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CRANIAL NERVES Like spinal nerves cranial nerves are bundles of

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CRANIAL NERVES Like spinal nerves cranial nerves are bundles of Powered By Docstoc
					                                                              CRANIAL NERVES

Like spinal nerves, cranial nerves are bundles of sensory or motor fibers that innervate muscles or glands; carry impulses from sensory receptors,
or show a combination of these fiber types. They are called cranial nerves because they emerge through foramina or fissures of the cranium and
are covered by tubular sheaths derived from the cranial meninges. There are 12 pairs of cranial nerves. Their names reflect their general
distribution or function.

Cranial nerves carry one or more of the following five main functional components

*Thieme P.66- Topographic organization of cranial nerves

MOTOR FIBERS

    1) Motor fibers to voluntary (striated) muscle
           a) Somatic motor (general somatic efferent)- axons innervate striated muscle NOT derived from pharyngeal arches such as ocular
               muscles, tongue, sternocleidomastoid, trapezius
           b) Branchial motor (special visceral efferent)- axons innervate striated muscle such as muscle of mastication/chewing and derived
               from pharyngeal arches such as face, palate, pharynx and larynx

    2) Motor fibers involved in innervating involuntary (smooth) muscles or gland
          a) Visceral motor (General visceral efferent)- axons that constitute the cranial outflow of the parasympathetic division of the
               autonomic system (ANS), presynaptic (preganglionic) fibers that emerge from the brain synapse outside the central nervous
               system (CNS) in a parasympathetic ganglion, postsynaptic ganglion (post ganglionic) fibers continue to innervate smooth
               muscles and glands (sphincter papillae, lacrimal gland)

SENSORY FIBERS

    3) Fibers conveying sensation from the viscera (general visceral afferent)- fibers conveying information from the carotid body and sinus,
       pharynx, larynx, trachea, bronchi, lungs, heart and GI tract
    4) Fibers transmitting general sensation such as touch, pressure, heat, cold etc- from the skin and mucous membranes and include
       general sensory (general somatic afferent )fibers mainly carried by CN 5 (Trigeminal) but also by CN 7 (Facial), CN 9
       (Glossopharyngeal), and CN 10 (Vagus)
    5) Fibers transmitting unique sensations- include special sensory fibers conveying taste and smell (special visceral afferent fibers) and
       those those serving special senses of vision, hearing, and balance (special somatic afferent fiber)
A characteristic feature of cranial nerves is that their sensory and motor fibers enter and exit brainstem at the SAME sites. This differs from the
spinal nerves, in which the sensory fibers enter the spinal cord through the dorsal roots while the motor fibers leave the spinal cord through the
ventral roots.

From Dr. Bivins:
Motor- no 2nd order neuron, neuromuscular junction ONLY, synapse with muscle
Sensory- 1st and 2nd order neuron, synapse with 2nd order neuron
Nerve- bundle of neurons (comprised each of axon, soma, dendrites)
Nucleus- compilation of neuron bodies of the nerve
Brainstem- midbrain, pons, medulla
Nucleus- yellow highlighted!

*TELENCEPHALON (FOREBRAIN)

OLFACTORY NERVE (CN I)
*FYI:
-The first TWO cranial nerves, Olfactory and Optic nerves, are NOT peripheral nerves in the true sense but rather extensions of the brain, ie: they
are CNS pathways that are covered by meninges and contain cell types occurring exclusively in the CNS (oligodendrocytes and microglial cells)
-Olfactory nerve consists of 20 fiber bundles, Bipolar sensory neuron
-Is the ONLY cranial nerve that goes into the forebrain
-Sheathed by meninges

Nucleus (Nerve cell body) location:
Olfactory epithelium (olfactory cells)- Olfactory bulb (Forebrain)
P.1129 Moore

Function of Branches:
Sensory: Smell from nasal mucosa of roof of each nasal cavity and superior side of nasal septum and superior concha

Neuronal Order:
1st order afferent neuron- Olfactory epithelium of nasal cavity: GANGLION?
1st order neuron axons pass from nasal cavity  cribiform plate of ethmoid bone  anterior cranial fossa  synapse with mitral cells (2nd order
neuron) in olfactory bulb

2nd order afferent neuron - Olfactory bulb: NUCLEUS
2nd order neuron axons pass through olfactory tract  ending in the cerebral cortex of the prepiriform area, amygdala, or neighboring areas
Foramen Exit:
Foramina in cribiform plate of ethmoid bone

Structures near the nucleus:
Posterior to frontal sinus

What travels with this nerve:
Nothing (anterior and posterior ethmoid arteries)

What doesn’t work if the nerve or structures nearby are dysfunctional:

Fracture of cribiform plate
    a) Anosmia- loss of smell
    b) Cerebrospinal fluid rhinorrhea

