Y2S2 P2 Cranial Nerves + The Eye
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Questions and Answers

Which cranial nerve originates from the midbrain-pontine junction?

  • CN IV
  • CN IX
  • CN III (correct)
  • CN II

    • Which cranial nerve exits the skull through the jugular foramen?

  • CN XI (correct)
  • CN V2
  • CN VII
  • CN IX (correct)

    • What type of motor function is associated with the hypoglossal nerve (CN XII)?

  • General somatic motor (correct)
  • General somatic sensory
  • General visceral motor
  • Special visceral motor

    • Which cranial nerve is responsible for special visceral sensory functions, including taste?

    <p>CN IX</p> Signup and view all the answers

    From where do cranial nerves III to VIII arise?

    <p>Brainstem</p> Signup and view all the answers

    Which cranial nerve is responsible for the sensation of taste from the anterior two-thirds of the tongue?

    <p>Facial (VII)</p> Signup and view all the answers

    Which cranial nerve is primarily associated with vision?

    <p>Optic (II)</p> Signup and view all the answers

    Which of the following cranial nerves controls the lateral movement of the eye?

    <p>Abducens (VI)</p> Signup and view all the answers

    Which cranial nerve is involved in both hearing and balance?

    <p>Vestibulocochlear (VIII)</p> Signup and view all the answers

    Which of the following cranial nerves has a role in gland secretion?

    <p>Glossopharyngeal (IX)</p> Signup and view all the answers

    What is the primary function of the olfactory nerve (CN I)?

    <p>Special visceral sensory for smell</p> Signup and view all the answers

    Which structures do the olfactory receptors form before entering the cranial cavity?

    <p>Olfactory fascicles</p> Signup and view all the answers

    What type of cells in the olfactory mucosa provide structural support?

    <p>Sustentacular cells</p> Signup and view all the answers

    Which of the following conditions can lead to permanent anosmia?

    <p>Head injury</p> Signup and view all the answers

    What is the term for the absence of the sense of smell?

    <p>Anosmia</p> Signup and view all the answers

    Which type of cells in the olfactory mucosa develop into new olfactory cells?

    <p>Basal cells</p> Signup and view all the answers

    In which part of the central nervous system do axons of second-order neurons in the olfactory tract project?

    <p>Primary olfactory cortex</p> Signup and view all the answers

    Which neurodegenerative condition is associated with progressive anosmia?

    <p>Parkinson's disease</p> Signup and view all the answers

    What is the result of a lesion at the optic nerve?

    <p>Monocular blindness</p> Signup and view all the answers

    What does a lesion at the optic chiasm most likely cause?

    <p>Bilateral hemianopia</p> Signup and view all the answers

    What visual field loss is associated with a lesion in the upper optic radiation?

    <p>Contralateral inferior quadrantanopia</p> Signup and view all the answers

    How does a pituitary adenoma commonly affect vision?

    <p>Results in bilateral hemianopia</p> Signup and view all the answers

    In which location does contralateral homonymous hemianopia occur as a result of lesions?

    <p>Optic tract</p> Signup and view all the answers

    Which visual field is transmitted by the left optic tract?

    <p>Right field of view</p> Signup and view all the answers

    What type of visual loss results from a lesion at the visual cortex?

    <p>Contralateral homonymous hemianopia with macular sparing</p> Signup and view all the answers

    What anatomical pathway do fibers take from the nasal half of each eye at the optic chiasm?

    <p>They cross to the contralateral optic tract</p> Signup and view all the answers

    What does the ciliary muscle do when it contracts?

    <p>Causes the lens to become more spherical</p> Signup and view all the answers

    Which of the following conditions can lead to oculomotor nerve palsy?

    <p>Cavernous sinus infection</p> Signup and view all the answers

    What is the primary consequence of damage to the oculomotor nerve regarding pupil function?

    <p>Mydriasis</p> Signup and view all the answers

    Which extraocular muscle is NOT innervated by the oculomotor nerve?

    <p>Lateral rectus</p> Signup and view all the answers

    What results from unopposed activity of the lateral rectus and superior oblique muscles in oculomotor nerve palsy?

    <p>Down and out position of the eye</p> Signup and view all the answers

    What is the primary function of the trochlear nerve (CN IV)?

    <p>Innervates the superior oblique muscle</p> Signup and view all the answers

    Which statement accurately describes the course of the trochlear nerve?

    <p>It exits posteriorly from the midbrain and enters the cavernous sinus.</p> Signup and view all the answers

    Which condition is NOT associated with CN IV palsy?

    <p>Abducens nerve injury</p> Signup and view all the answers

    What symptom is commonly associated with loss of function of the superior oblique muscle due to CN IV damage?

    <p>Vertical diplopia exacerbated by looking down and in</p> Signup and view all the answers

    What is the smallest cranial nerve with the longest intracranial course?

    <p>Trochlear nerve (CN IV)</p> Signup and view all the answers

    Which of the following muscles is NOT innervated by the motor root of the trigeminal nerve?

    <p>Frontalis</p> Signup and view all the answers

    What type of pain is characterized by allodynia in trigeminal neuralgia?

    <p>Pain from a normally non-painful stimulus</p> Signup and view all the answers

    Which treatment option is typically used for managing pain in trigeminal neuralgia when other analgesics are ineffective?

    <p>Carbamazepine</p> Signup and view all the answers

    Which of the following nerve blocks provides anesthesia to the mandibular teeth and tongue?

    <p>Inferior alveolar block</p> Signup and view all the answers

    Which condition is NOT typically associated with trigeminal neuralgia?

    <p>Irritable bowel syndrome</p> Signup and view all the answers

    Which branch of the trigeminal nerve is responsible for sensory innervation of the cornea?

