The Twelve Cranial Nerves

• Review Quiz 5 is due on Friday, 3/21, at 11:59 p.m.
• Case Study 4 is due Friday, 3/21, and covers lessons L14-L17
• Review Quiz 6 was posted on Friday, 3/21, due Thursday, 3/27 at 11:59 p.m.
• The lecture focuses on the twelve cranial nerves

Introduction to Cranial Nerves

• Describes the location, pathways, and responsibilities of all twelve cranial nerves
• Know the origination point for each cranial nerve in the brain
• Describe how each cranial nerve reaches its target organ
• List the responsibilities of each cranial nerve like sensory (somatic, visceral, special) or motor (somatic, branchial, parasympathetic)
• Define major branches of each cranial nerve if applicable
• Cranial nerves are elaborations of the neural and gut tube that improve our ability to eat
• All cranial nerves assist with food capturing/processing or food detection
• Spinal Accessory (CN XI) is an exception
• Cranial nerves are numbered with Roman numerals I-XII
• The name describes target/function or appearance
• Except for CN XI, Cranial nerves originate in the brain
• CN I + II originate in the forebrain
• CN III-X & XII originate in the brainstem
• CN XI originates in the spinal cord

Cell Body Locations

• Motor cell bodies are in the motor nuclei of the brainstem
• Sensory cell bodies reside in named ganglia throughout the head
• Sensory ganglia include trigeminal, geniculate, vestibular, cochlear, superior and inferior ganglia of glossopharyngeal, and vagus
• Preganglionic parasympathetic cell bodies are located in brainstem nuclei
• Postganglionic parasympathetic ganglia are near the target organ
• These ganglia include ciliary, pterygopalatine, submandibular, otic, and ganglia in the thorax or abdomen for the vagus nerve
• Sympathetic fibers are NOT cranial nerves, but carried by the sympathetic nervous system
• Preganglionic sympathetic cell bodies are in the lateral horn T1-T2
• Postganglionic sympathetic cell bodies are in the superior cervical ganglion

Cranial Nerve Fiber Types

• Fiber types are described as General/Special and Somatic/Visceral
• General/Special fiber types are the same as spinal nerves vs unique to cranial nerves
• Somatic/Visceral fiber types are skin/skeletal muscle innervation vs. smooth muscle, cardiac muscle, or glandular innervation
• Fibers can also be Afferent (sensory) or Efferent (motor)

Cranial Nerve Fiber Types Include

• GSE (somatic motor): III, IV, VI (eye movement), XI (shoulder), XII (tongue movement)
• SVE (branchial motor): V, VII, IX, X (pharyngeal arch nerve innervation to feeding muscles)
• GVE (visceral motor): III, VII, IX, X (parasympathetics for smooth muscle, cardiac muscle, glands)
• GSA (general sensory): V, VII, IX, X (pharyngeal arch nerve innervation for feeding sensation)
• GVA (visceral sensory): IX, X (mucosa, carotid, and aortic baroreceptors/chemoreceptors)
• SSA (special sensory): I (smell), II (vision), VIII (hearing), VII, IX, X (taste)
• Cranial nerves can have multiple fiber types

Cranial Nerve Outlets

• Olfactory nerve (I) has outlets at the Cribriform Plate
• Optic nerve (II) has outlets at the Optic Canal
• Oculomotor (III) and Trochlear (IV) and Abducens (VI), and the Ophthalmic Division of Trigeminal (V.1) nerves have outlets at the Superior Orbital Fissure
• The Maxillary Division of Trigeminal nerve (V.2) has outlets at the Foramen Rotundum
• The Mandibular Division of Trigeminal nerve (V.3) has outlets at the Foramen Ovale
• Facial nerve (VII) and Vestibulocochlear nerve (VIII) have outlets at Internal Acoustic Meatus
• Glossopharyngeal nerve (IX), Vagus nerve (X) and Spinal Accesory nerve (XI) have outlets at the Jugular Foramen
• Hypoglossal nerve (XII) have outlets at the Hypoglossal Canal

