Session 3: Cranial Nerves Flashcards
Name the 12 cranial nerves and state whether they’re sensory, motor or both
Describe the organisation of the cranial nerves
The skin, viscera and muscles of the head and neck are supplied neutrally by 12 pairs of nerves flowing directly from the brain (from its inferior surface), hence collectively known as cranial nerves.
[*] 1 pair of these nerves actually originates in the spinal cord.
[*] The cranial nerves emerge through foramina or fissures in the cranium and are covered by tubular sheaths derived from the cranial meninges.
[*] NB: the optic (II) and vestibulocochlear (VIII) nerves will be examined in detail during the Nervous System module
[*] Cranial nerve I is most rostral (most anterior)
[*] Cranial Nerve XI is most caudal (most posterior).
[*] Cranial Nerve XII is the exception – it is just in front of CN XI
Cranial nerves can distribute not only sensory and motor fibres like any typical mixed nerve e.g. the median nerve but also autonomic nerves involved with special sensation like vision, taste, etc.
What are the cranial nerves?
What are Cranial Nerves?
[*] Cranial nerves are nerve bundles that issue from the brain (nerve bundles that connect sense organs to the brain (afferents) and connect the brain to muscles and glands (efferents)
[*] They innervate tissues of the head and neck region but some also supply viscera outside of the head and neck region.
[*] They have specialisations that make them distinct from other nerves of the body (spinal)
What is a nerve?
[*] A nerve cell is known as a neurone.
[*] All nerve cells have:
- A soma or cell body (n=1)
- Most somata are found in the CNS except for first order sensory neurones
- An axon (n=1): a long cyclindrical cell process that can be short or very long
- Nerve cells tend to straddle the CNS and PNS
- Short sections are in the CNS
- Long sections are in the PNS
[*] Nerve cells/neurones are distinct from nerve bundles e.g. Sciatic nerve
How is a nerve fibre different from a nerve bundle?
How is a nerve fibre different from a nerve bundle?
[*] A single neurone can be called a nerve (though this not correct)
[*] Collections of single neurones bound together comprise a single nerve
[*] Strictly, a nerve is a collection of single axons of neurones bound together by three layers of connective tissue.
[*] Connective tissue types of a nerve differ depending upon whether the nerve is in the CNS or PNS
Connective tissue binding a peripheral nerve are:
- Endoneurium
- Perineurium
- Epineurium
Connective tissue binding a CNS nerve are:
- Pia mater
- Arachanoid mater
- Dura mater
Most nerves are mixed nerves: most nerve bundles contain upwards of 100s if not 1000s of axons
[*] Axons of nerve bundles are mixed
[*] Some are myelinated – heavily or lightly
[*] Others are unmyelinated
[*] There are varied conduction velocities amongst nerves
[*] Some are afferent in function – diverse afferent modalities
[*] Some are efferent in function – some are motor, others are autonomic
Compare Cranial Nerves to Spinal Nerves
Cranial vs Spinal Nerves: nerves are classified as either cranial or spinal nerves
[*] The location of cell bodies of cranial nerves are in the brain
[*] The location of cell bodies of spinal nerves are in the spinal cord
[*] Axons of all nerves are in the PNS
[*] There are 2 exceptions to this rule: axons of 2 cranial nerves remain part of CNS though they lie in the PNS
Cranial Nerves
[*] 12 pairs
[*] Most are typical peripheral nerves apart from the first 2 which are atypical in that they are true brain tracts and not nerves (carry meninges)
[*] They supply largely the head and neck region
- Muscles (efferent)
- Viscera (afferent and efferent)
- General sensation (afferent)
- Special sense organs (afferent)
[*] Peculiarities of the Cranial Nerves
- Most supply head and neck structures that are derived from the same embryological branchial arches as themselves.
- BUT head and neck structures that do not derive from branchial arches are also innervated by cranial nerves
Spinal Nerves
[*] There are 31 pairs of spinal nerves, all originating from the spinal cord. They are largely bilaterally symmetrical.
[*] They supply general motor function, general sensation and autonomic functions of the rest the rest of the body.
[*] None have special sense functions
What is the Dermatomyotome?
