Sympathetic Pathways to Skin and Abdominal Organs

Sympathetic pathways to skin and abdominal organs

Overview

• This section describes how preganglionic sympathetic neurons travel from the spinal cord to their targets via the sympathetic trunk and collateral (prevertebral) ganglia.

• Key structural components mentioned: lateral horn, ventral root, dorsal root, dorsal root ganglion, dorsal ramus, ventral ramus, white ramus communicans, sympathetic trunk, trunk ganglion, gray ramus communicans, splanchnic nerves, collateral ganglia (e.g., celiac), and various effectors (skin and abdominal organs).

Anatomical components (as labeled in the diagram)

• Lateral horn (visceral motor zone)

  • Location of preganglionic sympathetic neuron cell bodies.

• Ventral root

  • Carries efferent (motor) fibers from the spinal cord toward spinal nerves.

• Sympathetic trunk

  • A longitudinal ganglionated chain adjacent to the vertebral column.

• Sympathetic trunk ganglion (trunk ganglion)

  • Site where preganglionic sympathetic fibers may synapse.

• Synapse in trunk ganglion at the same level

  • Preganglionic neuron enters the sympathetic trunk via the white ramus and synapses in a ganglion at the same spinal level.

• Dorsal root

  • Carries sensory fibers into the spinal cord.

• Dorsal root ganglion

  • Houses the cell bodies of sensory neurons.

• Dorsal ramus of spinal nerve

  • Supplies the back region.

• Ventral ramus of spinal nerve

  • Supplies the anterior and lateral body walls and limbs.

• Gray ramus communicans

  • Unmyelinated postganglionic fibers that exit the trunk and join spinal nerves to reach target tissues.

• White ramus communicans

  • Myelinated preganglionic fibers that enter the sympathetic trunk from the spinal nerve.

• 2 Synapse in trunk ganglion at a higher or lower level

  • Fibers may ascend or descend within the trunk to synapse in a trunk ganglion at a different level before exiting.

• ③ Pass through sympathetic trunk to synapse in a collateral ganglion anterior to the vertebral column

  • Some preganglionic fibers bypass immediate trunk ganglia and continue to collateral (prevertebral) ganglia (e.g., celiac, superior mesenteric, inferior mesenteric) located anterior to the vertebral column.

• © 2019 Pearson Education, Inc. Modified Figure 14.6

  • Source attribution for the diagram.

Targets and effector tissues

• Arrector pili muscles and sweat glands of skin

  • Sympathetic postganglionic fibers activate arrector pili (piloerection) and stimulate sweat secretion.

• Splanchnic nerve

  • Preganglionic sympathetic fibers travel via splanchnic nerves to collateral ganglia.

• Collateral ganglion (such as the celiac)

  • Prevertebral ganglia located anterior to the vertebral column; sites where preganglionic fibers synapse when traveling via splanchnic nerves.

• Smooth muscle of blood vessels

  • Postganglionic fibers regulate vasoconstriction/dilation in vascular smooth muscle.

• Effectors

  • Tissue targets of sympathetic postganglionic neurons.

• Smooth muscle and glands of abdominal organs (e.g., intestine)

  • Postganglionic fibers from collateral ganglia innervate abdominal viscera, regulating motility, secretion, and blood flow.

Pathways summarized

• Route A: Spinal nerve entry → white ramus communicans → trunk ganglion (same level) → gray ramus communicans → target (skin via dorsal/ventral rami pathways)

  • Target examples: skin structures (arrector pili, sweat glands).

• Route B: Spinal nerve entry → white ramus communicans → trunk ganglion (via ascent or descent to a different level) → exit without synapsing here, continue via gray ramus to specific pathways

  • Often used for distributing to neighboring dermatomes or regions supplied by nearby spinal nerves.

• Route C: Spinal nerve entry → white ramus communicans → pass through trunk → collateral (prevertebral) ganglion via splanchnic nerve → synapse in collateral ganglion (e.g., celiac) → postganglionic fibers travel to abdominal organs (smooth muscle of vessels and glands of intestines)

Functional and clinical relevance

• The sympathetic trunk and collateral ganglia allow a single preganglionic neuron to influence multiple target tissues across different body regions, contributing to coordinated autonomic responses.

• Distribution through gray rami communicans enables postganglionic fibers to reach both cutaneous (skin) targets and visceral targets supplied by spinal nerves.

• Collateral ganglia provide direct innervation to abdominal viscera, enabling control over gut motility, secretion, and blood flow during stress or exercise.

Notes on terminology and connections

• Lateral horn

  • Part of the spinal cord gray matter housing visceral motor neurons.

• White ramus communicans

  • Myelinated pathway carrying preganglionic sympathetic fibers from the spinal nerve to the sympathetic trunk.

• Gray ramus communicans

  • Unmyelinated pathway carrying postganglionic sympathetic fibers from the trunk to the spinal nerve, then distributed via ventral/dorsal rami.

• Dorsal ramus vs ventral ramus

  • Dorsal ramus: posterior body wall and back; Ventral ramus: anterior-lateral body wall and limbs.

• Collateral (prevertebral) ganglia

  • Examples include the celiac ganglion; located anterior to the vertebral column; receive input from splanchnic nerves.

Summary takeaway

• Sympathetic preganglionic neurons originate in the lateral horn and reach the sympathetic trunk via the ventral root and white ramus communicans.

• They may synapse at the same level, ascend/descend to synapse at a different trunk level, or bypass the trunk to synapse in collateral ganglia via splanchnic nerves.

• Postganglionic fibers exit via gray rami to reach skin and abdominal organs, with effector tissues including arrector pili, sweat glands, blood vessel smooth muscle, and intestinal glands and smooth muscle.

Selected references from the diagram

• Arrector pili muscles and sweat glands of skin

• Splanchnic nerve

• Collateral ganglion (such as the celiac)

• Smooth muscle of blood vessels

• Smooth muscle and glands of abdominal organs (e.g., intestine)

• Dorsal root ganglion and dorsal/ventral rami relationships

• White ramus communicans and gray ramus communicans

• Synapse locations: trunk ganglion at same level or different level; collateral ganglion anterior to vertebral column

For exam prep

• Be able to trace a preganglionic sympathetic fiber from a thoracic spinal cord segment to its ultimate target in the abdomen, listing all intermediate structures (lateral horn → ventral root → spinal nerve → white ramus → sympathetic trunk → either trunk ganglion at same/different level or splanchnic nerve to collateral ganglion → postganglionic fiber via gray ramus to the target).

• Recognize and label the roles of white vs gray rami communicantes and the difference between trunk and collateral ganglia.