Flashcards in Head And Neck Session 4 Deck (134):
What does a nerve bundle consist of?
Afferent nerve and efferent fibres
What are collections of cell bodies in the CNS called?
What are cell bodies in the PNS called?
Are all of the cranial nerves typical peripheral nerves?
No, 2 are atypical (brain tracts)
Which cranial nerves are brain tracts?
CNI and II
Name the 12 cranial nerves.
I: olfactory, II: optic, III: oculomotor, IV: trochlear, V: trigeminal, VI: abducens, VII: facial, VIII: vestibulocochlear, IX: glossopharyngeal, X: vagus, XI: accessory, XII: hypoglossal
Which cranial nerves arise from the forebrain?
CNIII and IV
Which cranial nerves arise from the Pons?
CNV, VI, VII and VIII
Which cranial nerves arise from the medulla?
CNIX, X, XI and XII
Describe the path of the olfactory nerve.
Olfactory mucosa --> olfactory receptor neurones --> cribriform plate --> olfactory bulbs
Where are the olfactory bulbs located?
Either side of the crista galli
What is a brain tract?
Outpouching of the brain
What can cause damage to the olfactory nerve and how would it be tested?
Trauma/meningitis/URTI. Test with strong smelling substance
Describe the path of the optic nerve.
Retina --> through optic canal --> cross at optic chiasm --> optic tract --> primary visual cortex in occipital lobe
What is assessed when testing the optic nerve clinically?
Visual acuity, colour vision, visual fields, pupillary reflexes, fundoscopy
What can testing the visual fields help to predict when testing the optic nerve?
Site of lesion
Describe the path of the oculomotor nerve.
Oculomotor and Edinger-Westphal nucleus --> superior orbital fissure --> superior to LPS, inferior to extraocular muscles
How is the oculomotor nerve tested clinically?
Ask patient to follow finger as you draw an H
What position is the pupil found in the affected eye in oculomotor palsy?
Down and out
What is mydriasis?
Blown pupil due to damage to the autonomic component of the oculomotor nerve
Why is ptosis often seen with mydriasis?
Often associated damage to the motor component of the oculomotor nerve
Describe the path of the trochlear nerve.
Trochlear nucleus --> superior orbital fissure --> dorsal midbrain --> cavernous sinus --> superior oblique muscle
Which nerve has the longest intracranial length?
Which important structures are found in the cavernous sinus?
Oculomotor nerve, abducens nerve, trigeminal nerve branches V1&2 and the ICA
What does a patient presenting with diplopoia on walking down stairs suggest?
Paralysis of the superior oblique muscle due to trochlear nerve damage
What might be seen O/E of a patient with trochlear nerve damage?
Subtle head tilt
Describe the path of the trigeminal nerve.
Trigeminal sensory nuclei in Pons --> trigeminal ganglion --> superior orbital fissure for ophthalmic branch, foramen rotundum for maxillary branch and foramen ovale for mandibular branch
What is trigeminal neuralgia?
Shooting pain in the distribution of the trigeminal nerve on light touch due to hyperactive sensory component
What gives innervation to the teeth?
Maxillary branch of trigeminal via superior alveolar nerve and mandibular branch of trigeminal via inferior alveolar nerve
How is the trigeminal nerve tested?
Corneal reflex (afferent branch), sensory function to face and clench muscles of mastication
Describe the path of the abducens nerve.
Abducens nucleus in Pons --> superior orbital fissure --> lateral rectus muscle of eye
What is 'false localising sign' in relation to the abducens nerve?
Any increase in ICP implicates the abducens nerve without necessarily indicating the site of pathology
What is seen on examination of a patient with damage to the abducens nerve?
Inability to abduct the affected eye
Describe the path of the facial nerve.
Motor and visceral nuclei in Pons --> IAM --> facial canal --> stylomastoid foramen --> 5 branches
What are the 5 branches of the facial nerve?
Temporal, zygomatic, buccal, mandibular and cervical
When does the facial nerve become extracranial?
When it enters the stylomastoid foramen
What gives special sensory innervation to the anterior 2/3 of the tongue?
What is given parasympathetic supply via the facial nerve?
Salivary and lacrimal glands
What is Bell's palsy?
Idiopathic one-sided facial paralysis
How can Bell's palsy be differentiated from a stroke on examination?
Forehead is spared in a stroke
How is the facial nerve tested clinically?
Test facial expression and ask about taste
Describe the path of the vestibulocochlear nerve.
Cerebellopontine angle --> IAM --> vestibular nerve goes to vestibular ganglion and semicircular canals, cochlear nerve goes to spiral ganglion in cochlea
Which two nerves travel together through the facial canal?
Facial and vestibulocochlear
What is vestibular schwannoma?
Benign neoplasm of Schwann cells that causes sensorineural hearing loss
What is the difference between sensorineural and conductive hearing loss?
Sensorineural is due to nerve damage whereas conductive is due to blockage of sound waves
How is the vestibulocochlear nerve tested clinically?
