Describe the locations of the cell bodies for various types of cranial nerve fibres
Sensory fibres - Ganglia outside the CNS (think pseudounipolar neurons)
- Some special sensory fibres use bipolar neurons (e.g. olfactory mucosa or retinal fibres)
Somatic Motor Fibres have cell bodies withing the CNS (Think Multipolar)
Autonomic Motor fibres have cells bodies within the CNS and then synapse outwith the CNS.
- Either pre-vertebral ganglia (sympathetic)
- Or Intramural Ganglia (Parasympathetic)
Describe the pathway and components of Cranial Nerve I:
- Olfactory Nerve
- Purely Special Sensory (smell)
Fibres start in receptors in the olfactory epithelium of the nasal cavity
- -> Pass through foramina in the cribriform plate of the ethmoid
- -> Enters the olfactory bulb in the anterior cranial fossa
Whats the clinical relevance of the 1st cranial nerve?
If you fracture the cribriform plate you can tear the olfactory nerve fibres leading to anosmia
Describe the pathway and components of the 2nd cranial nerve:
- Optic Nerve
- Purely Special Sensory (Vision)
- Retinal Nerve Fibres
- > Optic Disc -> Optic Nerve (in optic canal)
- > Fibres mix at the optic chiasm and nasal fibres swap sides
- > So temporal fibres and contralateral nasal fibres of each side form optic tracts
- > Synapse at LGB
- > Form Right and Left Optic Radiations
- > Feed into the left and right Primary Visual Cortex
Whats the clinical relevance of Cr N II:
Papilloedema (Optic Disc Swelling
- Due to increased Intracranial Pressure
Right Optic Nerve Damage
-> Blindness in right eye
Middle Optic Chiasm damage
- > Knocks out both sides of nasal fibres
- > Loss of temporal visual fields (Bitemporal Heminopia)
Right Optic Tract Damage
-> Blindness in Left Temporal and Right Nasal visual fields ( Left Hemonymous Hemianopia)
What could cause damage to the optic chiasm?
Pressure from a Pituitary Tumour
What are the components of the 3rd cranial nerve?
- Somatic Motor supply to most of the extraocular muscles
- Autonomic Motor (parasympathetic) to the constrictor pupillae and the ciliaris muscle
What extraocular muscles arnt supplied by the oculomotor nerve?
- Sup Oblique (Cranial Nerve IV - Trochlear)
- Lateral Rectus (Cranial Nerve VI - Abducens)
Whats the pathway of the 3rd cranial nerve?
- Arises from midbrain
- Emerges throught he superior orbital fissure
Whats the clinical relevance of the oculomotor nerve?
- Loss of somatic innervation to the levator palpebrae Superioris
Eyeball Abducted & Depressed:
- Due to loss of innervation to the extraocular muscles so the sup oblique depresses it and the lateral rectus abducts it
Loss of pupillary reflex
- Loss of autonomic motor innervation
No lens accomadation
- Loss of autonomic motor innervation
What are the components of the 4th cranial nerve?
Its Purely Somatic Motor to the superior oblique
Describe the pathway of the 4th cranial nerve?
Comes from the midbrain and emerges through the superior orbital fissure
The only Cr N to arise from the posterior surface of the brainstem
Clinical relevance of the trochlear nerve?
Lose innervation to the sup oblique so when you look down one eye doesnt depress properly leading to diplopia
Describe the pathway of the 5th cranial nerve
Emerges from pons and forms the trigeminal ganglion, then it divides into the 3 branches:
- Ophthalmic exits via Sup Orbital Fissure
- Maxillary exits through Foramen Rotundum
- Mandibular Exits through the Foramen Ovale
Whats the components of the trigeminal nerve branches?
- General Sensory to cornea/eyelid/scalp/nose/nasal&sinus mucosa
- General Sensory to face, upper teeth, TM joint, palate and nose
- General Sensory to face, lower teeth, TM joint, mouth mucosa & ant 2/3rds of tongue
- Somatic Motor to muscles of mastication, digastric, tensor veli palatine & Tensor Tympani
Whats the clinical relevance of the trigeminal nerve?
