Cranial Nerves and their Nuclei PDF

CRANIAL NERVES Nathanya Smith, MSc BRAINSTEM & CN The brainstem is the home of the origins/sites of termination of fibers in 9 of the 12 cranial nerves (CNs). Four cranial nerves emerge from the pons.  Cranial nerves VI, VII, and VIII emerge from the pontomedullary junction. BRAINSTEM...

CRANIAL NERVES Nathanya Smith, MSc BRAINSTEM & CN The brainstem is the home of the origins/sites of termination of fibers in 9 of the 12 cranial nerves (CNs). Four cranial nerves emerge from the pons.  Cranial nerves VI, VII, and VIII emerge from the pontomedullary junction. BRAINSTEM At all levels  Medial lemniscus  Spinothalamic tract  Corticospinal tract  Descending Hypothalamic Fibers ▪course with the spinothalamic fibers in the lateral part of the brain stem.  Medial Longitudinal Fasciculus  fiber bundle interconnecting centers for horizontal gaze, the vestibular nuclei, and the nerve nuclei of CN III, IV, and VI.  Lesions of the fasciculus produce internuclear ophthalmoplegia and disrupt the vestibulo-ocular reflex. MEDULLA CN Nuclei ▪Caudal medulla ▪Spinal nucleus of V ▪Pyramidal decussation ▪Solitary nucleus ▪Sensory decussation (dorsal ▪Nucleus Ambiguus ▪column nuclei (gracilis and cuneatus) ▪Dorsal motor nucleus of CN X ▪Ventromedially ▪Hypoglossal nucleus ▪corticospinal (pyramidal) tracts, ▪Accessory nucleus which are contained in the pyramids ▪Rostral medulla ▪lateral to the pyramids – olives. ▪olives contain the convoluted inferior olivary nuclei PONS Tracts Cranial Nerve Nuclei ▪corticospinal tracts ▪Abducens nucleus ▪medial lemniscus ▪Facial motor nucleus ▪spinothalamic tract and the descending hypothalamic fibers ▪Superior olivary nucleus continue to course together in the ▪Vestibular nuclei lateral pons. ▪Cochlear nuclei ▪lateral lemniscus ▪Trigeminal nuclei ▪an ascending auditory pathway ▪The medial longitudinal fasciculus (MLF) MIDBRAIN Substantia nigra is the largest nucleus CN Nuclei of the midbrain ▪mesencephalic nuclei of the Coursing together trigeminal nerve  medial lemniscus ▪nucleus of Edinger-Westphal  spinothalamic tract ▪Motor muscles of oculomotor N III  descending hypothalamic fibers ▪Trochlear N nucleus MLF  NERVES Efferent (motor) nerves  information goes from the brain to the periphery Afferent (sensory) nerves  Information goes from the periphery to the brain  Mixed nerves  Both afferent and efferent fibres  Spinal nerves are always mixed  Cranial nerves can be purely motor, purely sensory or mixed. NERVE CLASSIFICATION Special  travels from our special senses (vision, smell, taste, hearing and balance) General  describes information to/from everywhere else. Somatic  goes to/from the skin and skeletal muscles. Visceral (autonomic)  if it travels to/from our internal organs (smooth muscle, cardiac muscle and glands)  Possible directions and modalities, cranial nerves can be:  General somatic afferent (GSA) CRANIAL  General somatic efferent (GSE) NERVES  General visceral afferent (GVA)  General visceral efferent (GVE) MODALITIES  Special somatic afferent (SSA)  Special visceral afferent (SVA)  Special visceral efferent (SVE) BRAINSTEM CRANIAL NERVES: CN III CN III  the chief motor nerve supplying the eye.  Cranial nerve 3 is both a somatic and visceral efferent motor nerve.  MIDBRAIN: CN III  Nuclei  Nucleus of oculomotor nerve (GSE)  Recall LR6SO4O3  Accessory nuclei of oculomotor nerve (Edinger-Westphal nucleus) (GVE)  Parasympathetic motor fibers to sphincter pupillary ciliary muscles for accommodation. ACCOMMODATION The accommodation reflex is an adjustment of the eye for near vision. Three phenomena are involved: 1. Increased convexity of the lens.  