    <p>Ophthalmic (V1)</p> Signup and view all the answers

    What is the main motor function associated with the mandibular branch of the trigeminal nerve (V3)?

    <p>Mastication muscles</p> Signup and view all the answers

    Which of the following branches of the trigeminal nerve contains both sensory and parasympathetic fibers?

    <p>Auriculotemporal nerve</p> Signup and view all the answers

    What type of sensory information does the maxillary branch (V2) NOT provide?

    <p>Taste from the anterior tongue</p> Signup and view all the answers

    Which trigeminal nerve division exits the skull through the foramen rotundum?

    <p>Maxillary division (V2)</p> Signup and view all the answers

    Which nerve provides sensory innervation to the anterior two-thirds of the tongue?

    <p>Lingual nerve</p> Signup and view all the answers

    Which of the following structures does NOT originate from the trigeminal ganglion?

    <p>Ciliary ganglion</p> Signup and view all the answers

    Which statement accurately describes the autonomic fibers associated with the ophthalmic nerve (V1)?

    <p>Ophthalmic nerve does not contain autonomic fibers.</p> Signup and view all the answers

    What additional role does the inferior alveolar nerve serve aside from sensory innervation?

    <p>Motor nerve to mylohyoid muscle</p> Signup and view all the answers

    Which of the following functions does NOT fall under the role of the maxillary branch (V2)?

    <p>Motor to the mylohyoid muscle</p> Signup and view all the answers

    What is the clinical feature associated with abducens nerve damage?

    <p>Affected eye turned inwards</p> Signup and view all the answers

    Which structure is NOT innervated by the facial nerve?

    <p>Medial rectus muscle</p> Signup and view all the answers

    Which nerve branch does NOT contribute to facial expression innervation?

    <p>Lesser petrosal nerve</p> Signup and view all the answers

    What is the primary function of the greater petrosal nerve?

    <p>Parasympathetic supply to the lacrimal gland</p> Signup and view all the answers

    Which cranial nerve exits the cranial cavity via the stylomastoid foramen?

    <p>Facial nerve</p> Signup and view all the answers

    What can cause abducens nerve palsy?

    <p>Thrombophlebitis of the cavernous sinus</p> Signup and view all the answers

    Which of the following muscles is innervated by the buccal branch of the facial nerve?

    <p>Zygomaticus</p> Signup and view all the answers

    Which cranial nerves provide sensory innervation to the anterior two-thirds of the tongue?

    <p>CN V and CN VII</p> Signup and view all the answers

    Which muscle is directly innervated by C1/C2 fibers traveling with the hypoglossal nerve?

    <p>Thyrohyoid</p> Signup and view all the answers

    Which ganglion is associated with the post-ganglionic pathway for CN VII's greater petrosal branch?

    <p>Pterygopalatine ganglion</p> Signup and view all the answers

    What is the primary function of the muscles innervated by the ansa cervicalis?

    <p>Depress the hyoid bone</p> Signup and view all the answers

    Which cranial nerve provides parasympathetic fibers to the parotid gland?

    <p>Cranial Nerve IX</p> Signup and view all the answers

    Where do the post-ganglionic fibers from the ciliary ganglion primarily target?

    <p>Pupillary sphincter</p> Signup and view all the answers

    What is the expected vocal quality associated with unilateral recurrent laryngeal nerve injury?

    <p>Hoarseness</p> Signup and view all the answers

    Which muscle's weakness is directly associated with CN XI injury?

    <p>Trapezius</p> Signup and view all the answers

    What is the primary indication of CN XII palsy?

    <p>Tongue deviation towards the lesion</p> Signup and view all the answers

    What is the primary motor function of the hypoglossal nerve?

    <p>Tongue movement</p> Signup and view all the answers

    What happens to vocal fold movement following unilateral recurrent laryngeal nerve injury?

    <p>The other vocal fold crosses the midline</p> Signup and view all the answers

    Which of the following functions is associated with the ansa cervicalis?

    <p>Neck muscle innervation</p> Signup and view all the answers

    What is a common cause of CN XI palsy?

    <p>Cervical lymph node biopsy</p> Signup and view all the answers

    What is a potential outcome of bilateral recurrent laryngeal nerve injury?

    <p>Loss of vocal fold abduction and phonation</p> Signup and view all the answers

    What condition is characterized by inflammation of the vestibular branch leading to vertigo?

    <p>Vestibular Neuritis</p> Signup and view all the answers

    Which cranial nerve is responsible for the sensory innervation of the oropharynx, carotid body, and posterior third of the tongue?

    <p>Cranial Nerve IX</p> Signup and view all the answers

    Which cranial nerve exits the skull through the jugular foramen?

    <p>Cranial Nerve IX</p> Signup and view all the answers

    What is the primary motor function of the Vagus Nerve?

    <p>Modulating heart rate and gastrointestinal motility</p> Signup and view all the answers

    A patient with CSF leaking from the ear may have damage to which cranial nerve?

    <p>Cranial Nerve VIII</p> Signup and view all the answers

    Which branch of the Vagus Nerve provides visceral sensory innervation to the gastrointestinal tract?

    <p>Cardiac Branches</p> Signup and view all the answers

    The cochlear nerve is primarily associated with which function?

    <p>Hearing</p> Signup and view all the answers

    What neurological condition is characterized by loss of the gag reflex due to loss of afferent sensory signals?

    <p>Glossopharyngeal Palsy</p> Signup and view all the answers

    Which structure does the auricular branch of the Vagus Nerve innervate?

    <p>External Auditory Canal</p> Signup and view all the answers

    What type of hearing loss is associated with damage to the Vestibulocochlear Nerve?