Tumor and/or abscess (pus) in frontal lobe of brain or tumor of meninges (meningioma) in the anterior cranial fossa  compression of olfactory
bulb or tract
    a) Anosmia- loss of smell

If all nerve bundles on one side are torn
     a) Complete loss of smell will occur on that side

Lesions in the temporal lobe of the cerebral hemisphere  irritating the lateral olfactory area (deep to the uncus)
    a) Olfactory hallucinations- false percepetions of smell
    b) Temporal lobe epilepsy or “uncinate fits”- imaginary disagreeable odors and involuntary movements of

Injuries to the cribiform plate may damage the meningeal covering of the olfactory fibers, resulting in olfactory disturbances and cerebrospinal
fluid leakage from nose (runny nose after head trauma). There is an associated risk of ascending bacterial infection causing meningitis.
DIENCEPHALON (FOREBRAIN)

OPTIC NERVE (CN II)

*FYI:
-Not a true nerve but an extension of the diencephalon
-Sheathed by meninges
-Optic nerve develops in a completely different manner than other cranial nerves, the structures involved in receiving and transmitting optic
stimuli develop as evaginations of the diencephalon.
-Optic nerves are paired, anterior extensions of the forebrain (diencephalon) and are, therefore, actually CNS fiber tracts formed by axons of
retinal ganglion cells. Cell bodies located in the retina
-The optic nerve extends through the optic canal from the orbit in the middle cranial fossa. The other cranial nerves enter the orbit through the
superior orbital fissure
-Optic nerve passes from the eyeball through the optic canal into the middle cranial fossa . Many but NOT all, retinal ganglion axons cross the
midline to the contralateral side of the brain in the optic chiasm. The optic tract extends from the optic chiasm to the lateral geniculate body.
-Start in the retina of the eye and work their way back via the optic tract and geniculate bodies of the thalamus. Go through the temporal and
parietal lobes and end in the occipital lobe.

Nucleus (Nerve cell body) location: *1 sensory nucleus
Retina (Ganglion cells)- forebrain

Function of Branches:
Sensory: Vision from retina

Neuronal Order:
1st order neuron: Retina (Ganglion Cells)
2nd order neuron: Lateral Geniculate body of the diencephalon

Foramen Exit:
Optic canal of sphenoid bone

Structures near the nucleus:
Runs near the olfactory tract

What travels with this nerve:
Extensions of the cranial meninges, subarachnoid space (filled with CSF), and olfactory tract
What doesn’t work if the nerve or structures nearby are dysfunctional:
Direct trauma to orbit or eyeball; fracture involving optic canal
    a) Loss of pupillary constriction

Pressure on optic pathway; laceration or intracerebral clot in the temporal, parietal or occipital lobes of the brain
    a) Visual field defects

Because the optic nerves are actually CNS tracts, the myelin sheath that surrounds the sensory fibers from the point at which the fibers penetrate
the sclera is formed by oligodendrocytes rather than by Schwann cells, as in other cranial and spinal nerves. Consequently, the optic nerves are
susceptible to the effects of demyelinating diseases of the CNS, such as multiple sclerosis (MS), which usually do NOT affect other nerves of the
PNS

Optic Neuritis
-lesions of the optic nerve that cause diminution of visual acuity, with or without changes in peripheral fields
-can be caused by inflammatory, degenerative, demyelination, or toxic disorders



MESENCEPHALON (MIDBRAIN)

OCULOMOTOR NERVE (CNIII)

*FYI:
-Cranial nerves of the extraocular muscles: Oculomotor nerve (CN III), Trochlear nerve (CN IV), Abducent nerve (CNVI)
-All 3 nerves that supply the extraocular muscles emerge from the brainstem. The nuclei of the oculomotor nerve and trochlear nerve are located
in the midbrain (mesencepahlon), while the nucleus of the abducent nerve is located in the pons.
-Note: of the 3 nerves, the oculomotor (CNIII) is the ONLY one that contains somatic efferent and visceral efferent and supplies several
extraocular muscles
-The nerve runs anteriorly from the mesencepahlon (midbrain- highest level of brainstem) and enters the orbit through the superior orbital fissure

Nucleus (Nerve cell body) location: *2 motor nuclei
   1) Ocular motor nucleus- somatic efferent (motor)- midbrain
   2) Edinger-Westphal nucleus- visceral efferent (motor)- midbrain
Function of Branches:
   1) Ocular motor nucleus- somatic efferent (motor)
         a) Levator palpebrae superioris- raises superior eye lid
         b) Superior, medial and inferior rectus and inferior oblique- extraocular muscles, turns eyeball medially, inferiorly and superiorly

