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Questions and Answers
Which nerve is responsible for innervating the muscles of mastication?
Which nerve is responsible for innervating the muscles of mastication?
What is the primary function of the Supraorbital Nerve?
What is the primary function of the Supraorbital Nerve?
Which branch of the maxillary nerve innervates the upper lip and part of the nasal cavity?
Which branch of the maxillary nerve innervates the upper lip and part of the nasal cavity?
Which nerve carries autonomic fibers to the submandibular and sublingual glands?
Which nerve carries autonomic fibers to the submandibular and sublingual glands?
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What does the Lacrimal Nerve supply?
What does the Lacrimal Nerve supply?
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What is the primary role of the amygdala?
What is the primary role of the amygdala?
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Which structure in the brain is responsible for forming memories related to scents?
Which structure in the brain is responsible for forming memories related to scents?
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What is the pathway of visual information from the retina to the primary visual cortex?
What is the pathway of visual information from the retina to the primary visual cortex?
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Which cranial nerve is primarily responsible for pupil constriction and lens accommodation?
Which cranial nerve is primarily responsible for pupil constriction and lens accommodation?
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What are optic radiations associated with?
What are optic radiations associated with?
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What influences the loss of the sense of smell on perception?
What influences the loss of the sense of smell on perception?
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Where is the nucleus of the oculomotor nerve located?
Where is the nucleus of the oculomotor nerve located?
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Which cranial nerve is associated with CN III palsy?
Which cranial nerve is associated with CN III palsy?
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Which muscle is not innervated by the hypoglossal nerve?
Which muscle is not innervated by the hypoglossal nerve?
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Which cranial nerve is primarily responsible for the movement of tongue muscles?
Which cranial nerve is primarily responsible for the movement of tongue muscles?
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What is the consequence of damage to the hypoglossal nerve?
What is the consequence of damage to the hypoglossal nerve?
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Where do the fibers of the hypoglossal nerve exit the skull?
Where do the fibers of the hypoglossal nerve exit the skull?
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Which cranial nerves have mixed functionality?
Which cranial nerves have mixed functionality?
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What is one method to assess the function of the hypoglossal nerve?
What is one method to assess the function of the hypoglossal nerve?
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Which cranial nerves are classified purely as sensory nerves?
Which cranial nerves are classified purely as sensory nerves?
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Which cranial nerve innervates the sphincter muscle for pupil constriction?
Which cranial nerve innervates the sphincter muscle for pupil constriction?
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Which nerve is NOT classified as a somatomotor nerve?
Which nerve is NOT classified as a somatomotor nerve?
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What is the primary motor function of the inferior oblique muscle?
What is the primary motor function of the inferior oblique muscle?
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What can lead to episodes of Superior Oblique Myokymia?
What can lead to episodes of Superior Oblique Myokymia?
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Which condition is associated with the palsy of the Superior Oblique muscle?
Which condition is associated with the palsy of the Superior Oblique muscle?
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Where is the trigeminal motor nucleus located?
Where is the trigeminal motor nucleus located?
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Which of the following best describes the trigeminal ganglion?
Which of the following best describes the trigeminal ganglion?
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Which of the following cranial nerve divisions provides sensory innervation to the forehead?
Which of the following cranial nerve divisions provides sensory innervation to the forehead?
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Which of the following is NOT a function of the trigeminal nerve?
Which of the following is NOT a function of the trigeminal nerve?
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What type of nerve is the trigeminal nerve classified as?
What type of nerve is the trigeminal nerve classified as?
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Which type of fibers are responsible for the motor component of the trigeminal nerve?
Which type of fibers are responsible for the motor component of the trigeminal nerve?
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What could cause decompensated fovea in relation to ocular muscles?
What could cause decompensated fovea in relation to ocular muscles?
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What is a common consequence of 6th cranial nerve palsy related to increased intracranial pressure?
What is a common consequence of 6th cranial nerve palsy related to increased intracranial pressure?
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Which branch of the facial nerve is responsible for the muscles controlling the forehead and above the eyes?
Which branch of the facial nerve is responsible for the muscles controlling the forehead and above the eyes?
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What function does the cochlear branch of the vestibulocochlear nerve primarily serve?
What function does the cochlear branch of the vestibulocochlear nerve primarily serve?