    <p>Sensorineural Hearing Loss</p> Signup and view all the answers

    Which muscle is innervated by the external laryngeal branch of the Vagus Nerve?

    <p>Cricothyroid</p> Signup and view all the answers

    Which branch of the Cranial Nerve IX is responsible for taste sensation from the posterior third of the tongue?

    <p>Glossopharyngeal Branch</p> Signup and view all the answers

    What structure does the recurrent laryngeal nerve loop under on the right side?

    <p>Subclavian Artery</p> Signup and view all the answers

    Which cranial nerve is NOT associated with the extra-ocular muscles?

    <p>Trigeminal nerve</p> Signup and view all the answers

    What type of fracture is characterized by the herniation of orbital contents following blunt force trauma?

    <p>Blowout Fracture</p> Signup and view all the answers

    Which bone forms the roof of the bony orbit?

    <p>Frontal</p> Signup and view all the answers

    Which symptom is least likely to present with a fracture of the bony orbit?

    <p>Nasal bleeding</p> Signup and view all the answers

    What is the primary characteristic of oculomotor nerve (CN III) palsy at rest?

    <p>The affected eye turns down and out</p> Signup and view all the answers

    Which of the following symptoms is most indicative of damage to the sympathetic trunk?

    <p>Partial ptosis</p> Signup and view all the answers

    Which cranial nerve is responsible for innervating the superior oblique muscle, and what is a distinctive symptom of its palsy?

    <p>Trochlear nerve; diplopia and head tilt away from the affected side</p> Signup and view all the answers

    What structure in the eyeball is primarily responsible for refracting light?

    <p>Cornea</p> Signup and view all the answers

    Which of the following conditions can potentially cause Horner's syndrome?

    <p>Thyroid carcinoma</p> Signup and view all the answers

    What is the function of the lacrimal fluid?

    <p>To clean, nourish, and lubricate the eyes</p> Signup and view all the answers

    Which structure is involved in draining the lacrimal fluid after it accumulates in the lacrimal lake?

    <p>Lacrimal puncta and canaliculi</p> Signup and view all the answers

    Which nerve provides sensory innervation to the lacrimal gland?

    <p>Lacrimal nerve</p> Signup and view all the answers

    How does the sympathetic innervation affect the secretion of the lacrimal gland?

    <p>It inhibits secretion of lacrimal fluid</p> Signup and view all the answers

    Which of the following correctly describes the path of the parasympathetic innervation to the lacrimal gland?

    <p>Facial nerve → Pterygopalatine ganglion → Zygomatic nerve</p> Signup and view all the answers

    What is the main role of the pigmented layer of the retina?

    <p>Absorb light to prevent scattering</p> Signup and view all the answers

    What is the significance of the optic disc in the eye?

    <p>Entry point of the optic nerve without light-detecting cells</p> Signup and view all the answers

    Which structure within the eye acts as a major source of nourishment for the retina?

    <p>Choroid</p> Signup and view all the answers

    Which part of the eyelid is primarily responsible for gently closing the eyelids?

    <p>Palpebral part of the orbicularis oculi</p> Signup and view all the answers

    What is the primary function of the Meibomian glands found in the eyelids?

    <p>Secrete oil to prevent tear evaporation</p> Signup and view all the answers

    What is the primary effect of occlusion of the central retinal artery?

    <p>Complete blindness in the affected eye</p> Signup and view all the answers

    What role does the ciliary body play regarding the lens of the eye?

    <p>Changes the shape of the lens to affect light refraction</p> Signup and view all the answers

    Which layer of the eyelid helps in the distribution of tears across the eye?

    <p>Orbicularis oculi muscle</p> Signup and view all the answers

    Where are the lacrimal glands primarily located?

    <p>Superolaterally in the orbit</p> Signup and view all the answers

    What distinguishes aqueous humor from vitreous humor?

    <p>Aqueous humor is produced by the ciliary body and is drained, while vitreous humor is gel-like and not drained</p> Signup and view all the answers

    What condition results in the presence of cotton wool spots in the retina?

    <p>Diabetic retinopathy</p> Signup and view all the answers

    What is the primary physical manifestation of cataracts as they progress?

    <p>Blurred, hazy vision</p> Signup and view all the answers

    What type of glaucoma is characterized by a rapid onset of blindness due to iris obstruction?

    <p>Closed-angle glaucoma</p> Signup and view all the answers

    Which of the following conditions is associated with high intracranial pressure affecting the optic disc?

    <p>Papilloedema</p> Signup and view all the answers

    In diabetic retinopathy, what describes the pre-proliferative stage?

    <p>Mild or no symptoms with slight vision blurring</p> Signup and view all the answers

    What symptom is typical of macular degeneration as it progresses?

    <p>Chronic distortion of vision</p> Signup and view all the answers

    Which of the following treatments is typically performed for cataracts?

    <p>Cataract surgery</p> Signup and view all the answers

    What is the main risk factor for developing cataracts aside from age?

    <p>Diabetes</p> Signup and view all the answers

    What visual phenomenon may patients with cataracts experience at night?

    <p>Halos around lights</p> Signup and view all the answers

    What is a distinguishing feature of proliferative diabetic retinopathy?

