Neuroscience: Cranial Nerves Notes 2025 PDF

Neuroscience: Cranial Nerves Page 1 of 25 Dr. Paul Walker Session Objectives By the end of this session, students will be able to accurately: 1. Identify cranial nerves that remain within the cranial cavity following removal of the...

Neuroscience: Cranial Nerves Page 1 of 25 Dr. Paul Walker Session Objectives By the end of this session, students will be able to accurately: 1. Identify cranial nerves that remain within the cranial cavity following removal of the brain. 2. Relate openings in the dry skull (e.g., foramen, fissures, etc.) to cranial nerves that pass through them. 3. Identify cranial nerves on the ventral surface of the gross brain and match to their brainstem location. 4. Identify cranial nerve nuclei within cross sections of the brain and spinal cord. 5. Summarize and discuss the functional components of each cranial nerve. 6. Discuss signs and symptoms of cranial nerve lesions. Session Outline I. Overview of the Cranial Nerves II. Functional Anatomy of Each Cranial Nerve A. CN I Olfactory B. CN II Optic C. CN III Oculomotor D. CN IV Trochlear E. CN V Trigeminal F. CN VI Abducens G. CN VII Facial H. CN VIII Vestibulocochlear I. CN IX Glossopharyngeal J. CN X Vagus K. CN XI Accessory L. CN XII Hypoglossal Supplemental Reading Gray’s Anatomy for Students, 4th Ed (2020) Drake, Vogl, Mitchell (Elsevier) Fundamental Neuroscience for Basic & Clinical Applications, 5 th Ed (2018) Haines & Mihailoff. Elsevier. Nolte’s The Human Brain, 8th Ed (2021), TW Vanderah & DJ Gould, Elsevier. Neuroscience: Cranial Nerves Page 2 of 25 Dr. Paul Walker I. Overview of the Cranial Nerves A. Identify Cranial Nerves After Brain Removal The 12 cranial nerves are peripheral nerves that pass-through holes or gaps (e.g., foramina or fissures) of the skull. Hence the term cranial nerves. Most cranial nerves originate from the brainstem or have peripheral ganglia associated closely with the brainstem either within the cranium or at the skull base. Fig 1 below is an idealized drawing of what you’ll see in the cranial cavity after the brain is removed in gross anatomy lab. In gross anatomy, your goals are to identify the 12 cranial nerves in the cranial cavity as well as relate them to their cranial fossa location and skull foramina/fissures traversed. Fig 1 Gray’s Anatomy for Students Neuroscience: Cranial Nerves Page 3 of 25 Dr. Paul Walker B. Cranial Nerve Relationships in the Dry Skull The dry skull is an excellent way to review relationships of the cranial nerves with their cranial fossa location and skull foramina/fissures traversed. Look for the Anatomy of the Skull link on the GA Resource module on Canvas to practice the identification of skull foramen as related to the cranial nerves that pass through them. It is common to tag foramen on the dry skull in questions on the GA practical exam. Fig 2 Skull Module on Canvas Neuroscience: Cranial Nerves Page 4 of 25 Dr. Paul Walker C. Cranial Nerves Identification on the Ventral Gross Brain The Neuroscience portion of this course will provide opportunities to learn the cranial nerves as related to their location on the gross brain. Fig 3 shows cranial nerves relationships on the ventral surface of the gross brain after it has been removed from the cadaver. Fig 3 Gray’s Anatomy for Students The 12 Cranial Nerves are represented by Roman Numerals (CN I to CN XII) CN I Olfactory CN VII Facial CN II Optic CN VIII Vestibulocochlear CN III Oculomotor CN IX Glossopharyngeal CN IV Trochlear CN X Vagus CN V Trigeminal CN XI Accessory CN VI Abducens CN XII Hypoglossal Neuroscience: Cranial Nerves Page 5 of 25 Dr. Paul Walker D. Cranial Nerve Organization in the Brainstem The Neuroscience portion of this course also emphasizes how cranial nerve nuclei are organized in the brainstem. This is important because certain lesions affect specific regions of the brainstem and patients may show signs and symptoms of cranial nerve dysfunction. Fig 4 is a schematic diagram that illustrates the organization of cranial nerve nuclei within the brainstem. Some are organized into small, localized clusters