Name and describe the course of CNI
The Olfactory Nerve
Stemming from the left and right olfactory bulbs, exits the Skull through the cribriform plate and terminating in the roof of the nasal cavity, this nerve governs the olfactory nerve fibers which register smell.
Name and describe the course of CN II
The Optic Nerve Stemming on the left and right side from the optic chiasm, exiting the skull through the optic canal and terminating in the eye, this nerve governs the ocular and sensory functions.
Name and course of CNIII
The Oculomotor Nerve
Stemming from the mesial superior margin of the left and right side of the pons, exiting the skull through the superior orbital fissure and terminating in the muscles of the eye: ciliary, sphincter pupillae and all the external eye muscles except: superior oblique and lateral rectus.
This nerve motorically innervates the previously mentioned eye muscles and allows the eye to move within the orbit
Name and course of CN IV
The Trochlear Nerve
Stems from the lateral superior margin of the left and right side of the pons, exiting the skull through the superior orbital fissure and terminating in the superior oblique eye muscle
Motorically governs the abduction, depression and internal rotation of the eye.
Name and course of CN V
The Trigeminal Nerve
Stems from the lateral superior margin of the left and right side of the pons, this nerve branches into three: V/I ophthalmic, V/II maxillary and V/III mandibular nerves. These branches exit the skull through the superior orbital fissure (V/I), the foramen rotundum (V/II) and the foramen ovale (V/III).
This nerve governs the sensory innervation of the face, sinuses and teeth.
Name and course of CN VI
The Abducent Nerve
Stems from the medial inferior margin of the left and right side of the pons and the left and right pyramids, this nerve exits the skull via the superior orbital fissure and innervates the lateral rectus muscle of the eye, which retracts the eye within the orbit.
How many cranial nerves are there? State whether they are part of the CNS of PNS.
Name and course of CN VII
The Facial Nerve
Stems from the lateral inferior margin of the left and right side of the pons and the left and right olives, this nerve exits the skull through the Internal acoustic meatus.
It supplies the muscles of the face with motoric fibers and taste sensation to the anterior two thirds of the tongue.
Name and course of CN VIII
The Vestibulocochlear Nerve
Stemming from the lateral inferior margin of the left and right side of the pons and the cerebellum, exiting the skull via the internal acoustic meatus, this single nerve contains both vestibular and cochlear fibers. The cochlear fibers terminate in the cochlea and the vestibular fibers terminate in the ampullae of the vestibulum.
They supply sensory innervation to the inner ear.
Name and course of CN IX
The Glossopharyngeal Nerve
Stemming from between the olives and the cerebellum, this nerve exits the skull via the jugular foramen.
Name and course of CN X
The Vagus Nerve
Stemming from between the olives and the cerebellum, this nerve exits the skull via the jugular foramen.
It motorically innervates the heart, lungs, palate, pharynx, larynx, trachea, bronchi and gastrointestinal tract. It provides sensation to the heart, lungs, trachea, bronchi, larynx, pharynx, gastrointestinal tract and the external ear.
Name and course of CN XI
The Accessory Nerve
Stemming from between the cuneate fasciculus and lateral funiculus and exiting the skull via the jugular foramen, this nerve motorically innervates the Sternocleidomastoid muscles and Trapezius muscles.
Name and course of CN XII
The Hypoglossal Nerve
Stemming from between the gracile and cuneate fasciculus, this nerve exits the skull via the hypoglossal canal. It motorically innervates the muscles of the tongue, except the palatoglossus, which is innervated by the vagus nerve (CN X). It also gives C1-3 fibers to the strap muscles (infrahyoid muscles).
How is the optic nerve different from the other cranial nerves?
The optic nerve is surrounded by cranial meninges (not by epi-, peri- and endoneurium like most other nerves).
Describe the contents of the left and right optic tracts.
Left optic tract – contains fibres from the left temporal (lateral) retina, and the right nasal (medial) retina.
Right optic tract – contains fibres from the right temporal retina, and the left nasal retina.