    <p>Growth of fragile new blood vessels</p> Signup and view all the answers

    Study Notes

    Cranial Nerve Overview

    • Twelve pairs of cranial nerves emerge from the brain and control various functions, including sensory input, motor output, and autonomic regulation.
    • Olfactory (I): Smell, Optic (II): Vision, Oculomotor (III): Eye movement, Trochlear (IV): Eye movement, Trigeminal (V): Facial sensation and mastication, Abducens (VI): Eye movement, Facial (VII): Facial expression, taste, Vestibulocochlear (VIII): Hearing and balance, Glossopharyngeal (IX): Taste, swallowing, Vagus (X): Autonomic functions, Accessory (XI): Neck and shoulder muscles, Hypoglossal (XII): Tongue movement

    Origin of Cranial Nerves

    • Cranial nerves I and II (olfactory and optic) originate from the cerebrum.
    • The remaining cranial nerves originate from the brainstem.
      • Midbrain-pontine junction: III
      • Posterior side of the midbrain: IV
      • Pons: V, VI, VIII
      • Pontine-medulla junction: IX, XI (from superior to inferior)
      • Medulla: IX, XI, XII (from posterior to anterior)

    Cranial Foramina

    • Cranial nerves exit the cranium through foramina:
      • Cribriform plate: CN I
      • Optic canal: CN II
      • Superior orbital fissure: CN III, IV, V1 (ophthalmic), VI
      • Foramen rotundum: CN V2 (maxillary)
      • Foramen ovale: CN V3 (mandibular)
      • Internal acoustic meatus: CN VII, VIII
      • Jugular foramen: CN IX, X, XI
      • Hypoglossal canal: CN XII

    Cranial Nerve Modalities

    • Sensory:
      • General somatic sensory (GSS): Sensation from the skin
      • General visceral sensory (GVS): Sensation from the viscera
      • Special sensory: - Special visceral sensory (SVS): Sight, smell, taste, hearing, balance
    • Motor:
      • General somatic motor (GSM): Skeletal muscles
      • Special visceral motor (SVM): Muscles derived from pharyngeal arches
      • General visceral motor (GVM): Smooth muscles of the gastrointestinal tract and autonomic motor: - Parasympathetic - Sympathetic

    CN I: Olfactory Nerve

    • Function: Smell
    • Sensory or Motor: Special visceral sensory (only)
    • Course: Shortest cranial nerve
      • Olfactory receptors in the nasal epithelium detect smell
      • Receptors assemble into olfactory fascicles (nerve bundles)
      • Fascicles penetrate the cribriform plate to enter the cranial cavity
      • Fascicles then enter the olfactory bulb
      • They synapse with mitral cells at the olfactory glomeruli in the olfactory bulb
      • Second-order neurons pass into the olfactory tract
      • The tract divides into medial and lateral stria to reach the primary olfactory cortex

    The Olfactory Mucosa

    • Location: Roof of the nasal cavity
    • Function: Detecting smell and some aspects of taste
    • Structure: Pseudostratified columnar epithelium containing:
      • Basal cells: Form new stem cells for olfactory cell development
      • Sustentacular cells: Provide structural support
      • Olfactory receptor cells: Bipolar neurons consisting of:
        • Dendritic Process: Projects to the surface of the epithelium and has short cilia (olfactory hair) projecting into the mucous membrane for odor detection
        • Central Process (Axon): Projects through the basement membrane

    CN I Pathology - Anosmia

    • Anosmia: Absence of smell
    • Causes: Damage or disruption to CN I
      • Types:
        • Temporary: Infection (meningitis), Local disorders of the nose (common cold, COVID-19)
        • Permanent: Head injury, Tumors in the olfactory groove (meningioma)
        • Progressive: Parkinson's, Alzheimer's, Neurodegenerative conditions (often precedes motor symptoms)
        • Congenital: Kallmann syndrome (puberty issues), Primary Ciliary Dyskinesia (defective cilia)

    Optic Nerve Function & Course

    • Function: Vision (Special Somatic Sensory)
    • Course:
      • Extracranial:
        • Light detected by photoreceptors (rods & cones) in the eye.
        • Photoreceptors stimulate retinal ganglion cells, which converge to form the optic nerve.
        • Optic nerve travels through the optic canal to enter the cranial cavity.
        • Lesion #1: Damage at the optic nerve = Monocular blindness
      • Intracranial:
        • Optic Chiasm:
          • Two optic nerves form the optic chiasm (near the pituitary gland).
          • Lesion #2: Damage at the optic chiasm = Bilateral hemianopia (loss of vision in half of the visual field on both sides)
          • Pituitary adenoma can compress the optic chiasm causing this lesion.
        • Optic Tract:
          • Fibers Cross: Nasal/medial fibers from each eye cross to the contralateral optic tract, while temporal/lateral fibers remain ipsilateral.
          • Left Optic Tract: Transmits the right field of vision.
          • Right Optic Tract: Transmits the left field of vision.
          • Lesion #3: Damage at the optic tract = Contralateral homonymous hemianopia (loss of vision in the same half of the visual field on both sides).
        • Lateral Geniculate Nucleus:
          • Optic tracts travel to the lateral geniculate nucleus in the corresponding cerebral hemisphere.
          • Lesion #5: Damage at the lateral geniculate nucleus (affecting both optic radiations) = Contralateral homonymous hemianopia.
        • Optic Radiations:
          • Optic tracts synapse before dividing into upper and lower optic radiations.
          • Upper Optic Radiation: Transmits lower quadrant field of vision, travels through the parietal lobe to the upper bank of the calcarine fissure.
          • Lesion #6: Damage at the upper optic radiation = Contralateral inferior quadrantanopia (loss of vision in the lower quadrant of the contralateral visual field).
          • Lower Optic Radiation (Meyer's Loop): Transmits upper quadrant field of vision, travels through the temporal lobe to the lower bank of the calcarine fissure.
          • ** lesion #4:** Damage at the lower optic radiation = Contralateral superior quadrantanopia (loss of vision in the upper quadrant of the contralateral visual field).
        • Visual Cortex:
          • Optic radiations converge at the visual cortex.
          • Lesion #7: Damage at the visual cortex = Contralateral homonymous hemianopia with macular sparing (loss of vision in the same half of the visual field on both sides, but the central vision is spared).
        • Macular Sparing Theories:
          • Vascular: Dual blood supply to the occipital pole by the middle cerebral artery (MCA) and posterior cerebral artery (PCA).
          • Cortical: Dual representation of the macula in both occipital cortices.