[*] Embryonic precursors of skin and muscle units are known as dermatomyotomes
[*] Each dermatomyotome eventually differentiates into skin (dermatomes) and muscle (myotome) in the adult)
[*] Dermatomyotomes develop in relation to a specific neural level of the embryonic neural tube tissue that will become the adult spinal cord.
[*] Differentiated skin and muscle units of a dermatomytome always have a common source of nervous supply.
[*] The adult nervous supply to the skin and muscle of a dermatomyotome is that which develops from the neural tube-locus originally associated with that embryonic dermatomyotome
General Guide to Cranial Nerve Examination
[*] Cranial nerves are paired
[*] One side can be used as control, whilst the other side is tested and vice-versa (but systemic disease often affects both sides, sometimes one side more than the other)
[*] Some tests require that 2 separate cranial nerves are tested simultaneously
[*] A knowledge-base of what modalities are sub-served by each of the cranial nerves is a requisite.
[*] Knowledge-base of central anatomical course of the each nerve is also a requisite (advanced).
[*] Knowledge of central connections of each of the cranial nerves is necessary (advanced)
[*] Most cranial nerves arise in specific nuclei in the brain (advanced)
[*] Receptive fields of cranial nerves
- Remember that when a nerve is being tested, it only perceives a limited part of the periphery
- For a stimulus to be effective, it must be presented to an appropriate part of the periphery sub-served by the nerve in question
- Peripheral territory to which a nerve responds when an appropriate stimulus is presented is called “the receptive field” for that nerve
Describe the Olfactory Nerve
The olfactory (I) is distributed to the uppermost part of the nasal cavity and is concerned with smell; it contains only special sensation fibres. It is an entirely ‘sensory nerve’.
[*] It is not a true nerve but a brain tract (covered by meninges hence atypical.
[*] Let and right nasal cavities are supplied by separate left and right olfactory nerves
[*] Olfactory nerve processes leave the nasal cavity to ascend intra-cranially via the cribiform plate of the ethmoid bone, where they form the olfactory bulb.
[*] Fractures of the (cribiform plate of) ethmoid involving the dura mater may be associated with leakage of the CSF from the nose (rhinorrhea).
[*] Fractures of the cribiform plate may result in anosmia (absence of sense of smell)
[*] Testing the Cranial Nerve
- Sense of smell is tested for each nostril separately.
- Sense of smell is tested using specific odours in vials, coffee, peppermint, vanilla etc
- Sense of smell can be temporarily lost in Upper Respiratory Tract infections
[*] The olfactory nerve is a unique cranial nerve. Its sensations are conveyed to the cerebral cortex, directly without going through the thalamus
- This may explain why smelling salts can be used to re-boot the brain after loss of consciousness
- Some hallucinations involve sensation of smell without sensory source
- Olfactory ensheathing cells ensheath the non-myelinated axons of olfactory neurons and like Schwann cells, have the property of assisting axonal regeneration. They are also capable of phagocytosing axonal debris.
Describe the Optic Nerve
[*] Subserves Vision
[*] It is also atypical – a brain tract, not a peripheral nerve
[*] Examination of the visual system is complex: it involves testing many things concurrently: visual acuity, colour vision, visual fields, pupillary reflexes, fundoscopy. These can be grouped into 3 General Categories:
- Apparatus of the eye itself: fundoscopy, visual acuity, colour vision
- Reflexes of the pupils
- Connections of the retina (or eye) to the visual cortex (if connection is not complete, people will be blind even though normal reflexes are still possible)
[*] Functional and Applied Anatomy of CN II:
- Assessing visual field defects
- Testing for early signs of meningitis
- Tumours of the hypothalamus lead to disturbances of vision
- Aneurysms of the internal carotid artery near the hypothalamus lead to disturbances of vision.
- The central retinal artery and vein pass through the nerve which is surrounded by 3 meningeal layers and bathed within the CSF in the subarachnoid space.
- Elevated CSF pressure secondary to elevated intracranial pressure is transmitted to the optic nerve and disc =- resulting in retinal vein engorgement and blurring of the margins of the optic discs (papilledema)
[*] Direct trauma to eye or orbit, fracture of optic canal or pressure on optic pathway may result in nerve lesions => loss of pupillary constriction and visual field defects.
