Cranial nerves Cycle 6

Trigeminal Nerve

• Forehead and eye are innervated by the ophthalmic nerve
• Face is innervated by the maxillary nerve
• Mastication (chewing) muscles are innervated by the mandibular nerve
• Cornea, ciliary body, lacrimal gland, and conjunctiva are supplied sensory innervation by the ophthalmic nerve
• Mucous membrane of the nasal cavity, and the skin of the eyelids, eyebrow, forehead, and nose are also supplied by the ophthalmic nerve
• Infections of the trigeminal ganglion can cause painful sensations along the path of the trigeminal nerve (e.g., shingles)
• Areas innervated by the ophthalmic nerve are mostly affected by infections of the trigeminal ganglion

Maxillary Nerve

• Branches of the maxillary nerve include: zygomatic nerve, nasopalatine nerve, posterior superior alveolar nerve, greater and lesser palatine nerves, and pharyngeal nerve
• Zygomatic nerve passes through the inferior orbital fissure
• Lesions of the maxillary nerve can cause intense hot and cold sensations in the teeth

Mandibular Nerve

• Main trunk of the mandibular nerve gives off sensory and motor branches in the infratemporal fossa, near the skull base
• Motor branches of the mandibular nerve innervate: tensor tympani, tensor veli palatini, and muscles involved in mastication (e.g., temporalis, masseter, and lateral and medial pterygoid muscles)
• Motor root of the mandibular nerve originates from the motor nucleus of the trigeminal nerve
• Mandibular division of the nerve passes between the medial pterygoid and tensor veli palatini muscles
• Anterior division of the mandibular nerve produces motor branches for the masticatory muscles and the buccal nerve
• Posterior division of the mandibular nerve divides into: auriculotemporal, lingual, and inferior alveolar nerves
• Posterior division of the mandibular nerve innervates: anterior belly of the digastric muscle and the mylohyoid muscle

Cranial Nerve VI (Abducens)

• Fibers of Cranial Nerve VI leave from the inferior pons
• Fibers of Cranial Nerve VI enter the orbit through the superior orbital fissure
• Cranial Nerve VI primarily innervates the lateral rectus muscle, which abducts the eye
• Injury to the Abducens nerve can result in weakness or paralysis of the lateral rectus muscle, leading to difficulty in moving the eye laterally

Cranial Nerve VII (Facial)

• Fibers of Cranial Nerve VII travel through the internal acoustic meatus and emerge through the stylomastoid foramen to the lateral aspect of the face
• Motor functions of Cranial Nerve VII include: facial expression and the transmittal of autonomic impulses to lacrimal and salivary glands
• Sensory function of Cranial Nerve VII includes taste from the anterior two-thirds of the tongue via the chorda tympani

Cranial Nerve IX (Glossopharyngeal)

• Lingual branch of the glossopharyngeal nerve innervates the mucous membrane of the posterior (base) third of the tongue, including sensory and taste fibers
• Palsy of the IX nerve can result in loss of taste on the posterior 1/3 of the tongue and loss of sensation of the soft palate

Cranial Nerve X (Vagus)

• Main motor fibers of the vagus nerve are responsible for parasympathetic fibers to the heart, lungs, and visceral organs
• Vagus nerve leaves the skull through the lateral part of the jugular foramen
• Vagus nerve shares a common sheath with Cranial Nerve XI (Accessory Nerve)
• Glossopharyngeal nerve forms the superior ganglion in the jugular foramen
• Palsy of the Vagus nerve can result in soft palate and uvula deviation, vocal cord paralysis, and other autonomic dysfunction

Cranial Nerve XI (Accessory)

• Formed by a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord
• Spinal root of the accessory nerve enters the cranium through the foramen magnum

Facial Nerve

• Supplied by parasympathetic function: submandibular and sublingual salivary glands, nasal, palatine, and pharyngeal mucous glands, and lacrimal glands
• Two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone
• Within the facial canal, the two roots fuse to form the facial nerve, and the nerve forms the geniculate ganglion
• Gives rise to: greater petrosal nerve (parasympathetic fibers to mucous glands and lacrimal gland), nerve to stapedius, and chorda tympani
• First extracranial branch: posterior auricular nerve
• Splits into five branches within the parotid gland: temporal, zygomatic, buccal, marginal mandibular, and cervical
• Branches innervate muscles of facial expression
• Intracranial lesions: muscles of facial expression will be paralyzed or severely weakened
• Symptoms of intracranial lesion:
  • Reduced salivation and loss of taste on the ipsilateral 2/3 of the tongue (related to Chorda tympani)
  • Ipsilateral hyperacusis (hypersensitive to sound) (related to Nerve to stapedius)

