Anatomy Theme 8

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  • Created by: Splodge97
  • Created on: 12-05-17 17:34
How does the structure of the external auditory meatus prevent infection?
Lined with hairy skin and serbaceous glands which form a waxy layer; prevents stagnant water
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What are the malleolar folds?
Small, superior lax part of the tympanic membrane
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What is the umbo?
Tip of the malleus, from which a cone of light can be observed using an otoscope (if not ear infected)
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What is present on the anterior wall of the tympanic cavity?
The pharyngotympanic tube
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What is present on the medial wall of the tympanic cavity?
Fenestra cochlae, fenestra vestibuli, pomontory (projection from 1st turn of cochlea). Stapes attaches here via a ligament.
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What is present on the posterior wall of the tympanic cavity?
Pyramid (containing stapedius). Malleus attaches here via a ligament.
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What is present on the lateral wall of the tympanic cavity?
Epitympanic recess, tympanic membrane
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What forms the roof of the tympanic cavity?
Tegemen tympani (incus attached here via a ligament)
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What comprises the pharyngotympanic tube?
Air filled tube with thensor tympani muscle superior to it (tendon attached to bony lip projecting into the tympanic cavity)
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What mechanisms ensure external sound is blocked?
Incus acts as counterweight to malleus so only parallel soundwaves (from external auditory meatus) are detected. Also tensor tympani pulls long process of malleus so harder for vibrations to occur perpendicular to it.
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How does sound move the ossicles?
Waves make tympanic membrane move medially --> malleus manubrium moves medially --> malleus rotates laterally on anterior-posterior axis into epitympanic recess --> incus rotates --> stapes footplate pushes on fenestra vestbibuli
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What causes amplification of sound?
Lever action of ossciles, larger size of tympanic membrane than fenestra vestibuli
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What are the functions of tensor tympani and stapedius?
Respectively attach malleus/incus and stapes to walls of tympanic cavity to different degrees so adapt to pitch (reflex contraction too slow to protect from loud noise)
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How is sound transduced in the inner ear?
Perilymph vibrates --> displaces basilar membrane (more towards apex in low frequency, more towards base in high frequency as gets thinner) --> AP's generated in stereocilia of Organ of Corti at fenestra cochlae --> impulses down VIII to brain
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What are the parts of the temporal bone?
Petrous (develops as cartilage then bone), squamous, tympanic ring (observed as external auditory meatus) and styloid process
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What branches join to form the facial nerve?
Nervous intermedius (providing sensory and parasymapthetic axons) and motor root of VII (providing motor axons to muscles of facial expression)
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Describe the course of the greater petrosal nerve
Intra-petrous branch of VII given off from geniculate ganglion; exitis petrous temporal bone via hiatus of greater petrosal nerve, meets deep petrosal nerve to form nerve of pterygoid canal (through pterygoid canal), enters pterygopalatine ganglion
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Where are the cell bodies of chorda tympani?
Within the geniculate ganglion
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What is acoustic neuroma?
Tumour crushes the facial nerve within petrous temporal bone (may cause facial paralysis, prevent tear secretion via greater petrosal nerve, reduce stapedius function via nerve to stapedius or remove taste sensation via chorda tympani)
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Which bones comprise the orbit?
Maxilla, ethmoidal, lacrimal, sphenoid (body plus lesser and greater wings), orbital plate of frontal bone, zygomatic
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What are the openings of the orbit?
Superior orbital fissure, inferior orbital fissure, infraorbital groove, opening of nasolacrimal duct, posterior and anterior ethmoidal foramina
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What blood vessels pass through the superior orbital fissure?
Orbital branch of middle meningeal artery, superior opthalmic vein
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Which extraocular muscle isn't posteriorly attached to the common tendinous ring?
Inferior oblique, attached to wall of orbit
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What is the function of a saccade?
Images processed as snapshots so reduced blindspot and prevetion of photoecells bleaching in excessive light
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What is the action of medial rectus?
Adducts
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What is the action of lateral rectus?
Abducts - innervated by VI
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What are the actions of superior rectus?
Adducts, elevates, rotates pupil inwards
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What are the actions of inferior rectus?
Adducts, depresses, rotates pupil outwards
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What are the actions of superior oblique?