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Which nuclei are responsible for the motor and sensory functions of the glossopharyngeal nerve?
Which nuclei are responsible for the motor and sensory functions of the glossopharyngeal nerve?
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What is the primary role of the greater petrosal nerve?
What is the primary role of the greater petrosal nerve?
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Which cranial nerve is responsible for transmitting taste sensations from the anterior two-thirds of the tongue?
Which cranial nerve is responsible for transmitting taste sensations from the anterior two-thirds of the tongue?
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What role does the paramedian pontine reticular formation (PPRF) play in eye movement?
What role does the paramedian pontine reticular formation (PPRF) play in eye movement?
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What is the function of the chorda tympani?
What is the function of the chorda tympani?
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Which condition is characterized by sudden, temporary weakness or paralysis of facial muscles?
Which condition is characterized by sudden, temporary weakness or paralysis of facial muscles?
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What are common assessments for hearing and balance disorders related to cranial nerves?
What are common assessments for hearing and balance disorders related to cranial nerves?
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Study Notes
Amygdala and Hippocampus
- Amygdala connects smells with emotional responses and memories.
- Hippocampus is involved in forming memories related to scents.
- Hippocampus plays a role in the perception of taste, and loss of smell significantly affects taste perception.
Optic Nerve (CN II)
- Develops from an outpouching from the diencephalon.
- Its head is the nucleus of CN II.
- Composed of ganglion cell layer, which is the 8th out of 10 layers of the retina.
- Arises from retinal ganglion cells.
- RPE (light-sensitive layer) converts light to neural signals via hyperpolarization.
- Optic nerve fibers originate from ganglion cells, receiving signals from outer layers.
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Pathway:
- RPE hyperpolarization initiates phototransduction.
- Retinal ganglion cells receive visual signals from photoreceptors and outer layers.
- Optic nerve bundles axons of retinal ganglion cells, exiting the eye through the optic disc.
- Optic chiasm is where nasal fibers cross.
- Optic tracts project to the lateral geniculate nucleus (LGN) in the thalamus, the primary relay station for visual information.
- Optic radiations transmit visual information from the LGN to the primary visual cortex in the occipital lobe.
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Functions:
- Recognition of shapes, colors, and movement.
- Depth perception and three-dimensional vision.
- Contrast and brightness differentiation.
Cranial Nerves III - XII
- Originate from the brainstem.
- Embryologically homologous to spinal nerves.
- Nuclei are derived from cell columns homologous to spinal cord columns.
Cranial Nerve III (Oculomotor)
- Nucleus located in the midbrain, at the level of the superior colliculus.
- Controls extrinsic eye muscles (EOMs).
- Contains parasympathetic functions through the Edinger-Westphal nucleus (accessory).
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Oculomotor nucleus:
- Fibers exit the brainstem through the cerebral peduncles and via the interpeduncular fossa.
- Passes between the posterior cerebral and superior cerebellar arteries before entering the orbit through the superior orbital fissure.
- Branches into:
- Superior division: innervates lateral rectus (LR) and superior rectus (SR) muscles.
- Inferior division: innervates medial rectus (MR), inferior oblique (IO), and inferior rectus (IR) muscles.
- Carries parasympathetic fibers to the ciliary ganglion for controlling pupil constriction and lens accommodation.
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Motor functions:
- Elevation, depression, adduction, and lateral rotation of the eye.
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Parasympathetic functions:
- Pupil constriction.
- Accommodation (focusing).
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Clinical correlations:
- CN III palsy with or without pupil sparing:
- With pupil sparing: likely due to ischemia (e.g., uncontrolled diabetes).
- Without pupil sparing: aneurysm in the posterior inferior cerebellar artery.
- Motor function: depression, abduction (minimal), and intorsion.
- CN III palsy with or without pupil sparing:
Cranial Nerve IV (Trochlear)
- Motor function: depression, abduction (minimal), and intorsion.
- Clinical correlations:
- Superior Oblique Myokymia: brief episodes of involuntary vertical and torsional movements of the eye. Can indicate irritation or damage to the trochlear nerve.
- Superior Oblique Muscle Palsy (SOM palsy): causes include trauma, vascular issues, mass effect (midbrain tumors), and systemic conditions (e.g., multiple sclerosis).