Describe the Oculomotor Nerve
[*] It is a mixed nerve: somatic motor and autonomic
[*] Somatic Motor: innervates the extraocular muscles, the ciliary muscles and sphincter pupillae apart from the lateral rectus (LR6) and superior oblique (SO4). It also innervates the Levator Palpaebrae Superioris Muscle of the upper eyelid – opens the upper eyelid
[*] Autonomic (Parasympathetic): constrictor pupillae of the eye
[*] Applied Anatomy of CN III:
- Somatic motor fibres innervate the levator palpebrae superioris (opens upper eyelid) + 4 extraocular muscles except the lateral rectus and superior oblique
- Autonomic: preganglionic parasympathetic fibres => ciliary ganglion => postganglionic neurones (short ciliary nerves) => Ciliary and sphincter pupillae muscle (smooth) => constriction of pupils and curvature of lens (accommodation)
Describe the functional and applied anatomy of the Oculomotor Nerve
- Extraocular muscles: patient is asked to look at a finger as it is moved in directions that elicits adduction and abduction of the eye, elevation and depression of the eye when it is adducted, and elevation and depression of the eye when it is abducted
- Oculomotor nerve palsy relatively common; eye is “down and out” (involvement of extraocular muscles).
- Levator palpebrae superioris – patient is asked to look upward so as to observe if elevation of the eyelid accompanies this effort. Oculomotor nerve palsy => drooping of the upper eyelid (ptosis)
- Oculomotor nerve palsy associated with pathological conditions such as – aneurysms of the posterior communicating artery which compresses the nerve; cavernous sinus thrombosis
- Parasympathetic pathway:
- Constrictor pupillae – shining a light in the patient’s eye; the pupil should constrict – pupillary light reflex is ‘consensual’ (shining a light in one pupil into only one eye causes both pupils to constrict)
- Oculomotor nerve palsy > dilated pupil and absent pupillary light reflex (paralysis of constrictor muscle); absent accommodation reflex (paralysis of ciliary muscle)
- Sympathetic pathway:
- Dilator pupillae – shielding an eye from light; pupil dilates – reflex is ‘consensual’
Describe the presentation of an Oculomotor Nerve Palsy
[*] Fractures involving the cavernous sinus or aneurysms may cause lesions => dilated pupil, ptosis, eye turns down and out, pupillary reflex on side of lesion is lost.
[*] Palsies of the Motor Division of CN III:
- The denervated eye assumes a down and out position at rest due to the unopposed actions of lateral rectus and superior oblique.
- Complete ptosis of the upper eyelid due to denervation of the levator palpaebrae superioris muscle (complete closure of the upper eyelid)
- Note in Horner’s the ptosis is not complete but partial
[*] Palsies of the Parasympathetic Division of CN III:
- The pupil of the affected eye becomes fixed (unresponsive) and dilated due to denervation of the constrictor pupillae
Describe the Trochlear Nerve
[*] Emerges from dorsal aspect of midbrain
[*] Motor: innervates the superior oblique of the eye.
[*] Stretching of the nerve during its course around the brainstem or orbit fractures may lead to nerve lesions => diplopia (double vision) occurs - inability to look downwards and in-wards (adduction).
[*] Diplopia presents when patient goes down the stairs.
[*] To test, ask the patient to look medially and downwards. The patient is able to look medially (due to the 3rd cranial nerve and medial rectus) but not downwards.
Describe the Trigeminal Nerve
Cranial nerve V, the trigeminal, is the great sensory nerve of the head and neck.
[*] Largest cranial nerve in the body
[*] It is divided into 3 divisions: the ophthalmic (CN Vi), maxillary (CN Vii) and mandibular (CN Viii)
[*] It is a mixed nerve: The ophthalmic and maxillary branches are entirely sensory but the mandibular nerve also contains motor fibres which innervate the muscles of mastication.
- Temporalis
- Masseter
- Medial Pterygoids
Describe the Ophthalmic Nerve
[*] The ophthalmic supplies skin and cornea and is responsible for the corneal reflex. Deficits of this division will only lead to altered sensation
- Sensory territories of skin: scalp, forehead, upper eyelid, dorsum of nose.