while others are in elongated cell columns that span different brainstem regions. Fig 4 Nolte Cranial nerve nuclei are organized in clusters or long columns mostly in midbrain, pons, and medulla. Cranial nerve nuclei are arranged during development in medial to lateral location according to functional component. One cranial nerve nucleus is in the cervical spinal cord. Which one? Which 2 cranial nerves are associated with structures rostral to the midbrain? A subsequent lecture on Neural Development will explain why nuclei with motor function are positioned medially while those with sensory function are more lateral. Neuroscience: Cranial Nerves Page 6 of 25 Dr. Paul Walker E. Functional Components of the Cranial Nerves Remember the functional components of nerves associated with the spinal cord? There are 4 functional components carried by peripheral nerves of the spinal cord: somatic afferent (SA), visceral afferent (VA), somatic efferent (SE), and visceral efferent (VE). The functional components for cranial nerves are more complicated than spinal nerves. In addition to the 4 functional components found in spinal nerves, there are 2 more associated with certain cranial nerves: special sensory afferent (SSA, for the special senses of smell, vision, hearing, taste, and balance carried by CNs I, II, VII, VIII, IX, X) and special visceral efferent (SVE, for motor innervation of head structures derived from the pharyngeal arch mesoderm carried by CNs V, VII, IX, & X). As such, spinal nerves have 4 functional components while cranial nerves can carry 1-5 components (none have all 6). The below table in Fig 5 matches the cranial nerves to the various functional components. Some cranial nerves are entirely sensory (I, II, VIII) and some are entirely motor (III, IV, VI, XI, XII). Some are mixed sensory and motor (V, VII, IX, X). Fig 5 Functional Abbrev Function Cranial Nerve component Somatic Afferent SA Sensory from body V, VII, IX, X Visceral Afferent VA Sensory from viscera IX, X Special Sensory Special Senses: smell, taste, vision, SSA I, II, VII, VIII, IX, X Afferent hearing, and balance Somatic Efferent SE Motor to skeletal muscles III, IV, VI, XI, XII Motor to smooth muscle, heart Visceral Efferent VE III, VII, IX, X muscle, and glands Special Visceral Motor to skeletal muscles derived from SVE V, VII, IX, X Efferent* pharyngeal arch mesoderm *A subsequent lecture on Face and Pharyngeal Development that will provide you with a better understanding of how Special Visceral Efferent (SVE) components are derived embryologically. Combined with the Neural Development lecture, this information will help you better understand the SVE component of CNs V, VII, IX, and X. Neuroscience: Cranial Nerves Page 7 of 25 Dr. Paul Walker II. Functional Anatomy of Each Cranial Nerve Fig 6 Gray’s Anatomy for Students A. CN I Olfactory Nerve (Figs 6-7) Functional Component: SSA Skull Relationship: Anterior Cranial Fossa. Location of Primary Neuron: Cell bodies of olfactory sensory neurons located in nasal mucosa in roof of the nasal cavity. Foramen Relationship: Olfactory fibers pass through the cribiform plate of ethmoid bone to enter the anterior cranial fossa and connect to neurons located in the olfactory bulb. Olfactory processes from sensory neurons in the olfactory mucosa travel through the cribiform plate of ethmoid bone and synapse in the olfactory bulb. Fig 7 Nolte Neurons of the olfactory bulb (Fig 7) relay smell information to specific regions of the cerebral cortex involved in the interpretation of odors and the regulation of behaviors associated with the sense of smell (feeding, reproductive, fear, etc.). Clinical Correlations Anosmia is the term for the loss of the sense of smell. CN I can be damaged by traumatic brain injury. Loss of smell may occur early in Alzheimer or Parkinson diseases. Also decreases with normal aging. Pathologies affecting the nasal cavity (e.g., polyps, mucosal swelling) can reduce sense of smell. Kallmann syndrome: X-linked disorder with delayed puberty. Abnormal migration of olfactory cells in this disorder causes anosmia. Neuroscience: Cranial Nerves Page 8 of 25 Dr. Paul Walker B. CN II Optic Nerve (Figs 8-9) Fig 8 Gray’s Anatomy for Students Functional Component: SSA Skull Relationship: Middle Cranial Fossa Location of Primary Neuron: Retinal ganglion cells Foramina Relationship: Optic nerve passes through optic canal to enter middle cranial fossa. Some retinal axons cross the midline to the opposite side via the optic chiasm. This structure is related to the sella turcica, pituitary gland, and cavernous sinus. Main target for conscious visual perception is the occipital cortex. Retinal signals are relayed to the occipital cortex by the lateral geniculate nucleus of the diencephalon (Fig 9). Fig 9 Nolte Other visual circuits that regulate the movements of both eyes together as well as reflexes that change the diameter of the pupil will be learned in this course. Clinical Correlations High blood glucose levels in Diabetes can damage the retina and cause optic nerve degeneration (diabetic retinopathy). Increased intraocular pressure in Glaucoma can also damage the optic nerve. Inflammation of the optic nerve (optic neuritis) in Multiple Sclerosis can cause vision loss. Lesions of the optic nerve, optic chiasm, optic tracts, and the rest of the visual pathway produce specific visual deficits that will be discussed. Neuroscience: Cranial Nerves Page 9 of 25 Dr. Paul Walker C. CN III Oculomotor (Figs 10-12) Fig 10 Gray’s Anatomy for Students Functional Components: SE, VE SE fibers to most extra-ocular muscles VE preganglionic PANS fibers to ciliary ganglion. Pupillary constriction (efferent limb of light reflex) via sphincter pupillae muscle Lens accommodation (rounding up) for near vision via ciliary muscles. Skull Relationship: Middle Cranial Fossa Foramina Relationship: CN III traverses the superior orbital fissure to enter the orbit Location of Primary Neuron: Oculomotor complex located in the rostral midbrain. (Fig 11). Fig 11 Clinical Correlation: CN III lesion causes the affected eye position to be inferior and lateral (down and out). There is also a ptosis (drooped eyelid), dilated pupil (no pupillary constriction), and blurred vision for near objects (lateral strabismus because lateral rectus is unopposed). CN III: SE innervation of superior rectus, inferior rectus, medial rectus, inferior oblique muscles (Fig 12). Fig 12 Netter Neuroscience: Cranial Nerves Page 10 of 25 Dr. Paul Walker D. CN IV Trochlear (Figs 13-15) Fig 13 Gray’s Anatomy for Students Functional Components: SE SE fibers to superior oblique muscle Skull Relationship: Middle Cranial Fossa Location of Primary Neuron: Trochlear nucleus located in the caudal midbrain. Foramina Relationship: CN IV traverses the superior orbital fissure to enter the orbit. Clinical Correlation: CN IV lesion causes paralysis of the superior oblique muscle so the patient cannot depress the eye from the adducted position (look in and down). They tend to tilt their head toward the unlesioned side when walking downstairs in order to align the fovea in both eyes and prevent blurred vision. Fig 14 CN IV: SE innervation of superior oblique muscle (Fig 15). Fig 15 Netter Neuroscience: Cranial Nerves Page 11 of 25 Dr. Paul Walker E. CN V Trigeminal (Figs 16-19) Fig 16 Gray’s Anatomy for Students Functional Components: SA, SVE SA fibers provide sensation to the head/face, cornea, nasopharynx, nasal cavity/sinuses, oral cavity, external ear. SVE fibers provide motor to muscles of mastication, anterior belly digastric, mylohyoid, tensor veli palatini, tensor tympani. Skull Relationship: Middle Cranial Fossa Location of Primary Neuron: Trigeminal ganglion (SA) and mid-pons (SVE). Foramina Relationship: 3 divisions of CN V exit the skull via 3 foramen/fissures: V1 Ophthalmic: superior orbital fissure V2 Maxillary: foramen rotundum V3 Mandibular: foramen ovale SVE motor root travels on the medial surface of V3 and exits via foramen ovale. Fig 18 Gray’s Anatomy for Students Fig 17 Netter Neuroscience: Cranial Nerves Page 12 of 25 Dr. Paul Walker Fig 19 The trigeminal nerve is associated with 4 trigeminal nuclei. Chief sensory nucleus V Motor nucleus V