Describe the effect of a pituitary tumour pressing on the optic chiasm
This produces visual defect affecting the peripheral vision in both eyes, known as a bitemporal hemianopia
Describe the cell types found within the olfactory mucosa
Basal cells: Form the new stem cells from which the new olfactory cells can develop.
Sustentacular cells: Tall cells for structural support. These are analogous to the glial cells located in the CNS.
Olfactory receptor cells: bipolar neurons which have two processes, a dendritic process and a central process. The dendritic process projects to the surface of the epithelium, where they project a number of short cilia, the olfactory hairs, into the mucous membrane. These cilia react to odors in the air and stimulate the olfactory cells. The central process (also known as the axon) projects in the opposite direction through the basement membrane.
In addition to the epithelium, there are Bowman’s glands present in the mucosa, which secrete mucus.
Where does the olfactory bulb lie?
What does the superior branch of the occulomotor nerve innervate and what are its actions?
Superior rectus – Elevates the eyeball
Levator palpabrae superioris – Raises the upper eyelid.
What does the inferior branch of the occulomotor nerve innervate?
Inferior rectus – Depresses the eyeball
Medial rectus – Adducts the eyeball
Inferior oblique – Elevates, abducts and laterally rotates the eyeball
What two structures of the eye recieve parasympathetic input from CNIII? What actions does this produce?
Sphincter pupillae – Constricts the pupil, reducing the amount of light entering the eye.
Ciliary muscles – Contracts, causes the lens to become more spherical, and thus more adapted to short range vision.
Desrcribe/draw the different branches of the occulomotor nerve and what they innervate
Three causes of CNIII lesion
Increasing intracranial pressure – this compresses the nerve against the temporal bone.
Aneurysm of the posterior cerebral artery.
Cavernous sinus infection or trauma.
How does a CNIII lesion present clinically?
Ptosis (drooping upper eyelid) – due to paralysis of the levator palpabrae superioris.
Eyeball resting in the ‘down and out‘ location – due to the paralysis of the superior, inferior and medial rectus, and the inferior oblique. The patient is unable to elevate, depress or adduct the eye.
Dilated pupil – due to the unopposed action of the dilator pupillae muscle.
How does a lesion of the trochlear nerve present and list some causes
Patients will present with diplopia when looking down and in, such as when reading or going down the stairs
The most common cause is congenital fourth nerve palsy, a condition in which the development of the trochlear nerve or nucleus is abnormal. This may be curable with surgery.
Other causes include diabetic neuropathy, thrombophlebitis of the cavernous sinus and raised intracranial pressure (e.g. due to haemorrhage or oedema) ( in these cases, it is rare for the trochlear nerve to be affected in isolation).
The trigeminal nerve is associated with derivatives of which pharyngeal arch?
Describe the different functions of the trigeminal nerve (sensory, motor & parasympathetic)
Sensory: The three terminal branches of CN V innervate the skin, mucous membranes and sinuses of the face. Their distribution pattern is similar to the dermatome supply of spinal nerves (except there is little overlap in the supply of the divisions).
Motor: Only the mandibular branch of CN V has motor fibres. It innervates the muscles of mastication: medial pterygoid, lateral pterygoid, masseter and temporalis. The mandibular nerve also supplies other 1st pharyngeal arch derivatives: anterior belly of digastric, tensor veli palatini and tensor tympani.
Parasympathetic Supply: The post-ganglionic neurones of parasympathetic ganglia travel with branches of the trigeminal nerve. (But note that CN V is NOT part of the cranial outflow of PNS supply)
What is the corneal reflex and what does its absence indicate?
The corneal reflex is the involuntary blinking of the eyelids – stimulated by tactile, thermal or painful stimulation of the cornea.
In the corneal reflex, the ophthalmic nerve acts as the afferent limb – detecting the stimuli. The facial nerve is the efferent limb, causing contraction of the orbicularis oculi muscle.
If the corneal reflex is absent, it is a sign of damage to the trigeminal/ophthalmic nerve, or the facial nerve.
What are the branches of CN Viii?
Inferior alveolar nerve
Where is an inferior alveolar nerve block administered and what are its effects?