Overview of Individual Cranial Nerves

• Olfactory Nerve (CN I): special sense of smell
• Olfactory cells enter the cranium via the cribriform plate
• Olfactory cells join the olfactory bulb and travels to the primary olfactory cortex in the temporal lobe
• Optic Nerve (CN II): special sense providing vision
• Retina > optic nerve > passes through optic canal of sphenoid > optic chiasm > optic tract that ends at the thalamus and occipital lobe
• Occulomotor Nerve (CN III): somatic motor to most extraocular muscles and parasympathetic to pupil sphincter and ciliary muscles
• Originates on the midbrain and passes through the supraorbital fissure to get to the orbit
• Trochlear Nerve (CN IV): somatic motor for the superior oblique muscle
• Originates on the midbrain
• Passes through the supraorbital fissure to get to the orbit
• Trigeminal Nerve (CN V), has three divisions (V.1, V.2, V.3) and is a pharyngeal/branchial arch nerve
• Has branchial motor for the muscles of mastication, tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the diagastric
• Somatic sensory provides general sensation of the face, cornea, mucous membrane of the nose and mouth, meninges, and anterior 2/3 tongue
• Abducens Nerve (CN VI): somatic motor to the lateral rectus muscle
• Originates on the pons
• Passes through the supraorbital fissure to get to the orbit
• Facial Nerve (CN VII): pharyngeal/branchial arch nerve
• Branchial motor controls muscles of facial expression, stylohyoid, the posterior belly of digastric, and stapedius
• It's somatic sensory serves the external auditory canal
• Taste for the anterior 2/3 tongue
• Parasympathetic to lacrimal gland or tears
• Submandibular, sublingual salivary glands, and mucosal glands of the nose and mouth
• Vestibulocochlear Nerve (CN VIII): special sense for hearing and balance
• Nerves from the cochlea and vestibule enter the cranium via the internal acoustic meatus
• Enters between the pons and medulla oblongata
• Glossopharyngeal Nerve (CN IX): pharyngeal/branchial arch nerve
• Branchial motor controls the stylopharyngeus muscle
• The somatic sensory provides to the posterior 1/3 of tongue
• Middle ear, pharynx, carotid body and sinus are viscero-sensory
• Parasympathetics for the parotid gland, and buccal mucosa
• Vagus Nerve (CN X): pharyngeal/branchial arch nerve
• Branchial motor controls pharyngeal, palatal, and laryngeal muscles
• The Somatic sensory extends external ear
• Larynx, pharynx, epiglottis, thoracic and abdominal organs are viscero-sensory
• The taste for the epiglottis is a special sense
• Parasympathetics extend to thyroid glands, thoracic organs, foregut, and midgut
• Spinal Accessory Nerve (CN XI): somatic motor to the trapezius because sternocleidomastoid muscles arise in the spinal cord, and can enter and exit via the foramen magnum and jugular foramen, respectively.
• Hypoglossal Nerve (CN XII): somatic motor controls tongue muscles
• It originates at the medullar oblongata, and exits cranium by the hypoglossal canal

Pharyngeal Arches

• Five arches (although one disappears quickly) form from what used to be gills
• These arches lead to a more elaborate and effective head
• These arches contain branchial or "feeding" nerves
• Complex with many branches and many responsibilities, making it motor and sensory
• Each nerve is associated with an arch
• Structures formed by an arch are typically innervated by that cranial nerve

Pharyngeal Arch Cranial Nerves

• 1st arch is Trigeminal (V)
• Connects to Alisphenoid, Incus, Maxilla, Zygomatic, Squamous part of Temporal, Mandible, malleus and Mekel's Cartilage
• Provides support to Muscles of Mastication/Anterior belly of Digastric/Mylohyoid, Tensor Tympani, Tensor Veli Palatini
• 2nd arch is Facial (VII)
• Connects to Stapes, Styloid Process, Lesser Horns of Hyoid, Upper Rim of Hyoid, and Reichert's Cartilage
• Provides support to the muscles of facial expression/Posterior belly of Digastric/Stylohyoid/Stapedius
• 3rd arch is Glossopharyngeal (IX)
• Connects to Lower Rim and Greater Horns of Hyoid to Stylopharyngeus
• 4th arch is Vagus (X)
• Connects to Epiglottis/Laryngeal Cartilages to Pharyngeal Constrictors/Cricothyroid/Levator Veli Palatini to Thyroid and Parathyroids and Epiglottis
• 6th arch is Vagus (X)
• Connects to Laryngeal Cartilages that connect to Intrinsic Muscles of Larynx

