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CRANIAL NERVES

JULIAN RIZALDY C. RACA JR., M.D.

DIPLOMATE

PHILIPPINE BOARD OF SURGERY

 

 

 


The Nervous System

 

I.  Central nervous system

l        Brain

l        Spinal cord

 

II. Peripheral nervous system

l        12 pairs of cranial nerves

l        31 pairs of spinal nerves

 

Functionally:

 

l        Somatic nervous system

          -- controls motor activities

 

l        Autonomic nervous system

          -- controls involuntary activities

 

Nervous System and Endocrine System

 

l            Controls and integrates activity of the different parts of the body.

 

12 Pairs of Cranial Nerves

 

l        All nerves are distributed in the head and neck except vagus nerve which also supplies structure in the thorax and abdomen.

 

l        Purely sensory nerves

                                    --Olfactory

                                    --optic

                                    -- vestibulocochlear

 

l        Purely motor nerves

                                    --oculomotor

                                    --trochlear

                                    --abducens

                                    --accesory

                                    --hypoglossal

 

l        Mixed

                                    --trigeminal

                                    --facial

                                    --glossopharyngeal

                                    --vagus

 

CNI Olfactory Nerve

 

l        Nerves of smell

 

l        Originates as central processes of the olfactory receptor nerve cells in the mucous membrane of the upper part of the nose.

 

 

l        Pass through openings in the cribriform plate of ethmoid bone.

 

l        End in the olfactory bulb in the anterior cranial fossa.

 

l        Emerging from the posterior end of the olfactory bulb is a white band of olfactory tract, which passes backward to the olfactory area of the cerebral cortex

 

CNII Optic Nerve

 

l        Nerve of sight

 

l        About 1.6 inches (4cm) long

 

l        Leaves the orbital cavity passing through the optic canal with the opthalmic artery and enters the cranial cavity.

 

l        Surrounded by three meninges within the orbit—Dura, Arachnoid, and Pia—which carry with them an extension of the subarachnoid space.

 

l        Optic tract emerges from the posterolateral angle of the optic chiasm and passes backward around the lateral side of the midbrain to reach the lateral geniculate body.

 

l        Few fibers bypass the lateral geniculate body and go directly to the pretectal nucleus and superior colliculus.

 

l        From the lateral geniculate body, the optic radiation curves backward to the visual cortex of the cerebral hemisphere.

 

CNIII Oculomotor Nerve

 

l        Motor nerve

 

l        Supplies extrinsic muscles of the  eye within the orbit---

                        *levator palpebrae superioris

                        *superior rectus

                        *medial rectus

                        *interior rectus

                        *interior oblique

           

l        --also supplies sphincter pupillae and the ciliary    muscle   with parasympathetic fibers.

 

l        Emerges from the anterior aspect of the midbrain medial to the cerebral peduncle.

 

l        Passes close to end between the posterior cerebral and superior cerebellar arteries.

 

l        Runs forward in the lateral wall of the cavernous sinus and divides into a superior and inferior ramus, which enters the orbit through the superior orbital fissure.

 

CNIV Trochlear Nerve

 

l        Motor nerve.

 

l        Most slender of the cranial nerves.

 

l        Supplies the superior oblique muscle in the orbit.

 

 

l        Emerges from the posterior surface of the midbrain, just below the inferior colliculi.

 

l        Curves forward around the lateral side of the cerebral peduncle.

 

l        Runs forward in the lateral wall of the cavernous sinus, lying slightly below the oculomotor nerve.

 

l        Enters the orbit through the superior orbital fissure.

 

CNV Trigeminal Nerve

 

l        Both sensory and motor nerve.

 

l        Largest cranial nerve.

 

l        Supplies sensory fibers to:

                        *skin of the scalp

                        *the face

                        *the mouth

                        *the teeth

                        *the nasal cavity

                        *the paranasal air sinuses

                       

l        Supplies motor fibers to:

            *muscles of mastications---

                        ---tensor veli palatini

                        ---tensor tympani

                                   

l        Emerges from the anterior surface of the pons by a large sensory and small motor root, motor root lying medial to the sensory root.

 

l        Passes forward out of the posterior cranial fossa,    below the superior petrosal sinus, and carries with it a pouch from the meningeal layers of dura mater.

 

l        On reaching the depression on the apex of the petrous portion of the temporal bone in the middle cranial fossa, it forms the trigeminal ganglion – large sensory root; (crescentic and lies with in the pouch of dura mater called trigeminal cave.)

 

l        Motor root is situated below the sensory ganglion and is completely separate from it.

 

l        3 nerves arise from the anterior border of the ganglion.

                        *ophthalmic

                        *maxillary

                        *mandibular

 

Cnv trigeminal: ophthalmic nerve

 

l        Purely sensory

 

l        Smallest division

 

l        Runs forward in the lateral wall of the cavernous sinus below the oculomotor and trochlear nerves.

 

l        Divides into three branches

                        ---lacrimal nerve

                        ---frontal nerve

                        ---nasociliary nerve         

                   

l         Enters the orbital cavity through the superior orbital fissure.

 

CNV Trigeminal: Maxillary Nerve

 

l        Purely sensory

 

l        Runs forward along the lower part of the lateral wall of the cavernous sinus.

 

l        Leaves the skull through the foramen rotundum to enter the pterygopalatine fossa.

 

CNV Trigeminal: Mandibular Nerve

 

l        Motor and sensory

 

l        Largest division

 

l        Large sensory root leaves the lateral part    of the trigeminal ganglion and passes bthrough the foramen ovale.