- Paralysed Muscles of mastication
- Loss of corneal or sneezing reflex
- Loss of facial sensation
- Trigeminal Neuralgia
Describe the pathway, components and clinical relevance of the 6th cranial nerve?
- Emerges from between pons & Medulla then out via the Sup Orbital Fissure
- Contains purely somatic motor nerves to the lateral rectus
- Loss of this nerve leads to medial deviation of the eye and diplopia
What are the components of the facial nerve?
- Muscles of facial expression, stapedius & Digastric
- Salivary Glands (not parotid)
- Lacrimal glands
- Other glands in the nose/palate
- Taste to Ant 2/3rds of tongue
- External Acoustic Meatus
Whats the pathway of the facial nerve?
Emerges from between Pons & Medulla
Then exits via the internal acoustic meatus through the facial canal and out stylomastoid foramen.
Whats the clinical relevance of Cranial Nerve VII
- Its the most commonly injured due to its long external path
- Damage leads to facial palsies
E.g. Bell’s Palsy where you cant frown, close your eyelid or bare teeth on one side
Whats the pathway of the 8th cranial nerve?
Emerges from between Pons and Medulla
Exits through internal acoutis meatus
Divides into Vestibular and Cochlear nerves in the middle ear
What are the components of the vestibulocochlear nerve?
- Vestibular Sensation from semi-circular ducts, utricle & Saccule
- Hearing from the cochlea
Clinical relavance of the 8th cranial nerve?
- Sensorineural deafness
Describe the pathway of the glossopharyngeal nerve?
Emerges from the medulla
Exits via the jugular foramen
What are the components of the 9th cranial nerve?
- Special Sensory to post 3rd of the tongue
- General Sensory to the middle ear and post oral cavity/post 3rd of tongue
- Visceral Sensory to carotid body/sinus
- Autonomic motor to the parotid gland
- Somatic Motor to the Stylopharyngeus (swallowing)
Clinical application of cranial nerve 9?
- Loss of gag reflex & taste from back of tongue
- Associated with X & XI injuries (Jugular Foramen Syndrome)
PAthway of the 10th cranial nerve?
Vagus exits the medulla and passes through the jugular foramen
Components of the Vagus Nerve?
Special Sensory (Taste) to epiglottis and palate
General Sensory to auricle and EAM
Visceral Sensory to pharynx and below
Autonomic motor to bronchi, gut and heart
Somatic Motor to swallowing muscles and speaking muscles. (pharynx, larynx & Oesophagus)
Clinical relevance of Cr N X?
- Difficulty swallowing if you damage the pharyngeal branches
- Difficulty speaking/hoarseness if you damage the laryngeal branches
- Jugular Foramen Syndrome (Damage to IX/X/XI)
What are the components of the 11th cranial nerve?
Somatic Motor to soft palate, pharynx and larynx muscles. Also the SCM and Trapezius
Describe the pathway of the Accessory Nerve:
Has both medullary and spinal roots, the spinal roots ass up into the skull.
It all exits via the jugular foramen
Clinical relevance of the accessory nerve?
Weakness when shrugging or turning the head
What are the components of the hypoglossal nerve?
Somatic motor to the tongue muscles
Describe the pathway of the hypoglossal nerve?
- Emerges from medulla
- Exits via hypoglossal canal (in the wall of the foramen magnum)
Whats the clinical relevance of the 12th cranial nerve?
- Damaged in a tonsillectomy
- Paralyses the ipsilateral side of the tongue, the tip also deviates towards the affected side
What foramen do the various cranial nerves exit?
I - Foramina in the Cribriform plate II - Optic Canal III - Sup Orbital Fissure IV - Sup Orbital Fissure V1 - Sup Orbital Fissure V2 - Foramen Rotundum V3 - Foramen Ovale VI - Sup Orbital Fissure VII - Internal Auditory Meatus -> Stylomastoid foramen VIII - Internal Auditory Meatus IX - Jugular Foramen X - Jugular Foramen XI - Jugular Foramen XII - Hypoglossal Canal