At rest  suspensory ligament maintains tension on lens periphery such that it remains flat.  Accommodation  Parasympathetic neurons of EW nucleus cause contraction of ciliary muscle, releases tension.  ACCOMMODATION 2. Pupillary constriction.  Parasympathetic fibers convey the impulse for the contraction of the sphincter pupillae.  The pupil constricts and thereby increases the depth of focus. 3. Convergence of the eyes.  The oculomotor nuclei send the impulses for contraction of both medial rectus muscles, causing the eyes to converge. CN III: DEFICITS MIDBRAIN : CN IV CN IV is a general somatic motor nerve. Nucleus of trochlear nerve  Innervates superior oblique.  move the eye in the down-and-out position.  intort the eye. CN IV: DEFICITS  PONS: CN V Cranial nerve 5 is a mixed nerve.  Contains special visceral fibers.  Contains general somatic fibers. CN V Nuclei 1. Motor nucleus of trigeminal nerve (SVE) 2. Principal sensory nucleus of trigeminal nerve (GSA) 3. Spinal nucleus of trigeminal nerve (GSA) 4. Mesencephalic nucleus of trigeminal nerve (GSA) PONS: CN V 1. Motor nucleus of 2. Principal sensory nucleus of trigeminal nerve (SVE) trigeminal nerve (GSA) tactile sensation in addition to Muscles of mastication receiving proprioceptive input from the temporomandibular joint. 3. Spinal nucleus of trigeminal nerve (GSA) pain and temperature sensations from the oral cavity and the surface of the face. 4. Mesencephalic nucleus of trigeminal nerve (GSA) proprioception of the face V1- The corneal polysynaptic reflex causes bilateral eyelid closure upon light corneal touch. CN V: DEFICITS PONS: CRANIAL NERVE VI Cranial nerve 6 is a general somatic efferent nerve. Nucleus  Abducens N nucleus  Lateral Rectus  Abduction of the eyeball CN VI: DEFICIT  PONS: CN VII Cranial nerve 7 is a multimodal nerve carrying both general fibers. and special fibers. Nuclei 1. Superior salivatory nucleus (GVE) 2. Motor nucleus of facial nerve (SVE) 3. Nuclei of solitary tract (GVA, SVA) 4. Spinal nucleus of trigeminal nerve (GSA) PONS: CN VII Superior salivatory nucleus (GVE)  Nuclei of solitary tract (GVA, SVA)  Parasympathetic fibers.  visceral sensation from the  Via submandibular ganglion - roof of the oral cavity and submandibular and sublingual anterior two-thirds of the glands. tongue.  stimulates secretion of saliva  Spinal nucleus of trigeminal nerve (GSA)  Via pterygopalatine ganglion – lacrimal gland.  external auditory meatus  stimulate the secretion of lacrimal fluid.  Motor nucleus of facial nerve (SVE)  Muscles of facial expression.  CN VII: DEFICITS Review Bell’s Palsy vs corticobulbar tract lesions  CRANIAL NERVE VIII Cranial nerve 8 is a special somatic afferent nerve.  comprised of two parts:  the vestibular nerve (balance and motion)  the cochlear nerve (hearing)  Nuclei (pontomedullary junction)  Vestibular nuclei  Dorsal and ventral cochlear nuclei CN VIII: DEFICITS  CRANIAL NERVE IX Cranial nerve 9 is another multimodal (mixed) nerve. Nuclei of CN IX 1. Nucleus ambiguus (SVE, GVA) 2. Inferior salivatory nucleus (GVE) 3. Nuclei of solitary tract (SVA, GVA) 4. Spinal nucleus of trigeminal nerve (GSA) CN IX: NUCLEI Nucleus Ambiguus (SVE) Nuclei of solitary tract (SVA, GVA) ▪common nucleus of the efferent ▪ visceral sensation from tonsils, fibers for glossopharyngeal (CN tongue, palate, pharynx and IX) and vagus (CN X) nerves. posterior one-third of the tongue. ▪supplies somatic muscles ▪receives sensory information from (stylopharyngeus) of the the