Abducts, depresses, rotates pupil inwards - innervated by IV
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What are the actions of inferior oblique?
Abducts, elevates, rotates pupil outwards
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Where is lavator palpebrae superioris?
Superior to superior rectus, medial to superior oblique
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What muscles are innervated by the inferior division of III?
Medial rectus, inferior rectus, inferior oblique
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What muscles are innervated by the superior division of III?
Lavator palpebrae superioris, superior rectus
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What muscles contract to cause pure elevation of the eye?
Superior rectus and inferior oblique
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What muscles contract to cause pure depression of the eye?
Inferior rectus and superior oblique
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What muscles contract to cause pure adduction of the eye?
Medial rectus, superior rectus, inferior rectus (all adductive muscles - allows greater control than just medial rectus)
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What muscles contract to cause pure abduction of the eye?
Lateral rectus, inferior oblique, superior oblique (all abductive - gives greater control than lateral rectus alone)
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What is the menumonic to remember the movement of the extraocular muscles?
In Ottowah Super Rabbits Snack On Incredible Risotto
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What are the functions of V1?
Transmitting sensory information from the face/scalp (via lacrimal, frontal and nasociliary branches) and giving sympathetic fibres to the dilator pupillae via long ciliary nerves (via nasociliary branch)
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What does the lacrimal nerve recieve?
Zygomatic branch of V2 (runs along superior rectus to supply postganglionic innervation via pterygopalatine ganglion to lacrimal glands)
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On what does the frontal nerve run?
Along lavator palpebrae superioris (then branches into supraorbital and supratrochlear)
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What is an effect of damage to the zygomatic branch of VII?
Paralysed palpebral part of orbicularis oculi, so no washing of debris off eye by tears (causing discomfot). If repairs, commonly slower blinking in affected eye.
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What is the external coat of the eyeball?
Fibrous coat (opaque sclera posteriorly, transparent cornea anteriorly)
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Waht is the middle coat of the eyeball?
Vascular coat (choroid - pigmented to prevent distortion - posteriorly, ciliary body muscle then iris anteriorly)
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What is the innermost coat of the eyeball?
Neural coat (retina)
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What holds the shape of the eyball?
Vitreous body (aqueous humour in cornea, bending lens and iris into correct place)
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Which ligaments hold the lens in place?
Suspensory (from ciliary body muscle), check (from medial and lateral rectus)
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What is the parasympathetic root of the ciliary ganglion?
Oculomotor nerve (gives parasympathetic innervation to sphincter pupillae and ciliary body muscle)
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What is the symapthetic root of the ciliary ganglion?
From superior cervical ganglion, forms peri-arterial plexus around internal carotid, nnervates orbital blood vessels
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What is the sensory root of the ciliary ganglion?
Nasociliary nerve, recieves from touch receptors of cornea and mechanoreceptors of iris)
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What does endochondral mean?
Formed from conversion of mesoderm to cartilage to bone - cranial base formed this way
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What does intermembraneous mean?
Formed from conversion of mesoderm (for cranial vault) or neural crest (facial skelton) to bone
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Describe the anatomy of the pterion
Congenital thinning of skull (prone to comminutive fractures, pressed fractures and breaks) - middle meningeal artery runs underneath, corresponds to primary motor cortex
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What is rhinorrhoea?
Leakage of CSF from nose (due to cribriform plate fracture)
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What does the anterior cranial fossa contain? What are its boundaries?
Contains crista galli, cribriform plate and orbital plate of frontal bone. Broundaries are lesser wings of sphenoid (lateral) and jugum sphenoidale (medially) - separated by anterior clinoid processes.
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What does the medial cranial fossa contain? What are its boundaries?
Greater wing of sphenoid, parietal bone, petrous temporal bone and sella turcica (depression of pituitary fossa). Borders are superior borders of petrous temporal bone (laterally) and dorsum sellae (medially) - posterior clinoid processes separate
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What does the posterior cranial fossa contain?
Internal occipital protuberance and cerebella fossa of occipital bone
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What are the layers of the dura mater?
External endostial layer, internal meningeal layer
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What is contained in the sub-arachnoid space?
