Anatomy of Cranial Nerves in a Nutshell

Anatomy of Cranial Nerves

Most difficult nerves: III, VII, IX, X

There is interplay with V, and thus must consider it as well.

Somatic afferent component: Always have sensory ganglion

• One branch heads into CNS
• One branch heads out through rami to skin (receptors)

Somatic efferent: works for somatic muscles and those from pharyngeal arches

• Multipolar neuron with soma in ventral horn
• Axon goes out through rami and end on skeletal muscle

Visceral efferent (parasympathetic) component of cranial nerves:

• First neuron is in the CNSà sends preganglionic fibers to ganglion
• Second neuron is in an autonomic ganglionà sends post ganglionic fiber to effector

Sympathetic Visceral Efferent:

• 2 cell chain with ganglion in between
• Preganglionic→ganglion→postganglionic
• Upper Thoracic levels’ (T1-T4) Lateral horns give rise to prenganglionic neuron
• PreGN goes up through chain to Superior cervical ganglion (using eye as example)
• Post GN in SCG travel on blood vessels to their targets
• In example of the eye, post GN will form Carotid Plexus on Internal Carotid→follows ophthalmic artery to the back of the eye
• Post GN goes through Ciliary ganglion→goes through eye to Iris where acts on the Pupil Dilator.
• In every case of sympathetic components- have a similar pathway:
  • Lateral horn of T1-T4
  • Travel in chain to cervical ganglion (could be superior / middle / etc.) where it synapses
  • Post GN follows blood vessels to target as a “plexus” (“carotid plexus” etc.)

CN III: Occulomotor Nerve

• Somatic Efferent: Motor to skeletal muscle
  • Cell body must begin in CNS, final effector is skeletal muscle
  • Occulomotor nucleus: a collection of axons that innervate the extraoccular muscles
  • superior branch

1. 1. • Levator Palplebrae superioris
      • Superior rectus

• • Inferior branch

1. 1. • Medial rectus
      • Inferior rectus

• • • Inferior oblique

• Visceral Efferent: Parasympathetic
  • Goes to smooth muscle

1. 1. • To papillary sphincter
      • To ciliary muscles

1. • In the brains stem, have nucleus close to motor nucleus

1. 1. • Sends axons that course in Occulomotor nerve
      • Goes through superior orbital fissure

• • • Travels in the inferior branch of CN III and heads toward Ciliary ganglion of the eye where it synapses
    • Post GN fibers go to targets after going on to posterior eye

1. • Note: Sympathetic Post GN fibers also go through Ciliary Ganglion but do not synapse.

1. 1. • Their origin is the Superior Cervical Ganglion
      • Post GN fibers traveled on internal carotid as Carotid plexus→end up in Ciliary Ganglion→leave through short ciliary nerves (also containing both parasympathetics and sensory fibers).

1. • Clinical:

1. 1. • Lesion in midbrain as occulomotor nerve ends vs lesion in either superior / inferior root
      • Each has different symptoms, thus pathways of fibers are relevant to diagnosis.

• • • Lesion at root:
      1. Get “third nerve palsy” – have complete ptosis, can’t lift upper eye lid (no innervation to levator palpebrae superioris)
      2. Sympathetics are unaffected- have not come in yet

CN V1: Ophthalmic Division of the Trigeminal Nerve

Somatic Sensory:

• Pain, touch, temperature- similar to path in spinal nerve
• Semilunar ganglion (aka Trigeminal ganglion) houses soma for sensory neuron
• V1 passes through superior orbital fissure and branches
  • One branch:

1. 1. • Frontal nerve: Supraorbital / supratrochlear branches supply skin of forehead, scalp, upper eye lid, conjunctiva, cornea
      • Lacrimal nerve: supplies skin in region of lateral orbit / eye

1. • Nasociliary branch:

1. 1. • Gives off long ciliaries: go to the globe of the eye- sclera, cornea
      • Posterior ethmoid: to ethmoid air cells (sinuses)

• • • Anterior Ethmoid: To other air cells. External nasal branch to skin of dorsum of the nose.

