The SNS increases alertness and energy expenditure, while the PNS promotes relaxation and energy storage.
• Origin of Nerves: The SNS originates from the thoracic and lumbar regions of the spinal cord, and the PNS originates from the brainstem and sacral region of the spinal cord.
• Response to Stress: The SNS dominates during stress, while the PNS is less active.
• Sweat Glands: The SNS stimulates sweat glands, while the PNS has no effect.
• Salivary Glands: The SNS reduces salivation (thick mucus), and the PNS increases salivation (watery).
• Blood Vessels: The SNS constricts most blood vessels, and the PNS dilates vessels to the gut.
• Adrenal Medulla: The SNS stimulates the secretion of epinephrine and norepinephrine, and the PNS has no direct effect.
• Bladder: The SNS relaxes the bladder wall and constricts the sphincter, while the PNS constricts the bladder wall and relaxes the sphincter.
• Thermoregulation: The SNS influences sweating and blood vessel diameter, and the PNS has a minor role.
• Response Duration: The SNS has a prolonged response due to norepinephrine lingering in the synapse, and the PNS has a shorter response due to rapid hydrolysis of acetylcholine.
• Clinical Significance: The SNS is involved in anxiety disorders and hypertension, while the PNS is involved in overactive bladder and vasovagal syncope.
• Cranial Nerves: The SNS is not directly associated with cranial nerves, while the PNS is associated with Oculomotor (III), Facial (VII), Glossopharyngeal (IX), and Vagus (X) cranial nerves.