CRANIAL NERVES I, II, IV, VI, VIII, XI, XII
Modalities • SSS: Special Sensory: Special senses derived from ectoderm: Sight, sound, balance. • SVS: Special Visceral Sensory: Special senses derived from endoderm: Taste • SVM: Special Visceral Motor: Muscles derived from pharyngeal arches.
Modalities • GVS: General Visceral Sensory: General sensation from viscera. • GVM: General Visceral Motor: To smooth muscles of gut tract. Autonomic motor • GSS: General Somatic Sensory: General senses from ectoderm (skin). • GSM: General Somatic Motor: Skeletal muscles.
Generalizations • Cranial nerves have same basic structure as spinal nerves. Dorsal root and ventral root. Dorsal root ganglion. • Motor components of cranial nerves begin within brain within motor nuclei. Comparable to spinal cord anterior horns. • Cell bodies of sensory fibers are located in dorsal root (cranial) ganglia.
Generalizations • Special sensory cranial nerves: Are actually tracts. No motor nuclei and no sensory ganglia. • Motor cranial nerves: Begin in cranial motor nuclei. Have no sensory roots and no sensory root ganglia. • Mixed cranial nerves: Have both cranial motor nuclei and sensory ganglia. Sensory ganglia are usually given specific names.
Generalizations • For each cranial nerve know: Modality (modalities). Function (functions). Sensory areas and/or muscles innervated. Foramen through which it passes. Specific ganglion (if applicable). Specific information included in this slide presentation.
Olfactory Nerve (CN I) • Olfactory nerve fibers pass from: Olfactory receptor cells. Through: Cribriform plate. To: Olfactory bulbs. • Modality: SVS
Optic Nerve (CN II) • Begins in ganglionic layer of retina (not rods and cones). • Exits orbit through optic canal. • 50% decussation in optic chiasma: Near pituitary gland. Near internal carotid. • Modality: SSS
Oculomotor Nerve (CN III) • Supplies four of the six extrinsic muscles of the eye. • Has a parasympathetic component. • Will be discussed in a group with other parasympathetic nerves.
Trochlear Nerve (CN IV) • Enters orbit through superior orbital fissure. • Innervates superior oblique muscle of the eye. • Modality: GSM. • Only crossed cranial nerve. • Only cranial nerve that emerges dorsally.
Abducens Nerve (CN VI) • Enters orbit through superior orbital fissure. • Lies on medial aspect of lateral rectus muscle. • Innervates lateral rectus muscle of the eye. • Modality: GSM.
Vestibulocochlear Nerve (CN VIII) • Leaves cranial cavity via internal acoustic meatus: Accompanied by facial nerve. • Modality: SSS • Auditory (cochlear) component: Cell bodies in spiral ganglion of cochlea. Function: Hearing.
Vestibulocochlear Nerve (CN VIII) • Vestibular component: Cell bodies in vestibular ganglion. From receptors for balance and equilibrium. Function: Balance.
Spinal Accessory Nerve (CN XI) • Arises from C1-3 (4). • Single trunk enters cranial cavity through foramen magnum. • Temporarily joins cranial root. Cranial roots leave with vagus nerve.
Spinal Accessory Nerve (CN XI) • Spinal accessory trunk exits cranial cavity via jugular foramen. • Supplies: Sternocleidomastoid and trapezius. • Modality: SVM.
Hypoglossal Nerve (CN XII) • Exits cranial cavity via hypoglossal foramen. • Descends anteriorly in neck between internal carotid and internal jugular. • In neck gives rise to superior root of ansa cervicalis and a nerve to thyrohyoid muscle. • Supplies extrinsic and intrinsic muscles of tongue. • Modality: GSM.