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Decompensated fovea: refers to a situation where the central part of the macula, known as the fovea, is no longer able to function effectively.
This can lead to a loss of central vision.
Cranial Nerve V (Trigeminal)
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Trigeminal motor nucleus:
- Located in the pons.
- Contains cell bodies of motor neurons that supply the muscles of mastication (chewing).
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Sensory ganglia:
- Trigeminal ganglion (Gasserian) located in the trigeminal cave of the temporal cranial fossa.
- Three nuclei (mesencephalic, principal sensory, and spinal trigeminal) located in the pons and medulla oblongata.
- Mixed nerve: somatomotor and somatosensory fibers.
- Somatomotor fibers: muscles of mastication.
- Somatosensory fibers: entire face, from the lower margin of the mandible to the top of the scalp.
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Trigeminal (Gasserian) ganglion:
- Plays a crucial role in sensory and motor functions of the face.
- Located in Meckel's cave at the cranial fossa, near the temporal bone.
- Composed of cell bodies of sensory neurons (divisions).
- Ophthalmic nerve (V1): sensory innervation to the forehead, upper eyelid, and cornea.
- Maxillary nerve (V2): sensory innervation to the midface, including the cheek, upper teeth, and part of the nasal cavity.
- Mandibular nerve (V3): sensory innervation to the lower face, including the lower teeth, chin, and part of the tongue; also contains motor fibers that innervate the muscles of mastication.
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Clinical correlations:
- Sixth cranial nerve palsy: may be a sign of increased intracranial pressure, trauma to the base of the skull, ischemic insult, or demyelinating disease (e.g., multiple sclerosis).
- Internuclear Ophthalmoplegia (INO): a dysfunction in nerves that control eye movements, resulting in the inability to move one eye towards the side of the lesion. The affected eye will not move past midline.
- Frontal Eye Field: a region in the frontal lobe responsible for initiating voluntary eye movements. A lesion in the Frontal Eye Field can limit conjugate eye movements.
- Paramedian Pontine Reticular Formation (PPRF): a network of neurons that plays a critical role in controlling horizontal eye movements. Lesions in the PPRF can cause issues in controlling gaze.
Cranial Nerve VII (Facial)
- Motor nucleus in the pons, along with sensory nuclei (nucleus of the solitary tract for taste) extending to the medulla.
- Originates at the pons, travels through the internal acoustic meatus, and emerges at the stylomastoid foramen.
- Controls muscles of facial expression.
- Transmits taste sensations from the anterior two-thirds of the tongue.
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Motor function:
- Muscles of facial expression (smiling, frowning, closing the eyes).
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Sensory function:
- Taste from the anterior two-thirds of the tongue.
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Parasympathetic functions:
- Submandibular and sublingual salivary glands.
- Lacrimal gland.
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Components:
- Motor nucleus: controls muscles of facial expression.
- Sensory nucleus: involved in taste sensations, part of the rostral nucleus solitarius.
- Parasympathetic nuclei: include the superior salivatory nucleus, responsible for parasympathetic innervation of the lacrimal gland and salivary glands.
- Temporal branch: muscles of facial expression in the forehead and above the eyes.
- Zygomatic branch: muscles that control the upper cheeks.
- Buccal branch: muscles of the cheeks and upper lip.
- Marginal mandibular branch: muscles of the lower lip and chin.
- Cervical branch: platysma muscle in the neck.
- Chorda tympani: carries taste sensations from the anterior two-thirds of the tongue and parasympathetic fibers to the submandibular and sublingual salivary glands.
- Greater petrosal nerve: provides parasympathetic innervation to the lacrimal gland and nasal mucosa.
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Clinical correlations:
- Bell's palsy: sudden, temporary weakness or paralysis of the muscles on one side of the face.
Cranial Nerve VIII (Vestibulocochlear)
- Arises from two nuclei located in the pons and medulla oblongata:
- Cochlear nucleus: processes auditory information from the cochlear branch.
- Vestibular nucleus: processes balance and spatial orientation information from the vestibular branch.
- Nuclei originate at the junction of the pons and medulla oblongata.
- Fibers emerge and travel through the internal acoustic meatus (temporal bone), traveling with CN VII.
- Branches into the cochlear branch and the vestibular branch after the internal meatus.