- Sensations of the eye: cornea and conjunctiva
[*] Functional and Applied Anatomy – the Ophthalmic Division
- Test for responsiveness of the skin of the forehead to touch and prick
- Corneal reflex – sensation via V(i) or V(ii) => brain – fibres synapse with facial neurones innervating the palpebral portion of orbicularis oculi => contracts, producing a blink reflex (bilateral aka consensual)
- Corneal reflex disturbed if either the sensory or the motor limb is damaged; sensory limb > neither eyelid will blind – if cornea of one eye produces a blink in the opposite eye, the ophthalmic nerve is ok and the defect is in the facial nerve
Describe the Maxillary Nerve
[*] The maxillary supplies skin, mucous membrane of nose, palate and upper dental arcade.
Sensory territories: skin of lower eyelid, skin of cheek, skin of upper lip, mucosa of nasal cavity, mucosa lining paranasal sinuses, mucosa lining palate, roots of upper teeth N.B: canthi (angle) of the eye and mouth form useful boundaries
- Test sensation of CN Vii by assessing the responsiveness of the skin over the front of the cheek (infraorbital nerve) to touch and pain.
- Nasal, palatal and upper dental sensation are affected by damage to Vii (but these are not routinely tested)
Describe the Mandibular Nerve
[*] The mandibular is a mixed sensory and motor branch - supplies sensory innervation to the skin, lower teeth, cheek and anterior 2/3rd of tongue (general sensation) and supplies motor innervation to the muscles of mastication.
- Sensory Territories: skin of the temples, skin of cheeks, skin of chin, mucosa of inner cheek, anterior two-thirds of tongue (general sensation), roots of lower teeth
- Branchial Motor function: to elevate or close the jaw, innervating the muscles of mastication
- Temporalis (closing)
- Masseter (closing)
- Medial pterygoids (opening)
- Lateral pterygoids (closing)
- Anterior belly of digastric (opening)
Test for sensory fibres in Viii confined to skin over the chin (mental nerve) and the side of the cheek (buccal nerve)
General sensation to the front of the tongue (lingual nerve)
Test for the strength of the masseter and pterygoids
[*] Nerve lesions lead to paralysis of muscles and sharp, intense facial pain
Describe the relationships of cranial nerves, ICA and cavernous sinus
Cavernous Sinus
[*] Plexus of extremely thin-walled veins on upper surface of sphenoid (on either side of pituitary gland)
[*] Contents
Internal carotid artery
CNIII oculomotor
CNIV trochlear
CNVI abducent
2 branches of trigeminal – CNV1 ophthalmic and CNV2 maxillary
Describe the Abducens Nerve
The Abducens nerve (CVI) supplies motor innervation to the lateral rectus.
[*] Has a long intra-cranial course therefore it is liable to damage in cases of raised intracranial pressure.
[*] Fractures involving the cavernous sinus or orbit may lead to nerve lesions.
[*] When damaged, the patient is then unable to look outwards - eye fails to move laterally, diplopia (double vision) or squint on lateral gaze
Describe CN VII
The facial nerve VII is a complex nerve as it contains motor, general and special sensory and parasympathetic fibres – it is a mixed nerve.
[*] The motor division is referred to as the facial nerve.
[*] The sensory division is referred to as the Nervus Intermedius
[*] The autonomic division is also a part of Nervus Intermedius. The Greater Petrosal Nerve is its largest branch.
[*] Its motor fibres are distributed to muscles of facial expression as well as the posterior belly of digastrics, stylohyoid and stapedius muscles.
- Parasympathetic secretomotor to submandibular and sublingual salivary glands via the chorda tympani
- Parasympathetic also secretomotor to the lacrimal gland and mucosal membranes of nasal mucosa, paranasal sinuses and hard palate.
[*] General sensory fibres supply part of the external acoustic meatus and auricle – supplies general sensation of the concha of the auricle.
