Chapter 17 Cranial Nerves

The nervous system uses 2 types of cells to process information, ____________ and ___________ cells. Each information type is involved with body structures that are either __________ or ______________. Somatic or visceral structures are further divided based on ________ or ________ fibers.

-general (cells that originate on the surface of the body and process general information through general receptors; e.g. pain, temperature) -special (these cells process special information though functionally committed cells in nervous system with dedicated, specialized receptors; e.g. vision, smell, taste, audition) -somatic (striated skeletal embryonically derived from somites) -visceral (nonstriated muscles concerned with vegetative tasks to relate to internal vital organs involved in respiration, vascular, and digestive systems controlled by the ANS) -afferent (motor) -efferent (sensory) Summary: →General/special cells → used for either somatic/visceral structures → consisting of either efferent/afferent fibers → 7 FUNCTIONAL COMPONENTS of nervous system: a. GSE, GSA, GVE, GVA, SSA, SVE, SVA

CN V Trigeminal

Mixed GSA, SVE principal sensory nerve for head, face, orbit, and cavities (oral, nasal, and orbital) mediates sense of pain, temperature, discriminative touch has small motor component that supplies jaw muscles along with other muscles and controls mastication sensory and motor components together form pathway for jaw-jerk reflex mediates kinesthetic and proprioceptive awareness information, which is responsible for stretch receptor feedback for masticators GSA (general somatic afferent) responsible for cutaneous (touch, pain, and temperature) and proprioceptive (awareness of posture and muscle movement) sensations from the face, head, oral and nasal cavities, sinuses, teeth, anterior 2/3 of tongue, anterior half of the pinna, external auditory meatus, external surface of tympanic membrane, and cortical dura mater sensory function is organized along 3 neurons (semilunar/trigeminal ganglion, trigeminal complex, and ventral posteromedial nucleus) 3 sensory branches: ophthalmic, maxillary, and mandibular 1.) ophthalmic nerve: mediates sensation of touch, pain, temperature, and proprioception from the skin of the forehead, anterior scalp, vertex, eyeball, upper eyelid, cornea, conjunctivum, anterior and lateral surfaces of the nose, frontal and nasal sinuses, and tentorium cerebelli 2.) maxillary nerve: mediates sensation from the skin of temples, posterior portion of the nose, upper cheeks, lower eyelids, and upper lips; additional innervated oral structures include the upper gum, teeth (molar and premolar), mucosal membrane, and soft and hard palate; also receives sensations from the nasal cavity, maxillary sinus, and dura mater in the medial cranial fossa 3.) mandibular nerve: largest of trigeminal branches; mediates sensations from the skin on the sides of the scalp, the mucosal membrane of the lower gum, the mouth, and the meninges of the anterior and middle cranial fossa; additional innervated structures include the anterior half of the pinna, external auditory meatus, external surface of the tympanic membrane, and the mucosa of the anterior 2/3 of tongue SVE (special visceral efferent) trigeminal motor nucleus supplies muscles of mastication, which include internal and external pterygoid, temporalis, and maseter; other muscles supplied by trigeminal motor nucleus include mylohyoid, anterior belly of digastric, tensor veli palatini (soft palate), and tensor tympani (middle ear) CLINICAL CORRELATES (sensory) damage to any peripheral branches would result in ipsilateral loss of sensation in area of distribution for the nerve, which includes the face, rostral tongue, teeth, and gingiva, the cavities of the nose, orbit, and mouth sneezing and blinking reflexes can be lost because of interrupted innervation of the nasal mucosa and exterior surface of the eye trigeminal neuralgia (pain) or tic douloureux --> MOST COMMON; sudden and repetitive bursts of pain; marked by excruciating pain of unknown cause, usually in the territory of ophthalmic or mandibular branch; pain often described as burning or stabbing; can be elicited by slightest tactile stimulus in trigger zones of trigeminal distribution; often surgically treated by transecting the involved nerve branch or by sectioning the sensory nerve root (motor) LMN syndrome characterized by a flaccid paralysis of the ipsilateral muscles of mastication; jaw slightly deviates toward side of injury; also causes muscle twitch and gradual atrophy; jaw jerk is absent unilateral UMN injury is likely to have only mild affect on masticator muscles bilateral UMN lesions produce marked paralysis of masticators bilaterally; mandible hangs low; causing structural difficulty in production of vowels and labial and and lingual consonant sounds TESTING (sensory) affected branch of nerve and related modality (touch, pain, temperature) of sensation can be determined by clinical testing with various sensory stimuli (cotton and pinprick) and by assessing the sneeze and corneal reflexes (motor) motor strength in patients with masticator palsy is assessed by asking them to bite down on a tongue depressor, move the jaw laterally against resistance, or open jaw against resistance functional quality can be assessed by examining the precision in the articulation of phonemes that require jaw support, for example, bilabial, labiodental, dental, and palatal sounds.