    CN III: Oculomotor Nerve

    • Function:

      • Somatic motor: Innervates most extraocular muscles (superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae superioris)
      • Visceral motor: Parasympathetic innervation of the sphincter pupillae (pupil constriction) and ciliary muscles (lens accommodation)
      • Sympathetic fibers: Travel with CN III to innervate the superior tarsal muscle (helps raise the eyelid)

    • Course:

      • Emerges from the midbrain's anterior surface
      • Enters the cavernous sinus after piercing the dura mater
      • Joins sympathetic fibers from the internal carotid plexus within the cavernous sinus
      • Exits the skull through the superior orbital fissure, dividing into:
        • Superior branch: Innervates the superior rectus and levator palpebrae superioris muscles, plus sympathetic fibers to the superior tarsal muscle
        • Inferior branch: Innervates the inferior rectus, medial rectus, and inferior oblique muscles, plus parasympathetic fibers to the ciliary ganglion

    Parasympathetic Innervation

    • Preganglionic fibers: Travel with the inferior branch of CN III to the ciliary ganglion
    • Synapse: Occurs at the ciliary ganglion
    • Postganglionic fibers: Travel via the short ciliary nerves to:
      • Sphincter pupillae: Constricts the pupil
      • Ciliary muscles: Contraction makes the lens more spherical for near vision

    CN III Palsy

    • Causes:

      • Increased intracranial pressure (ICP)
      • Posterior communicating artery aneurysm
      • Cavernous sinus infection or trauma

    • Clinical Features:

      • "Down and out" eye position: Due to unopposed action of the lateral rectus and superior oblique muscles
      • Ptosis: Paralysis of the levator palpebrae superioris and unopposed action of the orbicularis oculi muscle
      • Mydriasis (dilated pupil): Paralysis of the sphincter pupillae and unopposed action of the dilator pupillae muscle

    Trochlear Nerve (CN IV)

    • The trochlear nerve is responsible for controlling the superior oblique muscle, which rotates the eye downwards and inwards.
    • It is the smallest cranial nerve by size but has the longest intracranial course.
    • Fibers from each trochlear nucleus cross within the midbrain.
    • It is the only cranial nerve to exit the brainstem posteriorly, emerging from the posterior aspect of the midbrain.
    • The trochlear nerve travels anteriorly in the subarachnoid space before piercing the dura mater to enter the cavernous sinus.
    • It exits the cranial cavity via the superior orbital fissure to reach the orbit.

    Trochlear Nerve Palsy

    • Damage to the trochlear nerve can result in a loss of function of the superior oblique muscle, leading to a range of difficulties.
    • The most common causes of trochlear nerve palsy include:
      • Microvascular damage: Often caused by diabetes or hypertension.
      • Congenital malformations.
      • Increased intracranial pressure (ICP).
      • Thrombophlebitis of the cavernous sinus (inflammation of the vein).
    • Symptoms include:
      • Head tilt: The affected side of the head will tilt away from the affected eye to compensate for the unopposed extortion (outward rotation) of the eye.
      • Vertical diplopia: Double vision that is worse when looking downwards and inwards. This can be particularly challenging activities like reading or walking down stairs.

    CN V: Trigeminal Nerve

    • Function:

      • Sensory: Skin, mucous membranes, and sinuses of the face
      • Motor: Muscles of mastication (V3 branch)
      • Parasympathetic: Fibres travel with branches

    • Course:

      • Originates from 4 nuclei (3 sensory, 1 motor)
        • Mesencephalic (sensory)
        • Principal sensory (sensory)
        • Spinal nucleus (sensory)
        • Motor nucleus (motor)
      • Three sensory nuclei merge at the pons
      • Forms the trigeminal ganglion in the middle cranial fossa
      • Divides into 3 branches:
        • Ophthalmic (V1): Exits through superior orbital fissure
        • Maxillary (V2): Exits through foramen rotundum
        • Mandibular (V3): Exits through foramen ovale
      • Motor root joins V3.

    CN V1: Ophthalmic Branch

    • Branches:
      • Frontal (largest): Sensory to upper eyelid, conjunctiva, scalp
        • Supraorbital
        • Supratrochlear
      • Lacrimal (smallest): Sensory + parasympathetic
        • Sensory to lacrimal gland
        • Parasympathetic from CN VII
      • Nasociliary: Sensory + sympathetic
        • Long ciliary: Cornea and sympathetic fibres to dilator pupillae
        • Anterior ethmoid: Frontal, ethmoid, sphenoid sinuses, nasal cavity
        • Posterior ethmoid: Sphenoid sinus
        • Infratrochlear: Bridge of nose, upper eyelid, conjunctiva
    • Ophthalmic nerve itself does not contain autonomic fibres.