Mesencephalic nucleus V Spinal nucleus of V The first 3 of these are clustered at a single level of the brainstem: mid- pons. They will be distinguished in Neuro Labs 02-03. The 4th trigeminal nucleus (spinal nucleus of V) is an elongated column of cells extending from caudal pons through medulla and into the first 2 cervical spinal cord levels (C1-C2). Trigeminal neuroanatomy in the brainstem is complex and you’ll receive a separate lecture on this topic during the course. Clinical Correlation: CN V lesions produce a loss of the afferent limb of the corneal reflex, loss of sensation to head/face regions innervated by V1, V2, and V3 divisions, paralysis of the muscles of mastication on the affected side, slight jaw deviation toward lesioned side when mouth opened, hyperacusis (sounds loud in affected ear). Trigeminal neuralgia (tic douloureux) is a neurological disease caused by CN V compression (sometimes by a nearby blood vessel). Neuroscience: Cranial Nerves Page 13 of 25 Dr. Paul Walker F. CN VI Abducens (Figs 20-22) Fig 20 Gray’s Anatomy for Students Functional Components: SE SE fibers to lateral rectus muscle. Skull Relationship: Posterior & Middle Cranial Fossae Location of Primary Neuron: Abducens nucleus located in the caudal pons (Fig 21). CN VI emerges from the brainstem at the inferior pontine sulcus (Fig 21) and has a long intracranial course that includes a trip through the cavernous sinus of the skull. Here it is related closely in position to the internal carotid artery and an early sign of aneurysm from the ICA is damage to CN VI and paralysis of the lateral rectus muscle. Foramina Relationship: CN VI traverses the superior orbital fissure to enter the orbit. Fig 21 Clinical Correlation: CN VI lesion paralyzes the lateral rectus muscle and the patient cannot move the affected eye laterally. There is a medial strabismus that causes blurred vision because of the unopposed action of the medial rectus muscle in the affected eye. CN VI: SE innervation of lateral rectus muscle (Fig 22). Fig 22 Netter Neuroscience: Cranial Nerves Page 14 of 25 Dr. Paul Walker G. CN VII Facial (Figs 23-28) Fig 23 Gray’s Anatomy for Students Functional Components: SA, SSA, SVE, VE SA fibers provide sensation from the external ear. SSA fibers provide taste sensation from anterior 2/3 of the tongue SVE fibers provide motor to muscles of facial expression, posterior belly digastric, stylohyoid, stapedius. VE fibers provide parasympathetic motor axons to pterygopalatine and submandibular ganglia to stimulate salivation and lacrimation. Skull Relationship: Posterior Cranial Fossae Location of Primary Neuron: Geniculate ganglion (SA, SSA) and caudal pons (SVE, VE). Foramina Relationship: connects to brainstem via internal acoustic meatus and the periphery via the stylomastoid foramen. Two branches of the facial nerve, chorda tympani and greater petrosal nerves, emerge through other foramen discussed later. Fig 24 CN VII is mainly associated with the caudal pons (Fig 24). This is where motor nuclei are located for both SVE and VE functions. The facial nerve is found at the cerebellopontine angle next to CN VIII. This is very close to the junction between pons and medulla and lateral to the emergence of CN VI from the inferior pontine sulcus. The geniculate ganglion is the location of sensory neuronal cell bodies that convey SA and SSA information associated with CN VII. It is located within the bony confines of the temporal bone near the internal acoustic meatus. The next pages break apart the functional components of CN VII. Neuroscience: Cranial Nerves Page 15 of 25 Dr. Paul Walker CN VII Somatic Afferent (SA) Fig 25 Fig 25 Gray’s Anatomy for Students Sensory from auricle and external acoustic meatus (Fig 25) Sensory neuronal cell body located in the Geniculate Ganglion (within the temporal bone) Peripheral process traverses stylomastoid foramen to innervate skin of external ear Central process connects to brainstem via the internal acoustic meatus Fig 26 Gray’s Anatomy for Students CN VII Special Sensory Afferent (SSA) Fig 26 Taste from Anterior 2/3 Tongue Sensory neuronal cell