- Cochlear branch: enters the cochlea and transmits sound information.
- Vestibular branch: connects to semicircular canals for balance.
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Functions:
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Hearing:
- Tympanic membrane (TM) picks up sound vibrations.
- Ossicles (malleus, incus, stapes) amplify vibration signals.
- Organ of Corti contains hair cells, bending of which causes transduction.
- Cochlear branch: transmits neural signals to the auditory cortex via the cochlear nucleus.
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Balance:
- Movement and position signals are detected in the semicircular canals and otoliths (endolymph, utricles/saccules).
- Ampulla hair cells are activated, causing transduction.
- Vestibular branch: transmits neural balance and equilibrium signals to brain areas controlling balance and coordination, via the vestibular nucleus.
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Hearing:
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Assessment:
- Auditory Brainstem Response (ABR): measures brain's electrical activity in response to sound.
- Dix-Hallpike maneuver: checks for calcium crystals displacement.
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Clinical correlations:
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Hearing loss:
- Neurosensorial (acoustic neuroma).
- Conductive (barotrauma).
- Vestibular disorders: Benign Paroxysmal Positional Vertigo (BPPV), Meniere's disease.
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Hearing loss:
Cranial Nerve IX (Glossopharyngeal Nerve)
- Originates from several nuclei in the medulla oblongata:
- Nucleus ambiguous (motor): controls motor function.
- Solitary nucleus (sensory): receives sensory information for taste and visceral sensation.
- Mixed nerve: somatosensory, somatomotor, viscerosensory, and visceromotor fibers.
- Somatosensory: general sensation (pain) from the tongue (posterior 1/3) and pharynx.
- Somatomotor: muscles of the pharynx.
- Viscerosensory: taste from the posterior 1/3 of the tongue, swallowing reflex, carotid sinus.
- Visceromotor: parasympathetic innervation to the parotid gland (along with V3).
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Branches:
- Pharyngeal: contributes to the pharyngeal plexus and provides motor innervation to the stylopharyngeus muscle (swallowing).
- Tonsillar: sensory innervation to the palatine tonsil (sensation of touch and pain).
- Lingual: carries sensory fibers for taste and general sensation from the posterior one-third of the tongue.
- Carotid sinus: innervates the carotid sinus and carotid body, involved in blood pressure regulation.
- Auricular: sensory innervation to a portion of the external ear and the external auditory canal.
Cranial Nerve X (Vagus Nerve)
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Originates from several nuclei in the medulla:
- Dorsal motor nucleus: responsible for parasympathetic innervation of the heart, lungs, and digestive tract.
- Nucleus ambiguous: controls motor function to the larynx, pharynx, and soft palate.
- Solitary nucleus: receives taste and visceral sensations.
- Mixed nerve: combines sensory, motor, and autonomic fibers.
- Somatosensory: innervates the ear canal, pharynx, and larynx.
- Viscerosensory: receives sensory information from the heart, lungs, and digestive tract.
- Somatomotor: controls palatoglossus muscle and muscles of the larynx and pharynx.
- Visceromotor: controls parasympathetic innervation to the heart, lungs, and digestive tract.
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Branches:
- Pharyngeal: contributes to the pharyngeal plexus and helps control swallowing.
- Superior laryngeal: innervates the larynx, including the cricothyroid muscle.
- Recurrent laryngeal: supplies motor and sensory innervation to the larynx.
- Cardiac: provides parasympathetic innervation to the heart.
- Pulmonary: carries parasympathetic fibers to the lungs.
- Esophageal: provides parasympathetic innervation to the esophagus.
- Gastric: innervates the stomach.
- Hepatic: innervates the liver.
- Splenic: innervates the spleen.
- Pancreatic: innervates the pancreas.
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Clinical correlations:
- Dysphagia: difficulty swallowing.
- Hoarseness: voice changes due to vocal cord paralysis.
- Tachycardia: rapid heart rate.
- Bradycardia: slow heart rate.
- Gastrointestinal issues: problems with digestion and motility.
Cranial Nerve XI (Accessory Nerve)
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Originates from two nuclei:
- Cranial nucleus: located in the medulla oblongata.
- Spinal nucleus: extends down the spinal cord.
- Motor nerve: controls muscles of the neck and shoulders.