Bilateral vs. contralateral

BILATERAL This means that both the left and right members of a pair of cranial nerves are innervated by the motor strip areas of both the left and right hemispheres Almost all of the cranial nerves receive bilateral innervation from the fibers of the pyramidal tract. This redundancy is a safety mechanism. If there is a unilateral lesion on the pyramidal tract, both sides of body areas connected to cranial nerves will continue to receive motor messages from the cortex. The message for movement may not be quite as strong as it was previously but paralysis will not occur. CONTRALATERAL/UNILATERAL This means that they get information only from fibers on the opposite side of the brain. The two exceptions to this pattern are the portion of CN XII that provides innervation for tongue protrusion and the part of CN VII that innervates the muscles of the lower face. These only receive contralateral innervation from the pyramidal tract. ***UMN DAMAGE*** unilateral upper motor neuron lesion could cause a unilateral facial droop or problems with tongue protrusion on the opposite side of the body. For example, a lesion on the left pyramidal tract fibers may cause the right side of the lower face to droop and lead to difficulty in protruding the right side of the tongue. The other cranial nerves involved in speech and swallowing would continue to function almost normally as both members of each pair of nuclei still receives messages from the motor strip. Because most cranial nerves receive bilateral innervation, lesions of the upper motor neurons of the pyramidal tract must be bilateral in order to cause a serious speech problem. (The effects of the inability to protrude the tongue and of paralysis of the lower face on speech are negligible.) ***LMN DAMAGE*** unilateral lesions of the lower motor neurons may cause paralysis. This occurs because the lower motor neurons are the final common pathway for neural messages traveling to the muscles of the body. At the level of the lower motor neurons, there is no alternative route which will allow messages from the brain to reach the periphery. Muscles on the same side of the body as the lesion will be affected.

Why are the muscles related to speech (phonation, mastication ,deglutition, and articulation) classified as visceral (special visceral efferent) rather than somatic?

Because somatic structures are skeletal muscles, you would think the muscles related to speech would be consider somatic because they are under voluntary control, and similar to many other skeletal muscles However, these muscles are classified as visceral based on their evolution from the pharyngeal arches of the embryo; early in human development 6 embryonic arches emerge; each arch relates to specific groups of muscles: -1st pharyngeal arch (mandibular): CN V; muscles of mastication -2nd pharyngeal arch: CN VII; muscles of facial expression -3rd pharyngeal arch: CN IX; muscles of sylopharyngeus -4th, 6th, pharyngeal arch: CN X; muscles of pharyngeal and laryngeal region *5th arch disappears

Cranial Nerve Video (Sam Webster)