Trigeminal Nerve

• Motor fibers supplied by: mandibular nerve (V3)
• Function: mastication (temporalis, masseter, and lateral and medial pterygoid muscles)
• Ophthalmic nerve supplies sensory innervation to: cornea, ciliary body, lacrimal gland, and conjunctiva
• Ophthalmic nerve also supplies nerves to: mucous membrane of the nasal cavity, and the skin of the eyelids, eyebrow, forehead, and nose
• Infections of the trigeminal ganglion by herpes zoster virus (shingles) cause painful sensations along the path of the trigeminal nerve
• Areas affected by infections of the trigeminal ganglion: areas innervated by the ophthalmic nerve

Maxillary Nerve

• Branches: zygomatic nerve, nasopalatine nerve, posterior superior alveolar nerve, greater and lesser palatine nerves, pharyngeal nerve
• Zygomatic nerve passes through the inferior orbital fissure
• Trigeminal neuralgia: characterized by severe pain in the face and jaw
• Lesions of the maxillary nerve cause: intense hot and cold sensations in the teeth

Mandibular Nerve

• Main trunk gives off sensory and motor branches in the infratemporal fossa, near the skull base
• Motor branches: tensor tympani, tensor veli palatini, and muscles involved in mastication (temporalis, masseter, and lateral and medial pterygoid)
• Motor root originates from the motor nucleus of the trigeminal nerve
• Mandibular division passes between the medial pterygoid and tensor veli palatini muscles
• Anterior division produces: motor branches for the masticatory muscles and the buccal nerve
• Posterior division divides into: auriculotemporal, lingual, and inferior alveolar nerves
• Posterior division innervates: anterior belly of the digastric muscle and the mylohyoid muscle

Abducent Nerve

• Fibers originate from the inferior pons
• Fibers enter the orbit through the superior orbital fissure
• Primarily innervates the lateral rectus muscle, abducting the eye
• Injury to the Abducent nerve: weakness or paralysis of the lateral rectus muscle, leading to difficulty in moving the eye laterally

Facial Nerve

• Supplied by parasympathetic function: submandibular and sublingual salivary glands, nasal, palatine, and pharyngeal mucous glands, and lacrimal glands
• Two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone
• Within the facial canal, the two roots fuse to form the facial nerve, and the nerve forms the geniculate ganglion
• Gives rise to: greater petrosal nerve (parasympathetic fibers to mucous glands and lacrimal gland), nerve to stapedius, and chorda tympani
• First extracranial branch: posterior auricular nerve
• Splits into five branches within the parotid gland: temporal, zygomatic, buccal, marginal mandibular, and cervical
• Branches innervate muscles of facial expression
• Intracranial lesions: muscles of facial expression will be paralyzed or severely weakened
• Symptoms of intracranial lesion:
  • Reduced salivation and loss of taste on the ipsilateral 2/3 of the tongue (related to Chorda tympani)
  • Ipsilateral hyperacusis (hypersensitive to sound) (related to Nerve to stapedius)

Trigeminal Nerve

• Motor fibers supplied by: mandibular nerve (V3)
• Function: mastication (temporalis, masseter, and lateral and medial pterygoid muscles)
• Ophthalmic nerve supplies sensory innervation to: cornea, ciliary body, lacrimal gland, and conjunctiva
• Ophthalmic nerve also supplies nerves to: mucous membrane of the nasal cavity, and the skin of the eyelids, eyebrow, forehead, and nose
• Infections of the trigeminal ganglion by herpes zoster virus (shingles) cause painful sensations along the path of the trigeminal nerve
• Areas affected by infections of the trigeminal ganglion: areas innervated by the ophthalmic nerve

Maxillary Nerve

• Branches: zygomatic nerve, nasopalatine nerve, posterior superior alveolar nerve, greater and lesser palatine nerves, pharyngeal nerve
• Zygomatic nerve passes through the inferior orbital fissure
• Trigeminal neuralgia: characterized by severe pain in the face and jaw
• Lesions of the maxillary nerve cause: intense hot and cold sensations in the teeth

Mandibular Nerve

• Main trunk gives off sensory and motor branches in the infratemporal fossa, near the skull base
• Motor branches: tensor tympani, tensor veli palatini, and muscles involved in mastication (temporalis, masseter, and lateral and medial pterygoid)
• Motor root originates from the motor nucleus of the trigeminal nerve
• Mandibular division passes between the medial pterygoid and tensor veli palatini muscles
• Anterior division produces: motor branches for the masticatory muscles and the buccal nerve
• Posterior division divides into: auriculotemporal, lingual, and inferior alveolar nerves
• Posterior division innervates: anterior belly of the digastric muscle and the mylohyoid muscle

Abducent Nerve

• Fibers originate from the inferior pons
• Fibers enter the orbit through the superior orbital fissure
• Primarily innervates the lateral rectus muscle, abducting the eye
• Injury to the Abducent nerve: weakness or paralysis of the lateral rectus muscle, leading to difficulty in moving the eye laterally