baroreceptors of the carotid pharynx, larynx, and soft palate. sinus (GVA) Inferior Salivatory nucleus Spinal nucleus of trigeminal nerve ▪Parasympathetic fibres (GSA) ▪Via otic ganglion to parotid ▪Caudal part gland ▪Receives fibers via the petrosal (inferior) ganglion. ▪Minor sensory contributions CN IX: DEFICITS  CRANIAL NERVE X Cranial nerve 10 is also a multimodal nerve (longest CN). It originates from multiple nuclei in the brainstem. Nuclei 1. Posterior nucleus of vagus nerve (dorsal motor nucleus) (GVE) 2. Nucleus ambiguus (SVE) 3. Nuclei of solitary tract (SVA, GVA) 4. Spinal nucleus of trigeminal nerve (GSA) – (minor input)  CN X: NUCLEI Posterior nucleus of vagus nerve Solitary nucleus (dorsal motor nucleus)  afferents from visceral organs. (GVA) ▪Parasympathetic efferent primarily to the abdominal ▪Chemoreceptors in aortic bodies viscera (GIT) and lungs. (GVE) adjacent to aortic arch (GVA) ▪taste information (SVA) ▪Nucleus ambiguus ▪ supply the muscles of the soft Spinal trigeminal nucleus palate, pharynx and larynx. ▪relay sensory information regarding (SVE) pain, temperature and deep touch of ▪branchial efferent fibers and the outer ear, the dura of the posterior preganglionic parasympathetic cranial fossa and the mucosa of the neurons for the heart. (GVE) larynx. CN X: DEFICITS  CRANIAL NERVE: XI Cranial nerve 11 is an efferent nerve originating from the brainstem and spinal cord.  I.e.. described as having both spinal (external ramus) and cranial roots (internal ramus). Nuclei  Nucleus Ambiguus (cranial nucleus of the spinal nerve)  Spinal Nucleus of the accessory nerve (C1-C5) CN XI: NUCLEI Nucleus ambiguus/Cranial nucleus of Accessory N. ▪emerges along posterior border of the olive (postolivary sulcus) ▪innervation to the muscles of the soft palate, larynx, and pharynx. Spinal accessory nerve ▪arise from the ventral horn cells in the cord between C1 and C5 of the cervical plexus ▪Innervates trapezius muscle and the sternocleidomastoid. (SVE) CN XI: DEFICITS  CN XII general somatic efferent nerve originating from the brainstem. Nuclei ▪Nucleus of hypoglossal nerve (GSE) ▪Intrinsic tongue muscles, extrinsic tongue muscles (except for the palatoglossus) CN XII: DEFICITS SPECIAL NUCLEI: NUCLEUS AMBIGUUS This motor nucleus is shared by cranial nerves IX, X, and XI. Initiate the mechanism of swallowing and phonation.  CN IX  stylopharyngeus muscles and pharyngeal constrictor muscles.  CN X  innervate the muscles of the soft palate, larynx, pharynx  parasympathetic cardiac regulation (inhibit HR)  CN XI  ‘ambiguus’ originates from its difficult-to-find location and variation in different species. Location: RF in medulla. SPECIAL NUCLEI: NUCLEUS (OF TRACTUS) SOLITARIUS a major sensory nucleus in the dorsal medulla that receives cardiovascular, visceral, respiratory, gustatory, and orotactile information.  Receives input from facial, glossopharyngeal, vagus, and trigeminal nerves. Functions of the nucleus solitarius:  Receive taste inputs (Rostral nucleus solitarius from CN VII, IX, X)  Receive inputs from chemoreceptors and baroreceptors in the aortic arch and carotid body (CN X)  Modulate response to hemostatic changes  Participates in limbic system activity  Participates in carotid reflex, gag reflex, cough reflex, and vomiting reflex SPECIAL NUCLEI: SPINAL NUCLEUS OF CN V largest trigeminal nucleus and is in the lateral tegmentum of the medulla and caudal pons. Unique to this nucleus is that it receives sensory information from cranial nerves VII, IX, and X (ear, tongue, pharynx, and larynx). CRANIAL NUCLEI & THEIR LOCATIONS