CN I Olfactory Nerve -sensory -olfactory tracts, olfactory bulbs -sensory information from nose is carried up through the olfactory bulbs and then to the brain; majority of fibers terminate in temporal lobe of the primary olfactory area, called the piriform (pyriform) cortex - CN II Optic Nerve -sensory -brings visual information from retina to brain -two optic nerves cross at optic chiasm; some nerves from retina cross to the other side at the optic chiasm, some nerves stay on same side - information eventually passes to visual cortex in occipital lobe - damage along the pathway will have different affects - if right side of optic tract was severed or compressed, patient would experience loss of left visual field (because optic tract is AFTER the crossing at the optic chiasm) - if left side of optic tract was severed or compressed, patient would experience loss of right visual field (because optic tract is AFTER the crossing at the optic chiasm) CN III Oculomotor Nerve -motor - innervates almost all extrinsic muscles of the eye - innervates most of muscles within the eye (dilating pupil, contricting pupil, lens accommodation) - parasympathetic nervous system innervates muscle that constricts pupil (innervation comes from CN III) - comes from midbrain CN IV Trochlear (like a "pully") - motor *there are muscles attached to the eye and two nerves innervating those muscles, CN IV, CN VI - innervates superior obilque muscle (tilt you head back and forth and notice your eye stays level as your head tilts, that's your superior oblique muscle in action) CN V Trigeminal - sensory and motor - large nerve - major sensory nerve of the face - splits into 3 branches: opthalmic, maxillary, mandibular - opthalmic: area of face superior to eye - maxillary: maxillary region and upper teeth - mandibular: mandibular region, lower jaw, lower teeth - carries sensory info from tongue, nasal cavity - comes from pons - major sensory nerve of face - motor component is in mandibular branch of CN V and passes to muscles of mastication CN VI Abducens ("to abduct") - motor - innervates the lateral rectus muscle which abducts your gaze, pulls your gaze laterally; causes abduction of your gaze CN VII Facial - sensory and motor - major motor nerve of face - innervates muscles for facial expression - splits into 5 branches?? - CN VII also helps with secretion of tears for eyes (lacrimal glands) - chorda tympani branch passess down to underneath the tongue, so carries sensory info from anterior 2/3 of tongue CN VIII Vestibulocochlear - sensory - innervates areas for hearing and balance (cochlea and SSCs) CN IX Glossopharyngeal - sensory and motor - carries general sensory information AND special sensory information from posterior 1/3 of the tongue - muscle for swallowing (small motor component) - plays sensory role in gag reflex (vagus nerve plays motor role) CN X Vagus ("wandering") - sensory and motor - BIG, BUSY - innervates intrinsic muscles of larynx - innervates muscles of pharynx, palate, small region of external ear - sensory information from pharynx, larynx, thorax, abdomen, carotid body, and aortic body - innervation of glands and muscles in heart, blood vessels, trachea, bronchi, esophagus, stomach, and intestine CN XI Accessory - motor - innervates sternoclydomastoid and trapezius muscles - also has rootlets coming from spinal cord (hence "spinal accessory" nerve) CN XII Hypoglossal ("below" "tongue" - motor - innervates all intrinsic and almost all extrinsic muscles of the tongue

Summary of cranial nerve innervation patterns outline in table 17-5

CN III, IV, VI: contralateral gaze control CN V: bilateral (function spared after unilateral lesion) CN VII: Upper face: bilateral (spared after unilateral lesion) Lower face: contralateral (face affected after a unilateral lesion) CN IX, X: Swallowing: bilateral (transient affection after unilateral lesion) Phonation: bilateral (transient affection after unilateral lesion) CN XI: head turning: contralateral shoulder shrugging: contralateral CN XII: tongue movement: contralateral

UMN and LMN (motor projections)

Corticonuclear fibers arise from the motor cells (UMNs) in the lower part of the precentral cortex and descend through the genu of the internal capsule to synapse on the motor cranial nerve nuclei (LMN) in the brainstem Before synapsing on the cranial nerve motor nuclei, the corticonuclear fibers cross the midline at different brain stem locations (see figure 17-5 for a diagrammatical view of corticonuclear fibers and their crossed projections to the contralateral cranial nerve motor nuclei in the brainstem; keep in mind this is for MOTOR projections)

Identify cranial nerves in the forebrain, midbrain, pons, and medulla

FOREBRAIN CN I (found in roof of nasal cavity) CN II MIDBRAIN CN III CN IV PONS CN V CN VI CN VII CN VIII (in both pons AND medulla) MEDULLA CN VIII (in both pons AND medulla) CN IX CN X CN XI (in medulla and ventral horn of C1-C5) CN XII

7 functional types of cranial nerves

GSA - V GVA - IX, X GSE - III, IV, VI, XII GVE - III, VII, IX, X SVA - I, VII, IX, X SSA - II, VIII SVE - V, VII, IX, X, XI

CN VI Abducens

GSE (general somatic efferent) controls ocular movements in upper tegmentum of pons within a loop formed by facial nerve CN VI enters the orbit and innervates the lateral rectus muscle, which moves the eye laterally CLINICAL CORRELATES highly susceptible to disruption due to its long intracranial course injuries cause affected eye to turn in medially (medial strabismus or squint) because with paralyzed lateral rectus muscle, the medial rectus muscle functions are unopposed with subsequent misalignment of eyes, patient experiences double vision when looking straight ahead or to affected side isolated bilateral damage to abducens nuclei would result in medial deviation of both eye because of unopposed activity of both medial recti muscles lesions involving medial longitudinal fasciculus (MLF) severely affect gaze control; the MLF projects bilaterally into CN III, CN IV, and CN VI TESTING asking patient to follow the vertical and horizontal finger/light movement

