Lecture 9 - Cranial Nerve Innervation

Are cranial nerves generally considered part of the CNS or PNS?

Peripheral nervous system (PNS).

What is the autonomic nervous system responsible for?

Involuntary functions of the body.

What are the three major parts of the brain?

• Cerebral cortex

• Cerebellum

• Brainstem.

What functions are associated with the cerebral cortex?

Sensory integration, thinking, speaking, personality, and higher cognitive functions; contains four lobes.

What functions are associated with the cerebellum?

Coordination, balance, and fine motor skills.

What functions are associated with the brainstem?

Basic automatic bodily functions necessary for survival.

What are the three components of the brainstem?

• Midbrain

• Pons

• Medulla.

What functions are associated with the midbrain?

Motor control, eye movements, and hearing; it is the uppermost part of the brainstem.

What functions are associated with the pons?

Face and eye movements and balance; it is the middle portion of the brainstem

What functions are associated with the medulla?

Regulation of breathing, heart rate, and blood pressure; it is the lowest portion of the brainstem.

What does ipsilateral mean?

On the same side of the body.

What does contralateral mean?

On the opposite side of the body.

What is an upper motor neuron?

A neuron that originates in the brain (cerebral cortex or brainstem).

What is a lower motor neuron?

A neuron that originates in the spinal cord and innervates skeletal muscles.

What is an interneuron?

A neuron within the brain or spinal cord that connects neurons to each other and does not directly innervate muscles.

How do upper motor neurons connect to lower motor neurons?

Through interneurons.

Which cranial nerves provide sensory innervation to ocular structures?

CN II (optic) and CN V (trigeminal).

Which cranial nerves provide motor innervation to ocular structures?

CN III (oculomotor)
CN IV (trochlear)
CN VI (abducens)
CN VII (facial).

What is the function of afferent pathways?

Transmit sensory information to the CNS.

Which cranial nerves are involved in ocular afferent pathways?

CN II and CN V.

Which ocular structures provide sensory information via afferent pathways?

Cornea, iris, conjunctiva, and sclera.

What types of sensations are carried from ocular structures?

Primarily pain, but also touch, pressure, and temperature.

What are the three major divisions of the trigeminal nerve?

• Ophthalmic nerve (V1)

• Maxillary nerve (V2)

• Mandibular nerve (V3).

Which nerves form the ophthalmic nerve (V1)?

• Nasociliary nerve

• Frontal nerve

• Lacrimal nerve.

(NFL)

Which branches combine to form the nasociliary nerve?

• Infratrochlear nerve

• Ethmoid nerves (anterior and posterior)

• Long ciliary nerves (medial and lateral)

• Short ciliary nerves (many).

What structures receive sensory innervation from the nasociliary nerve?

Cornea, iris, and nose.

What structures are innervated by the infratrochlear nerve?

Medial canthus, medial eyelids, and skin on the side of the nose.

Where does the infratrochlear nerve enter the orbit?

Below the trochlea and runs along the medial side of the orbit.

What structures are innervated by the ethmoid nerves?

Nasal mucosa, ethmoid sinuses, and skin on the center of the nose.

Where do the ethmoid nerves enter the orbit?

Through foramina within the frontoethmoid suture.

What ocular structures are innervated by the long ciliary nerves?

Cornea, iris, ciliary body, and bulbar conjunctiva

What autonomic fibers do the long ciliary nerves carry?

Efferent sympathetic fibers to the iris dilator muscle and the ciliary muscle.

What structures are innervated by the short ciliary nerves?

Cornea, iris, and ciliary body.

Where do long and short ciliary nerves exit the eye?

They exit the sclera posteriorly.

How many long ciliary nerves are typically present?

Two — one on either side of the globe.

Where do the short posterior ciliary nerves exit the sclera?

In a ring surrounding the optic nerve.

After exiting the sclera, where do the short posterior ciliary nerves travel?

Posteriorly to enter the ciliary ganglion.

Where do the branches of the nasociliary nerve merge before exiting the orbit?

Anterior to the superior orbital fissure (SOF).

Through which structures do nasociliary nerve fibers exit the orbit?

The superior orbital fissure (SOF) and the common tendinous ring (CTR).

(NOA)

Which nerves join to form the frontal nerve?

• Supratrochlear nerve

• Supraorbital nerve.

What structures are innervated by the supratrochlear nerve?

Skin and muscles of the forehead, medial upper eyelid, and conjunctiva.

Through which anatomical structure does the supratrochlear nerve enter the orbit?

The supratrochlear notch or foramen.

What structures are innervated by the supraorbital nerve?

Skin and muscles of the forehead and scalp, and the central upper eyelid and conjunctiva.

Through which anatomical structure does the supraorbital nerve enter the orbit?

The supraorbital notch or foramen.

Where do the supratrochlear and supraorbital nerves join to form the frontal nerve?

After entering the orbit.

Along what part of the orbit does the frontal nerve travel?

Along the superior aspect of the orbit.

Between which structures does the frontal nerve travel within the orbit?

Between the levator palpebrae superioris and the periorbita.

Through which opening does the frontal nerve exit the orbit?

The superior orbital fissure, above the common tendinous ring (CTR).

LOFT

What structures receive sensory innervation from the lacrimal nerve?

• Lacrimal gland

• Lateral upper eyelid and conjunctiva

• Temple

Which autonomic fibers does the lacrimal nerve carry?

Parasympathetic fibers from CN VII responsible for tear production.

Along which part of the orbit does the lacrimal nerve travel?

