Head and Neck, Session 4 Flashcards
What is the first cranial nerve, and what does it supply?
olfactory nerve: contains only special sensation fibres and is distributed to uppermost part of nasal cavity, and is concerned with smell
why might a loss of smell be associated with a fracture of the ethmoid bone?
the olfactory nerve concerned with smell reaches the nose via the cribiform plate of the ethmoid bone.
Fractures of ethmoid involving dura mater may be assoc. with CSF leakage from nose
general sensory fibres of facial nerve supply what?
part of external acoustic meatus and auricle
how is innervation provided to the carotid sinus and carotid body?
via the the sinus nerve branch of the glossopharyngeal nerve
general sensory distribution of glossopharyngeal nerve?
pharynx, oropharyngeal isthmus, dorsum of palate, auditory tube + assoc structures, mastoid antrum, mastoid cells
which nerves are sensory to the external acoustic meatus and auricle?
facial and vagus nerves
vagus- back of auricle
which palate muscle is not supplied by the vagus nerve?
tensor veli palatine
which cranial nerve has both a cranial and spinal part?
accessory nerve (XI) cranial root accessory to vagus
fibres from which roots are contained by the spinal root of the accessory nerve?
C2,C3,C4
motor supply of hypoglossal nerve?
all muscles of tongue, except palatoglossus
other name given to infrahyoid muscles?
strap muscles of neck
what is formed by some cervical nerves frrom C1, C2 and C3 being looped onto the hypoglossal nerve?
ansa cervicalis
these fibres are distributed to strap muscles of neck
where do the cervical sympathetic trunks lie?
pass vertically up to base of skull, lying on prevertebral fascia and muscles, and lying deep to carotid sheath
where do the postganglionic fibres from the superior cervical ganglion pass?
with the external and internal carotid artery and its branches, to the pharyngeal plexus, to the upper 4 cervical nerves and in a cardiac branch to the cardiac plexus
with which artery do the post-ganglionic fibres of the middle cervical ganglion pass?
inferior thyroid
where do the post-ganglionic fibres of the middle cervical ganglion run to?
the 5th and 6th cervical nerves and in a cardiac branch to the cardiac plexus
how is the stellate ganglion formed?
combination of inferior cervical ganglion and 1st thoracic ganglion
with which artery do post ganglionic fibres from inferior cervical ganglion pass?
vertebral artery
what are the 4 pairs of parasympathetic ganglia in the head?
ciliary- oculomotor nerve
pterygopalatine- facial nerve
submandibular- facial nerve
otic- glossopharyngeal nerve
where is the ciliary ganglion?
lies in orbital cavity, lateral to optic nerve
PNS fibres pass to ciliary muscles and sphincter papillae
where is the pterygopalatine ganglion?
lies in pterygopalatine fossa
connected to maxillary nerve by small branches
receptive field territory of olfactory nerve?
nasal cavity, L and R supplied by separate L and R nerves
how does olfactory nerve form olfactory bulb?
nerve process leaves nasal cavity to ascend intra-cranially via foramina of cribiform plate of ethmoid, where they form olfactory bulb in the anterior cranial fossa
how may fracture of cribiform plate be experienced by a patient if olfactory nerve involvement?
anosmia, CSF rhinorrhea- drainage of CSF into the nose
when may sense of smell be tempoararily lost?
URTIs
e.g. allergic rhinitis- inflammation of nasal mucous membrane
why is loss of smell associated with ageing?
progressive reduction of olfactory receptor neurones in olfactory epithelium
why is each nostril tested separately for sense of smell with specific odours e.g. coffee, vanilla
as anosmia tends to be unilateral- and person may not be aware of this until clinical testing
when might CSF rhinorrhea occur?
cranial base fracture, with dura mater involvement, or fractures of cribiform plate
how might olfactory nerve/bulb be compressed causing anosmia?
tumor/abscess in frontal lobe of brain, or tumor of meninges (meningioma) in A cranial fossa
what may accompany lesions in temporal lobe of the cerebral hemisphere?
olfactory hallucinations- sensation of smell without sensory source
why may smelling salts be used to re-boot the brain after loss of consciousness?
stimulate the olfactory nerve whose sensations are conveyed to the cerebral cortex directly without going through the thalamus- derivative of diencephalon
describe the course of optic nerve fibres?
arise from ganglion cells in retina. nerve fibres exit orbit via optic canals to enter middle cranial fossa where optic chiasm formed where fibres from medial half of each retina cross in chiasm and join uncrossed fibres from lateral half of retina to form optic tract
what must be tested to examine visual system?
visual acuity colour vision visual fields pupillary reflexes fundoscopy
why are optic nerves susceptible to multiple sclerosis which does not normally affect other nerves of parasympathetic nervous sytem?
optic nerves are actually CNS tracts so myelin sheath surrounding fibres from point at which they penetrate the sclera is formed by oligodendrocytes rather than schwann cells
what is optic neuritis?
lesions of optic nerve that cause diminution of visual acuity, with or without changes in peripheral fields of vision
how might loss of pupillary constriction result?
direct trauma to orbit or eyeball, fracture involving optic canal
how can visual field defects be produced?
pressure on optic pathway, laceration or intra-cerebral clot in temporal, parietal or occipital lobes of brain
tumours of hypothalamus can disturb vision, as well as aneurysms of internal carotid artery near the hypothalamus
muscles innervated by oculomotor nerve?
all extraoccular muscles except lateral rectus and superior oblique
levator palpebrae superioris muscle of upper eyelid
autonomic- PNS: through ciliary ganglion to smooth muscle of sphincter pupillae, causing constriction of pupil and ciliary muscle, producing accomodation- allows lens to become more rounded for near vision
first sign of oculomotor nerve compression and why?
ipsilateral slowness of pupillary response to light as autonomic fibres of nerve superficial, so affected 1st, and cause pupil to dilate progressively on injured side
result of oculomotor nerve lesion?
ipsilateral oculomotor nerve palsy- eye is down and out- involvement of extraocular muscles with unopposed actions of superior oblique and lateral rectus
what may cause a lesion of CNIII?
aneurysms of posterior cerebral or superior cerebellar, fracture involving cavernous sinus, cavernous sinus thrombosis, pressure from herniating uncus on nerve- uncus is part of olfactory area of brain
(as nerve lies in lateral wall of cavernous sinus)
abnomal findings if CNIII lesion?
dilated pupil, ptosis- due to non-functioning levator palpebrae superioris, eye turns down and out, pupillary reflex on side of lesion will be lost
how can levator palpebrae superioris be tested?
patient asked to look upward to see if elevation of eyelid accompanies this effort
pupillary reflex is consensual, what does this mean?
shining a light in 1 pupil into only 1 eye cause both pupils to constrict
paralysis of which muscle causes absent accomodation reflex?
ciliary muscles- ANS innervation from CNIII