endocrine

Sympathetic Nervous System Overview

• Sympathetic nervous system operates through preganglionic fibers originating from T10 to L2.
• Fibers descend through sympathetic trunk to lumbar and sacral ganglia.
  • Two significant collateral ganglia: inferior mesenteric and inferior hypogastric.
• Activation effects include:
  • Inhibition of urination and defecation.
  • Increase in sexual responses (ejaculation/orgasm).
• Adrenaline/Epinephrine Release:
  • Triggered by sympathetic response, prolongs sympathetic effects via adrenal medulla releasing adrenaline into bloodstream.
  • Results in sustained sympathetic response, e.g., increased heart rate, sweating, dilation of pupils during stress events (e.g., seeing police lights).

Parasympathetic Nervous System Overview

• Known as the cranial-sacral division:
  • Cranial outflow: originates from the brain (innervates head, neck, thoracic, and abdominal organs).
  • Sacral outflow: originates from S2-S4, innervates pelvic organs.
• Preganglionic fibers:
  • Long in parasympathetic division; Few branches for targets.
• Major Cranial Nerves innervating parasympathetic actions:
  • Cranial Nerve III (Oculomotor):
  • Function: Innervates eye smooth muscle (pupil constriction).
  • Preganglionic fibers originate in the midbrain; postganglionic fibers in ciliary ganglion.
  • Cranial Nerve VII (Facial):
  • Function: Stimulates salivary and lacrimal glands.
  • Cranial Nerve IX (Glossopharyngeal):
  • Function: Secretions from the parotid gland.
  • Preganglionic fibers located in the inferior salivatory nucleus.
  • Cranial Nerve X (Vagus):
  • Extends from the brain to the abdomen; regulates digestive activities, heart rate, and respiratory rate.
  • Preganglionic fibers in the medulla; postganglionic fibers are found in the walls of target organs.

Vagus Nerve Plexuses

• Major Plexuses from vagus nerve that synapses in the ganglia:
  • Cardiac plexus: regulates heart rate.
  • Pulmonary plexus: regulates respiratory functions.
  • Esophageal plexus: regulates esophageal functions.
  • Celiac plexus: innervates abdominal organs.
  • Superior mesenteric plexus: innervates small intestines and proximal colon.

Sacral Outflow and Reflexes

• Governs organs within the pelvic region, including colon, rectum, bladder, and genitals.
• Originates from sacral spinal nerves S2-S4; utilizes pelvic splanchnic nerves.
• Visceral Reflexes: Key reflexes are defecation and micturition, integrated through centralized pathways in the spinal cord.

Neurotransmitter and Receptor Functions

• Cholinergic Neurons:
  • Release acetylcholine (ACh). Found in both sympathetic and parasympathetic systems.
  • Receptors:
  • Nicotinic receptors: Always excitatory; associated with both divisions.
  • Muscarinic receptors: Can be excitatory (parasympathetic response) or inhibitory (sympathetic response).
• Adrenergic Neurons:
  • Release norepinephrine (mostly sympathetic).
  • Can bind norepinephrine and epinephrine.

Development of the Autonomic Nervous System

• Develops from both the neural tube (preganglionic) and the neural crest (postganglionic).
• Sympathetic ganglia arise from ventral migration of cells, with prevertebral ganglia forming via dorsal migration.
• Autonomic function declines with age, leading to challenges in eliciting either sympathetic or parasympathetic responses.

Referred Pain

• Pain perceived in areas different from actual organ injury due to fewer nociceptors in visceral organs.
• Example areas of referred pain:
  • Heart and liver: Left side.
  • Lungs: Shoulder.
  • Kidneys: Lower back region.

Integration Centers of the Autonomic Nervous System

• Brainstem: Medulla oblongata and reticular formation regulate autonomic responses.
• Hypothalamus: Main integration center; coordinates sympathetic and parasympathetic activities.
• Cerebral Cortex and Limbic System: Higher brain functions can regulate autonomic responses via emotional states or cognitive activities (e.g., relaxation techniques like yoga).