⚡️ CN I: Olfactory nerve

 

Function

• smell

 

Type of fibre

• special sensory afferents

 

Foramen through which it passes

• cribriform plate of the ethmoid bone

 

Causes of anosmia

• head trauma

• COVID-19

• Kallmann syndrome

• Parkinson’s disease

 

⚡️ CN II: Optic nerve

 

Function

• sight

 

Type of fibre

• special sensory afferents

 

Foramen through which it passes

• optic canal

 

Clinical relevance

• damage to the optic nerve and its tributaries can affect the visual fields

 

⚡️ CN III: Oculomotor nerve

 

Function

• controls these extraocular muscles of the eye:

  • superior rectus

  • inferior rectus

  • medial rectus

  • inferior oblique

• controls the muscle that elevates the eyelid:

  • levator palpebrae superioris

• pupillary constriction

  • controls sphincter pupillae

 

Type of fibres

• somatic motor efferents

• general visceral efferents (parasympathetic supply)

• proprioceptive fibres

  • these tell the brain about the location and movement of the eye

 

Foramen through which it passes

• superior orbital fissure

 

3rd nerve palsy

• “down and out”

  • due to unopposed actions of the lateral rectus and superior oblique

• dilated pupil

  • remember that the oculomotor nerve also carries parasympathetic fibres alongside the motor fibres

  • these parasympathetic fibres are more superficial

  • if something were to compress the oculomotor nerve, the parasympathetic fibres would be affected FIRST

    • therefore the first sign to arise is a dilated pupil!

• ptosis

  • due to impaired levator palpebrae superioris muscle

 

⚡️ CN IV: Trochlear nerve

 

Function

• controls the superior oblique muscle (causes the eye to move down)

 

Type of fibres

• somatic motor efferents

• proprioceptive fibres

 

Foramen through which it passes

• superior orbital fissure

 

4th nerve palsy

• defective downward gaze

• vertical diplopia (image is seen on top of each other)

 

⚡️ CN V: Trigeminal nerve

 

Function

• sensation of the face

• mastication

 

Type of fibres

• general somatic sensory fibres

• somatic (branchial) motor efferents

 

Roots

• the trigeminal nerve gives off two roots:

  • a large sensory root

  • a small motor root (travels with the mandibular division)

 

Divisions

• ophthalmic nerve (CN V1)

  • general somatic sensory fibres

  • participates in the corneal reflex

• maxillary nerve (CN V2)

  • general somatic sensory fibres

• mandibular nerve (CN V3)

  • general somatic sensory and somatic (branchial) motor fibres

  • provide motor supply to the muscles of mastication

 

Foramen through which it passes

• CN V1: superior orbital fissure

• CN V2: foramen rotundum

• CN V3: foramen ovale

 

Lesions of the trigeminal nerve can cause

• loss of the corneal reflex (afferent)

• impaired facial sensation

• paralysis of the muscles of mastication

• trigeminal neuralgia

 

Relation to the parasympathetic nervous system

• each of the cranial parasympathetic ganglia receives sensory fibres from the trigeminal nerve

  • ciliary ganglion

    • relevant cranial nerve: oculomotor nerve (CN III)

    • branch of the trigeminal nerve: ophthalmic nerve (CN V1)

    • function: pupil constriction

  • pterygopalatine ganglion

    • relevant cranial nerve: facial nerve (CN VII)

    • branch of the trigeminal nerve: maxillary nerve (CN V2)

    • function: lacrimation

  • submandibular ganglion

    • relevant cranial nerve: facial nerve (CN VII)

    • branch of the trigeminal nerve: mandibular nerve (CN V3)

    • function: salivation from the sublingual and submandibular glands

  • otic ganglion

    • relevant cranial nerve: glossopharyngeal nerve (CN IX)

    • branch of the trigeminal nerve: mandibular nerve (CN V3)

    • function: salivation from the parotid gland

 

⚡️ CN VI: Abducens nerve

 

Function

• controls the lateral rectus (allows lateral movement of the eye)

 

Type of fibres

• somatic motor efferent

• proprioceptive fibres

 

Foramen through which it passes

• superior orbital fissure

 