    2) Edinger-Westphal nucleus- visceral efferent (motor) – its parasympathetic
         a) Pupillary sphincter- intraocular muscle, constricts pupil
         b) Ciliary muscle- intraocular muscle, accommodates lens of eye/helps lens focus

Neuronal Order:
1st order neurons for each nuclei:
     a) 1st order neuron- Ocular motor nucleus (synapse at neuromuscular junction)
     b) 1st order neuron- Edinger-Westphal nucleus (synapse at neuromuscular junction)

Foramen Exit:
Superior orbital fissure

Structures near the nucleus:
Structures near the Ocular motor nucleus and Edinger-Westphal nucleus
    a) Nucleus of the trochlear nerve
    b) Mesencephalic nucleus of the trigeminal nerve

What travels with this nerve:
  a) Trochlear nerve (CN4)
  b) Abducens nerve (CN6)
  *Refer to Thieme P.90 for more structures

What doesn’t work if the nerve or structures nearby are dysfunctional:
Oculomotor palsy, severity depending on the extend of injury. Effects of complete oculomotor palsy (paralysis of the extraocular and intraocular
muscles and levator palpebrae):
   a) Ptosis (dropping of the eyelid)
   b) Downward and lateral gaze
   c) Diplopia (in the absence of complete ptosis)
   d) Mydriasis (pupil dilated due to sphincter papillae paralysis)
   e) Accomodation difficulties (ciliary paralysis- lens cannot focus)
Pressure from herniating uncus on nerve; fracture involving cavernous sinus; aneurysms
    a) Dilated pupil
    b) Ptosis
    c) Eye turns down and out
    d) Papillary reflex on the side of the lesion will be lost

TROCHLEAR NERVE (CN IV)

*FYI:
-The trochlear nerve contains ONLY somatic efferent fibers
-The trochlear nerve emerges from the posterior surface of the brainstem near the midline, courses anteriorly around the cerebral peduncle and
enters the orbit through the superior orbital fissure
-Trochlear nerve is the ONLY cranial nerve in which all the fibers cross to the opposite side
-Consequently, lesions of the nucleus or of nerve fibers very close to the nucleus, before they cross the, result in trochlear nerve palsy on the side
opposite to the lesion (contralateral palsy). A lesion past the site where the nerve crosses the midline leads to trochlear nerve palsy on the same
side as the lesion (ipsilateral palsy)
-The trochlear nerve is the ONLY cranial nerve that emerges from the *dorsal side of the brainstem
-It has the longest intradural course of the 3 extraocular motor nerves

Nucleus (Nerve cell body) location:
Nucleus of Trochlear Nerve - midbrain

Function of Branches:
Nucleus of Trochlear Nerve
   a) Superior oblique muscle- assists in turning eye inferolaterally (or inferiorly when adducted)

Neuronal Order:
1st order neuron- Nucleus of Trochlear Nerve (synapses at neuromuscular junction)

Foramen Exit:
Superior orbital fissure

Structures near the nucleus:
    a) Nucleus of oculomotor nerve
    b) Visceral oculomotor nerve
    c) Mesencephalic nucleus of Trigeminal nerve
What travels with this nerve:
  a) Oculomotor nerve (CN III)
  b) Abducens nerve (CN IV)
  *Refer to Thieme P.90 for structures

What doesn’t work if the nerve or structures nearby are dysfunctional:
The affected eye is higher and is also deviated medially because the inferior oblique (responsible for elevation and abduction) becomes dominant
due to loss of the superior oblique.

Diplopia

Stretching of the nerve during its course around brainstem; fracture of orbit
    a) Inability to look down when eye is adducted


PONS

TRIGEMINAL NERVE (CN V)

*FYI:
-The larger sensory nuclei of the trigeminal nerve are distributed along the brainstem and extend downward into the spinal cord
-The sensory root (portio major) of the trigeminal nerve thus forms the bulk of the fibers, while motor root (portio minor) is formed by fibers
arising from the small motor nucleus in the pons. They supply motor innervations to the muscles of mastication
-Trigeminal nerve is made up of 3 branches: Opthalmic, Maxillary, Mandibullary divisions


Nucleus (Nerve cell body) location:
Sensory
Mesencephalic nucleus of trigeminal nerve- pons
   1) Principal (Pontine) nucleus of trigeminal nerve- pons
   2) Spinal nucleus of trigeminal nerve-pons

Motor
  1) Motor nucleus of trigeminal nerve- pons and medulla
Foramen:
   1) Opthalmic division- Superior orbital fissure (enters orbit)
   2) Maxillary division- Foramen rotundum (enters pterygoid palatine fossa)
   3) Mandibular division- Forament ovale (enters interior surface of base of skull, ONLY division with motor fibers)


Function of Branches:

Sensory (all are found in all 3 branches of the trigeminal nerve)
   1) Mesencephalic nucleus of trigeminal nerve- proprioceptive fibers of muscles of mastication
   2) Principal (Pontine) sensory nucleus- chiefly mediates touch (facial skin, nasopharyngeal mucosa, anterior 2/3 of tongue)
   3) Spinal nucleus- pain and temperature sensation, also touch

Motor (mandibular branch- 3rd branch of trigeminal nerve)
   1) Motor nucleus of trigeminal nerve

                 -muscles of mastication (temporalis, masseter, medial and lateral pterygoid)
                 -oral floor muscles (mylohyoid, anterior belly of the digastric)
                 -middle ear muscle (tensor tympani)
                 -pharyngeal muscle (tensor veli palatine)

Specific functions of the branches of the trigeminal nerve
   1) Opthalmic- sensation from cornea, ksin of forehead, scalp, eyelids, nose and mucosa of nasal cavity and paranasal sinuses
   2) Maxillary- Sensation from skin of face over maxilla, including upper lip, maxillary teeth, mucosa of nose, maxillary sinuses and palate
   3) Mandibular- Sensation from skin and over side of mandible including lower lip, mandibular teeth, temporomandibular joint, mucosa of
        mouth and anterior 2/3 of tongue. Motor to muscles of mastication, mylohyoid, anterior belly of digastrics tensor veli palatine, and tensor
        tympani

Neuronal Order:

Sensory
   1) Mesencephalic nucleus of trigeminal nerve- 1st order neuron- trigeminal ganglion, 2nd order neuron- nucleus
   2) Principal (Pontine) sensory nucleus- 1st order neuron- trigeminal ganglion, 2nd order neuron- nucleus
   3) Spinal nucleus-1st order neuron- trigeminal ganglion, 2nd order neuron- nucleus
Motor
   1) Motor nucleus of trigeminal nerve- 1st order neuron- nucleus, synapses at the neuromuscular junction


Structures near the nucleus:
    a) Nucleus of the solitary tract
    b) Vestibulucochlear nuclei- vestibular part
    c) Vestibulocochlear nuclei- cochlear part
    d) Spinal nucleus of accessory nerve
    e) Nucleus of the hypoglossal nerve
    f) Dorsal vagal nucleus
    g) Nucleus ambiguous
    h) Inferior salivatory nucleus
    i) Superior salivatory nucleus
    j) Facial nucleus
    k) Nucleus of abducens nerve


What travels with this nerve:

Opthalmic division branches:
   a) Lacrimal nerve
   b) Frontal nerve
   c) Nasociliary nerve

Maxillary division branches:
   a) Zygomatic nerve
   b) Ganglionic branches to the pterygopalatin ganglion
   c) Infraorbital nerve

Mandible division branches:
   a) Auriculotermporal nerve
   b) Lingual nerve
   c) Inferior alveolar nerve
   d) Buccal nerve
        “Visceral afferent pathway”
             Gustatory fibers from the facial nerve (chorda tympani) travel by the lingual nerve (branch of CNV3) to supply the anterior 2/3 of
             The tongue

        “Visceral efferent pathway”
               The visceral efferent fibers of some cranial nerves adhere to branches of sub branches of the trigeminal nerve, by which they
               travel to their destination:

                 a) Lacrimal nerve (branch of CNV1) conveys parasympathetic fibers from the facial nerve along the zygomatic nerve (branch of
                    CNV2) to the lacrimal gland
                 b) Auriculotermporal nerve (branch of CNV3) conveys parasympathetic fibers from the glossopharyngeal nerve to the parotid
                    gland
                 c) Lingual nerve (branch of CNV3) conveys parasympathetic fibers from the facial nerve along the chorda tympani to the
                    submandibular and sublingual gland.


What doesn’t work if the nerve or structures nearby are dysfunctional:

Sensory disturbances and defecits may arise in various conditions:
   a) Sensory loss due to traumatic nerve lesions
   b) Herpes Zoster ophtalmicus (involvement of the territory of the 1st division of the trigeminal nerve, including the skin and/or the eye, by the
       varicella zoster virus); herpes zoster of the face
   c) Afferent fibers of the trigeminal nerve (like the facial nerve) are involved in the corneal reflex

Injury to terminal branches (particularly CNV2) in roof of maxillary sinus; pathological processes affecting trigeminal ganglion:
Loss of pain and touch sensations; paraesthesia; masseter and temporalis muscles do not contract; deviation of mandible to side of lesion when
mouth is opened
ABDUCENT NERVE (CN VI)

*FYI:
-Abducent nerve contains ONLY somatic efferent fibers
-The nerve follows a long extradural path before entering the orbit through the superior orbital fissure

Nucleus (Nerve cell body) location:
Nucleus of abducent nerve (pons/midlevel brainstem)