    CN V2: Maxillary Branch

    • Function:
      • Sensory:
        • Lower eyelid and conjunctiva
        • Nasal cavity (inferior posterior)
        • Lateral nose
        • Cheeks and maxillary sinus
        • Upper lip, teeth, gingiva, palate
      • Parasympathetic: (From CN VII)
        • Lacrimal gland
        • Mucous glands of nasal mucosa

    CN V3: Mandibular Branch

    • Sensory Branches:

      • Auriculotemporal:
        • Sensory: Anterior auricle, external acoustic meatus, tympanic membrane, lateral temple
        • Parasympathetic: Parotid gland (from CN IX)
      • Buccal: Sensory to buccal membranes and molar teeth
      • Inferior Alveolar: Sensory and motor
        • Mylohyoid branch: Motor to mylohyoid and anterior digastric
        • Sensory to mandibular teeth
        • Mental nerve: Sensation to lower lip and chin
      • Lingual: Sensory
        • General sensation to anterior 2/3 of tongue
        • Taste to anterior 2/3 of tongue (from CN VII)
        • Autonomic to submandibular and sublingual glands (from CN VII)

    • Motor Branches:

      • Muscles of mastication: Masseter, medial/lateral pterygoid, temporalis
      • Tensor tympani
      • Tensor veli palatini
      • Suprahyoid muscles: Anterior belly of digastric, mylohyoid

    CN V: Trigeminal Nerve Pathology

    • Trigeminal Neuralgia:

      • Chronic neuropathic pain over the distribution of the nerve
      • Types:
        • Hyperalgesia
        • Allodynia
      • Causes:
        • Multiple sclerosis
        • Stroke
        • Trauma
      • Treatment:
        • Carbamazepine (anticonvulsant)
        • Surgical destruction (permanent loss of sensation)

    • Herpes Zoster:

      • Herpes simplex virus (HSV) can remain dormant within the trigeminal ganglion
      • Shingles: Reactivation of the virus causes painful vesicles within the distribution of a single branch
      • Most common in V1 branch

    CN V: Trigeminal Nerve Blocks

    • Infraorbital: Anaesthesia of upper lip and maxillary incisors
    • Mental: Anaesthesia of lower lip and chin
    • Buccal: Anaesthesia of cheek
    • Inferior Alveolar: Anaesthesia of mandibular teeth and tongue (due to proximity to lingual nerve)

    CN VI: Abducens Nerve

    • Function: Controls the lateral rectus muscle, responsible for eye abduction (turning the eye outwards)
    • Course:
      • Emerges from the brainstem at the pontomedullary junction
      • Travels through the subarachnoid space, pierces the dura mater, and enters Dorello's canal
      • Continues through the cavernous sinus
      • Exits the cranial cavity via the superior orbital fissure
    • CN VI Palsy:
      • Caused by damage to the abducens nerve, potentially due to:
        • Space-occupying lesions compressing the brainstem
        • Diabetic neuropathy
        • Thrombophlebitis of the cavernous sinus
      • Clinical Features:
        • Affected eye turns inwards (adducted) due to unopposed activity of the medial rectus
        • Diplopia (double vision)

    CN VII: Facial Nerve

    • Functions:
      • Motor: Controls muscles of facial expression, posterior belly of digastric, stylohyoid, and stapedius
      • Sensory: Receives sensory input from the concha of the auricle
      • Special Sensory: Carries taste sensation from the anterior two-thirds of the tongue
      • Parasympathetic:
        • Innervates the submandibular and sublingual salivary glands, as well as nasal, palatine, and pharyngeal mucous glands
        • Controls the lacrimal glands

    CN VII: Facial Nerve - Intracranial Course

    • Motor and Sensory Roots: Travel together through the internal acoustic meatus
    • Facial Canal: Roots fuse, form the geniculate ganglion, and branch into:
      • Greater petrosal nerve
      • Nerve to stapedius
      • Chorda tympani
    • Exit: Exits the facial canal and skull via the stylomastoid foramen

    CN VII: Facial Nerve - Extracranial Course

    • Branches: After exiting, it gives off three posterior and inferior branches:
      • Posterior auricular nerve
      • Nerve to digastric
      • Nerve to stylohyoid
    • Motor Root: Continues into the parotid gland and splits into five branches that innervate the muscles of facial expression:
      • Temporal branch
      • Zygomatic branch
      • Buccal branch
      • Marginal mandibular branch
      • Cervical branch

    CN VII: Facial Nerve - Motor Functions

    • Nerve to stapedius: Controls the stapedius muscle
    • Posterior auricular nerve:
      • Innervates intrinsic and extrinsic muscles of the outer ear (auricular branch)
      • Supplies the occipitalis muscle (occipital branch)
    • Nerve to digastric: Controls the posterior belly of the digastric muscle
    • Nerve to stylohyoid: Controls the stylohyoid muscle
    • Temporal branch: Innervates the frontalis, orbicularis oculi, and corrugator supercilii muscles
    • Zygomatic branch: Innervates the orbicularis oculi muscle
    • Buccal branch: Controls the orbicularis oris, buccinator, and zygomaticus muscles
    • Marginal mandibular branch: Controls the mentalis muscle
    • Cervical branch: Controls muscles in the neck region

    CN VIII: Vestibulocochlear Nerve

    • Function: Hearing and balance
    • Course: Vestibular and cochlear components originate separately, combine in the pons, exit via the internal acoustic meatus
      • Intracranially, splits back into vestibular and cochlear nerves
      • Vestibular nerve → Vestibular system of inner ear → Vestibular ganglion → Balance
      • Cochlear nerve → Cochlea of inner ear → Spiral ganglia → Hearing
    • Vestibular Neuritis: Inflammation of the vestibular branch
      • Vertigo
      • Nystagmus
      • Loss of equilibrium
      • Nausea and vomiting
    • Vestibulocochlear Nerve Damage: Sensorineural hearing loss
      • Damage can occur as the nerve passes through the internal acoustic meatus due to a basilar skull fracture
      • Bleeding from the ears and nose, and CSF leaking from the ears (CSF otorrhoea) and nose (CSF rhinorrhoea)