6th nerve palsy

• CN VI is affected with raised intracranial pressure

• causes impaired abduction

• horizontal diplopia (double image is seen side by side)

 

⚡️ CN VII: Facial nerve

 

Type of fibres

• visceral parasympathetic efferents

• general sensory afferents

• special sensory afferents

• somatic (branchial) motor efferents

 

Functions

• visceral parasympathetic efferents

  • lacrimation and salivation (from the sublingual and submandibular glands)

• general sensory afferents

  • supplies to a small area of skin close to the external acoustic meatus

• special sensory afferents

  • taste to the anterior 2/3rds of the tongue

• somatic (branchial) motor efferents

  • muscles of facial expression

  • nerve to stapedius (the smallest muscle in the human body!)

 

Foramen through which it passes

• internal acoustic meatus

  • travels with the vestibulocochlear nerve

 

Facial nerve palsy

• impaired corneal reflex (efferent)

• flaccid paralysis of the upper and lower face

• loss of taste from the anterior 2/3rds of the tongue

• hyperacusis (due to impaired function of the stapedius muscle)

 

⚡️ CN VIII: Vestibulocochlear nerve

 

Function

• vestibular portion —> balance

• cochlear portion —> hearing

 

Type of fibre

• special sensory afferents

 

Foramen through which it passes

• internal acoustic meatus

  • travels with the facial nerve

 

Clinical relevance

• can lead to vertigo, hearing loss and tinnitus if affected

 

⚡️ CN IX: Glossopharyngeal nerve​

 

Type of fibres

• somatic (branchial) motor efferents

• visceral parasympathetic motor efferents

• somatic (general) sensory afferents

• special sensory afferents

• visceral sensory afferents

 

Function

• somatic (branchial) motor efferents

  • it only supplies ONE muscle! It’s the stylopharyngeus muscle of the pharynx

• visceral parasympathetic motor efferents

  • salivation to the parotid gland

• somatic (general) sensory afferents

  • sensation from the oropharynx

• special sensory afferents

  • taste to the posterior 1/3rd of the tongue

• visceral sensory afferents

  • from the carotid body and sinus

    • carotid sinus = baroreceptors (sensitive to blood pressure)

    • carotid body = peripheral chemoreceptors (sensitive to the partial pressure of oxygen)

 

Foramen through which it passes

• jugular foramen

  • travels with the vagus and spinal accessory nerves, and the internal jugular vein

 

Clinical relevance

• jugular foramen syndrome

• impaired gag reflex (afferent)

• hypersensitive carotid sinus reflex

 

⚡️ CN X: Vagus nerve

 

Type of fibres

• somatic (branchial) motor efferents

• visceral parasympathetic motor efferents

• somatic (general) sensory afferents

• visceral sensory afferents

 

Function

• somatic (branchial) motor efferents

  • swallowing and phonation

• visceral parasympathetic motor efferents

  • thoracic and abdominal viscera till the splenic flexure

• somatic (general) sensory afferents

  • dura of the posterior cranial fossa

  • skin posterior to the ear

  • external acoustic meatus

• visceral sensory afferents

  • baroreceptors of the arch of the aorta

  • chemoreceptors in the aortic bodies

 

Foramen through which it passes

• jugular foramen

 

Clinical relevance

• impaired gag reflex (efferent)

• uvula deviates to the contralateral side of the lesion

 

⚡️ CN XI: Spinal accessory nerve

 

Type of fibres

• branchiomotor efferent

 

Function

• controls the sternocleidomastoid (SCM) and trapezius muscles which control the movement of the head and shoulders

  • if you turn your head to the left, this is the right SCM muscle (and vice versa)

 

Foramen through which it passes

• jugular foramen

 

Clinical relevance

• weakness with turning the head and shrugging the shoulders

 

⚡️ CN XII: Hypoglossal nerve

 

Type of fibres

• primarily general somatic efferents

 

Function

• innervation of the intrinsic and extrinsic muscles of the tongue

 

Foramen through which it passes

• hypoglossal canal

 

Clinical relevance

• may be affected from a tonsillectomy

• the tongue will deviate towards the side of the lesion