CN IV Trochlear

GSE (general somatic efferent) only cranial and motor nerve to exit dorsally from brainstem CN III fibers cross the midline in the anterior medulla and exit dorsally from the brainstem below the inferior colliculus nerve fibers enter the orbit with the oculomotor nerve (CN III) and innervate the superior oblique muscle; contraction of this muscle moves the eye downward and laterally CLINICAL CORRELATES weakness or paralysis of superior oblique muscle (from denervation, compression, or peripheral neuropathy) often results in diplopia (double vision) when looking downward and inward, causing misalignment of the eyes; eye is fixed with an upward medial gaze because the actions of the inferior oblique, superior, and medial recti muscles are unopposed; patient often reports difficulty walking down stairs lesions involving medial longitudinal fasciculus (MLF) severely affect gaze control; the MLF projects bilaterally into CN III, CN IV, and CN VI

CN III Oculomotor

GSE (general somatic efferent) and GVE (general visceral efferent) GSE splits in the orbital cavity to supply the four ocular muscles: 1.) medial rectus - adducts eyeball medially 2.) superior rectus - upward and inward; upward gazing and rotating eye upward and outward 3.) inferior rectus - downward and inward 4.) inferior oblique - upward gazing and rotating eye upward and outward oculomotor fibers innervate the levator palpebrae superioris muscle (which lifts the upper eyelid and is implicated in ptosis (upper eyelid paralysis) looking to the left entails contraction of lateral rectus of left eye, contraction of medial rectus of right eye, and simultaneous relaxation of opposite muscles which is coordinated by brainstem gaze center GVE Edinger-Westphal nucleus is the visceral oculomotor nucleus and is responsible for the parasympathetic innervation of the intrinsic eye muscles (such as the circular fibers of the iris for pupillary constriction, and ciliary muscles for lens accommodation) Light reflex (mediated through the Edinger-Westphal nucleus; see table 17-9) postganglionic fibers from ciliary ganglion supply the constrictor (circular) pupillary fibers of the iris in the dark, the Edinger-Westphal nucleus is inhibited and the dilation of the pupils is activated through the sympathetic projections to the dilator (radial) fibers of the iris muscle accommodation reflex (adjustments in the lens shape to keep a nearing object in focus); involves participation of visual cortex; consists of 3 components 1.) ocular convergence 2.) pupillary constriction and 3.) lens thickening; tested by asking patient to focus on an object moving closer to the eyes CLINICAL CORRELATES ocular muscles are prone to all diseases that affect skeletal muscles, including myasthenia gravis; weakness of levator palpebrae superioris and extraocular muscles is first clinical sign in most patients neuritis nerve compression TBI lesion that affects nucleus and/or oculomotor nerve CN III may result in weakness/paralysis of three recti muscles, inferior oblique muscles, and palpebrae superioris muscles; also causes paralysis of pupillary sphincter muscle and ciliary muscle, leaving pupil dilated and lens flat ophthalmoplegia (paralysis of extrinsic or intrinsic eye muscles); external or internal (see below) external ophthalmoplegia: affected eye deviates to side due to paralysis of extrinsic ocular muscles; eye deviates laterally (lateral strabismus) and ventrally because of the unopposed action of the intact superior oblique and lateral rectus muscles; failure to direct both eyes toward an object straight, or in the direction opposite to the paralyzed side, results in diplopia (double vision) internal ophthalmoplegia; with interruption of the parasympathetic projections to the constrictors of the iris, the pupil is permanently dilated (mydriasis) because unopposed activity of the dilator muscles with sympathetic innervation ptosis (upper eyelid paralysis); with paralysis of levator palpebrae superioris, the affect upper eyelid droops often closing the eye; patient may compensate by contracting frontalis muscle to raise the eye lid or keeping the neck extended lesions involving medial longitudinal fasciculus (MLF) severely affect gaze control; the MLF projects bilaterally into CN III, CN IV, and CN VI

7 Functional Components of Nervouse System

GSE, GSA, GVE, GVA, SSA, SVE, SVA i. SSA (special somatic afferent) - audition ii. SVE (special visceral efferent) - articulation and swallowing iii. GSA (general somatic afferent) - pain and temp iv. SVA (special visceral afferent) - taste and smell v. GSE (general somatic efferent) - limb movement vi. GVE (general visceral efferent) - Autotomic Nervous System activity vii. GVA (general visceral afferent) - organ content