body located in the Geniculate Ganglion Peripheral process travels with chorda tympani n to the oral cavity (you will learn the route later) Central process connects to brainstem via the internal acoustic meatus CN VII Visceral Efferent (VE) Fig 27 Motor neuronal cell body in brainstem (Superior Salivatory Nucleus of the Caudal Pons) Axons go through internal acoustic meatus. Travel to gland target in chorda tympani nerve or greater petrosal nerve. PANS to: Submandibular Gland (via chorda tympani) Sublingual Gland (via chorda tympani) Lacrimal Gland (via greater petrosal) Small unnamed glands of the oral mucosa (via greater petrosal) Fig 27 Grays Atlas of Anatomy Neuroscience: Cranial Nerves Page 16 of 25 Dr. Paul Walker CN VII Special Visceral Efferent (SVE) Fig 28 Fig 28 Gray’s Anatomy for Students Motor neuronal cell bodies in Facial Motor Nucleus in the Caudal Pons Axon exits brainstem with Facial n. and travels through internal acoustic meatus and exits skull via the stylomastoid foramen. Motor to: Muscles of Facial Expression Stapedius m Posterior digastric m. & stylohyoid m. Clinical Correlation: There are several disorders involving CN VII paralysis including Bell’s Palsy. Causes ipsilateral paralysis of muscles of facial expression, hyperacusis due to stapedius paralysis, loss of taste to anterior 2/3 tongue, dry eye and mouth due to loss of VE innervation to lacrimal gland and oral cavity salivary glands. Stroke damage affecting caudal pons or cerebral cortex can also affect CN VII function. This will be explained later in the course. Neuroscience: Cranial Nerves Page 17 of 25 Dr. Paul Walker H. CN VIII Vestibulocochlear (Figs 29-31) Fig 29 Gray’s Anatomy for Students Functional Component: SSA Skull Relationship: Posterior Cranial Fossa Location of Primary Neuron: Internal (inner) ear located in the petrous portion of the temporal bone associated with the cochlea or the vestibular apparatus (Fig 30). Auditory portion- cells located in Spiral Ganglion of the cochlea. Vestibular portion- cells located in Vestibular (Scarpa’s) Ganglion of the vestibular apparatus. Foramina Relationship: Sensory fibers traverse the Internal Acoustic Meatus to connect to the brainstem. Fig 30 Netter Fig 31 Brainstem nuclei that receive input from vestibular and cochlear parts of CN VIII are located in the caudal pons and rostral medulla (Fig 31). The vestibular nuclear complex is located in the dorsal part of both caudal pons and rostral medulla. The cochlear nucleus is located dorsolaterally in the rostral medulla Clinical Correlations: CN VIII damage causes: Hearing loss and sometimes tinnitus (ringing in ears). Vestibular symptoms affect balance & equilibrium and may include nystagmus (oscillation of eyes), vertigo (room spinning), and nausea & vomiting. Neuroscience: Cranial Nerves Page 18 of 25 Dr. Paul Walker I. CN IX Glossopharyngeal (Figs 32-38) Fig 32 Gray’s Anatomy for Students Functional Components: SA, VA, SSA, SVE, VE SA fibers provide sensation from the middle ear, auditory tube, posterior 1/3 tongue, oropharynx. VA fibers provide sensation from the carotid body and sinus. SSA fibers provide taste sensation from posterior 1/3 of the tongue SVE fibers provide motor to the stylopharyngeus muscle. VE fibers provide parasympathetic motor axons to otic ganglia to stimulate salivation from parotid gland. Skull Relationship: Posterior Cranial Fossae Foramina Relationship: CN IX exits the skull via the jugular foramen. Fig 33 CN IX is mainly associated with the rostral medulla near CNs VIII and X (Fig 33) This is where motor nuclei are located for both SVE and VE functions. The SVE nucleus is part of the nucleus ambiguus and the VE nucleus is called the inferior salivatory nucleus. The sensory ganglia associated with CN IX are called the superior and inferior ganglia of IX and are located within or just below the jugular foramen. The neurons located here convey SA and SSA information associated with CN IX mainly to the solitary nucleus of the medulla. The next pages break apart the functional components of CN IX. Neuroscience: Cranial Nerves Page 19 of 25 Dr. Paul