Between arachnoid mater and piamater, filled with CSF (to absorb shocks/so brain floats)
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What is present in the sub-dural space?
Between meningeal layer of dura mater and arachnoid mater, filled with loose connective tissue (can be pushed aside by blood/air)
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What is the function of the diaphragma sella?
Smallest of the meninges, roofs pituitary fossa to prevent infection spread from sphenoid sinus
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Where is the tentorium cerebelli attached?
Largest of the meninges - attached to occipital bone and superior borders of the petrous temporal bone (also has free border from anterior clinoid processes around foramen magnum called tentorial incisure)
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Which venous sinuses form the internal jugular vein at the jugular foramen?
The inferior petrosal sinus (from the cavernous sinus) and the sigmoid sinus (from junction of transverse and superior sagittal sinuses)
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What are the branches of the cavernous sinus? What does it enclose?
Superior and inferior petrosal sinuses. Encircles internal carotid (to cool blood, transports to emissary veins if still too hot), V1, V2, III, IV and VI)
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Why does infection commonly spread to the cavernous sinus?
Infra/supraorbital branches of the facial vein and the pterygoid plexus connect with it, so migrates from these areas
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Where does the falx cerebri rest?
On the corpus callosum (separating the hemispheres)
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What is bevelling?
Overlapping of the sutures of the skull so they interdigitate, making them stronger
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What is butressing?
Thickened bars of bone which support the fragile zones around apertures. There are the canine (anterior), maxillo-zygomatic (middle) and pterygoid tuberosity (posterior) butresses plus the superciliary bar and thickened lower orbital margin.
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Which buttress best resists head on impacts?
Pterygoid tuberosity butress (aided by canine butress)
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Where do extradural haemorrhages occur?
Between the skull bone and the dura mater due to tearing of the middle meningeal artery (cause nausea in 24 hours)
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Where do subdural haemorrhages occur?
In sub-dural space between dura mater and arachnoid mater. Occurs due to slow bleeding from the superior cerebral veins (common in elderly when brain shrinks so veins torn easily).
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Where do sub-arachnoid haemorrhages occur?
In sub-arachnoid space between the arachnoid mater and piamater. May occur rapidly through aneurysm or slowly through angioma.
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Where do infracerebral haemorrhages occur?
More serious as occur within the brain itself, usually through middle cerebral artery being blocked/bursting due to high blood pressure). Radiographically seen as lop-sided falx cerebri.
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Where may infection spread in serious cases?
Tongue (causing swelling which blocks airway iin Ludwig's angina), intracranial, to the pericardial space (causing cardiac tamponade) or the pleural space (causing pneumonia)
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Which fractures are most destuctive/hardest to treat?
Hoizontal blows to masseter and medial pterygoid most destructive; indirect, comminutive fractures hardest to treat
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What is reduction?
The repositioning of misaligned bones (may be open - causing scarrring/using existing lacerations - or closed - via keyhole surgery)
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What are the symptoms of orbital fractures?
Tethering of extraocular muscles, diplopia (double vision), numbness (through infraorbital nerve damage), enopthalamos (eye sinks back in socket) and retroorbital bulbar haemorrhaging (bleeding swells the eye, drained laterally)
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What are the symptoms of zygoma fracture?
Swelling/flattening, trismus (mouth can't open), sub-conjunctival haemorrhage (around eye) and orbital floor injury
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What is Rowe's elevation technique?
Used to lift zygoma after fracture (via incision made just above the ear), fixed with a plate. Doesn't compromise fascia planes so little infection spread.
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What are the disadvantages of Poswillo's hook?
Hook used to pull zygoma through incision lateral to the nose; quicker but often leads to fracture as not secured with a plate
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What are the symptoms of mandibular fractures?
Step deformities (adjacent bones displaced), numbness (through IAN damage), malocclusion, triismus (mouth can't close), growth disturbances and bony ankyloses (bones of TMJ unite due to loss of articular cartilage, causing trismus)
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Other cards in this set

Card 2

Front

What are the malleolar folds?

Back

Small, superior lax part of the tympanic membrane

Card 3

Front

What is the umbo?

Back

Preview of the front of card 3

Card 4

Front

What is present on the anterior wall of the tympanic cavity?

Back

Preview of the front of card 4

Card 5

Front

What is present on the medial wall of the tympanic cavity?

Back

Preview of the front of card 5
View more cards

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