    CN IX: Glossopharyngeal Nerve

    • Function: Sensory, special sensory, parasympathetic, and motor
      • Sensory: Oropharynx, carotid body and sinus, posterior ⅓ tongue, middle ear, Eustachian tube
      • Special sensory: Posterior ⅓ tongue taste
      • Parasympathetic: Parotid gland
      • Motor: Stylopharyngeus muscle
    • Palsy: Loss of gag reflex

    CN IX: Glossopharyngeal Nerve - Course

    • Leaves the cranium via the jugular foramen
      • Gives off the tympanic nerve → tympanic plexus → sensation to middle ear, tympanic membrane, Eustachian tube
    • Descends down the neck with the ICA to innervate stylopharyngeus and the carotid sinus and body via the carotid sinus nerve
    • Passes between the superior and middle pharyngeal constrictors to terminate in the pharynx with three branches
      • Lingual: Mucosa of oropharynx
      • Tonsil: Palatine tonsils
      • Pharyngeal: Posterior ⅓ of tongue sensation and taste
    • Parasympathetics travel with the tympanic nerve → lesser petrosal nerve → otic ganglion → auriculotemporal nerve → parotid gland (promote secretions)

    CN X: Vagus Nerve

    • Function: Sensory, motor, and parasympathetic
    • Course: Longest cranial nerve, originates from the medulla
      • Within the cranium: Gives off the Auricular branch
      • Exits the cranium via the jugular foramen
      • Within the neck: Travels in the carotid sheath (with IJV and common carotid), passing anterior to the subclavian
      • Several branches arise in the neck:
        • Pharyngeal (pharynx and soft palate muscles)
        • Superior laryngeal
          • Internal (laryngopharynx sensation)
          • External (cricothyroid muscle)
      • Gives off the Recurrent laryngeal nerve (larynx muscles)
        • Right recurrent laryngeal loops under the subclavian
        • Left recurrent laryngeal loops under the aortic arch
      • Within the thorax:
        • Right vagus → Posterior vagal trunk
        • Left vagus → Anterior vagal trunk
        • Branches from each contribute to the oesophageal and cardiac plexus
      • The vagal trunks enter the abdomen via the oesophageal hiatus of the diaphragm
      • Within the abdomen: Vagus supplies parasympathetic innervation and sensation to the oesophagus, stomach, small and large bowel (up to the splenic flexure)

    CN X: Vagus Nerve - Sensory

    • Somatic sensory: Skin of posterior external auditory canal and external ear (auricular)
    • Visceral sensory:
      • Laryngopharynx and larynx up to the vocal cords (internal laryngeal)
      • Heart (cardiac branches)
      • GIT up to the splenic flexure
    • Special sensory: Taste at the root of the tongue and epiglottis

    CN X: Vagus Nerve - Motor

    • Muscles of the pharynx except stylopharyngeus (pharyngeal branches):
      • Pharyngeal constrictor muscles
      • Palatopharyngeus
      • Salpingopharyngeus
    • Muscles of the larynx (recurrent laryngeal):
      • Thyroarytenoid
      • Posterior and lateral crico-arytenoid
      • Transverse and oblique arytenoids
      • Vocalis
    • Cricothyroid (external laryngeal)
    • Palatoglossus and soft palate muscles

    CN X: Vagus Nerve - Parasympathetic

    • Heart (cardiac branches):
      • Supplies the SA and AV nodes
      • Constant vagal tone keeps the heart rate at a normal level
      • Damage to vagus = more rapid resting HR
    • Gastrointestinal:
      • Branches supply the oesophagus, stomach, small intestine and large intestine up to the splenic flexure
      • Stimulates smooth muscle contraction and glandular secretion

    CN X: Vagus Nerve Lesions

    • Key Features:

      • Uvula deviation away from the side of the lesion
      • Loss of gag reflex
      • Dysphagia
      • Hoarse voice (if recurrent laryngeal nerve is involved)

    • Paralysis of the vocal cords:

      • Unilateral recurrent laryngeal nerve injury = hoarse voice
      • Bilateral recurrent laryngeal nerve injury = stridor

    CN XI: Spinal Accessory Nerve

    • Function: Somatic motor → Sternocleidomastoid and trapezius muscles
    • Course:
      • Cranial portion: Leaves the cranium via the jugular foramen, then becomes part of the vagus nerve
      • Spinal portion: C1-C5/C6 nerve roots
        • These fibers join then run superiorly to enter the cranial cavity via the foramen magnum
        • Traverse the posterior cranial fossa to exit via the jugular foramen, briefly meeting the cranial portion
        • Descends with ICA to innervate the sternocleidomastoid then crosses the posterior triangle superficially to innervate the trapezius
    • Palsy: Paralysis of SCM and trapezius
      • SCM: Weakness/inability to rotate the head
      • Trapezius: Weakness/Inability to shrug the shoulders
      • +/- Muscle wasting
      • Commonly iatrogenic

    CN XII: Hypoglossal Nerve

    • Function: Somatic motor → Muscles of the tongue (except palatoglossus)
    • Course:
      • Exits the cranium via the hypoglossal canal before being joined by branches of the cervical plexus (C1/C2 fibers)
      • Passes inferior to the angle of the mandible and across the carotids before moving anteriorly to the tongue
    • Palsy: Paralysis of the tongue muscles
      • Extrinsic (Genioglossus, Hyoglossus, Styloglossus, NOT palatoglossus (vagus innervation))
      • Intrinsic (Superior longitudinal, Inferior longitudinal, Transverse, Vertical)
      • Tongue deviates towards the side of the lesion +/- fasciculations or wasting
      • Causes include malignancy, penetrating trauma or dissection of the ICA