Walker CN IX Somatic Afferent (SA) Fig 34 Fig 34 Gray’s Anatomy for Students Sensory from oropharynx, posterior 1/3 tongue, auditory tube, middle ear cavity (Fig 16). Sensory neuronal cell bodies located in Superior & Inferior Ganglia of glossopharyngeal nerve. Peripheral processes travels with glossopharyngeal nerve. Central process goes through jugular foramen to connect to brainstem Afferent limb of the gag reflex is carried by CN IX SA fibers. CN IX Visceral Afferent (VA) Fig 35 Fig 35 Netter Sensory from carotid body & carotid sinus Sensory neuronal cell body located in superior & inferior ganglia of IX. Peripheral processes travels with glossopharyngeal nerve and sends carotid sinus branch. Central process goes through jugular foramen to connect to brainstem. Fig 36 Gray’s Atlas of Anatomy CN IX Special Sensory Afferent (SA) Fig 36 Taste sensation from oropharynx, posterior 1/3 tongue. Sensory neuronal cell body located in located in superior & inferior ganglia of IX. Peripheral processes travels with glossopharyngeal nerve. Central process goes through jugular foramen to connect to brainstem Neuroscience: Cranial Nerves Page 20 of 25 Dr. Paul Walker CN IX Visceral Efferent (VE) Fig 37 Fig 37 Gray’s Atlas of Anatomy Motor neuronal cell body in the Inferior Salivatory Nucleus of the rostral medulla Axons exit jugular foramen along with CN IX but return to skull through floor of middle ear cavity. Travel to postganglionic target in the Lesser Petrosal Nerve. This nerve travels under the dura of the middle cranial fossa to reach foramen ovale. Target ganglion- Otic Ganglia Target gland of postganglionic PANS fibers- Parotid Gland Postganglionic axons travel with auriculotemporal branch of V3 to get to parotid gland. CN IX Special Visceral Efferent (SVE) Fig 38 Fig 38 Gray’s Anatomy for Students Motor neuronal cell bodies in Nucleus Ambiguus of rostral medulla Axon travels through jugular foramen along with CN IX. Stylopharyngeus muscle is the only muscle innervated by CN IX. Clinical Correlation: CN IX paralysis can occur as a result of neurovascular pressure or a tumor growing in the posterior cranial fossa. This can cause sudden pain in the throat that radiates down the neck anterior to the auricle. A problem affecting CN IX at the jugular foramen may also affect CN X & CN XI producing mixed symptoms involving these nerves. Neuroscience: Cranial Nerves Page 21 of 25 Dr. Paul Walker J. CN X Vagus (Figs 39-44) Fig 39 Gray’s Anatomy for Students Functional Components: SA, VA, SSA, SVE, VE SA fibers provide sensation from the middle ear, laryngopharynx. VA fibers provide sensation from the aortic chemoreceptors and stretch receptors, thoracic and abdominal viscera. SSA fibers provide taste sensation from epiglottic region. SVE fibers provide motor to the laryngeal muscles. VE fibers provide parasympathetic motor axons to mucus glands of the pharynx and larynx, pulmonary system, gastrointestinal tract, as well as to cardiac muscle and smooth muscle of the pulmonary and gastrointestinal systems. Fossa Relationship: posterior cranial fossa Foramen Relationships: CN X exits the skull via the jugular foramen Fig 40 CN X is mainly associated with the rostral medulla near IX (Fig 40). This is where motor nuclei are located for both SVE and VE functions. The SVE nucleus is part of the nucleus ambiguus and the VE nucleus is called the dorsal motor nucleus of X. The sensory ganglia associated with CN X are called the superior and inferior ganglia of X and are located within or just below the jugular foramen. The neurons located here convey SA and SSA information associated with CN X mainly to the solitary nucleus of the medulla. The next pages break apart the functional components of CN X. Neuroscience: Cranial Nerves Page 22 of 25 Dr. Paul Walker Fig 41 Gray’s Anatomy for Students CN X Somatic Afferent (SA) Fig 41 Sensory from laryngopharynx (including larynx) & external acoustic meatus (Fig 20). Sensory neuronal cell body located in Superior & Inferior Ganglia of the vagus nerve. Peripheral processes travels with vagus nerve. Central process goes through jugular