The anaesthetic solution is administered at the mandibular foramen, causing numbness of area supplied by the inferior alveolar nerve. The anaesthetic fluid also spreads to the lingual nerve which originates near the inferior alveolar nerve, causing numbness of the anterior 2/3 of the tongue.
What is the relation of the parotid gland to the facial nerve?
The main trunk of the nerve (the motor root of the facial nerve), runs anteriorly and inferiorly into the parotid gland and then divides into five branches
(Note however, that the facial nerve does not contribute towards the innervation of the parotid gland).
What are the branches of the facial nerve responsible for facial expression?
Temporal branch – Innervates the frontalis, orbicularis oculi and corrugator supercilii
Zygomatic branch – Innervates the orbicularis oculi.
Buccal branch – Innervates the orbicularis oris, buccinator and zygomaticus muscles.
Marginal Mandibular branch– Innervates the mentalis muscle.
Cervical branch – Innervates the platysma
The facial nerve begins as two roots; a large motor root, and a small sensory root.
Describe their intracranial course
The two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone. Here, they are in very close proximity to the inner ear.
Still within the temporal bone, the roots leave the internal acoustic meatus, and enter into the facial canal. The canal is a ‘Z’ shaped structure. Within the facial canal, three important events occur:
1) The two roots fuse to form the facial nerve.
2) The nerve forms the geniculate ganglion (a ganglion is a collection of nerve cell bodies)
3) The nerve gives rise to the greater petrosal nerve (parasympathetic fibres to glands), the nerve to stapedius (motor fibres to stapedius muscle), and the chorda tympani (special sensory fibres to the anterior 2/3 tongue).
The facial nerve then exits the facial canal (and the cranium) via the stylomastoid foramen.
Branches of the facial nerve are responsible for innervating derivatives of the which pharyngeal arch.
What are the three motor branches of the facial nerve given off between the stylomastoid foramen and the parotid gland?
Posterior auricular nerve – Ascends in front of the mastoid process, and innervates the intrinsic and extrinsic muscles of the outer ear. It also supplies the occipital part of the occipitofrontalis muscle.
Nerve to the posterior belly of the digastric muscle – Innervates a suprahyoid muscle of the neck. It is responsible for raising the hyoid bone.
Nerve to the stylohyoid muscle – Innervates a suprahyoid muscle of the neck. It is responsible for raising the hyoid bone
The parasympathetic functions of the facial nerve are carried out by what branches?
What would be the effect of a lesion effecting the chorda tympani branch?
Reduced salivation and loss of taste on the ipsilateral 2/3 of the tongue.
What would be the effect of a lesion effecting the nerve to stapedius?
Ipsilateral hyperacusis (hypersensitive to sound).
What would be the effect of a lesion effecting the greater petrosal nerve?
Ipsilateral reduced lacrimal fluid production
List some causes and the effect of extracranial lesions to the facial nerve
There are various causes of extracranial lesions of the facial nerve:
Parotid gland pathology – e.g a tumour, parotitis, surgery.
Infection of the nerve – particularly by the herpes virus.
Compression during forceps delivery – the neonatal mastoid process is not fully developed, and does not provide complete protection of the nerve.
Idiopathic – If no definitive cause can be found, the disease is termed Bell’s palsy
Only the motor function of the facial nerve is affected, resulting in paralysis or severe weakness of the muscles of facial expression.
What is vestibular neuritis and how does it present?
Vestibular neuritis refers to inflammation of the vestibular branch of the vestibulocochlear nerve. The aetiology of this condition is not fully understood, but some cases are thought to be due to reactivation of the herpes simplex virus.
It presents with with symptoms of vestibular nerve damage:
Vertigo – a false sensation that oneself or the surroundings are spinning or moving.
Nystagmus – a repetitive, involuntary to-and-fro oscillation of the eyes.
Loss of equilibrium (especially in low light).
Nausea and vomiting.
The condition is usually self-resolving. Treatment is symptomatic, usually in the form of anti-emetics or vestibular suppressants
What is labyrinthitis? What other symptoms separate it from vestibular neuritis?