Function of Branches:
Motor to lateral rectus muscle- turns eye laterally

Neuronal Order:
1st order neuron- Nucleus of abducent nerve (pons)

Synapses at neuromuscular junction of lateral rectus muscle


Foramen Exit:
Superior orbital fissure

Structures near the nucleus:
    a) Fibers of the facial nerve (wraps around the abducent nerve nucleus) – Thieme P.69
    b) Fibers from nucleus of solitary tract
    c) Vestibulocochlear nuclei; vestibular part
    d) Principal (pontine) sensory nucleus of trigeminal nerve

What travels with this nerve:
  a) Oculomotor nerve (CN III)
  b) Trochlear nerve (CN IV)
  *Refer to Thieme P.90 for structures

What doesn’t work if the nerve or structures nearby are dysfunctional:
The affected eye is deviated medially (inability to abduct the eye due to the unopposed action of the medial rectus muscle).

Diplopia (double vision).
FACIAL NERVE (CN VII)

*FYI:
-The facial nerve mainly conveys special visceral efferent (branchiogenic) fibers from the facial nerve nucleus which innervate the striated
muscles of facial expression
-The other visceral efferent (parasympathetic) fibers from the superior salivatory nucleus are grouped with the visceral afferent (gustatory) fibers
from the nucleus of the solitary tract to form the nervus intermedius and aggregate with the visceral efferent fibers from the facial nerve nucleus
-Nervus intermedius- Superior salivatory nucleus and Nucleus of the solitary tract  Nervus intermedius + Facial nucleus  Facial nerve
-Facial nucleus (genu) wraps around the abducens nucleus
-The facial nerve emerges in the cerebeloopontine angle between the pons and olive

Passes through the acoustic meatus into the petrous part of the temporal bone, where it divides into its branches: motor, sensory and
parasympathetic

After passing through internal acoustic meatus to enter the petrous bone it forms the external genu of the facial nerve, which marks the location of
the geniculate ganglion. The bulk of visceral efferent fibers for the muscles of expression pass through the petrous bone and leave it at the
stylomastoid foramen. The facial nerve gives off 3 branches between the geniculate ganglion and stylomastoid foramen: Greater Petrosal nerve,
Stapedial nerve, Chorda tympani.
    a) Greater petrosal nerve- geniculate ganglion  foramen lacerum  pterygopalatine ganglion
    b) Stapiedal nerve- passes muscle of the same name
    c) Chorda tympani- branches from the facial nerve above the stylomastoid foramen, it contains gustatory fibers (taste) as well as
        presynamptic parasympathetic fibers, it runs through the tympanic cavity and petrotympanic fissure and unites with the lingual nerve

From the facial nucleus, the special visceral efferent axons that innervate the muscles of facial expression first loop backward around the abducent
nucleus, where they form the internal genu of the facial nerve. Then they run forward and emerge at the lower border of the pons

The superior salivatory nucleus contains visceromotor, presynaptic parasympathetic neurons. Together with the viscerosensory fibers
(gustatory/taste) fibers from the nucleus of the solitary tract (superior part), they emerge from the pons as the nervus intermedius and then are
bundled with the visceromotor axons from the facial nucleus together to form the facial nerve.

Parotid
The parotid gland is found in the subcutaneous tissue of the face, overlying the mandibular ramus and anterior and inferior to the external ear. The
gland occupies the parotid fascial space, an area posterior to the mandibular ramus, anterior and inferior to the ear. The gland extends irregularly
from the zygomatic arch to the angle of the mandible. This gland is effectively palpated bilaterally. Start anterior to each ear and move to the
cheek area and then inferior to the angle of the mandible. The facial nerve and its branches pass through the parotid gland, as does the external
carotid artery.
Nucleus (Nerve cell body) location:
Motor
   1) Facial Nerve Nucleus (special visceral motor)
   2) Superior Salivatory Nucleus (visceral motor/parasympathetic)

Sensory
   1) Nucleus of the Solitary Tract (viscerosensory)



Function of Branches:

Motor
   1) Facial Nerve Nucleus- muscles of facial expression, stylohyoid, posterior belly of digastrics, stapedius
   2) Superior Salivatory Nucleus (parasympathetic)- lacrimal gland, small glands of the nasal mucosa and of the hard and soft palate,
      submandibular gland, sublingual gland, small salivary glands on the dorsum of the tongue

Sensory
   1) Nucleus of the Solitary Tract
        a) Special visceral afferent- central fibers of pseudounipolar ganglion cells from the geniculate ganglion synapse in the nucleus of the
            solitary tract. The peripheral processes of these neurons form the chorda tympani (gustatory/sense of taste from the anterior 2/3 of
            the tongue)
        b) Somatic afferent neurons- some sensory fibers that supply the auricle, skin of the auditory canal, and the outer surface of the
            tympanic membrane travel by way of the facial nerve and the geniculate ganglion to the trigeminal sensory nuclei. Their precise
            course is unknown.