[*] Special sensory fibres supply tastebuds of the anterior two thirds of the tongue via chorda tympani (nerve of facial nerve origin that hitchhikes onto trigeminal nerve, so when damage to trigeminal nerve occurs, this nerve is also damaged)
What happens when CN VII is damaged? Describe a facial nerve palsy? What’s a Bell’s Palsy?
[*] Damage to motor division of CN VII leads to:
- Loss of facial expression
- Loss of sphincter function => inability to chew foods correctly and inability to blink correctly
- Loss of naso-labial fold
- Hyperacusis – normal sounds are painful due to oversensitivity
- NOTE: forehead sparing
- Facial Palsy generally refers to weakness of the facial muscles, mainly resulting from temporary or permanent damage to the facial nerve. Each side of the face has its own facial nerve so damaging the left facial nerve will only affect the left side of the brain, and vice versa (if it is a lower motor neurone lesion). Paralysis of the muscles can affect movement of the eye(S) and/or the mouth – the face sags and is drawn across to the opposite side on smiling. Voluntary eye closure may not be possible.
- Bell’s Palsy is thought to be viral in origin and the facial nerve is damaged by inflammation, which causes facial paralysis on the affected side. Facial palsy is the most common acute condition involving only one nerve and Bell’s palsy is the commonest cause of facial palsy, accounting for ~60% of all cases.
[*] Damage to facial nerve (outside of the cranial canal - distal to the stylomastoid foramen) > paralysis of muscles of facial expression.
[*] Damage within posterior wall of the tympanic cavity (damage to the chorda tympani which supplies the anterior 2/3rds of the tongue and on salivation and lacrimation) can alter taste sensation, salivation and lacrimation.
[*] Tumours within the petrous part of the temporal bone will affect the facial nerve.
[*] Laceration or contusion in the parotid region could result in
- Paralysis of facial muscles, eye remains open, angle of mouth droops, forehead does not wrinkle
[*] Fracture of Temporal Bone
- Bell’s Palsy (weakness of the facial muscles)
- Involvement of cochlear nerve and chorda tympani; dry cornea; loss of taste in anterior 2/3rds tongue
[*] Intracranial Haematoma
- Forehead wrinkles because of bilateral innervation of frontalis muscle
- Paralysis of contralateral facial muscles (upper motor neurone lesion)
What are the Facial Nerve Tests?
- Raise eyebrows
- Wrinkle forehead (frontalis), close the eyes tightly (orbicularis oculi)
- Broad smile for several muscles for symmetry
- Puffing out the cheeks (buccinators) tests orbicularis oris as well
Describe the Vestibulocochlear Nerve
[*] Close relationship with the facial nerve
[*] Sensory
[*] It is a compound (conjugate) nerve subserving 2 special sense modalities:
- Balance controlled by the vestibular nerve
- Hearing controlled by the cochlear nerve
[*] Can be tested by whispering numbers to each ear with the other ear closed.
[*] Important in testing for brain death.
[*] Cochlear Nerve Tests
- Tests for hearing acuity
- Loss of hearing is called deafness
There are 2 recognised forms of deafness:
- Sensori-neural (nerve)
- Conductive (blockage)
Rinne’s test and Weber’s test are used to differentiate between sensori-neural vs conductive deafness
[*] Skull fractures, ear infections, tumour of the nerve (acoustic neuroma) may all cause nerve lesions:
- Progressive, unilateral hearing loss, tinnitus, vertigo
- Acoustic neuroma frequently impairs Facial Nerve (CNVII) too
Describe the Glossopharyngeal Nerve
The glossopharyngeal nerve (IX) also contains four types of nerve fibres and has both sensory and motor functions:
[*] Motor
- Branchiomotor – Stylopharyngeus
- Visceromotor (parasympathetic fibres) – Parotid gland (but the facial nerve passes through it)
[*] Sensory
- Fibres of special sensation innervate the posterior third of the tongue. Deep lacerations of the neck may cause nerve lesions => loss of taste to posterior 1/3rd tongue.
- General sensory fibres are widely distributed to the pharynx and oropharyngeal isthmus, the dorsum of the palate, the auditory tube and associated structures, the mastoid antrum and mastoid cells.