CN X Vagus

Mixed GVA, GVE, SVA, SVE more extensive distribution than any other nerve large sensory component, small motor component controls muscles used for phonation and swallowing (deglutition) innervates cardiac muscles and smooth muscles of esophagus, stomach, and intestine, as well as muscles of pharynx and larynx mediates sensation of pain, touch, and pressure from mucosa of pharynx, inferior surface of epiglottis, the trachea, bronchi, esophagus, and stomach mediates general somesthetic (pain) input and special stretch afferent feedback (SSA) from the pharyngeal and laryngeal muscle GVA involved with regulation of cardiovascular, respiratory, and gastrointestinal functions mediates general sensation (touch, pain, tension, and temperature) from receptors in the walls of the viscera: the pharynx, larynx, thorax, abdomen, heart, bronchi, carotid sinus and esophagus GVE As part of ANS, GVE fibers parasympathetically innervate viscera including the cardiac muscles and smooth muscles of the trachea, bronchi, esophagus, stomach, and intestines SVA mediate taste sensation from the pharyngeal area SVE innervate muscles that are important to professionals in communicative disorders: those of the larynx, pharynx, and upper part of esophagus supplies three constructor muscles (superior, middle, and inferior) of hte pharynx and all soft palate muscles, except for the tensor palatini (supplied by CN V) 3 branches: 1.)Pharyngeal Branch -Pharyngeal constrictor muscles except stylopharyngus (CN 9); Superior, middle and inferior constrictors -All velum muscles except tensor veli palatini (CN V); levator palatini , palatoglossus 2.)Superior laryngeal branch -Internal is sensory from mucous membranes of larynx, epiglottis, base of tongue, and aryepiglottic folds -External is motor to the cricothyroid (pitch 3.) Recurrent laryngeal branch -Intrinsic muscles of larynx except cricothyroid ) and sensory to the vocal cords -Left side wraps around the aorta CLINICAL CORRELATES breathy unilateral VF paralysis decreased pitch control hoarseness frequent coughing decreased pharyngeal motility nasal regurgitation high risk for aspiration autonomic functions and visceral reflexes are impaired, such as coronary circulation ,heart rate, and relaxation and contraction of trachial and bronchial muscles lethal consequences if large medullary lesions occur because the vagus nerve participates in reflexes like swallowing, gagging, coughing, sneezing, breathing, vomiting, and cardiac rate) TESTING visual examination of soft palate during rest and action (phonation of "ahhh" visual inspection of pharyngeal cavity assessment of quality in phonation (breathy, hoarse, altered voicing, and diplophonia) tasks assessment of quality swallowing tasks

CN IX Glossopharyngeal

Mixed GVA, GVE, SVA, SVE nerve consists of inferior salivatory nucleus, nucleus ambiguus, and nucleus solitarius (the latter 2 shared with vagus nerve) overlapping nuclei and proximity to other cranial nerves (e.g. CN X) GVA concerned with initiation of reflexes mediate touch, pain, tension , and temperature sensations from intraoral visceral structures including upper pharynx, tonsils, eustachian tube, middle ear cavity, soft palate, and mucosa of posterior third of the tongue receive input from carotid body and middle ear carotid sinus baroreceptors respond to increased blood pressure and reflexively control the flow of blood by dilating blood vessels mediate pain from middle ear GVE concerned with autonomic control of visceral body structures including glands and cardiac muscles SVA mediate information from taste buds in posterior 1/3 of tongue and scattered throughout oral pharynx SVE contribue to swallowing by innervating the stylopharyngeus CLINICAL CORRELATES lesion selectively affecting CN IX is rare lesion would result in partial paresis of unilateral stylopharyngeal muscle, impairing ipsilateral posterior third of tongue; impaired cutaneous sensation from the posterior tongue would cause a loss of gag reflex; poor control of parotid gland would lead to excessive oral secretion TESTING usually assessed with dysfunctioning of vagus nerve