Neuronal Order:
   1) Facial nerve nucleus- 1st order neuron located here, synapses at neuromuscular junction
   2) Superior salivatory nucleus- 1st order neuron located here, synapses at neuromuscular junction
   3) Nucleus of solitary tract- 1st order neuron in geniculate ganglion, 2nd order neuron synapses at nucleus of solitary tract

Foramen Exit:
   1) Facial nerve nucleus fibers- Stylomastoid foramen to base of skull
   2) Superior salivatory fibers and Nucleus of solitary tract fibers- Petrotympanic fissure to base of skull
Structures near the nucleus:
Facial nucleus
    a) Nucleus of abducent nerve
    b) Vestibulocochlear nuclei, vestibular part
    c) Spinal nucleus of trigeminal nerve

Superior salivatory nucleus
   a) Vestibulocochlear nuclei, vestibular part
   b) Spinal nucleus of trigeminal nerve

Nucleus of solitary tract fibers
   a) Nucleus of hypoglossal nerve
   b) Dorsal vagal nucleus
   c) Nucleus ambiguus


What travels with this nerve:

The facial nerve, accompanied by the vestibulocochlear nerve, passes through the internal acoustic meatus to enter the petrous bone.

Chorda Tympani (Branch of Facial Nerve) runs with the Lingual nerve (Mandibular division of Trigeminal nerve)

Thieme P.81

What doesn’t work if the nerve or structures nearby are dysfunctional:

*Lesion of the facial nerve near its origin (geniculate ganglion- lesion of PNS)
a) Accompanied by motor loss, taste and autonomic functions. The motor paralysis of facial muscles involves superior and inferior parts of the
face on the ipsilateral side

*Lesion of the facial nerve (lesion of CNS)
a) Results in paralysis of muscles in the inferior face on the contralateral side; consequently forehead wrinkling is not visibly impaired because it is
innervated bilaterally. Lesions between the geniculate ganglion and origin of chorda tympaniproduce the same effects as that resulting from injury
near the ganglion, except that lacrimal secretion is NOT affected.

Bells Palsy
The principal signs and symptoms are different depending upon the exact site of the lesion in the course o the facial nerve through the bone.

Laceration or contusion in parotid region
   a) Paralysis of facial muscles; eye remains open; angle of mouth droops; forehead does NOT wrinkle

Fracture of the temporal bone
    a) As above, plus associated involvement of cochlear nerve and chorda tympani; dry cornea; loss of taste on anterior 2/3 of tongue

Intracranial hematoma (stroke)
    a) Forehead wrinkles because of bilateral innervations of the frontalis muscle; otherwise paralysis of contralateral facial muscles



MEDULLA OBLONGOTA

VESTIBULOCOCHLEAR NERVE (CN VIII)

*FYI:

*Sensory ONLY

Vestibular cochlear nerve emerges from the junction of the pons and medulla and enters the internal acoustic meatus, here it separates into
vestibular and cochlear nerves.
    1) Vestibular nerve- equilibrium, composed of central processes of bipolar neurons in the vestibular ganglion, the peripheral processes extend
        to the maculae of the utricle and saccule (position of head) and to ampullae of the semicircular ducts (sensitive to rotations acceleration)
    2) Cochlear nerve- concerned with hearing, it is composed of the central processes of bipolar neurons in the spinal ganglion, the peripheral
        processes of the neurons extend to the spiral organ

The vestibulocochlear nerve is a sensory nerve that consists anatomically of 2 components:
    1) Vestibular root- transmits impulses FROM the vestibular apparatus
    2) Cochlear root- transmits impulses FROM the auditory apparatus
The roots are surrounded by a common connective tissue sheath. They pass from the inner ear through the internal acoustic meatus to the
cerebellopontine angle, where they enter the brain
Vestibular ganglion (sensory)
-contains bipolar ganglion cells whose central processes pass TO the 4 vestibular nuclei on the floor of the rhomboid fossa of the medulla
oblongata
-their peripheral processes begin at the sensory cells of the semicircular canals, saccule, and utricle

Spiral ganglion (Cochlear, sensory)
-contains bipolar ganglion cells whose central processes pass to the 2 cochlear nuclei, which are lateral to the vestibular nuclei in the rhomboid
fossa of the medulla oblongata
-their peripheral processes begin at the hair cells of the organ of corti

Nucleus (Nerve cell body) location:
Vestibular nuclei (4)- Floor of rhomboid fossa of the medulla oblongata
   1) Superior vestibular nucleus
   2) Medial vestibular nucleus
   3) Lateral vestibular nucleus
   4) Inferior vestibular nucleus