Labyrinthitis refers to inflammation of the membranous labyrinth, resulting in damage to the vestibular and cochlear branches of the vestibulocochlear nerve.
The symptoms are similar to vestibular neuritis, but also include indicators of cochlear nerve damage:
Sensorineural hearing loss.
Tinnitus – a false ringing or buzzing sound.
The vestibular and cochlear portions of the vestibulocochlear nerve are functionally discrete, and so originate from different nuclei in the brain - which are?
Vestibular component – arises from the vestibular nuclei complex in the pons and medulla.
Cochlear component – arises from the ventral and dorsal cochlear nuclei, situated in the inferior cerebellar peduncle.
The glossopharyngeal nerve is associated with the derivatives of which pharyngeal arch?
Outline the innervations of the glossopharangeal nerve
Sensory: Innervates the oropharynx, carotid body and sinus, posterior 1/3 of the tongue, middle ear cavity and Eustachian tube.
Special Sensory: Provides taste sensation to the posterior 1/3 of the tongue.
Parasympathetic: Provides parasympathetic innervation to the parotid gland.
Motor: Innervates the stylopharyngeus muscle of the pharynx.
Describe the sensory function of CN IX
The tympanic nerve arises as the nerve traverses the jugular foramen. It penetrates the temporal bone and enters the cavity of the middle ear. Here, it forms the tympanic plexus – a network of nerves that provide sensory innervation to the middle ear, internal surface of the tympanic membrane and Eustachian tube.
At the level of the stylopharyngeus, the carotid sinus nerve arises. It descends down the neck to innervates both the carotid sinus and carotid body, providing information regarding blood pressure and oxygenation respectively.
The glossopharyngeal nerve terminates by splitting into several sensory branches:
Pharyngeal branch – combines with fibres of the vagus nerve to form the pharyngeal plexus. It innervates the mucosa of the oropharynx.
Lingual branch – provides the posterior 1/3 of the tongue with general and taste sensation
Tonsillar branch – forms a network of nerves, known as the tonsillar plexus, which innervates the palatine tonsils.
The vagus nerve is associated with the derivatives of the which pharyngeal arch?
Outline functions of CN X
Sensory: Innervates the skin of the external acoustic meatus and the internal surfaces of the laryngopharynx and larynx. Provides visceral sensation to the heart and abdominal viscera.
Special Sensory: Provides taste sensation to the epiglottis and root of the tongue.
Motor: Provides motor innervation to the majority of the muscles of the pharynx, soft palate and larynx.
Parasympathetic: Innervates the smooth muscle of the trachea, bronchi and gastro-intestinal tract and regulates heart rhythm.
Causes and clinical presentation of a CN XI lesion?
The most common cause of accessory nerve damage is iatrogenic (i.e. due to a medical procedure). In particular, operations such as cervical lymph node biopsy or cannulation of the internal jugular vein can cause trauma to the nerve.
Clinical features include muscle wasting and partial paralysis of the sternocleidomastoid, resulting in the inability to rotate the head or weakness in shrugging the shoulders. Damage to the muscles may also result in an asymmetrical neckline.
Describe the presentation of a hypoglossal nerve palsy
Patients will present with deviation of the tongue towards the damaged side on protrusion, as well as possible muscle wasting and fasciculations (twitching of isolated groups of muscle fibres) on the affected side.
(Damage to the hypoglossal nerve is a relatively uncommon cranial nerve palsy. Possible causes include tumours and penetrating traumatic injuries. If the symptoms are accompanied by acute pain, a possible cause may be dissection of the internal carotid artery).
Name the four parasympathetic cranial ganglia
Note: the autonomic ganglia of the Vagus nerve (VII) form lie outside of the head, frequently within the organ which they innervate. In the case of the gut, for example, the autonomic neurones do not form distinct ganglia, but rather the preganglionic neurons synapse within the Enteric nervous system.
Name the cranial sensory ganglia
Superior (jugular) ganglia of glossopharyngeal
Inferior (petrosal) ganglia of glossopharyngeal
Superior (rostral) ganglion of vagus nerve
Inferior (nodose) ganglion of vagus nerve