Cranial Nerves

Types of Cranial Nerve Fibers – as in spinal cord, a nerve may have Sensory fibers, Motor fibers, or Both

Motor fibers may be either Autonomic or Somatic

Autonomic fibers may be either Parasympathetic or Sympathetic

autonomic fibers arising from the CNS are pre-ganglionic (CN synapse in cranial nerve ganglia)

parasympathetic arise from sacral spine or brain stem; the latter provides all autonomic fibers for cranial n.

sympathetic arise from thoracic and lumbar spine: not involved in cranial nerves

Somatic fibers innervate striated muscles; arise from brainstem (includes the midbrain, the pons, and the medulla)

mesenchymal origin of muscle corresponds to location of CNS innervation (three possibilities: somatic (tongue), branchial arch derivatives, branchiomeric (larynx and pharynx))

Sensory nerve fibers are associated with a primary sensory (unipolar) neuron in a peripheral ganglion (cranial sensory ganglion)

synapse on specialized nuclei (exceptions are CN I and II ); like spinal nerves except they innervate viscera

Nuclei: make associations between motor and sensory neurons in the brain stem; any one cranial nerve may be associated with more than one nucleus (i.e. Vagus has 3)

Cranial Nerves – different cranial nerves arise from different parts of the brain

forebrain has 2 CN's, brainstem has 10 (Midbrain has 2 CN’s; Pons has 4 CN’s; Medulla has 4 CN’s)

CN III, VII, IX, X carry parasympathetic fibers

Telencephalon – cerebrum

CN I: Olfactory: microscopic; not a distinct nerve, but made up of the axons of chemoreceptors in olfactory epithelium

Sensory, enters through cribiform plate into the olfactory bulb, transmit chemo-reception, smell

Diencephalon

CN II: Optic: visible nerve; formed by axons of retinal ganglion cells (derived from CNS tissue-unique peripheral nerve)

Sensory; exits via optical canal to optic chiasm; photoreception = vision

Midbrain

CN III: Oculomotor: arises from the medial edges of the cerebral peduncles (axon bundle between cortex and brain stem)

Motor; exits via superior orbital fissure, innervates superior, inferior, medial rectus and inferior oblique muscles of the eye as well as levator palpebrae of eyelid
associated with Edinger-Wesphal nucleus via ciliary ganglion to pupilary and ciliary muscles of eyeball

CN IV: Trochlear: slender nerves; only nerve to cross midline or exit dorsally; also arises from the cerebral peduncles

Motor; exits via superior orbital fissure; innervates the superior oblique muscles of the eye.

Pons

CN V: Trigeminal : large nerves; arise from ventral pons; unique mechanosensory route: enters brain at mid pons

Both Sensory and Motor: sensory to face; motor to jaw, exits via superior orbital fissure, foramen rotundum, foramen ovale

trigeminal brain complex:

(1) principal nucleus – mechanosensory

(2) spinal nucleus – pain and heat

(3) mesencephalic nucleus

CN VI: Abducens: arise from medial caudal border of pons and medulla

Motor; exits via Superior orbital fissure; innervates lateral rectus eye muscle

CN VII: Facial: 2 roots = facial nerve proper and nerve intermedius (chorda tympani and greater petrosal nerve); arise lateral to Abducens; facial and superior salvitory nuclei

Both Sensory and Motor: sensory (anterior 2/3 of tongue) motor (somatic to facial muscles; parasympathetic to lacrimal and salivary glands)

CN VIII: Auditory (vestibulo-cochlear): lateral to VII

Sensory, exits via internal acoustic meatus; hearing and balance function

Medulla

CN IX: Glossopharyngeal: caudal to auditory nerves, dorsal to Olive; exits via jugular foramen

Both Sensory and Motor: Sensory (posterior taste and carotid baroreceptors); Parasympathetic info from inferior salvatory nucleus Þ parotid gland / Motor info from nucleus ambiguous Þ pharynx muscles