- Viscerosensory: Finally, via its sinus nerve branch, it supplies the carotid sinus and carotid body that monitor blood pressure and arterial oxygen levels respectively.
[*] Functional and Applied Anatomy – CN IX
- Test for CN IX function is the ‘gag reflex’ aka the pharyngeal reflex
- Consists of reflex pharyngeal constriction when the back wall of the oropharynx is touched by non-food substances.
- CN IX is the sensory limb of the reflex.
- CN X (i.e. vagus nerve) is the motor limb of the reflex
- Posterior 1/3rd of tongue for taste
- Salivation (parotid gland)
Describe the Vagus Nerve
The vagus (X) nerve has an enormous territory extending into the abdomen – widest distribution in the body
[*] In the head and neck, it is sensory to the lower part of the pharynx, the airways and oesophagus.
[*] It provides general sensation, parasympathetic fibres and motor fibres to the lower parts of the pharynx (motor to all of the pharynx except the stylopharyngeus), the larynx, trachea and oesophagus.
[*] Motor fibres innervate the intrinsic muscles of the larynx and pharynx, muscles of the palate smooth muscle – bronchi, digestive tract and secretomotor – thoracic and abdominal viscera.
[*] It supplies (special sensory) taste fibres to taste buds associated with the epiglottis
[*] It provides sensory fibres to the external ear, auditory canal and eardrum, pharynx and larynx + visceral sensation to the thorax and abdomen
Describe the Superior, Middle and Inferior Cervical Ganglion
The sympathetic innervation of the head and neck is by way of the cervical sympathetic trunks that pass vertically upwards to the base of the skull, anterolateral to the vertebral column, lying on the prevertebral fascia and muscles and lying deep to the carotid sheath.
[*] Each trunk originates from 3 ganglia (superior, middle and inferior), which are continuous and part of the sympathetic thoracic trunk, also known as the sympathetic chain (of ganglia).
[*] Preganglionic fibres arise mainly in the first thoracic neural segment and synapse in one of three cervical ganglia (i.e. superior, middle or inferior).
[*] After synapsing, postganglionic fibres travel as external and internal carotid nerves along the blood vessels to target tissues; with blood vessels themselves being the main primary targets.
[*] The postganglionic fibres from the superior cervical ganglion pass with the external and internal carotid arteries and its branches, to the pharyngeal plexus, to the upper four cervical nerves and in a cardiac branch to the cardiac plexus.
[*] The postganglionic fibres from the middle cervical ganglion pass with the inferior thyroid artery, to the 5th and 6th cervical nerves, and in a cardiac branch to the cardiac plexus.
[*] The postganglionic fibres from the inferior cervical ganglion pass with the vertebral artery, to the 7th and 8th cervical nerves, and in a cardiac branch to the cardiac plexus.
- The inferior cervical ganglion is a small ganglion and may combine with the 1st thoracic ganglion to form the stellate ganglion (in 80% of people)
What are the 4 pairs of parasympathetic ganglia in the head? And the cranial nerves associated with them?
There are 4 pairs of parasympathetic ganglia in the head. Four cranial nerves (the occulomotor, facial, glossopharyngeal and vagus) have brainstem nuclei containing preganglionic, parasympathetic neurones but only three of these nerves have branches that reach these ganglia; the vagus nerve does not have discrete ganglion associated with it. The four ganglia and their associated cranial nerves are the:
- [*] Ciliary ganglion (Oculomotor nerve CIII)
- [*] Pterygopalatine ganglion (Facial nerve CVII)
- [*] Submandibular ganglion (Facial nerve CVII)
- [*] Otic ganglion (Glossopharyngeal nerve CIX)
[*] Preganglionic fibres pass in these four cranial nerves and synapse either in the four ganglia or in the walls of the organs they supply in the neck, thorax and abdomen. The ganglia, as well as containing parasympathetic synapses, also give uninterrupted passage to sympathetic and somatic fibres.
Describe the Ciliary Ganglion
The ciliary ganglion lies in the orbital cavity, lateral to the optic nerve.
[*] The parasympathetic fibres are derived from the oculomotor nerve (CIII) and pass to the sphincter papillae and ciliary muscles.