 

l        Small sensory root passes beneath the ganglion through the foramen ovale.

 

l        Motor root joins the sensory root after emerging from the foramen.

 

CNVI Adbucent Nerve

 

l        Small motor nerve

 

l        Supplies lateral rectus muscle of the eyeball.

 

l        Emerges from the anterior surface of thebrain, between the lower border of the pins and medulla oblongata. 

 

l        Lies at first in the posterior crannial fossa.

 

l        Then turns sharply forward crossing the superior border of the petrous part of the temporal bone.

 

l        Runs forward with the internal carotid artery.

 

l        Enters the orbital cavity through the superior orbital fissure.

 

CNVII Facial Nerve

 

l        Medial motor root

 

l        Lateral sensory root – nervus intermedius

 

l        Motor root supplies the:

                                    *muscles of the face

                                    *scalp

                                    *auricle

                                    *buccinator       

                                    *platysma

                                    *stapedius

                                    *stylohyoid

                                    *posterior belly of digastric

 

l        Sensory root carries:

*taste fibers from the anterior 3rd of tongue

*floor of mouth

*palate

 

l        Also conveys parasymphatetic secretomotor fibers to the:

*submandibular and sublingual salivary glands

*lacrimal glands

*glands of nose and palate

l        Two roots emerge from the anterior surface of the brain, between the lower border of the pons and the medulla oblongata.

 

l        Pass laterally and forward in the posterior cranial fossa with the vestibulocochlear nerve to the opening in the internal acoustic meatus.

 

l        At the bottom of the meatus, nerve enters the facial canal and runs laterally above the vestibule of the labyrinth until it reaches the medial wall of the tympanic cavity.

 

CNVIII Vestibulocochlear Nerve

 

2 sets of sensory fibers

 

1. Vestibular fibers

--- concerned with equilibrium.

--- represents central processes of nerves cells of the vestibular ganglion.

--- located on the outer part of the internal acoustic meatus.

 

2. Cochlear fibers

--- concerned with hearing

--- represents the central processes of nerve cells of the spiral ganglion of the cochlea.

--- the two parts leave the anterior surface of the brain between the lower border of the pons and the medulla olbongata.

--- they cross the posterior cranial fossa and enter the internal acoustic meatus with the facial nerve.

 

CNIX Glossopharyngeal Nerve

 

l        Motor and sensory nerve

 

l        Motor fibers supply the stylopharyngeus muscle; parasymphatetic secremotor fibers supply the parotid salivary gland.

 

l        Sensory fibers (including taste fibers), pass to the posterior 3rd of the tongue and the pharynx.

 

l        Emerges from the anterior surface of the upper part of the medulla oblongata by 3 or 4 rootlets between the olive and the inferior cerebellar peduncle.

 

l        Passes forward and laterally beneath the cerebellum in the posterior cranial fossa.

 

l        Leaves the skull by passing downwrd through the central part of the jugular foramen.

 

l        The superior and inferior sensory glossopharyngeal ganglia are situated in the nerve as it passes through the jugular foramen.

 

CNX Vagus

 

l        Motor and sensory fibers

 

l        Supplies heart and major part of respiratory and intestinal tracts.

 

l        Emerges from the anterior surface of the upper part of the medulla oblongata by 8 or 10 rootlets between the olive and the inferior cerebellar peduncle.

 

l        Lies below the glossopharyngeal nerve.

 

l        Passes beneath the cerebellum and leaves the skull through the central part of the jugular foramen.

 

l        The superior vagal sensory ganglion is situated on the nerve as it passes through the jugular foramen.

 

l        The inferior vagal sensory ganglion lies on the nerve a short distance below the foramen.

 

CNXI Accessory Nerve

 

l        Motor nerve

 

l        Small cranial root that is distributed through the branches of the vagus nerve to the muscles of the:

                                    *soft palate

                                    *pharynx

                                    *larynx

 

l        Large spinal root that inerrvates the sternocleidomastoid and trapezius muscles.

 

l        Cranial root emerges from the anterior surface of the upper part of the medulla oblongata by 4 or 5 rootlets between the olive and the inferior cerebellar peduncle; lies below the vagus nerve; nerve runs laterally beneath the cerebellum in the posterior cranial fossa and joins the spinal root.

 

l        The spinal root arises from the nerve cells in the anterior gray column of the upper 5 segments of the cervical part of the spinal cord.

 

l        Emerge in the lateral surface of the spinal cord and form a nerve trunk.

 

l        Ascends alongside the spinal cord and enters the skull through the foramen magnum; then turns laterally to join the cranial root.

 

l        They pass through the jugular foramen then the cranial portion separates from the spinal root and become adherent to the inferior ganglion of the vagus.

 

l        Fibers of the cranial root are distributed chiefly in the pharyngeal and recurrent laryngeal branches of the vagus.

 

l        The spinal root runs backward, crossing the internal jugular vein to reach the upper part of the sternocleido mastoid muscle.

 

CNXII Hypoglossal Nerve

 

l        Motor nerve

 

l        Supply all intrinsic muscles of the tongue; also:

                        *styloglossus

                        *hypoglossus

                        *genioglossus

 

l        Emerges as a number of rootlets on the anterior surface of the medulla oblongata between the pyramid and the olive.

 

l        Runs laterally in the posterior cranial fossa and leaves the skull through the hypoglossal canal.