Cervical Plexus and Cranial Nerves I, II, IV, VI, VIII, XI, XII

Abducent nerve -CN VI

Course and Distribution Somatic Motor, General Somatic Efferent • Anterior surface of hindbrain, at the pontomedullary junction • Passes forward with internal carotid artery through Cavernous sinus • Enters orbit through superior orbital fissure to lateral rectus muscle. Primary function: - Motor to Lateral rectus (abduction) Origin: - Abducens nucleus Path through Skull: - Superior orbital fissures of sphenoid Cavernous Sinus • Surrounds the sella turcica • Receives blood from the superior and inferior ophthalmic veins • Drains into the superior and inferior petrosal sinuses • In the sinus: - ICA, CN III, IV, V1, V2, VI Lesion • Diplopia - Double vision • Medial (internal) strabismus

Cervical plexus

Includes an anterior and posterior ramus of spinal nerves C1-C4. *Some times may include C5 depends on individual or text. C5 is always part of brachial plexus. Ventral rami located deep to the sternocleidomastoid Runes next to CN XII for a short distance. Innervates: -Neck -Thoracic Cavity -Diaphragmatic muscles

Phrenic Nerve

Mix (sensory and motor neurons to diaphragm for contraction ) Formed from branches of ventral rami of C3, C4 and C5 Runs along anterior scalene muscle, deep to the carotid sheet.

Ansa cervicalis

Motor Loop of nerve fibers -Superior root -Inferior root Found within the carotid sheath that surrounds the carotid artery). Formed from branches of ventral rami of C1, C2, and C3 Travels with CN XII Innervates: 1. Omohyoid 2. Sternohyoid 3. Sternothyroid

Erb's point

Point where four branches of the cervical plexus emerges from posterior to sternocleidomastoid 1. Lessor occipital nerve 2. Great auricular nerve 3. Transverse cervical nerve 4. Supraclavicular nerve. Injuries during birth or fall on shoulder will remove sensation.

Damage above C3, C4 and C5

Quadriplegic and NOT able to breath on it's own.

Damage bellow C3, C4 and C5

Quadriplegic but able to breath on it's own.

Lessor occipital nerve

Sensory Formed from branches of ventral rami C2 Innervates: Skin of neck and scalp posterior to ear.

Transverse cervical nerve

Sensory Formed from branches of ventral rami of C2 and C3 Innervates: Lateral and anterior parts of neck.

Great auricular nerve

Sensory Formed from branches of ventral rami of C2 and C3 Innervates: Skin of inferior parotid region, era, mastoid area.

supraclavicular nerve

Sensory Formed from branches of ventral rami of C3 and C4 Innervates: Skin over clavicle and shoulder.

Cervical Plexus Branches (6 branches)

Sensory 1. Lessor occipital nerve 2. Great auricular nerve 3. Transverse cervical nerve 4. Supraclavicular nerve Motor 1. Ansa cervicalis Mix (sensory and motor neurons) 1. Phrenic Nerve Gp-last

Trochlear nerve (CN IV) - Motor

Somatic Motor, General Somatic Efferent Course and Distribution • Most slender nerve • Posterior surface of midbrain • Middle cranial fossa • Lateral cavernous sinus • Superior orbital fissure • Superior oblique Cavernous Sinus • Surrounds the sella turcica • Receives blood from the superior and inferior ophthalmic veins • Drains into the superior and inferior petrosal sinuses • In the sinus: - ICA, CN III, IV, V1, V2, VI Primary function: - Motor to superior oblique - Depression, abduction and medial rotation (down and out) Origin: - Trochlear nucleus Path through Skull: - Superior orbital fissure of sphenoid Lesion: • Diplopia= Double vision • Weakness looking down with adducted eye • Trouble going down stairs • Head tilts away from lesioned side

Hypoglossal Nerves (CN XII)

Somatic Motor, General Somatic Efferent • Anterior surface of the medulla as rootlets • Rootlets join together to form CN XII • Travels through the hypoglossal canal • Enters the root of the tongue superior to the hyoid bone and lateral to the hyoglossus. Primary function: • Motor to all intrinsic and extrinsic muscles of the tongue, except palatoglossus. • Controls shape and movement of the tongue Origin: • Hypoglossal nucleus The path through Skull: • Hypoglossal canals of the occipital bone Lesion: • Abnormal tongue protrusion - Supranuclear lesions cause contralateral paralysis - Peripheral lesions cause ipsilateral paralysis • Unilateral injury, the tongue deviates to the side of the lesion on protrusion • 'Lick your wounds' • Difficulty saying 'la-la-la'

