Cranial Nerves VII - XII and Autonomic Nervous System Notes

Cranial Nerves VII - XII

Learning Objectives

• Modalities of Cranial Nerves: List the modalities carried by each of the cranial nerves.
• Identify Cranial Nerves: Recognize each of the cranial nerves on the brainstem.
• Pathways and Innervation: Describe the pathway and innervation of each cranial nerve.
• Functions of ANS: Explain the functions of the autonomic nervous system (ANS).
• Preganglionic & Postganglionic Pathways: Describe the preganglionic and postganglionic pathways for both the sympathetic and parasympathetic nervous systems.

Cranial Nerves Overview

• Cranial Nerve VII (Facial Nerve)

  • Course: Passes through the internal acoustic meatus.
  • Functions:
  • Motor: Muscles of facial expression.
  • Special Sensory: Taste from the anterior 2/3 of the tongue.
  • Sensory: General sensation from the ear.
  • Parasympathetic: Innervates salivary and lacrimal glands.

• Cranial Nerve VIII (Vestibulocochlear Nerve)

  • Course: Also travels through the internal acoustic meatus.
  • Functions:
  • Vestibular Apparatus: Balance information.
  • Cochlea: Sound detection.
  • Pathway: Relays information in the medial geniculate nucleus (MGN) of thalamus, projecting to primary auditory cortex.
  • Process: Sound waves collected → vibrations → cochlear fluid movement → hair cells activated → electrical signal generated.

• Cranial Nerve IX (Glossopharyngeal Nerve)

  • Course: Enters through the jugular foramen.
  • Functions:
  • Motor: Muscles of the pharynx.
  • Special Sensory: Taste from the posterior 1/3 of the tongue.
  • Sensory: General sensation from the posterior 1/3 of the tongue.
  • Parasympathetic: Innervates the parotid gland.

• Cranial Nerve X (Vagus Nerve)

  • Course: Also exits through the jugular foramen.
  • Functions:
  • Motor: Muscles of the palate, pharynx, and larynx.
  • Special Sensory: Taste from the epiglottis.
  • Sensory: General sensation for the neck, thorax, abdomen, and pelvis.
  • Parasympathetic: Extends to thoracic and abdominal organs.

• Cranial Nerve XI (Spinal Accessory Nerve)

  • Course: Enters through foramen magnum, exits via the jugular foramen.
  • Functions:
  • Motor: Sternocleidomastoid and trapezius muscles, aiding head movement.

• Cranial Nerve XII (Hypoglossal Nerve)

  • Course: Passes through the hypoglossal canal.
  • Functions:
  • Motor: Supplies intrinsic and extrinsic muscles of the tongue for speech and swallowing.

Autonomic Nervous System (ANS)

• Functions: Regulates the internal environment, maintaining homeostasis.
• Components: Includes pathways to the viscera, glands, smooth and cardiac muscle.
• Divisions:
  • Sympathetic Nervous System (SNS):
  • Type: Thoracolumbar.
  • Function: Activates the fight or flight response.
  • Parasympathetic Nervous System (PNS):
  • Type: Craniosacral.
  • Function: Promotes rest and digest activities.

Autonomic Pathways

• Structure: Comprised of a two-neuron chain:
  • Preganglionic Neuron: Located in spinal cord or brainstem.
  • Postganglionic Neuron: Located within a peripheral ganglion.
• Sympathetic Pathways:
  • Preganglionic Fibers: Short.
  • Postganglionic Fibers: Long.
• Parasympathetic Pathways:
  • Preganglionic Neurons: Cranial nerves III, VII, IX, X and sacral segments S2 – S4.
  • Postganglionic Neurons: Located in peripheral ganglia (e.g., ciliary, otic, submandibular).

Sympathetic vs. Parasympathetic Pathways

• Sympathetic:
  • Preganglionic Neurons: T1-L2, found in the lateral horn.
  • Ganglia: Sympathetic truck and prevertebral ganglia (e.g. celiac, superior mesenteric).
  • Postganglionic Neurons: Located in chain ganglia.
• Parasympathetic:
  • Preganglionic: Originates from specific cranial nerve nuclei and sacral spinal cord.
  • Postganglionic: Located in peripheral ganglia like the ciliary, submandibular, and otic ganglia.

Functions of Ganglia in Autonomic Control

• Ciliary Ganglion: Controls pupil constriction via CN III.
• Pterygopalatine Ganglion: Innervates the lacrimal gland via CN VII.
• Submandibular Ganglion: Related to submandibular and sublingual glands via CN VII and IX.
• Otic Ganglion: Serves the parotid gland via CN IX.
• Terminal Ganglia: Target various organs throughout the body, including the heart, lungs, digestive tract, and pelvic organs.

References

• Grant’s Atlas of Anatomy, 8th edition
• Grant’s Dissector, 16th edition
• Gray’s Anatomy: the anatomical basis of clinical practice
• Hollinshead’s Textbook of Anatomy, 5th edition
• Moore’s Clinically Oriented Anatomy, 7th edition
• Netter’s Atlas of Human Anatomy, 5th edition