The Divisions of the Trigeminal

• Trigeminal (V) provides motor, sensory and autonomic function
• Muscules of mastication, 'Tensors' of Head and Neck fall under the motor function
• Face, Eye, orbit and cornea, anterior 2/3rds of tongue, Teeth Palate and inner cheeks, Superior Pinna, Dura and Meninges fall under the sensory functions
• Taste, Sympathetics and Parasympathetics lie in the autonomic category
• The autonomic, sensory, and motor functions drive other nerves as well like the oculomotor or Glossopharyngeal

Trigeminal Ophthalmic Division (V.1)

• Sensory only, and associated with a variety of skin, sinus, and structure:
• Skin of forehead, superior eyelids, bridge of nose, cornea (conjunctiva)
• Frontal sinuses (mucus membranes), meninges
• Frontal and lacrimal n., and nasociliary n.
• All enter into the orbit and joint to form the ophthalmic division
• Enter via superior orbital fissure, through to the cavernous sinus
• bodies, and synapses in pons
• Carries parasympathetic with fibers from oculomotor, facial n., sympathetic postganglionic neurons to eye structures, nasal cavity/palate and Oculomotor to ciliary ganglion synapse

Trigeminal Maxillary Division (V.2)

• Sensory only:

• Skin over maxillae, cheek, superior lip, inferior eyelid, nasal cavity, nasopharynx, palate, meninges, maxillary teeth + gums

• Zygomatic and infraorbital n (cheek) runs from orbit to inferior orbital fissure to the nasopalatine; joins posterior superior alveolar n.

• Enters vault via foramen rotundum; bodies synapse in pons

• Carries parasympathetic fibers from facial and sympathetic postganglionic which influence nearby regions with trigeminal ganglion

The Branches and function of the Trigeminal Mandibular Nerve

• Controls somatic sensory

• Innervates the skin of the chin Mandibular Teeth and gums lining up around Mental n (Chin) enters foramen, joins interior alveolar n, buccal (tongue) and auriculartemporal Division leads (CheekTongueEartmj) is to sensory.

• Bodies of sensory neurons which synapses in both within trigeminal ganglionic

• Has Somatic Sensory

• Arises from skin of Chin, Mandibular Mouth lining up, and within temporomandibular, or ear Where Mental N(chin)/Enters mental foramen joins inferior alveolar (teeth),lingual;auricuotemporal:forms an sensory structure,

• Muscular Motor and Neurons will originate

• Vaults in and Exit, Then Separates

• Carries sympathetic, and sympathetic structures which are glangolic

Functions of the Facial Nerve

• The facial (VII nerve) is comprised of primary functions like motor, sensory as well as autonomic functions.
• The motor aspects of the muscles is to control facial expressions and miscellaneous movements of the Stapedius for head orientation.
• It regulates taste for the tongue and controls the cutaneous levels and other sensation like Pterycoid (inner canal).
• It also manages sympathetics which control the pterygoid process/canal.

Branchial Motor of Facial Nerves

• Innervates stapedius, stylohyoid, and posterior belly of digastric muscles
• Originates in the pons
• Exits cranial vault via the internal acoustic meatus
• The branch to stapedius occurs when passing middle ear
• The exits out of the skull via the stylomastoid foramen

Special Sensory of Facial Nerves

• Chorda tympani collects taste sensation over anterior 2/3 of the tongue
• Rides lingual never (Br. of CN V.3 until it reaches to its infratemporal fossa where it splits
• The petotympatic fissure is where joins enters to join back until this process repeats it self

Somatic Sensory of Facial Nerves

• Sensation from external acoustic canal joins facial nerve in petrous portion
• Enters cranial vault via the internal acoustic meatus and synapses in pons
• Preganglionic neurons originate in pons and enters petrous portion at internal acoustic meatus