Optic nerve (CN II)- Sensory

Special Sensory, Special Somatic Afferent Rods and cones to ganglion cells of the retina Primary function: - Vision Origin: - Ganglion cells of the retina • Bipolar neurons The path through Skull: (from most outer) • Optic canals of the sphenoid • Optic chiasm (some nerve fibers cross to another side) • Optic tract (medial (nasal) fibers opposite side, lateral (temporal) fibers same side) • Lateral geniculate body (thalamus) • The visual cortex of cerebrum (occipital lobe) Pupillary Light Reflex • Miosis - pupil constriction • Mydriasis - pupil dilation • Consensual reflex, both sides constrict together Sensory: CN II Motor: CN III, parasympathetic and Sympathetic nervous system (constrict and dilates pupil respectively). Accommodation Reflex of the Lens • Focusing near/distant objects Sensory: CN II responsible Motor: CN III, parasympathetic Lesion (3) 1. Anopsia, visual field deficits - Lesions of the optic nerve • Blindness - Lesions of the optic chiasm • Missing outer half of both visual fields - Lesions of the optic tract • Visual field loss on the same side of both eyes 2. Loss of pupillary light reflex with III 3. Only cranial nerve to be affected by MS

Vestibulocochlear nerve (CN VIII) -Sensory

Special Sensory, Special Somatic Afferent • Two sets of sensory fibers, vestibular and cochlear Primary function: Vestibular branch • Balance and equilibrium Cochlear branch • Hearing Origin: - Sensory cells in the vestibule and cochlea, via the vestibular and cochlear ganglia • Bipolar neurons Path through Skull: Internal acoustic meatus with facial nerve, in the posterior cranial fossa (temporal bone). Enter anterior surface of brain, at the pontomedullary junction to Associated Nuclei: - To vestibular and cochlear nuclei Clinical notes: Acoustic Neuroma • Benign tumor of Schwann cells • Cause hearing loss and gait ataxia • Can block CSF drainage of 4th ventricle leading to hydrocephaly-> Leading to vomiting, loss of consciousness and death Lesion: • Hearing loss, tinnitus. • Loss of balance, vertigo/dizziness

Olfactory nerve (CN I)- Sensory

Special Sensory, Special Viceral Afferent Chemoreceptors Olfactory nerve cells (first-order) pass through the cribriform plate. Synapse takes place at the Olfactory Bulb. The olfactory bulb connects to olfactory tract which is then connected to the olfactory area of the cerebral cortex in the temporal lobe. Primary function: Olfaction Origen: Olfactory receptor cells in nasal mucosa. Bipolar neurons. Path Through Skull: Olfactory foramina of the cribriform plate of the ethmoid bone. Lesion: Anosmia- Decrease or lack of olfaction. Trauma: Torn dura mater near cribriform plate can cause CNF to leak (will result in a runny nose) or tear olfactory neurons.

The only mixed nerve (B) with no parasympathetic innervation. SSMMBMBSBBMM

Trigeminal

Accessory Nerves- CN XI

• Cranial root: Anterior surface of the medulla • Runs laterally in the posterior cranial fossa and joins the spinal root • Spinal root: Anterior gray horn of the upper five segments of spinal cord • Ascends along the spinal cord • Enters skull through the foramen magnum • Turns laterally to join the cranial root • Two unite, leave skull thru jugular foramen. Roots separate. - Cranial joins the vagus (pharyngeal plexus) - Spinal to SCM and trapezius Cranial Root Branchial Motor, Special Visceral Efferent Primary function: - Motor to muscles of soft palate, pharynx, and intrinsic muscles of the larynx (via vagus, pharyngeal plexus) Origin: - Nucleus ambiguus The path through Skull: - Jugular foramina between occipital and temporal bones Spinal Root Branchial Motor, Special Visceral Efferent Primary function: - Motor to sternocleidomastoid and trapezius Origin: - Spinal accessory nucleus, spinal cord segments C1-C5 The path through Skull: - Jugular foramina between occipital and temporal bones and foramen magnum *Many anatomists do not consider the spinal root of the spinal accessory nerve to be a cranial nerve. Lesions: • Leads to partial paralysis of trapezius, shoulder droop - Drooping of the shoulder on the affected side - Also innervated by C3-C5 • Leads to complete (flaccid) paralysis of sternocleidomastoid - Weakness turning chin to the opposite side • Torticollis (Wry neck) - Unilateral injury, difficulty turning head to the opposite side - Bilateral injury, difficulty holding head up - Only innervated by CN XI.

Cavernous Sinus

• Surrounds the sella turcica • Receives blood from the superior and inferior ophthalmic veins • Drains into the superior and inferior petrosal sinuses • In the sinus: - ICA, CN III, IV, V1, V2, VI