Cochlear nuclei (2)- Rhomboid fossa of medulla oblongata, lateral to vestibular nuclei
   1) Anterior cochlear nucleus
   2) Posterior cochlear nucleus

Function of Branches:
Vestibular
   a) Vestibular sensation from semicircular ducts, utricle and saccule related to position and movement of head

Cochlear
   a) Hearing from spinal organ

Neuronal Order:
Vestibular:
-1st order neuron- Vestibular ganglion
-2nd order neuron- Vestibular nuclei (4)

Cochlear:
-1st order neuron- Cochlear (spiral) ganglion
-2nd order neuron- Cochlear nuclei (2)
Foramen Exit:
Internal acoustic meatus

Structures near the nucleus:

Vestibular nuclei (4)
   a) Facial nucleus
   b) Spinal nucleus
   c) Abducent nucleus
   d) Spinal nucleus of trigeminal tract
   e) Nucleus of Solitary tract
   f) Principal pontine (sensory nucleus) of trigeminal nerve

Cochlear nuclei (2)
   a) Superior salivatory nucleus
   b) Inferior salivatory nucleus
   c)
What travels with this nerve:

    1) Facial Nerve (CN VII)- motor root and intermediate nerve

What doesn’t work if the nerve or structures nearby are dysfunctional:

Every thorough physical examination should include a rapid assessment of both nerve components (hearing and balance tests). A lesion of the
vestibular root leads to dizziness, while a lesion to the cochlear root leads to hearing loss (ranging to deafness)

Tumor of the nerve (acoustic neuroma)
   a) Progressive unilateral hearing loss tinnitus (noises in the ear)

Acoustic neuroma (vestibular schwannomas)
-benign tumors of the cerebellopontine angle arising from the Schwann cells of the vestibular root of CN8
-as they grow they compress and displace the adjacent structures and cause slowly progressive hearing loss and gait ataxia. Large tumors can
impair the egress of CSF from the 4th ventricle, causing hydrocephalus and symptomatic intracranial hypertension (vomiting, impairment of
consciousness)
•   GLOSSOPHARYNGEAL NERVE (IX)- Mixed nerve (Thieme pg 84-85)

•   Contains motor fibers (special visceral and parasympathetic fibers) and sensory fibers (somatic and special and general visceral)

Where is its nucleus?

Motor (visceral): Nucleus ambiguous

Motor (parasympathetic): Inferior salivatory nucleus

Sensory (Somatic): Intracranial superior ganglion or extracranial inferior ganglion of the glossopharyngeal nerve to spinal nucleus
of the trigeminal nerve

Sensory (Special Visceral): Inferior ganglion and terminate in the superior solitary tract

Sensory (General Visceral): inferior ganglion to the nucleus of the inferior solitary tract

•   What is function of all branches?

Motor (special visceral): constrictor muscle of pharynx and stylopharyngeus

Motor (parasympathetic): parotid gland and to the buccal and labial glands

Sensory (Somatic): posterior two thirds of the tongue, soft palate, pharyngeal mucosa, and tonsils (gag reflex)

-Mucosa of tympanic cavity and Eustachian tube (tympanic plexus)

-Skin of external ear, auditory canal, and internal surface of the tympanic membrane (tympanic plexus)

-Sensory (Special visceral): Posterior two thirds of the tongue (special sense- gustatory fibers)

-Sensory (General visceral): Chemoreceptors in carotid body and Pressure receptors in carotid sinus

•   What is the neuronal order?
    Motor (special visceral): 1st order neuron in nucleus ambiguus and 2nd order neuron in ganglion of Glossopharyngeal nerve

    Motor (parasympathetic): 1st order neuron – inferior salivatory nucleus (parasympathetic presynaptic fibers) to 2nd order
    neuron -otic ganglion

    Sensory (Somatic): 1st order -neuron superior ganglion or inferior ganglion to 2nd order neuron - spinal nucleus of trigeminal
    nerve

    Somatic (Special visceral): 1st order neuron – inferior ganglion to 2nd order neuron- superior nucleus of solitary tract

    Somatic (General visceral): 1st order neuron- inferior ganglion to 2nd order neuron- inferior nucleus of solitary tract



•   Through which foramen does it exit?

