Comparisons between Sympathetic and Parasympathetic Nerves

• Sympathetic system has a broader distribution, innervating effectors throughout the body

  • Sympathetic fibers show greater ramification.

  • Sympathetic preganglionic fibers may traverse through many ganglia before terminiating at its post-ganglionic cell.

    • Synaptic terminal arborization results in a single preganglionic fiber terminating on many post-ganglionic cells.

  • This anatomical characteristic is the basis for the diffuse nature of sympathic response in the human and other species.

• Parasympathetic system is relatively limited

  • The parasympathetic system has its terminal ganglia near the end-organ.

  • Sometimes there is but a one-to-one ratio relationship between pre-and post-ganglionic fibers. The ratio between preganglionic vagal fibers and ganglion cells may be much higher, e.g. 1:8000 for Auerbach's plexus.

Sympathetic Nervous System

• Anatomical Outline

• "Parasympathetic Nervous System Anatomy"

  Attribution: Peter:  Parasympathetic Nervous System Anatomy Anatomy Zone https://www.youtube.com/watch?v=PiM_pLLrVto AZ AnatomyZone Youtube Channel:  https://www.youtube.com/channel/UCR9m1bxGaw3Ubrap34U-yDA

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    Parasympathetic System: Cranial-Sacral Outflow

    • Cell bodies of preganglionic fibers: found in intermediolateral columns of the spinal cord (first thoracic to second or third lumbar segments

    • Preganglionic fiber axons synapse with sympathetic ganglionic neurons which lie outside the cerebrospinal axis.

    • Sympathetic ganglia are found at three sites:

      • Paravertebral

      • Prevertebral

      • Terminal

    •  Paraverebral ganglia: 22 interconnected pairs on either sides of the vertebral column. (para: Gr: at the side of along side)

      • Myelinated preganglionic fibers (white rami: thoracolumbar outflow only) leave through the anterior spinal roots.

      • Postganglionic fibers (gray rami) runs back to spinal nerves for distribution to:

        • Blood vessesls of the skin

        • Blood vessels of skeletal muscle

        • Sweat glands

        • Pilomotor muscles

    •   Prevertebral Ganglia: abdominal and pelvic location, comprised of:

      • Celiac ganglia

      • Superior mesenteric ganglia

      • Aorticorenal and inferior mesenteric ganglia

    •   Terminal Ganglia: few, residing near the innervated organ, including

      • Ganglia associated with the urinary bladder and rectum

      • Cervical ganglia (neck): three ganglia (chain) mediating vasomotor, secretory, pupillodilatory and pilomotor responses of the head and neck)

      • All postganglionic fibers arise from cell bodies located within these ganglia; the preganglionic fibers come from upper thoracic segments: No sympathetic preganglionic fibers come from above the first thoracic level

    • Adrenal medulla is similar to sympathetic ganglia.

      • Difference:

        • Epinephrine is released (post-ganglionic sympathetic fibers release norepinephrine)

      • Chromaffin cells are innerved by preganglionic fibers that release acetylcholine.