• • • Sends Sensory Root to the Ciliary Ganglion as another pathway to the globe

CN V2: Maxillary Division of the Trigeminal Nerve

Somatic Sensory:

• Ganglion housing soma for sensory neuron is still in the Semilunar Ganglion (houses cell bodies for all three branches of trigeminal sensory neurons)
• V2 goes through foramen rotundum and gives branches
  • Zygomatic

1. 1. • Zygomaticotemporal
      • Zygomaticofacial

• • • Both go to skin of temple / face

1. • Infraorbital:

• • • Travels in infraorbital canal→exits infraorbital foramen
    • Branches
      1. External nasal- lateral nose
      2. Inferior palpebral- lower eye lid
      3. Superior labial- upper lip
      4. Also supplies skin of cheek
    • Posterior Superior Alveolar

1. 1. 1. 1. Gives branches to the upper teeth
         2. Upper teeth also have infraorbital contribution

1. 1. • Series of Branches (More in Nasal Cavity Lecture)

1. 1. 1. 1. Nasopalatine Is located on the nasal septumà goes through incisive foramen
         2. Nasal branches go to the Nasal Cavity
         3. Greater palatine branch goes through greater palantine foramen to the hard palate
         4. Lesser palatine branch goes through lesser palatine foramen to the soft palate
         5. Pharyngeal branch goes to nasopharynx

• Greater Petrosal nerve is from the Facial Nerve
  • Is Parasympathetic Pre GN fibers
  • Go through pterygoid canal and into pterygopalatine ganglion to synapse
  • The Post GN fibers are distributed along V2 branches:

• • • To the lacrimal gland:
      • Post GN fiber goes along zygomatic branch
      • Travels along zygomaticotemporal branchà joins with Lacrimal branch of V1→ to the lacrimal gland
      • Thus: key point = Lacrimal gland is innervated by CN VII parasympathetics to make tears. It used V1 and V2 to get to target.  Sympathetics do not participate in tears.
    • To mucous membranes of oral / nasal cavity:
      • Post GN travel along the series of branches for the Nasal / Oral cavity to their appropriate destinations
      • These V2 nerves were supplying sensory for these areas, and thus parasympathetics travel with them
      • Important: Sympathetics will travel along with them as branches from the Deep Petrosal Nerve.

CN V3: Mandibular Division of the Trigeminal Nerve

• Somatic Sensory Component
  • V3 goes through Foramen ovale and branches

• • • Auriculotemporal: to the skin on the ear
    • Long Buccal nerve: to the skin of the cheek- skin and mucous membrane.

• • Lingual nerve:
    1. Supplies the anterior 2/3 tongue (not taste)
    2. Supplies the sublingual fossa (floor of oral cavity

• • Inferior alveolar nerve:
    • Mandibular canal→ supplies lower teeth
    • Exits as mental nerve through mental foramen→ supplies skin of lower lip, chin, jaw

• Motor component to skeletal muscles from first pharyngeal arch:
  • Motor root is near / deep to the Semilunar ganglion
  • Goes through foramen ovale as well and branches
  • Supplies:

1. 1. • Muscles of mastication (temporalis, masseter, medial / lateral pterygoid)
      • Nerve to mylohyoid goes to mylohyoid muscle and the anterior belly of digastric

• • • Supplies Tensor tympani and Tensor palatini in middle ear

• • Clinical: may have impingement on either motor or sensory component or both.  Possible impingement as go through foramen ovale.
• Note: Taste Fibers travel along the chorda Tympani→ joins with lingual nerve→ travels to the tongue
• Lesser Petrosal nerve:
  • From CN IX comes into the Otic Ganglion
  • Post GN fibers go on to the Auriculotemporal nerve (branch of V3)→ leave to go to the parotid gland.

CN VII: Facial Nerve

• Motor Component to Skeletal muscle from the second pharyngeal arch
  • Motor nucleus in the brain stem sends axons that end in skeletal muscle
  • Facial nerve enters through internal Auditory meatus
  • Travel through Facial canal and exits through stylomastoid foramen
  • While in facial canal: supplies the Stapedius in the middle ear
  • When exit canal: branches

1. 1. • Supplies posterior belly of digastric
      • Stylohyoid

• • • While in Parotid- branches:
      1. Temporal
      2. Zygomatic
      3. Buccal
      4. Mandibular
      5. Cervical

• Visceral efferent (Parasympathetic)
  • Has 2 ganglion associated with it

1. 1. • Pterygopalatine Galgion: Effectors = Lacrimal gland, mucous glands of nasal / oral cavity
      • Submandibular Ganglion: Effectors = submandibular gland, sublingual gland

1. • Pterygopalatine Gangion:

1. 1. • Pre GN Travels with facial nerve through internal auditory meatus
      • Forms greater petrosal nerve→ goes through pterygoid canal and ends in Pterygopalatine ganglion where it synapses

• • • Post GN are distributed with V2 and V1

• • • Deep Petrosal nerve contains sympathetic Post GN → originated in Superior Cervical Ganglion
      1. Joins with parasympathetics to form the Nerve of the Pterygoid canal
      2. Goes through the canal and into Pterygopalatine Ganglion (though sympathetics just pass through)

1. • Submandibular Ganglion:

• • • Pre GN travel from a different nucleus through the internal auditory meatus
    • Travel through facial canal and then branches:
      1. Chorda Tympani
         1. Goes to Submandibular ganglion attached to lingual nerve of V3
         2. Here, it synapses and sends post GN to the submandibular and sublingual glands
    • Note: Chorda Tympani meets lingual nerve (still containing pre GN) before synapsing in the submandibular ganglion

• Sensory:
  • Very small somatic sensory distribution to the skin of the ear
  • Also has taste component (from anterior 2/3 of tongue)
  • Both “senses” have soma in the Geniculate Ganglion

1. 1. • Located at the Bend of the Facial Nerve
      • Fibers for Taste also use the Chorda Tympani as they travel to the tongue

CN IX: Glossopharyngeal Nerve

• Motor component to Skeletal muscle from the third pharyngeal arch
  • Cell bodies in brain sends axons through CN IXà exits through jugular foramen
  • Supplies the Stylopharyngeus muscle
• Visceral Efferent – Parasympathetic
  • Single effector: Parotid Gland
  • Uses the Otic Ganglion as point of synapse
  • Parasympathetic Pre GN in brain→ through Jugular foramen→ follow along the tympanic nerve
  • Lesser Petrosal nerve comes off of tympanic nerve

1. 1. 1. Travels to the Otic Ganglion where it synapses
      2. Post GN then travel on the Auriculotemporal branch of V3→ leave to the Parotid Gland.

• Sensory Components: (somatic, visceral, and Taste) uses 2 ganglia
  • Superior Glossopharyngeal (Petrosal) Ganglion
  • Inferior Glossopharyngeal (Petrosal) Ganglion
  • These are almost on top of each other, little difference seen clinically.
  • Somatic / Visceral supply

• • • Auditory Tube
    • Middle ear via Tympanic nerve
      1. Mucous membrane of middle ear
      2. Internal surface of tympanic membrane

• • Naso / Oropharynx via Tonsilar Nerve

• • to Carotid Body and Sinus
  • to sensory of Posterior 1/3 of tongue
  • Pharyngeal portion to superior portion of laryngopharyns

1. 1. • Taste From posterior 1/3 of the tongue

CN X: The Vagus Nerve

• Motor Component to Skeletal Muscle derived from Fourth / Sixth Pharyngeal Arches
  • Are muscles of the Soft Palate, Pharynx, Larynx
  • Motor Neurons go into Vagus and through Jugular Foramen (a collar like structure)

• • • Pharyngeal branch
      1. To soft palate
      2. To pharyngeal wall
  • Superior laryngeal external branch to cricothyroid muscle

• • Recurrent laryngeal branch to other laryngeal muscles

• Visceral Efferent component– Parasympathetic
  • Uses terminal Ganglion as synapse point
  • Goes to mucous glands lining the Palate, Pharynx, Larynx
  • Goes to smooth muscle / cardiac muscle and organs of thorax and abdomen.
  • Parasympathetic Pre GN: Synapse in Ganglion that are in the wall of the soft palate, pharynx, larynxà Post GN are very short Terminal Ganglia.
  • Superior Cardiac branches to the heart
  • Inferior Cardiac branches to the heart
  • Remainder goes to the gut
• Sensory:
  • All sensory information use 2 ganglia to house cell bodies:

1. 1. • Superior Jugular (Vagal) Ganglion
      • Inferior Jugular (Vagal) Ganglion

• • • We treat these as unified in function

1. • Auricular branch:

1. 1. • Sensory for external surface of tympanic
      • Skin around external auditory meatus

1. • Superior laryngeal branch carries sensory to mucous membrane of larynx above vocal folds
   • Recurrent laryngeal branch carries sensory to mucous membrane of larynx below vocal folds
   • Superior cardiac: has sensory information from the heart, lungs.
   • Also gains sensory from viscera
   • Taste: in area of the epiglottis.

Important Ganglion:

• CN III: Occulomotor
  • Sensory Ganglion: None
  • Parasympathetic Ganglion: Ciliary Ganglion- supplies papillary sphincter and ciliary muscle.
• CN V1,V2,V3: Trigeminal
  • Sensory Ganglion: Semilunar (Trigeminal) Ganglion
  • Parasympathetic: None
• CN VII: Facial
  • Sensory Gagnlion: Geniculate Ganglion
  • Parasympathetic

1. 1. • Pterygopalatine Ganglion- lacrimal gland, mucous glands of oral / nasa cavity
      • Submandibular Ganglion- submandibular and sublingual glands

• CN IX: Glossopharyngeal
  • Sensory:

1. 1. • Superior Petrosal
      • Inferior Petrosal

• 1. Parasympathetic: Otic Ganglion- Parotid gland
• CN X: Vagus
  • Sensory

1. 1. • Superior Jugular
      • Inferior Jugular

1. 1. 1. 1. Parasympathetic: Terminal Ganglion in walls of tissues / organs