CN VII Facial

Mixed GVE, SVA, SVE (general visceral efferent, special visceral afferent, special visceral efferent) primarily a motor nerve for muscles of facial expression and stapedius muscle of middle ear sensory component involves mediation of taste sensation from anterior 2/3 of tongue and nasopharynx facial nuclear complex consist of 3 nuclei: facial motor nucleus, superior salivatory nucleus, and nucleus solitarius before exiting the stylomastoid foramen, the nerve diverges to supply muscles of facial expression and the stapedius muscle of middle ear GVE these fibers arise from the superior salivatory nucleus and supply the lacrimal, submandibular, and sublingual glands with visceral efferent impulses SVA sensory root of facial nerve; carries gustatory sensation from taste buds in the anterior 2/3 of tongue SVE innervates all muscles of facial expression after exiting the caudal lateral pons, the nerve divides into the temporal, zygomatic, buccal, mandibular, and cervical branches to innervate muscles of facial expression you use for kissing, blowing, speaking, smiling, frowning, grimacing, and raising eyebrows buccinator muscle in particular contributes to swallowing by compressing the cheeks to prevent food accumulation in the buccal (facial) sulci CLINICAL CORRELATES injury near pons and surround area is likely to affect all three functions of facial nerve, resulting in: 1.) paralysis of ipsilateral facial muscles (Bell palsy) 2.) excessive or diminished secretion from glands 3.) loss of taste from anterior 2/3 of tongue injury in facial nerve fibers at or beyond the stylomastoid foramen, where its fibers separate, is likely to result in paralysis of the ipsilateral half of half of the facial muscles, sparing glandular secretion and taste sensation injury to the fibers before they merge with facial motor root would affect only taste sensation from anterior 2/3 of tongue and secretion from glands injury to GVE fibers of the pterygopalatine ganglion may cause secretory dysfunctions of glands in the eye and palate; in case of UMN lesions, there is never a complaint or oral dryness; in the case of LMN lesions, the lesion can take out ipsilateral sublingual gland if lesions is proximal to superior salivatory nucleus; effect remains ipsilateral interruption of efferents to middle ear causes paralysis of stapedius muscle (working jointly with tensor tympani) impaired control of stapedius muscle results in hyperacusia (a condition in which there is a heightened sensitivity to sounds so normal sounds seem very loud) UMN DAMAGE = lower face paresis or paralysis of contralateral face lesion in unilateral motor cortex (UMN) affects muscles in contralateral lower half of the face; patient is still able to wrinkle forehead and close eye; affects lower face and 1/2 of tongue bilateral corticonuclear (UMN) lesions, also known as pseudobulbar palsy, produce bilateral facial palsy and result in profound impairments of motor speech; preservation of emotional expression (known as pseudobulbar affect) LMN DAMAGE = paresis or paralysis entire ipsilateral face lesion in either of facial nucleus (LMN) cause a paralysis of facial or swallowing muscles on one side; muscle wasting; areflexia, and fasciculation are common LMN features; does not affect sensation; disastrous effects on articulation of labial and labiodental sounds Bell palsy, LMN syndrome; characterized by paresis or paralysis of all unilateral upper and lower facial muscles; patient is unable to wrinkle forehead, close the eyes, show the teeth, purse the lips on the side of lesion; additional symptoms include impairments of sublingual and submandibular salivary secretion, hyperacusis, and loss of taste from anterior 2/3 of tongue TESTING motor functions are tested by asking patient to smile, part the lips, show the teeth, puff out the cheeks, pucker the lips, and express emotions while examiner looks for signs of facial asymmetry careful examination of speech sounds also provides information about nerve integrity sugar, salt, and vinegar are used to assess taste from tongue

CN XI Spinal Accessory

Motor innervates trapezius and sternocleidomastoid (neck muscles) which assist in rotating head and jaw to opposite side CLINICAL CORRELATES impaired ability to control head movements (trapezius and sternocleidomastoid muscles, combined with other neck muscles, contribute to tilt, forward and backward extension, and lateral rotation of the head) interruption of nerve supply to trapezius muscle can lead to dropped shoulder damage to sternocleidomastoid restricts head turning to hte side AWAY from the lesion paralysis of these muscles may also indirectly affect speech resonance TESTING asking patient to turn head and raise shoulder against opposing force

In the somatic nervous system, the cranial nerves are part of the _____________with the exception of the optic nerve (cranial nerve II), along with the retina.

Peripheral Nervous System (PNS) *The second cranial nerve is not a true peripheral nerve but a tract of the diencephalon.

Describe the difference between spinal and cranial nerves in regard to general vs. specific functions?

SPINAL NERVES serve only general motor and general sensory functions involving both somatic and visceral muscles (GSE, GSA, GVE, and GVA) CRANIAL NERVES serve general motor and general sensory functions serve special functions (olfaction, vision, taste, audition, and equilibrium) *The somatic component of cranial nerves with special functions contains ONLY AFFERENT fibers, whereas the visceral component contains both afferent and efferent fibers.

