M01.02.023 Parasympathetic Innervation

The parasympathetic nervous system (PNS) is part of the autonomic nervous system, responsible for involuntary body functions. Its main function in the head and neck is linked to the “rest and digest” response, promoting homeostasis. This guide reviews the parasympathetic innervation of the head and neck, focusing on the anatomical structures, course, and clinical relevance.

Overview of Parasympathetic Supply

Parasympathetic fibers originate in the central nervous system (CNS) and are transmitted to the head and neck via four cranial nerves. These include:

• Oculomotor nerve (CN III)
• Facial nerve (CN VII)
• Glossopharyngeal nerve (CN IX)
• Vagus nerve (CN X)

These nerves synapse in ganglia located near the target organs, from which post-ganglionic fibers innervate structures such as glands and muscles.

Key Parasympathetic Ganglia in the Head and Neck:

• Ciliary ganglion
• Pterygopalatine ganglion
• Submandibular ganglion
• Otic ganglion

Each ganglion serves a distinct anatomical region and contributes to different physiological functions.

Key Parasympathetic Ganglia and Their Functions

1. Ciliary Ganglion

• Location: Bony orbit, anterior to the superior orbital fissure.
• Pre-ganglionic fibers: Arise from the Edinger-Westphal nucleus, carried by the oculomotor nerve.
• Post-ganglionic fibers: Travel via short ciliary nerves to the eye.
• Target organs:
  • Sphincter pupillae (pupil constriction)
  • Ciliary muscles (accommodation for near vision)
• Note: Sympathetic fibers from the internal carotid plexus and sensory fibers from the nasociliary nerve pass through without synapsing.

2. Pterygopalatine Ganglion

• Location: Pterygopalatine fossa, near the maxilla.
• Pre-ganglionic fibers: Arise from the superior salivatory nucleus, carried by the greater petrosal nerve.
• Post-ganglionic fibers: Hitchhike on branches of the maxillary nerve.
• Target organs:
  • Lacrimal gland
  • Nasal cavity, nasopharynx, and palate
• Note: Sympathetic and sensory fibers pass through without synapsing.

3. Submandibular Ganglion

• Location: Inferior to the lingual nerve.
• Pre-ganglionic fibers: Arise from the superior salivatory nucleus, carried by the chorda tympani.
• Post-ganglionic fibers: Travel directly to the submandibular and sublingual glands.
• Target organs: Submandibular and sublingual salivary glands.
• Note: Sympathetic fibers from the facial artery plexus also pass through.

4. Otic Ganglion

• Location: Infratemporal fossa, near the mandibular nerve.
• Pre-ganglionic fibers: Arise from the inferior salivatory nucleus, carried by the lesser petrosal nerve.
• Post-ganglionic fibers: Hitchhike along the auriculotemporal nerve.
• Target organs: Parotid gland.
• Note: Sympathetic fibers from the superior cervical chain also pass through.

Clinical Relevance: Adie’s Pupil

• Adie’s Pupil occurs when the ciliary ganglion is damaged, leading to the loss of sphincter pupillae muscle innervation. This results in a pupil that remains dilated and does not constrict in response to light.
• Etiology: Often caused by viral or bacterial infections.

Summary Table: Parasympathetic Nervous System Pathways

Points to Remember

• The parasympathetic nervous system regulates functions like pupil constriction, gland secretion, and digestive processes.
• The four parasympathetic ganglia in the head (ciliary, pterygopalatine, submandibular, otic) have distinct functions based on the cranial nerves they are associated with.
• Damage to the parasympathetic pathways, such as in Adie’s pupil, can lead to significant clinical symptoms like pupil dilation and impaired accommodation.
• Post-ganglionic fibers typically travel to target organs to facilitate their function, such as gland secretion or muscle contraction.