Whisper in each ear whilst making noise in the other. Rinne and Weber tests
Should sound conduct better through air or bone?
Describe the path of the glossopharyngeal nerve.
Medulla oblongata --> jugular foramen --> tongue, Otic ganglion to parotid gland, carotid and,stylopharyngeus
What innervation does the glossopharyngeal nerve give?
Sensation to oropharynx, posterior 1/3 of tongue and carotid sinus/body. Motor to stylopharyngeus muscle. Parasymapthatetic to parotid gland
How is the afferent branch of the glossopharyngeal nerve tested clinically?
What happens in a carotid sinus massage?
Increase in pressure is detected and signal via vagus nerve to decrease heart rate
What is the difference in neural supply to carotid sinus and aortic arch receptors?
Carotid sinus --> CNIX, aortic arch receptors --> CNX
Describe the path of the vagus nerve.
Medulla --> jugular foramen --> laryngopharynx, ear, pharynx, heart and lungs
What do the left and right recurrent laryngeal nerves hook around respectively?
Left= arch of aorta
Right = R. Subclavian artery
What innervation does the vagus nerve provide?
Sensation to the laryngopharynx and ear. Motor to muscles of pharynx and larynx. Parasympathetic innervation to the heart, lungs and GI tract
What does vagus stimulation cause in the lungs?
Where, other than the tonsils, can the gag reflex be stimulated?
What tests the efferent branch of the vagus nerve?
Carotid sinus massage
How might an aortic aneurysm present in relation to the left recurrent laryngeal nerve?
Hoarseness of voice
Describe the path of the accessory nerve.
Spinal nerve roots C1-5/6 --> up through foramen magnum --> down jugular foramen --> along ICA --> SCM and trapezius
What is the cranial portion of the accessory nerve often considered as?
Part of the vagus nerve
How is the accessory nerve assessed clinically?
SCM and trapezius wasting, rotate head against resistance, shrug shoulders against resistance
Describe the path of the hypoglossal nerve.
Hypoglossal nucleus in the medulla --> hypoglossal canal --> emerges just inferior to tongue
What innervation does the hypoglossal nerve provide?
Motor to intrinsic and extrinsic muscles of tongue
How is the hypoglossal nerve assessed clinically?
Fasciculations of the tongue, deviation towards site of lesion
Why does the tongue deviate to the side of the lesion in hypoglossal nerve damage?
Tongue is bilaterally innervated and usually muscles contract against each other therefore in damage opposition is lost
Which cranial nerves are exclusively sensory?
Olfactory, optic, vestibulocochlear
Which cranial nerves are exclusively motor?
Oculomotor, trochlear, abducens, accessory and hypoglossal
Which cranial nerves have both sensory and motor function?
Trigeminal, facial, glossopharyngeal and vagus
Which cranial nerves have associated autonomic fibres?
Oculomotor, facial, glossopharyngeal and vagus
How are nerves classified?
By general function (somatic or autonomic/visceral) and direction of conduction (afferent/sensory or efferent)
Which cranial nerves contain special visceral efferents?
CNV, VII, IX and X
What function do special somatic afferents have in the cranial nerves?
Equilibration, hearing and sight
What functions do the special visceral afferents of the cranial nerves give?
General taste and temperature of food and special test (sweet, sour etc)
How does a lesion of the spinal cord above the thoracic vertebral level present differently to a lesion below?
Above --> quadriplegia
Below --> paraplesia
Describe the overall structure of the parasympathetic nervous system.
High brain structures --> brainstem (medulla and midbrain)/spinal cord --> ganglia on wall of effector organ --> short post-ganglionic fibres to effector organ
Describe the general overall structure of the sympathetic nous system.
High brain structures --> spinal cord --> short preganglionic fibres to para-/prevertebral chain --> effector organ
How do efferent fibres of the ANS supply the head and neck?
Accompany visceral branches of sympathetic plexuses
Describe the passage of parasympathetic fibres from the Edinger-Westphal nucleus.
Enters orbit with inferior division of optic nerve, synapses at ciliary ganglion just lateral to optic nerve giving post-ganglionic fibres with short ciliary nerves to the eye
What function does the parasympathetic portion of CNIII have?
Constrict pupil and accommodation
Which ganglia are supplied by the superior salivatory nucleus?
Pterygopalatine and submandibular
What structures do fibres from the pterygopalatine ganglion innervate?
Lacrimal gland, mucus glands of neck and mucus glands of palate
What branches do fibres from the submandibular ganglion form?
Submandibular and sublingual salivary
Which ganglion is associated with the inferior salivatory nucleus?
What is the nerve called that travels between the inferior salivatory nucleus and Otic ganglion?
What is the name of the nerve that travels between the Otic ganglion and oropharynx/parotid gland?
How is the oropharynx supplied by the auriculotempral nerve?
Via the pharyngeal plexus synapsing at postganglionic cells in its wall
At what level do the postganglionic sympathetic fibres become associated with CNIII?
What do the postganglionic sympathetic fibres associated with CNIII supply?