CN II Optic Nerve

SSA (special somatic afferent) light rays enter the eye and are bent (refracted) by the curvature of the cornea photoreceptor cells transduce light energy into local and action potentials which travel through the optic nerve, optic chiasm, and optic tract optic tract fibers travel posteriorly around the pes pedunculi (of the midbrain) and terminate in the lateral geniculate body, the thalamic relay center for vision geniculocalcarine projections, also called optic radiations travel to the visual cortex in the occipital lobe primary visual cortex which is located in the upper and lower banks of the calcarine fissure, receives projections from both eyes CLINICAL CORRELATES injury to any part of visual pathway results in selected visual field loss area and type of loss depend on site and extent of lesion lesions of entire optic nerve would lead to a complete blindness in one eye cerebrovascular accidents and neuritis (an inflammation of optic nerve) are common causes of optic nerve disorders) common visual field defects are bitemporal hemianopsia, homonymous hemianopsia, homonymous superior quadrantanopia, and homonymous inferior quadrantanopsia TESTING can be informally tested by having patient close one eye and fix the other eye on a point straight ahead; the clinician then moves his/her index finger with arm outstretched, from the periphery to the midline from all directions (left, right, up, and down) and patient is asked to report point at which finger can be seen

CN I Olfactory Nerve

SVA (special visceral afferent) olfactory system consists of the sensory neuron in the nose, the olfactory bulb, the olfactory tract, part of the temporal cortex, and a limited region of the interior fronto-orbital cortex CLINICAL CORRELATES anosmia (impaired ability to smell) hyposmia (decreased olfactory sensation) hyperosmia (abnormally acute sense of smell) uncinate fits (due to lesion involving olfactory cortex, marked by imaginary odor and involuntary movements of the lips and tongue) olfactory loss may involve the neural mechanism of olfaction unilaterally or bilaterally; bilateral lesions have a drastic impact on olfatory function TESTING asking patient to identify various odors using one nostril at a time

CN VIII Vestibulocochlear

Sensory consists of vestibular and acoustic branches vestibular nerve vs. auditory nerve both branches are laterally attached to brainstem at junction of medulla and pons vestibular portion mediates head position and upright body posture (equilibrium) in space acoustic branch serves hearing VESTIBULAR NERVE (superior portion) reflexive sensorimotor system that controls equilibrium, including regulation of neck position helps coordinate head and body movements and retain a stable visual fixation point in space during body and head movements AUDITORY NERVE (inferior and more anterior) serves hearing CLINICAL CORRELATES disturbance of equilibrium and audition symptoms of vestibular nerve dysfunction are impaired equilibrium, vertigo or dizziness, nystagmus (rhythmic movement of eye in which eye moves slowly away from center and then returns rapidly) symptoms of auditory nerve dysfunction are conductive, sensorineural, and mixed hearing loss; tinnitus

Cranial nerves take a fixed path and exit through assigned openings in the skull. T or F?

T

The cranial nerves have only parasympathetic functions. T or F?

T

Cranial nerves represent an evolutionary modification of the basic organization pattern of the vertebrate CNS. T or F?

T The ancient gill-related muscles in mammals have evolved into many skeletal muscles of face, which were later modified for the visceral purposes of swallowing, phonation, and speech.

UMN vs LMN syndromes

UMN SYNDROME caused by interruption in coriticonuclear projections from motor cortex to cranial nerve nuclei on the opposite side characterized by loss of discrete and delicate motor control, muscle weakness, and brisk reflexes; milder effect on buccofacial muscles bilateral involvement of UMN (pseudobulbar palsy) profoundly affects cranial muscle function and motor speech; characterized by hypertonia and loss of discrete motor control; little or no spasticity in cranial muscles LMN SYNDROME affect motor cranial nuclei and their projections symptoms include flaccid paralysis of selected muscles alone, absent or reduced reflexes, muscular fibrillations and twitching, and muscular atrophy greatly affects functioning of ipsilateral buccofacial, glossal, laryngeal, and neck muscles

Common cranial nerve syndrome

Weer syndrome (midbrain lesion) Millard-Gubler syndrome (lower pons lesion) Locked-in syndrome (bilateral pontine lesions) Wallenberg syndrome (lateral medullary lesion) Dejerine syndrome (medial medullary lesion)

visceral functions

activities of the muscles of respiration, digestions, swallowing, phonation, and speech