    Jugular foramen

•   What is near its nucleus? (Look at Thieme, pg- 69 pic. B)

For nucleus ambiguus- spinal nucleus of accessory nerve, inferior salivatory nucleus, and spinal nucleus of trigeminal nerve

For inferior salivatory nucleus- superior salivatory nucleus, nucleus ambiguus and spinal nucleus of trigeminal nerve

For spinal nucleus of trigeminal nerve- vestibulococchlear nuclei, nucleus ambiguus, spinal nucleus of accessory nerve, superior
and inferior salivatory nucleus and nucleus of solitary tract

For solitary tract- nucleus ambiguus, spinal nucleus of trigeminal nerve, nucleus of hypoglossal nerve and Dorsal vagal nucleus

•   What travels with it?

      vagus nerve and accessory nerve

•   What doesn’t work if the nerve or the structures nearby are dysfunctional?
       Lesion at Brainstem or deep laceration of the neck- Loss of taste in posterior third of the tounge, loss of sensation on affected
       side of soft palate

       Structures nearby that get affected- lesions of vagus nerve and accessory nerve ( FYI: glossopharyngeal nerve, vagus nerve
       and accessory nerve runs together and emerge jointly from jugular foramen)



Vagus (X) nerve- Mixed Nerve

   •   Where is its nucleus?

       Special visceral efferent: Nucleus Ambiguus
       General visceral efferent: parasympathetic- Dorsal vagal nucleus
       Somatic afferent:
       Superior ganglion of the vagus nerve
       Special visceral afferent: inferior ganglion
       General visceral afferent: inferior ganglion


   •   What is function of all branches?

       Special visceral efferent: Motor to constrictor muscles of pharynx (except stylopharyngeus), intrinsic muscles of larynx, muscles of
       palate (except tensor veli palatine), and striated muscles in superior two thirds of esophagus
       General visceral efferent: parasympathetic innvervation to smooth muscle of trachea, bronchi, digestive tract, and cardiac muscle of
       the heart.
       Somatic afferent:
       Sensation from auricle, external acoustic meatus, and dura mater of posterior cranial fossa
       Special visceral afferent: Taste from epiglottis and palate
       General visceral afferent: visceral sensation from base of the tounge, pharynx, larynx, trachea, bronchi, heart, esophagus, stomach
       and intestine to left colic flexure
•     What is the neuronal order?

      General visceral efferent: 1st order: dorsal vagal nucleus
      To visceral layer of thorax and abdomen

     Through which foramen does it exit?

        Jugular Foramen



      Accessory (XI) nerve

     Visceral and Somatic Motor Nerve

•     Where is its nucleus?

      Cranial root: caudal part of nucleus ambiguous
      Spinal root: Spinal nucleus of accessory nerve in the Anterior horn of the spinal cord at C2-C5/C6 levels.

•     What is function of all branches?

      Cranial root:
      (Special visceral efferent fibers) Joins with Vagus (X) N. and runs with laryngeal recurrent N. and innervates all the laryngeal muscles
      except cricothyroid.
      Spinal root: (Somatic efferent fibers) external branches of Accessory N. supplies trapezius and sternocleidomastoid

•     What is the neuronal order?

       General visceral efferent: 1st order: dorsal vagal nucleus

      To visceral layer of thorax and abdomen

     Through which foramen does it exit?
       Jugular Foramen

•     What is near its nucleus?

      Cranial root: Dorsal Vagal nucleus, nucleus of hypoglossal nerve, spinal nucleus of trigeminal nerve, nucleus of slolitary tract

      Spinal root: Nucleus of solitary tract and spinal nucleus of trigeminal nerve

     What travels with it?
      Lateral to hypoglossal N and spinal cord. Cranial root joins vagus nerve and runs with laryngeal recurrent nerve

•     What doesn’t work if the nerve or the structures nearby are dysfunctional?

      Laceration of neck will produce paralysis of SCM and superior fibers of Trapezius causing drooping of shoulder
Cranial Nerve XII – Hypoglossal (Note = this is in a little different format because Dr. Bivins did this and it was copied right off his slide)




    •   Nucleus: in floor of rhomboid fossa (medulla); creates hypoglossal trigone
    •   Function: purely motor nerve that supplies all muscles of the tongue (except palatoglossus, by CN X)
    •   Neuronal order: 1° neuron in hypoglossal nucleus, fibers go directly to tongue muscles
    •   Foramen: hypoglossal canal
    •   Near its nucleus: dorsal vagal nucleus; nucleus of solitary tract; nucleus ambiguus
    •   Travels with: lateral to vagus nerve
    •   Dysfunction: ipsilateral tongue deviation with nuclear lesion; contralateral deviation with supranuclear lesion
GLOSSOPHARYNGEAL NERVE (CN IX)

VAGUS NERVE (CN X)

ACCESSORY NERVE (CN XI)

HYPOGLOSSAL NERVE (XII)



*TEMPLATE FOR NERVES

*FYI:

Nucleus (Nerve cell body) location:

Function of Branches:

Neuronal Order:

Foramen Exit:

Structures near the nucleus:

What travels with this nerve:

What doesn’t work if the nerve or structures nearby are dysfunctional:

				
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