- Cranial root: controls the palatoglossus muscle.
- Spinal root: emerges from the spinal cord and joins the cranial root to form the accessory nerve.
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Branches:
- Internal branch: joins the vagus nerve and contributes to the pharyngeal plexus.
- External branch: innervates the trapezius and sternocleidomastoid muscles.
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Clinical correlations:
- Weakness or paralysis of the sternocleidomastoid and trapezius muscles: can result from damage to the accessory nerve, causing difficulty turning the head and dropping the shoulder.
Cranial Nerve XII (Hypoglossal Nerve)
- Originates from the hypoglossal nucleus in the medulla oblongata.
- Motor nerve: controls all intrinsic and extrinsic muscles of the tongue, except the palatoglossus muscle.
- Fibers exit the skull through the hypoglossal canal.
- Travels downward and forward to reach the tongue, running close to the carotid arteries and the internal jugular vein.
- Function: can be assessed by asking the patient to stick out their tongue.
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Clinical correlations:
- Dysarthria: difficulty speaking.
- Dysphagia: difficulty swallowing.
- Tongue atrophy: can occur due to nerve damage, causing weakness and wasting away of the tongue muscles.
CN Pathways and Functions
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Sensory nerves:
- Olfactory nerve (I) and optic nerve (II) are outgrowths of the central nervous system.
- Vestibulocochlear nerve (VIII)
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Motor nerves:
- IV, VI, XII: somatomotor (voluntary).
-
III: somatomotor, visceromotor (involuntary).
- Parasympathetic: pupil constriction and accommodation.
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Mixed nerves:
- VII, IX, X: sensory, motor, somatic, and autonomic.
- V: sensory and motor somatic.
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Special motor:
- XI (motor, spinal fibers).
Ophthalmic Nerve (V1)
- Arises from the trigeminal ganglion.
- Branches:
-
Frontal nerve:
- Supraorbital nerve: innervates the forehead and scalp.
- Supratrochlear nerve: innervates the skin of the forehead and the medial part of the eyelid.
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Nasociliary nerve: provides sensory innervation to the nasal cavity, cornea, and ciliary body.
- Infratrochlear nerve: skin of the upper eyelid and side of the nose.
- Ethmoidal nerves: innervate the ethmoid sinus and nasal cavity.
- Lacrimal nerve: supplies sensory fibers to the lacrimal gland and carries parasympathetic fibers from the facial nerve (via the zygomatic branch of V2) to stimulate tear production.
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Frontal nerve:
Maxillary nerve (V2)
- Arises from the trigeminal ganglion.
- Travels through the foramen rotundum, entering the pterygopalatine fossa.
- Branches:
- Zygomatic nerve: sensation to the skin over the zygomatic (cheek) bone and contributes to the lacrimal nerve.
- Infraorbital nerve: largest branch, exits through the infraorbital foramen and innervates the lower eyelid, upper lip, part of the nasal cavity, and upper maxilla.
- Posterior superior alveolar nerve: provides sensation to the maxillary molars and adjacent buccal mucosa.
- Middle superior alveolar nerve: supplies the maxillary premolars and part of the maxillary sinus.
- Anterior superior alveolar nerve: innervates the maxillary incisors and canine teeth and the associated gingiva.
Mandibular Nerve (V3)
- Arises from the trigeminal ganglion.
- Travels through the foramen ovale to enter the infratemporal fossa.
- Branches:
- Motor branches: innervate the muscles of mastication (masseter, temporalis, medial and lateral pterygoid muscles).
-
Sensory branches:
- Buccal nerve: buccal mucosa and skin over the cheek.
- Auriculotemporal nerve: supplies sensation to the skin in front of the ear and parts of the temple, carries autonomic fibers to the parotid gland.
- Lingual nerve: provides sensory innervation to the anterior two-thirds of the tongue and the floor of the mouth, carries autonomic fibers from the facial nerve (VII) to the submandibular and sublingual glands.
- Inferior alveolar nerve: supplies sensation to the lower teeth, has a terminal branch (mental nerve), provides sensation to the chin and lower lip.
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Test your knowledge on the cranial nerves and their functions with this quiz. Explore the innervation of muscles of mastication, sensory functions, and autonomic fibers related to various glands. Perfect for students studying human anatomy and neuroanatomy.