[*] Sympathetic fibres come from the superior cervical ganglion via the plexus on the ophthalmic artery (first branch of the internal carotid artery) and are distributed to the eyeball.
[*] Sensory fibres from the eyeball pass to the nasociliary nerve.
Describe the Ptergyopalatine Ganglion
The pterygopalatine ganglion lies in the pterygopalatine fossa and is connected to the maxillary nerve by small branches.
[*] The parasympathetic fibres are derived from the facial nerve via the Greater Pterosal nerve. Postganglionic fibres supply the lacrimal glands and glands of the nose, palate and nasopharynx.
[*] Sympathetic fibres come from the superior cervical ganglion via the plexus on the internal carotid artery. The fibres are distributed to the nose, palate and nasopharynx.
[*] Sensory fibres from the nose, palate and nasopharynx pass in the branches of the ganglion to the maxillary nerve (2nd branch of the trigeminal nerve)
Describe the Submandibular Ganglion
The submandibular ganglion is suspended from the lingual nerve by small branches.
[*] Its parasympathetic fibres come from the facial nerve via its chorda tympani branch and then along the lingual nerve to the ganglion. Postganglionic fibres supply the submandibular and sublingual glands and other glands in the floor of the oral cavity.
[*] Sympathetic fibres come from the superior cervical ganglion along the facial artery and pass to the glands in the floor of the oral cavity.
- Taste fibres may pass through the ganglion.
Describe the Otic Ganglion + describe direct parasympathetic supply
[*] The parasympathetic fibres to the otic ganglion come from the glossopharyngeal nerve and pass with the auriculotemporal nerve (branch of the CN V3) to the parotid gland.
[*] Sympathetic fibres come from the superior cervical ganglion along the middle meningeal artery and pass into the parotid gland.
[*] Motor branches from the mandibular nerve (CV3) pass through the ganglion without synapsing.
- NB:
[*] Parasympathetic fibres from the glossopharyngeal nerve supply directly, or through the pharyngeal plexus, the glands of the oropharynx and the posterior third of the tongue.
Parasympathetic fibres from the vagus supply the glands of the laryngopharynx, larynx, oesophagus and trachea; in all these cases, the ganglion cells are on the viscera.
What are the brainstem nuclei of the four cranial nerves that have presynaptic parasympathetic fibres?
Edinger-Westphal
Superior Salivatory
Inferior Salivatory
Dorsal Vagal Motor Nucleus
Describe the foramina of the cranium
[*] They are holes in the base of the cranium through which nerves and blood vessels pass
[*] Due to their large numbers:
- They reduce the mass of the cranium, making it lighter
- They make the skull-base physically weak
[*] Trauma to the skull often leads to fractures at the base
[*] Nerves can be compressed as they pass through the foramina
[*] Peripheral nerve diseases and metastases can pass to the brain via foramina (foramina allow passage of blood vessels and nerves)
What nerves do the Cribiform Plate, Optic Canal, Superior Orbital Fissure and Foramen Rotundum allow to pass through?
Cribiform Plate: Olfactory
Optic Canal: Optic
Superior Orbital Fissure: Oculomotor, Trochlear, Abducens and Ophthalmic divison of Trigeminal
Foramen Rotundum: Maxillary division of Trigeminal
What nerves do the Foramen Ovale, Internal Acoustic Meatus, Jugular Foramen and Hypoglossal Canal allow passage through?
Foramen Ovale: Mandibular division of Trigeminal Nerve
Internal Acoustic Meatus: Facial and Vestibulocochlear Nerves
Jugular Foramen: Glossopharyngeal. Vagus and Spinal Accessory
Hypoglossal Canal: Hypoglossal
Where do autonomic fibres originate from?
[*] Cranio-sacral sources
- Parasympathetic function
- Cranial Nerves: III, VII, IX and X
- &
- S2, S3 and S4 segments of spinal cord
[*] Thoraco-lumbar sources:
- Sympathetic function
- All neural segments of spinal cord between T1 and L2
Lesions of the CNS may lead to imbalances of autonomic outflow to visceral organs
Unbalanced autonomic outflow will lead to disturbed autonomic reflexes.
This can easily lead to death if not managed expertly.