CN X: Vagus: caudal to IX, dorsal to Olive: exits via Jugular foramen

Both Sensory and Motor: Sensory: info from viscera of thorax, abdomen and sensation from pharynx; Motor: info from nucleus ambiguous Þ muscle of pharynx and larynx; visceral motor info all the way to pelvis

CN XI: Accessory: Cranial portion=rootlets caudal to vagus; Spinal Portion=rostral spinal cord between dorsal and ventral roots

Motor: info from accessory nucleus to tapezius and sternocleidomastoid, exits via Jugular foramen; Motor info from nucleus ambiguou to intrinsic muscles of larynx

CN XII: Hypoglossal: emerges between Olive and Pyramid, caudal to the abducens

Motor: info to intrinsic and extrinsic tongue muscles (exception: palatoglossus via X); exits via the Hypoglossal canal

Summary of Cranial Nerves

Nerve	Origin	Cranial Exit	Cell Bodies	Components	Chief Functions
I: Olfactory		Cribriform plate	Nasal mucosa	SVA	Smell
II: Optic		Optic canal	Ganglion cells of retina	SSA	Vision
III: Oculomotor	Midbrain	Superior orbital fissure	Nucleus CN III (midbrain)	GSE	Eye movements (superior, inferior, and medial recti; levator palpebrae superioris)
			Edinger-Westphal nucleus (midbrain)	GVE	Constricton of pupil (sphincter pupillae m) and accommodation (ciliary m)
IV: Trochlear	Midbrain	Superior orbital fissure	Nucleus CN IV (midbrain)	GSE	Eye movements (superior oblique m)
V: Trigeminal	Pons	Superior orbital fissure; foramen rotundum and foramen ovale	Motor nucleus CN V (pons)	SVE	Muscles of mastication (mylohyoid, anterior belly of digastric, tensor veli palatini, and tensor tympani mm)
			Trigeminal ganglion	GSA	Sensation in head (skin and mucous membranes of face and head)
VI: Abducens	Medulla	Superior orbital fissure	Nucleus CN VI (pons)	GSE	Eye movement (lateral rectus m)
VII: Facial	Medulla	Stylomastoid foramen	Motor nucleus CN VII (pons)	SVE	Muscle of facial expression (posterior belly of digastric, stylohyoid, and stapedius mm)
			Salvitory nucleus (pons)	GVE	Lacrimal and salivary secretion
			Geniculate ganglion	SVA	Taste from anterior two-thirds of tongue and palate
			Geniculate ganglion	GVA	Sensation from palate
			Geniculate ganglion	GSA	Sensation from external acoustic meatus
VIII: Vestibulocochlear	Medulla	Does not leave skull	Vestibular ganglion	SSA	Equilibrium
			Spiral ganglion	SSA	Hearing
IX: Glossopharyngeal	Medulla	Jugular foramen	Nucleus ambiguus (medulla)	SVE	Elevation of pharynx (stylopharyngeus m)
			Dorsal nucleus (medulla)	GVE	Secretion of saliva (parotid gland)
			Inferior ganglion	GVA	Sensation in carotid sinus and body, tongue, and pharynx
			Inferior ganglion	SVA	Taste from posterior one-third of tongue
			Inferior ganglion	GSA	Sensation in external and middle ear
X: Vagus	Medulla	Jugular foramen	Nucleus ambiguus (medulla)	SVE	Muscles of movement of pharynx, larynx, and palate
			Dorsal nucleus (medulla)	GVE	Secretion of saliva (parotid gland)
			Inferior ganglion	GVA	Sensation in pharynx, larynx, and other viscera
			Inferior ganglion	SVA	Taste from root of tongue and epiglottis
			Superior ganglion	GSA	Sensation in external ear and external acoustic meatus
XI: Accessory	Spinal cord	Jugular foramen	Spinal cord (cervical)	SVE	Movement of head and shoulder (sternocleidomastoid and trapezius mm)
XII: Hypoglossal	Medulla	Hypoglossal canal	Nucleus CN XII (medulla)	GSE	Muscles of movement of tongue