Anatomy Flashcards
What are the features of the bony orbit?
Apex=optic canal, roof, medial wall, lateral wall, floor
What is the base?
Clinically known as orbital rim. Combined orbital margins
What protects the eyes from a direct blow?
Orbital margins
What is an orbital blowout fracture?
A traumatic deformity of the orbital floor or medial wall, typically resulting from impact of a blunt object larger than the orbital aperture, or eye socket
What aspect of the medial wall and orbital floor put them at risk of an orbital blowout fracture?
They are extremely thin
In an orbital blowout fracture what can happen to the orbital contents?
It can become trapped
In an orbital blowout fracture what can happen to the infraorbital NVB?
It can be damaged
What is the external layer of the eyelid?
Orbicularis oculi- orbital and palpebral part (superior and inferior)
What is the orbital septum made up of?
Sheet of fascia
Where are the tarsal glands found?
Embedded in the tarsi
What do the tarsal glands secrete?
Lipids
What is the iris covered by?
Cornea
What is the punctum?
Opening for tears
What does the conjunctiva do in terms of foreign bodies?
Forms a defensive barrier to FBs penetrating deep into the orbit
What does the lacrimal gland produce?
Lacrimal fluid
Where is the lacrimal gland located?
In the lacrimal fossa of the orbit-superolateral to the eye
What is the innervation of the lacrimal gland?
CNVII parasympathetic
Where are tears collected?
Lacrimal sac
What happens to lacrimal fluid when it’s produced?
Washes over eye, pushed towards medial angle, draims through lacrimal puncta, eventually reaches inferior meatus
Through what duct do tears drain through?
Nasolacrimal duct
What are the 3 layers of the eye?
Fibrous, uvea, retina
What is the outer layer of the eye?
Fibrous
What are the 2 parts of the fibrous layer?
Sclera-muscle attachment, cornea-2/3 refractive power
What is the middle layer of the eye?
Uvea (vascular layer)
What are the 3 parts of the uvea?
Iris-pupil diameter, ciliary body-controls iris, shape of lens and secretion of aqueous humour, choroid-nutrition and gas exchange
What is the inner layer of the eye?
Retina (photosensitive)
What are the segments of the eye?
Anterior and posterior
What makes up the anterior segment?
Anterior chamber and posterior chamber
What is the anterior chamber?
Chamber of eye beween cornea and iris, contains aqueous humour
What is the posterior chamber?
Chamber of eye between iris and suspensory ligaments, contains aqueous humour
What is the posterior segment?
Segment of eye behind lens. Contains vitreous body
What is contained with the vitreous body?
Vitreous humour (holds choroid and retina against sclera)- common location for ‘floaters’
What is a cataract?
Clouding of the lens
What is the circulation pathway of aqueous humour?
Ciliary body> aqueous circulates within posterior chamber> aqueous then passes through pupil into anterior chamber> aqueous reabsorbed into scleral venous sinus at iridocorneal angle
What does the ciliary body do?
The ciliary processes secrete aqueous
What can raised Intra-ocular pressure cause?
Ischaemia of the retina
What is the fundus?
Posterior area where light is focused
What is within the fundus?
Optic disc, macula, fovea
What is significant about the optic disc?
Point of CNII formation, only point of entry/exit for blood vessels and CNII axons, blind spot to light
What is significant about the macula?
It has the greatest density of cones in the eye
Where is the fovea located?
Centre of the macula
What is the fovea?
Depression of 1.5mm diameter- the area of most acute vision
What does complete interruption of flow in a retinal artery branch/retinal vein cause?
Loss of an area of visual field corresponding to the area of ischaemia
What does complete interruption of the central (end) artery or vein cause?
Monocular blindness
What are the 3 layers of the retina and their position?
The photoreceptors, ganglion cells lie anterior to the photoreceptor cells , axons of ganglion cells lie anterior to the ganglion cells and photoreceptor cells
Where do the retinal veins and arteries lie in relation to the retina?
Anteriorly
What part of your brain will light from the right visual field be processed?
Left primary visual cortex
Where is light from objects in the lower visual field processed by?
Upper part of the primary visual cortex
What is the visual pathway?
R/L visual field>lens>retina> optic nerve> optic chiasm> lateral geniculate nucleus (LGN), primary visual cortex
Light from objects passing through which retina will cross over at the optic chiasm?
Nasal retina
Where is the central (end) artery of the retina?
Within the optic nerve
What is the significance of the central vein of the retina?
It is the only vein draining the retina (and is located within optic nerve)
What is the danger triangle?
Danger area for bacterial infection/squeezing spots etc. From upper lip/external nose to between eyebrows
Where does the inferior ophthalmic vein drain into?
Mainly into superior ophthalmic vein
Where does the orbit also drain into?
Anteriorly into the facial vein
How many extraocular muscles do we have?
7
What are the 4 rectus muscles?
Superior rectus, inferior rectus, medial rectus, lateral rectus
Where do all the rectus muscles originate and insert?
All originate from common tendinous ring, all insert onto sclera
What are the 2 oblique muscles?
Superior oblique and inferior oblique
Where do the oblique muscles insert?
Sclera
What does the leator palpebrae superioris do?
Lifts the upper eyelid
How can you remember the somatic motor innervation of EO muscles?
LR6 SO4 AO3 - Lateral rectus: CNVI, Superior Oblique: CNIV, All Others: CNIII
What movements can the eyeball make on the vertical axis?
Abduction/adduction-direction of gaze
What movements can the eyeball make on the transverse axis?
Elevation/depression-direction of gaze
What movements can the eyeball make on the anteroposterior axis?