Levator palpebrae superioris
Describe the path of fibres from the dorsal vagal motor nucleus.
Move into neck --> postganglionic cells in walls of target organs supplying glands of laryngopharynx, larynx, oesophagus and trachea
State the nucleus, organs and action of the parasympathetic autonomic division of CNIII.
Edinger-Westphal. Eye, pupil and ciliary. Pupillary constriction
State the nucleus, organs and action of the parasympathetic autonomic division of CNVII
Superior salivatory. Nasal, lacrimal, submandibular and sublingual glands. Serous secretions
State the nucleus, organ and action of the parasympathetic autonomic division of CNIX.
Inferior salivatory. Parotid. Serous secretions
State the nucleus, organs and action of the parasympathetic autonomic division of CNX.
Dorsal vagal motor nucleus, many and laryngeal function
Where does all CNS outflow originate from?
Entirely spinal, T1-L2/3
Where do axons of most preganglionic sympathetic ANS neurones terminate?
Immediately in the paravertebral sympathetic chain of ganglia (sympathetic trunk)
Where are sympathetic autonomic ganglia found?
All in peripheral nervous system
Where is the paravertebral chain located?
Bilaterally alongside vertebral column
Where is the prevertebral chain located?
Anterior to vertebral bodies in relation to carotids and anterior to the abdominal aorta
Where do the para- and prevertebral chains extend from and to?
Base of skull to coccyx
Why is there a difference between the number of neural levels and number of ganglia in the vertebral chains?
Some ganglia fuse
How many cervical ganglia are there in comparison to the number of neural levels there?
2/3 ganglia from 8 neural levels
How are somatic targets reached by fibres from the vertebral ganglia?
Along segmental nerves
How are visceral targets reached by fibres from the vertebral chains?
Along ganglionated trunks (like pre-ganglionic fibres of PSNS)
Is there sympathetic outflow from the cervical spinal cord?
Which 3 cervical ganglia supply the head and neck?
Superior, middle and inferior (Stellate)
Are the cervical ganglia supplying the head from the cervical spinal cord?
No, they are displaced thoracic ganglia
Where do each of the cervical ganglia lie in relation to other structures?
Superior: anterior to C1-4 (carotids)
Middle: anterior to C6 and inferior thyroid artery
Inferior: anterior to C7 (vertebral arteries)
What ascends along the ICA into the cranium to form the internal carotid plexus?
Internal carotid nerve
Which structures are associated with the internal carotid plexus?
Ophthalmic nerve, trochlear nerve, CNIII, CNIX, vessels from ICA, abducens nerve and pterygopalatine ganglion
How do sympathetic post-ganglionic fibres reach the head and neck targets?
Via walls of common, external and internal carotids outside of the carotid sheath
What is the somatic function of the superior cervical ganglion travelling along ICA and ECA?
Trigeminal Dermatome sweat glands
What is the visceral function of the superior cervical ganglion travelling along the ICA and ECA?
Dilator pupillae, smooth muscle of LPS, nasal glands and salivatory glands
What are the targets of the middle cervical ganglion fibres?
Lower larynx, trachea, hypo-pharynx and upper oesophagus
What are the targets of the inferior cervical ganglion fibres?
Posterior head and neck structures
What does a neurone consist of?
Dendrites, 1 cell body and 1 axon
What gives arterial supply to the extraocular muscles?
ICA via ophthalmic artery that becomes the central artery to retina
What provides venous drainage to the extraocular muscles?
Tributaries of the ophthalmic veins that drain via the superior ophthalmic vein into the cavernous sinus
What gives innervation to the extraocular muscles?
CNIII, IV and VI
What gives innervation to the orbital structures?
CNII, CNV-ophthalmic division
What are the seven muscles of the eye?
Superior rectus, superior oblique, lateral rectus, medial rectus, inferior rectus, inferior oblique and levator palpebrae superioris
What is the name of the small smooth muscle portion of the muscle that raises the superior eyelid with sympathetic innervation?
Superior tarsal portion of LPS
Which muscles closes the eye?
What gives innervation to obicularis oculi?
How are the recti muscles attached to the eye?
Arise from common tendinous ring surrounding the optic canal that attaches to the sclera on its anterior half
Why does occlusion of the central retinal artery cause ischaemia?
The terminal branches are end arteries
Where do the terminal branches of the central retinal artery travel?
Through the optic canal
How does the retina appear in central retinal artery occlusion?
Why does the macula/fovea still appear dark in central retinal artery occlusion?
It receives its blood supply from the choroid
Describe the mechanism by which papilloedema arises.
Raised ICP (tumour, haemorrhage, increased CSF pressure) --> impaired venous drainage --> oedema in retina --> optic disc swelling
How might a patient with papilloedema present?
Visual loss and headaches
How might a patient with central retinal vein occlusion present?
Slow, painless loss of vision
Why is central retinal vein occlusion said to give a 'stormy sunset appearance' on fundoscopy?
Stasis of blood causes formation of small haemorrhages with a normal sized optic disc