Sympathetic Nervous System

Objectives

• Describe the functions of sympathetic innervation to abdominal pelvic organs.
• Identify the origin of preganglionic and postganglionic sympathetic pathways.
• Describe the neurotransmitters used in these synapses.
• Explain exceptions in sympathetic pathways for the adrenal gland and skin.

Overview of Sympathetic Innervation

• Abdominal Pelvic Organs:
  • Liver: Releases glucose into the blood.
  • Gallbladder: Relaxes.
  • GI Tract (Stomach, Duodenum, Jejunum, Ileum, Colon): Decreases peristalsis and increases blood flow.
  • Penis: Causes ejaculation.

Origin of Sympathetic Pathways

• Preaortic Ganglia:
  • Celiac Ganglion: Innervates proximal GI tract and liver.
  • Superior Mesenteric Ganglion: Innervates small intestines.
  • Inferior Mesenteric Ganglion: Innervates the colon.
  • Inferior Hypogastric Plexus: Innervates pelvic organs like the penis.

Pathway Patterns

• More proximal GI tract is innervated by higher pre-aortic ganglia.
• More distal GI tract and pelvic organs are innervated by lower pre-aortic ganglia.

Central Nervous System Origin

• Sympathetics originate between T1 and L2 spinal cord levels.
• Preganglionic neurons are in the lateral horn of the spinal cord.

Pathway Details

• Greater Splanchnic Nerve: T5-T9, synapses in celiac ganglion.
• Lesser Splanchnic Nerve: T10-T11, synapses in superior mesenteric ganglion.

Exceptions

• Adrenal Gland:
  • Lacks postganglionic neurons.
  • Preganglionic neurons synapse directly in the adrenal medulla.
  • Adrenal medulla secretes epinephrine and norepinephrine into the bloodstream.
• Sweat Glands:
  • Use acetylcholine as postganglionic neurotransmitter.

Neurotransmitters

• Synapses:
  • Preganglionic to Postganglionic: Acetylcholine.
  • Postganglionic to Target Organs: Epinephrine (or norepinephrine).

Summary

1. Sympathetics originate from T1-L2 spinal cord levels.
2. They travel to pre-aortic ganglia via splanchnic nerves.
3. They follow arteries to target organs.
4. Postganglionic synapses use epinephrine at adrenergic receptors.

Review

• Sympathetic nervous system functions as a two-neuron chain.
• Important exceptions include the adrenal gland and sweat glands.
• Understanding of pathways and neurotransmitter uses is crucial for pharmacological interventions.