Along the lateral side of the orbit.

Through which structure does the lacrimal nerve exit the orbit?

The superior orbital fissure above the CTR.

LOFT

Which nerves join to form the ophthalmic nerve (V1) after exiting the orbit?

• Nasociliary nerve

• Frontal nerve

• Lacrimal nerve.

Through which structure does the ophthalmic nerve travel after leaving the orbit?

The lateral wall of the cavernous sinus.

Where does the ophthalmic nerve join the trigeminal ganglion?

Posterior to the cavernous sinus.

Which major branches arise from the maxillary nerve (V2)?

• Infraorbital nerve

• Zygomatic nerve.

Which facial structures receive sensory innervation from the infraorbital nerve?

• Lower eyelid
• Cheek
• Upper lip
• Upper teeth
• Maxillary sinus

Through which structure does the infraorbital nerve enter the maxillary bone?

The infraorbital foramen and canal.

Along which groove does the infraorbital nerve travel?

The infraorbital groove.

Through which structure does the infraorbital nerve exit the orbit?

The inferior orbital fissure (IOF).

Which two branches arise from the zygomatic nerve?

• Zygomaticotemporal nerve

• Zygomaticofacial nerve.

What structures are innervated by the zygomaticotemporal nerve?

The temple and lateral forehead.

What structures are innervated by the zygomaticofacial nerve?

The lateral cheek and lateral lower eyelid.

Through which structure do the zygomatic nerve branches exit the orbit?

The inferior orbital fissure.

Which autonomic fibers are carried by the zygomatic nerve?

Parasympathetic fibers from the pterygopalatine ganglion of CN VII.

Where do the infraorbital and zygomatic nerves join to form the maxillary nerve?

After exiting the orbit through the inferior orbital fissure (IOF).

Between which bones does the maxillary nerve travel after leaving the orbit?

Between the maxilla and the sphenoid bones.

Through which opening does the maxillary nerve enter the skull?

The foramen rotundum in the sphenoid bone.

ROMAX

Which division of the trigeminal nerve is the largest?

The mandibular nerve (V3).

Which types of fibers does the mandibular nerve contain?

Both sensory and motor fibers

What sensory function does the mandibular nerve provide?

Sensory innervation to the lower face.

What motor function does the mandibular nerve provide?

Motor innervation to the muscles of mastication.

Through which opening does the mandibular nerve enter the skull?

The foramen ovale in the sphenoid bone.

OMAN

How do trigeminal sensory fibers travel from the face to the brain?

From face/head structures → through the cavernous sinus (except V3) → trigeminal ganglion.

Where does the trigeminal nerve travel after leaving the trigeminal ganglion?

To the pons, then to various sensory nuclei.

What is the function of efferent pathways?

Transmit information from the CNS to target structures.

Which cranial nerves are responsible for efferent motor innervation of ocular structures?

CN III (oculomotor), CN IV (trochlear), CN VI (abducens), and CN VII (facial).

Which extraocular muscles are innervated by the oculomotor nerve?

• Levator palpebrae superioris
• Superior rectus
• Medial rectus
• Inferior rectus
• Inferior oblique.

Which autonomic targets receive fibers via the oculomotor nerve?

• Iris sphincter (parasymp)
• Ciliary muscle (parasymp)
• Smooth muscles of the eyelid (symp)

Where does the oculomotor nerve originate?

The oculomotor nucleus

Where are the oculomotor nuclei located?

Two nuclei located on each side of the midbrain.

What organization exists within the oculomotor nucleus?

It contains subnuclei for voluntary movement for each associated muscle.

Which oculomotor subnucleus controls both levator palpebrae superioris muscles?

The caudal nucleus.

Which extraocular muscles receive ipsilateral innervation from the oculomotor nucleus?

• Inferior rectus
• Inferior oblique
• Medial rectus.

(inferior division muscles → ipsilateral)

Which extraocular muscle receives contralateral innervation from the oculomotor nucleus?

The superior rectus.

(superior division = SR = contralateral)

What is the Edinger–Westphal nucleus?

An autonomic nucleus located within the oculomotor nucleus.

What type of fibers arise from the Edinger–Westphal nucleus?

Parasympathetic fibers.

Which structures receive parasympathetic innervation from the Edinger–Westphal nucleus?

• Ciliary muscle
• Iris sphincter.

Where do fibers of the oculomotor nerve emerge from the brainstem?

From the anterior aspect of the midbrain.

Which major vascular structure does the oculomotor nerve pass near?

The circle of Willis vessels

Through which structure does the oculomotor nerve enter the cavernous sinus?

The roof of the cavernous sinus, where it travels laterally.

Which fibers join the oculomotor nerve within the cavernous sinus?

Sympathetic fibers from the internal carotid artery (ICA) plexus.

Through which opening does the oculomotor nerve enter the orbit?

The superior orbital fissure (SOF).

Into which two divisions does the oculomotor nerve split in the orbit?

• Superior division
• Inferior division.

Which muscles are innervated by the superior division of CN III?

• Superior rectus
• Levator palpebrae superioris.

Which muscles are innervated by the inferior division of CN III?

• Medial rectus
• Inferior rectus
• Inferior oblique.

Where do parasympathetic fibers from the inferior division of CN III travel?

To the ciliary ganglion.

From which nucleus does the trochlear nerve originate?

The trochlear nucleus.

Where is the trochlear nucleus located?

Below the oculomotor nucleus in the midbrain.

What distinguishes the trochlear nerve anatomically among cranial nerves?

It is the longest and thinnest cranial nerve.