Cranial nerves

• • Trigeminal nerve is the largest cranial n
  • Mixed nerve
  • Emerges from anterior surface of pons in the form of two roots (small motor + thick sensory root).
• Trigeminal nerve main sensory nucleus and spinal sensory nucleus

  • Main sensory nucleu: located lateral to sulcus limitans. Related to discriminative touch and propioception
  • Spinal sensory nucleus: stretches along pons, medulla and upper segments of spinal cord. related to pain and temperature sensation.

  The main sensory nucleus + spinal sensory nucleus receives input from fibers coming from the dorsal root ganglia. The projecting fibers from these nuclei cross the midline and form trigeminal leminiscus which layer joins medial leminiscus.
• Trigeminal n has 4 different nuclei:

  • MAIN SENSORY NUCLEI
  • SPINAL SENSORY NUCLEI
  • MESENCEPHALIC NUCLEI OF TRIGEMINAL
  • MOTOR NUCLEI OF TRIGEMINAL
• The mesencephalic nuclei of trige n lies in midbrain but can also be found in pons. It is made of pseudounipolar neurons that project fibers to motor nucleus of trigeminal nerve to create the mandibular reflex.

  • Its peripheral process comes from muscles of mastication
  • Central process goes to motor nucleus of trigeminal n for mandibular reflex
• The motor nucleus of trigeminal n is located in pons lateral to main sensory nucleus

  • innervates muscles of mastication: masseter, medial pterygoid and temporal
  • innervates suprahyoid muscles: digrastric, mylohyoid, tensor timpani and tensor veli palati
• As the trigeminal nerve fibers merge from the nucleus it forms the trigeminal ganglion located in the trigeminal impression on the petrous part of temporal bone. Trigeminal ganglion then forms 3 branches aka peripheral branches (ophthalmic, maxillary and mandibular nerves.)
• Trigeminal nerve course and distribution

  
• Ophtalmic nerve Its s brach of trigeminal nerve.

  • it merges from trigeminal ganglia after passing trough the lateral wall of cavernous sinus it gives a small branch: recurrrent meningeal branch
  • After it further divided inti 3 bigger branches: Frontal nerve, lacrimal nerve and nasociliary nerve.

  
• Ophthalmic nerve branches

  • Frontal nerve: largest. It reaches orbit after passing through the sup orbital fissure and further divides into:
  • supraorbital n (emerges from supraorbital foramen and provided innervation to upper eyelid, conjunctiva, frontal sinus, skin on forehead and scalp.)
  • suprathrocheal nerve: curves around sup oblique and provides innervation for upper eyelid, conjunctiva and skin on forehead in medial plane.
• Ophthalmic nerve branches:

  • Lacrimal nerve: reaches orbit through superior orbital fissure and innervates lacrimal gland, conjunctiva and lateral part of upper eyelid.
  • Contains parasympathetic fibers which come from pterygopalatine ganglion through he communicating branch with zygomatic nerve, brach of maxillary.
• The ophthalmic nerve branches

  • Nasociliary nerve: reaches orbit thought the tendinous formed by extrinsic muscles of eye ring and gets sensory info of the eye. It further divided into:
  • Ant ethmoidal nerve: passes through ant ethmoidal foramen with ant ethmoidal artery.
  • Post ethmoidal n: passes through post ethmoidal foramen with ant ethmoidal artery.
  • Inferior trocheal n
  • long ciliary n: carries sympathetic fibers from sup cervical ganglion to innervate iris and ciliary muscle. Sympathetic fibers reaches this nerve by passing through the internal carotid plexus.
• Maxillary nerve

  
• Vestibulocochlear nerve (VIII)

  • Responsible for transmitting sound and equilibrium (balance) information from inner ear to brain
  • Sensory nerve
  • Two components: vestibular nerve + cochlear nerve
• Ear

  • Situated bilaterally on skull at same level of skull
  • Main function: hearing + maintaining balance
  • Anatomically divided into 3 parts: external ear, middle ear, internal ear.