foramen to connect to brainstem CN X Special Sensory Afferent (SSA) Fig 41 Taste sensation from epiglottis and surrounding regions of pharynx. Sensory neuronal cell body located in Superior & Inferior Ganglia of the vagus nerve. Peripheral processes travels with vagus nerve. Central process goes through jugular foramen to connect to brainstem. Fig 42 Gray’s Atlas of Anatomy CN X Visceral Afferent (VA) Fig 42 Sensory from baroreceptors & chemoreceptors from the aorta, sensory for reflexes from thoracic & abdominal viscera. Sensory neuronal cell body located in Superior & Inferior Ganglia of the vagus nerve. Peripheral processes travels with vagus nerve. Central process goes through jugular foramen to connect to brainstem. Neuroscience: Cranial Nerves Page 23 of 25 Dr. Paul Walker Fig 43 Netter CN X Visceral Efferent (VE) Fig 43 Motor neuronal cell body in Brainstem (Medulla) Preganglionic PANS axons exit skull via jugular foramen and travel with the vagus nerve. Innervates mucus glands of the pharynx and larynx, pulmonary system, gastrointestinal tract. Innervates cardiac muscle and smooth muscle of pulmonary and gastrointestinal systems (to midgut) CN X Special Visceral Efferent (SVE) Fig 44 Fig 44 Gray’s Anatomy for Students Motor neuronal cell bodies in Nucleus Ambiguus of rostral medulla. Preganglionic axons exit skull via jugular foramen and travel with the vagus nerve. Innervates: all laryngeal muscles all soft palate muscles except tensor veli palatini all pharyngeal constrictors all pharyngeal elevators except stylopharyngeus 1 tongue muscle (palatoglossus) Elevation of the soft palate occurs during vocalization so a useful clinical test for the vagus nerve is to look for sagging of the soft palate and deviation of the uvula away (contralateral) from the suspected side of the lesion while the patient says ‘ahhh’. Clinical Correlation: CN X lesions produce hoarseness due to paralysis of laryngeal muscles as well as difficulty in swallowing (dysphagia). The soft palate will sag on the side of the lesion due to paralysis of the levator veli palatini muscle and the uvula will deviate away from the lesion side when the patient vocalizes. Autonomic disturbances of cardiovascular, respiratory, and GI function will be present and especially obvious if problem is bilateral. Neuroscience: Cranial Nerves Page 24 of 25 Dr. Paul Walker K. CN XI Accessory (Figs 45-46) Fig 45 Gray’s Anatomy for Students Functional Components: SE SE fibers to trapezius and sternocleidomastoid muscles Skull Relationship: Posterior Cranial Fossae Location of Primary Neuron: Accessory nucleus located in C1-C5 spinal cord (Fig 46). Foramina Relationship: CN XI traverses the foramen magnum to enter the skull and then exits skull via jugular foramen. Fig 46 Clinical Correlation: CN XI lesion paralyzes the trapezius and SCM muscles, so the patient exhibits weakness in shoulder elevation (shrug shoulder) and head turning to the opposite (unaffected) side. Neuroscience: Cranial Nerves Page 25 of 25 Dr. Paul Walker L. CN XII Hypoglossal (Fig 47-49) Fig 47 Gray’s Anatomy for Students Functional Components: SE SE fibers to muscles that move the tongue Skull Relationship: Posterior Cranial Fossae Location of Primary Neuron: Hypoglossal nucleus located at the level of the mid-medulla. Foramina Relationship: CN XII exits the skull via the hypoglossal foramen. The hypoglossal nerve exits the mid-medulla at the pre-olivary sulcus. This is a depression between the bump of the pyramid medially and the bump of the olive laterally. The hypoglossal nerve innervates all the tongue muscles except the palatoglossus muscle that is innervated by the vagus nerve. The main tongue muscle useful for clinical testing is the genioglossus muscle that protrudes the tongue from the oral cavity. A useful test is to ask the patient to stick out their tongue and look for tongue deviation toward the side (ipsilateral) of the suspected lesion. Fig 49 Netter Fig 48 Clinical Correlation: CN XII lesion paralyzes the tongue muscles and produces a primary effect of the tongue pointing toward the side of the lesion when protruded.