Cranial nerves are named sequentially as they ______________.

descend (inferiorly)

The first 2 cranial nerves are part of the ____________, and the remaining 10 are part of the __________.

forebrain branstem

Note that ocular movements are controlled by 6 extrinsic muscles which are controlled by 3 cranial nerves. Name the muscles and the corresponding nerves.

medial rectus lateral rectus superior rectus inferior rectus superior oblique inferior oblique

XII Hypoglossal

motor controls tongue movement innervates all ipsilateral intrinsic and most extrinsic (geioglossal, styloglossus, hyoglossus) tongue muscles (except palatoglossal which is controlled by CN X) CLINICAL CORRELATES unilateral damage to hypoglossal nucleus or interruption of nerve projections results in LMN symptoms; ipsilateral half of tongue is paralyzed and becomes flaccid and wrinkled; presence of fasciculations; paralyzed half of tongue eventually atrophies; muscle weakness contribute to dysarthria and chewing difficulty; on protrusion, tongue deviates toward side of lesion bilateral LMN damage to nucleus is likely to cause severe difficulty in swallowing, eating and speaking after a unilateral supranuclear lesion, the loss of UMN influence causes loss of skill in using tongue during articulation, swallowing and eating TESTING ask patient to protrude, retract, raise, and move tongue laterally and by examining the quality of the lingual and dental sounds

visceral muscles

muscles of the heart, the spleen, the great vessels, and the digestive, respiratory, urogenital, endocrine, and speech systems, which are autonomically controlled

pseudobulbar affect

preservation of emotional expression associated with bilateral corticonuclear (UMN) lesions paralyzed for voluntary motor control, the facial muscles continue to respond involuntarily to genuine emotional stimuli and states

MLF (medial longitudinal fasciculus)

projects bilaterally into CN III, CN IV, and CN VI lesions involving medial longitudinal fasciculus (MLF) severely affect gaze control

GSE (General Somatic Efferent)

regulate skeletal muscles derived from somites include innervation of ocular muscles (CN III), trochlear muscles (CN IV), abducens muscles (CN VI), and lingual muscles (CN XII)

GVE (General Viseral Efferent)

regulate the autonomic (parasympathetic) functions of smooth muscles and glands GVE nuclei include the Edinger-Westphal nucleus (CN III), superior salivatory nucleus (CN VII), inferior salivatory nucleus (CN IX), and dorsal motor nucleus (CN X) these nerves serve pupillary constrictions, gland secretion, and muscles of the heart, trachea, bronchi, esophagus, and the lower viscera

Cranial nerve nuclei have different innervation patterns. Elaborate.

the corticonuclear regulation of several cranial nerve motor nuclei is largely bilateral -- the nuclei receive corticonuclear input from both of the motor cortices however, there are several muscles that receive contralateral innervation; these include: -lower facial muscles (CN VII) -sternoclydomastoid and trapezius muscles (CN XI) - tongue muscles (CN XII) - ocular muscles (CN III, CN IV, and CN VI) nuclei of some cranial nerves receive input from both sides of motor cortex (bilaterality); this bilaterality ensures that a cortical lesion would not profoundly impair the function of CN V, VII, IX, and X (see table 17-5 for breakdown of innervation patterns)

SVE (Special Visceral Efferent)

these nuclei control the muscles of the face, pharynx, larynx, and some neck muscles includes CN V, VII, IX, X, and CN XI in the C1-C5 segments these nerves control facial expression, mastication, phonation, deglutition, head turning, and shoulder elevation

GSA (General Somatic Afferent)

these nuclei mediate somesthetic input (pain, pressure, temperature, and touch sensations) from the skin and somatic muscles in the head, neck and face includes CN V

SVA (Special Visceral Afferent)

these nuclei mediate taste (gustation) and smell (olfaction) include CN I, VII, IX, and X

SSA (Special Somatic Afferent)

these nuclei regulate vision (CN II) and audition and equilibrium (CN VIII) functional component includes proprioception and stretch afferents from muscle spindles

GVA (General Visceral Afferent)

these nuclei serve general sensation (pain and temperature) from the visceral structures of the pharynx, palate, larynx, aorta, and abdomen includes CN IX and CN X

visceral organs

vital organs of the body that have nonstriated muscles, such as the larynx, pharynx, trachea, and lungs; these are innervated by the AND and serve respiration, phonation, and digestion