  
• External ear

  • external ear is outermost part of the ear and plays a crucial role in collecting and directing sound waves into the ear.
  • The external ear, like the middle ear, serves only to conduct sound to the inner ear. It consists of the auricle and external acoustic meatus (or ear canal). At the bottom of the ear canal is the tympanic membrane which establishes the border between the external and middle ear.

  
• • Oculomor nerve (cranial nerve III) plays role in controlling eye movements and pupil responses
  • Motor functions: controls eye movements (superior rectus, medial rectus, inferior rectus and inferior oblique). Elevates upper eyelid (levator palpabre sup)
  • Parasympathetic functions: edinger-westphal nucleus sends preglanglionic parasympathetic fibers through oculomotor to ciliary ganglion. Postglanglionic fibers innervates sphincter pupillae miscles causing pupil constriction (milsis) + ciliary muscle alowing for lens accommodation

  
• • Oculomotor nerve palsy: ptosis (dropping eyelid), double vision, eye is positioned down and out due to unopposed action of lateral rectus and superior oblique.
  • If parasympathetic fibers are affected: pupil may be dilated and non-responsive to light and accommodation may be impaired
• Trochlear nerve

  • IV cranial nerve
  • Purely motor nerve
  • Originates in midbrain at level of inferior colliculus
  • Innervates superior oblique m which is responsible for depression of eyeball, intorsion (inwards rotation) and abduction (mov away from midline)

  
• Trochlear nerve palsy

  • Weakness or completely paralysis of superior oblique
  • Vertical double vision, difficulty looking down, patients may compensate tilting head to side opposite of effected rue to reduce diplopia condition known as bielschowsky’s head tilt
  • Because the main intorting muscle is affected →Extortion of the eye
  • Axis of the eye will be pointing outwards. Because IV CN also depresses the eyeball →
  • Eyeball will move up underneath the eyelid. Because eyeballs will be looking at different directions → Diplopia.

  
• Abducens nerve

  • Cranial nerve VI
  • Originates from abducens nerve in pons near floor of 4 ventricle
  • Motor nerve
  • Motor function: innervates lateral rectus which is responsible for abduction of eyeball (move eyeblaterally away from nose)

  
• Abducens nerve palsy

  • Weakness/complete causesparalysis of lateral rectus which results in horizontal diplopia that worsens when looking towards affected eye and inability to abduct effected eye causing it to become medially deviated when attempting to look straight ahead.
  • Patients may turn head toward side of effected nerve to reduce double vision

  
• The cavernous sinus is a dural sinus. This is a space between the periosteal layer and the meningeal layer.

  In the wall of the cavernous sinus there are 4 nerves running through it:

  • CN III (Oculomotor Nerve)
  • CN IV (Trochlear Nerve)
  • CN V1 (Ophthalmic division of trigeminal nerve) -
  • CN V2 (Maxillary division of trigeminal nerve.
• Glossopharyngeal nerve (IX)

  • Mixed nerve (sensory, motor, parasympathetic)
  • Originates in medulla, emerging from lateral aspect btw olives and inferior cerebellar peduncles
  • Branches:
  • Tympanic nerve( tympanic cavity + forms tympanic plexus): sensory innervation to inner ear + parasympathetic fiber to parotid gland via lesser petrosal
  • Carotid branch: carotid body + sinus
  • pharyngeal branch: pharyngeal plexus + motor innervation to stylopharyngeus
  • lingual branch: sensory + taste innervation to post 1/3 of tongue
  • Tonsilar branch: sensiry innervation to palatine tonsil

  
• • Glossopharyngeal neuralgia: severe, sudden and recurrent episodes of pain in areas innervated by glossopharyngeal (throat, tonsil, base of tongue)
  • lesion to glossopharyngeal n: loss of taste sensation from post 1/3 of tongue, loss of gag reflex, dysphagia, difficulty in regulating blood pressure Due to disrupted signalling from carotid body and plexus.
• • Facial nerve (VII) has 3 nuclei
  • Motor nuclei: innervates muscle of facial expression, posterior belly of digastric, stylohyoid and stapedius muscle.
  • Nucleus of tractus solitarius: receives sensory + taste sensation from anterior 2/3 of tongue via chorda tympani
  • Superior salivatory nucleus: parasympathetic nucleus that innervates submandibular, sublingual and lacrimal glands.