Give the general structure of outflow of autonomic fibres and variation in central control of the ANS
[*] Autonomic ganglions are somewhere in the periphery.
- [*] Parasympathetic system: long pre-ganglionic neurones and short post-ganglionic neurones. Autonomic ganglions are largely located in the wall of effector organs*
- Sympathetic system: short pre-ganglionic neurones and long post-ganglion neurones*
Describe the General Layout of Parasympathetic ANS
General Layout of Parasympathetic ANS: distribution of parasympathetic outflow can be generalised to:
[*] Head and neck region: CN III, CN VII, CN IX, CN X (neck only)
[*] Visceral organs of the body: rest of CNX, S2-S4 (from spinal cord)
General Layout of Parasympathetic ANS to head and neck:
[*] Somata of all pre-ganglionic neurones are located within the brainstem
[*] These somata (cell bodies) constitute cranial nerve nuclei III, VII, IX and X. NB: cranial nerve sources are not same as the autonomic sources – source of oculomotor nerve is not same source as the autonomic nuclei.
[*] Axons of pre-ganglionic neurones travel to their targets as cranial nerves III, VII, IX and X (this is an over-simplification).
[*] Damage to cranial nerves III, VII, IX and X will lead to parasympathetic denervation of autonomic target organs.
[*] Axons of pre-ganglionic neurones terminate and synapse on
- Discrete parasympathetic (not within the walls of the organs) autonomic ganglia (n=4) – found within the substance of the face region. 4 ganglia supplied by 3 parasympathetic cranial nerves.
- Parasympathetic ganglia in walls of target organs: CN X does not terminate in discrete autonomic ganglia of the head and neck.
Parasympathetic autonomic ganglia:
[*] Pre-ganglionic axons from:
- Oculomotor nerve terminates in the ciliary ganglion [related to ophthalmic devision]
- Facial nerve terminates in either
- Pterygopalatine Ganglion (green) [maxillary division] OR
- Submandibular Ganglion [mandibular division] (yellow)
- Glossopharyngeal nerve terminates in the Otic Ganglion [mandibular division]
All these ganglia lie in association somewhere in relation with branches of the trigeminal nerve.
NB: pre-ganglionic axons from the vagus nerve do not terminate in discrete parasympathetic ganglia
Describe the Parasympathetic Output of the Facial Nerve
[*] Pre-ganglionic neurones are found in the superior salivatory nucleus
[*] They terminate in the Pterygopalatine ganglion or Submandibular ganglion
[*] Post-ganglionic fibres supply the Lacrimal gland, Mucous glands of the nose, Mucous glands of the palate, Submandibular salivary gland and Sublingual salivary glands.
[*] Pterygopalatine ganglion: previously known as the Sphenopalatine ganglion
- Supplied by the Greater Petrosal Branch of the Facial Nerve
- The Pterygopalatine ganglion supplies the Lacrimal gland, mucous glands of the nose, mucous glands of the palate
[*] Submandibular ganglion: supplied by the Chorda Tympani Branch of the Facial nerve (which also carries special sensory nerves supplying the anterior 2/3rds of the tongue)
- It supplies the submandibular gland, sublingual gland and mucous glands of the palate.
Describe the vascular branches of sympathetic output ganglia
[*] Pre-ganglionic fibres supplying the head and neck, arise from spinal neural levels T1-T2 (Note: there is no sympathetic outflow from the cervical segments of the spinal cord. Cervical sympathetic ganglia are displaced upper 3 thoracic ganglia from the thoracic sympathetic trunk)
[*] The superior cervical ganglion (located anterior to vertebrae C1, C2, C3 and C4 – most commonly C2/C3)
[*] The middle cervical ganglion (small, often absent, lying anterior to C6 and anterior to the inferior thyroid artery)
[*] The inferior cervical ganglion sometimes fused with the first thoracic ganglion to form the cervicothoracic (or stellate) ganglion (located anterior to C7)
Sympathetic Post-Ganglionic Fibres reach H&N targets by hitch-hiking on the arterial system of the Head & Neck via walls of
[*] Common carotids
[*] External carotids
[*] Internal carotids
They lie outside of the carotid sheath