    Ansa Cervicalis

    • Function: Motor → Neck muscles
    • Roots: C1/C2 (not cranial nerves)
    • Course:
      • Some C1/C2 fibers travel with the hypoglossal nerve and give branches to:
        • Geniohyoid (elevates hyoid bone)
        • Thyrohyoid (depresses hyoid bone)
      • A separate set of C1/C2 fibers descends and is joined by the above fibers to create the ansa cervicalis. This gives branches to:
        • Omohyoid
        • Sternohyoid
        • Sternothyroid
      • All depress the hyoid bone

    Parasympathetics of the Head and Neck (COPS 3977)

    • Cranial Nerve: | Pre-ganglionic: | Ganglion: | Post-ganglionic: | Target:
      • CN III | Oculomotor | Ciliary ganglion | Short ciliary | Pupillary sphincter
      • CN IX | Lesser petrosal | Otic ganglion | Hitchhike with auriculotemporal | Mucous membranes, Parotid gland
      • CN VII | Greater petrosal | Pterygopalatine ganglion | Hitchhike with maxillary nerve | Mucous membranes of nose and pharynx, Lacrimal gland
      • CN VII | Chorda tympani | Submandibular ganglion | - | Submandibular and sublingual salivary glands

    Bony Orbit

    • Pyramidal structure housing the eyeball, eyelids, extraocular muscles, nerves (CN II-VI), blood vessels, and orbital fat.
    • Roof: Frontal bone.
    • Floor: Maxilla.
    • Lateral: Zygomatic bone.
    • Medial: Maxilla, lacrimal, and ethmoid bones.
    • It has three major openings: optic canal, superior orbital fissure, and inferior orbital fissure.

    Fractures of the Bony Orbit

    • Orbital Rim Fracture: Fracture of the bones forming the outer rim of the orbit.
    • "Blowout" Fracture: Partial herniation of orbital contents through the bony orbit, usually due to blunt force trauma.
    • Common Symptoms: Pain, Exophthalmos (eye protrusion), involvement of surrounding structures (e.g., nerves causing eye muscle paralysis).

    The Eyeball

    • Fibrous Layer: Sclera (white, provides shape and support) and Cornea (transparent, refracts light).
    • Vascular Layer: Choroid (nourishes retina), Ciliary Body (controls lens shape), and Iris (controls pupil size).
    • Inner Layer: Pigmented layer (absorbs light), Neural layer (photoreceptors), Fovea centralis (high acuity vision), Optic disc (optic nerve entry).

    Other Structures in the Eyeball

    • Anterior/Posterior Chambers: Between cornea and lens, filled with aqueous humor.
    • Aqueous humor: Nourishes and protects the eye, produced and drained constantly.
    • Lens: Posterior to the pupil, alters shape to affect light refraction.
    • Vitreous humor: Behind the lens.

    Vasculature of the Eye

    • Arterial Supply: Ophthalmic artery, branch of internal carotid, supplying central retinal artery (critical for vision).
    • Venous Drainage: Superior and Inferior ophthalmic veins, draining into cavernous sinus.

    The Eyelids

    • Functions: Protection, distribution of tears.
    • Layers: Skin and subcutaneous tissue, Orbicularis oculi muscle, Tarsal plates, Conjunctiva.

    Layers of the Eyelid

    • Skin and subcutaneous tissue: No subcutaneous fat, contains ciliary glands and glands of Zeis.
    • Orbicularis oculi muscle: Palpebral, Lacrimal, and Orbital parts. Innervated by facial nerve.
    • Tarsal plates: Dense connective tissue, supports levator apparatus (levator palpebrae superioris muscle) and Meibomian glands.
    • Conjunctiva: Palpebral and Bulbar.

    Lacrimal Gland

    • Location: Superolaterally in the orbit, in lacrimal fossa of frontal bone.
    • Structure: Compound tubuloacinar structure.
    • Function: Secretes lacrimal fluid (cleans, nourishes, and lubricates eyes).
    • Arterial Supply: Lacrimal artery.
    • Venous Drainage: Superior ophthalmic vein.

    Innervation of the Lacrimal Gland

    • Sensory: Lacrimal nerve (ophthalmic nerve).
    • Parasympathetic: Stimulates secretion (facial nerve → pterygopalatine ganglion → maxillary nerve).
    • Sympathetic: Inhibits secretion (superior cervical ganglion → internal carotid plexus → deep petrosal nerve).

    Lacrimal Apparatus

    • Lacrimal fluid drains through the lacrimal puncta and canaliculi into the lacrimal sac, then into the nasolacrimal duct, and finally into the inferior meatus of the nasal cavity.

    Pathology

    • Glaucoma: Obstruction of aqueous humor drainage.
      • Open angle: Gradual peripheral vision loss.
      • Closed angle: Rapid blindness.
    • Cataract: Lens opacification.
    • Papilloedema: Swelling of optic disc due to raised intracranial pressure.
      • Causes: Intracranial mass lesions, intracranial haemorrhage, meningitis, hydrocephalus.

    Cataracts

    • Cloudiness of the lens, caused by tissue breakdown.
    • Causes: Ageing, injury, eye surgery, diabetes, other eye conditions, long-term steroid use.

    Diabetic Retinopathy

    • Microvascular diabetic complication causing retinal scarring.
    • Pre-proliferative Stage: Mild or no symptoms, retinal vessel leakage, nutrient and oxygen deprivation.
    • Proliferative Stage: New vessel growth, fragile and prone to rupture, haemorrhage, scarring.

    Macular Degeneration

    • Degenerative retinal disease causing central vision loss.
    • Caused by buildup of waste material (drusen) under the retina.

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