  
• • Fibers from sup salivatory nucleus + nuclei of tractus solitarius have ant course in pons: merge in pontocerebellar angle to form a single n: n. intermedius
  • Motor nucleus: motor fibers merge dorsally forming loop around abducens nuclei; later migrate to emerge at pontocerebellar angle
  • Facial nerve has 2 roots: motor root + parasympathetic and taste root carried in nerve intermedius. The two roots travel in internal acoustic meatus in petrous part of temporal bone and later reach facial canal where they fuse, theres formation of geniculate ganglion + formation of 3 intracranial branches.

  
• Within the parotid gland, VII CN gives off five motor branches that innervates muscles of facial expression:

  (v) Temporal: occipital frontalis, orbicukaris oculi, corrugator supercilli

  (vi) Zygomatic: zygomaticus major, zygomaticus minor, irbicularis oculi, levator labi superior

  (vii) Buccal: buccinator, orbicularis oris

  (viii) Mandibular: depressor labi inferioris, depressor anguli oris, mentalis

  (ix) Cervical; platysma

  
• Ophthalmic division of trigeminal nerve

  • Emerges from trigeminal ganglion and passes trough lateral wall of cavernus sinus and it releases the recurrent laryngeal branch which innervates part of tentorium cerebelli and falx cerebri
  • after this it divides into 3 bigger branches: frontal nerve, nasociliary nerve and lacrimal nerve

  
• Ophthalmic division of trigeminal

  
• Trigeminal nerve is responsible for all somatosensation of face except external ear and some parts of scalp
• Cranial nerve I

  • Olfactory Nerve (CN I)
  • Function: Sense of smell
  • Type: Sensory
• Cranial nerve II

  • Optic Nerve (CN II)
  • Function: Vision
  • Type: Sensory
• Cranial nerve III

  • Oculomotor Nerve (CN III)
  • Function: Eye movements (superior, medial, and inferior recti muscles; inferior oblique muscle), eyelid elevation (levator palpebrae muscle), pupil constriction (via parasympathetic fibers)
  • Type: Motor
• Cranial nerve IV

  • Trochlear Nerve (CN IV)
  • Function: Eye movements (superior oblique muscle)
  • Type: Motor
• Cranial nerve V

  • Trigeminal Nerve (CN V)
  • Function: Sensation from the face (ophthalmic, maxillary, and mandibular divisions), motor control of mastication (chewing) muscles
  • Type: mixed
• Cranial nerve V

  • Trigeminal Nerve (CN V)
  • Function: Both (Sensory and Motor)
  • Role: Responsible for sensation in the face and motor functions such as biting and chewing. It has three branches:
  • Ophthalmic (V1)
  • Maxillary (V2)
  • Mandibular (V3)
• Cranial nerve VI

  • Abducens Nerve (CN VI)
  • Function: Motor
  • Role: Controls the lateral rectus muscle, responsible for outward eye movement.
• Cranial nerve VII

  • Facial Nerve (CN VII)
  • Function: mixed (Sensory and Motor)
  • Role: Controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity.
• Cranial nerve VIII

  • Vestibulocochlear Nerve (CN VIII)
  • Function: Sensory
  • Role: Responsible for hearing and balance, with two branches:
  • Cochlear nerve (hearing)
  • Vestibular nerve (balance)
• Cranial nerve IX

  • Glossopharyngeal Nerve (CN IX)
  • Function: Both (Sensory and Motor)
  • Role: Innervates part of the tongue and pharynx; involved in taste sensation from the posterior one-third of the tongue, and contributes to swallowing and salivation.