Intorsion (medially)/extorsion (laterally)-superior pole of eyeball
What is the direction of your optical axis?
Straight forward (different to orbital axis)
Why do muscles of the eye usually have multiple movements?
Due to angle of attachment based on orbital canal position
True or false: The orbital septum lies just anterior to the orbicularis oculi muscle.
False
The tear film has antibacterial properties due to…?
Action of lysozyme
At what rate is the tear film produced by the lacrimal gland?
A constant rate
What is the pH of tears?
7.6
What is the conjunctiva composed of?
Palpebral and bulbar parts
What part of the conjunctiva is more vascular?
Bulbar
Where is the cornea thinnest?
In the middle(check)
How thick is the cornea?
540 microns thick
What does the stroma of the cornea contain?
Regularly spaced collagen fibres
How does the endothelium maintain transparency of the cornea?
By pumping fluid into the stroma
What is the lens attached to the ciliary body by?
Zonules
What does a decrease in tension of zonular fibres allow for?
Near focussing
Do the lens fibres have good or bad lens regeneration properties?
Bad
What is the outermost part of the lens known as?
The cortex
What is the uvea composed of?
Iris, ciilary body and choroid
What is the uvea’s role in absorbing reflected light in the eye?
It has none
What is the suspensory ligament?
A thick fascial sling that holds the eye just above the floor or the orbit
Where does the suspensory ligament attach to?
Zygoma laterally
What may result in the eye lowered towards the orbital floor?
Fractured zygoma. Diplopia may occur
What can damage to the infraorbital NVB?
Fractured zygoma
What can damage to the infraorbital NVB result in?
A general sensory deficit of facial skin
Where will a fractured zygoma tend to rotate?
Rotate medially towards floor of the orbit
What does CNV1 supply (general sensory)?
Upper eyelid, cornea, conjuctiva, forehead, skin of root/bridge/tip of nose
What does CNV2 supply (general sensory)?
Skin of lower eyelid, skin over maxilla, skin of ala of nose, skin mucosa of upper lip
What is the general sensory supply of the angle of the mandible?
Greater auricular nerve-branch of C2/3 spinal nerves
When a blink (corneal) reflex occurs how are APs conducted centrally?
Centrally via CNV1 to trigeminal ganglion then in CNV5 to pons
When a blink reflex occurs how are APs conducted peripherally?
Peripherally in CNVII to the eyelid part of orbicularis oculi
How can a blink be elicited?
Sterile point of cotton wool, gently touch the cornea
What is the space inbetween the pre-tracheal and prevertebral fascia?
Retropharyngeal space
What ganglion of the sympathetic cervical chain is associated with supply to the orbit?
Superior
What often fuses to form the stellate ganglion?
Inferior cervical and 1st thoracic ganglia
What cranial nerves contain parasympathetic axons?
CNIII,VII,IX,X
What ganglion does the CNIII parasympathetic axons synapse with and then supply ?
Ciliary ganglion in the orbit, and then to the eye
Where does CNIII connect with the CNS?
Near the midline at the junction between the midbrain and pons
Where does CNIII leave the cranial cavity?
Superior orbital fissure
What branches of CNIII come through the superior orbital fissure?
Superior and inferior
What does the superior branch of CNIII supply?
SR and LPS
What does the inferior branch of CNIII supply?
MR, IR, IO and ciliary ganglion (parasympathetic supply)
What plexus supplies the orbit?
Internal carotid plexus
What nerve do sympathetic axons travel in post optic canal and ciliary ganglion(do not synapse here)?
Long and short ciliary nerve
What nerve do parasympathetic axons travel post ciliary ganglion?
Short ciliary nerve
What do autonomic axons from the ciliary nerves do?
Control the diameter of the iris (and pupil) & the refractive shape of the lens
What do the long ciliary nerves form the first part of?
The afferent limb of the blink reflex
What are the autonomic reflexes of the eye?
Wide eye opening of fight or flight, light reflex, accomodation reflex, reflex tear production, vestibulo-ocular reflex, oculocardiac reflex
What CNS connections occur in the vestibulo-ocular reflex?
CNVIII & CNs III,IV, VI
What is the oculocardiac reflex?
Reflex bradycardia in response to tension on the extraocular muscles or pressure on the eye
What CNS connections occur in the oculocardiac reflex?
CNV1 and CNX
What are the sympathetic eye functions?
Open wider, get more light into eye, focus on far objects, emotional lacrimation
What are the parasympathetic eye functions?
Allow orbicularis oculi to work, get less light into eyes, focus on near objects, reflex lacrimation
What kind of muscle is levator palpebrae superioris?
Skeletal and smooth
What muscle dilates the pupil?
Dilatory pupillae fibres
What is the insertion of the dilator pupillae fibres?
All around the internal circumference of iris (mobile)
What is the origin of the dilator pupillae fibres?
All around the external circumference of iris (fixed_
What is the reflex in the stimulated eye?
The direct light reflex
What is the reflex in the non-stimulated eye?
The consensual light reflex
What is the special sensory limb of the light reflex?
The ipsilateral CNII
What is the motor limb of the light reflex?
Bilateral via CNs III
How many neurone chains in the light reflex?
4
What is the 1st neurone chain in the light reflex ?
Retinal ganglion cells pass via ipsilateral optic nerve to decussate in optic chiasm, then synpase in the pretectal nucleus of midbrain
What is the 2nd neurone chain (Bilateral) in the light reflex ?
Located entirely within midbrain and connect the pretectal nucleus to the next synapse in the Edinger Westphal nucleus (location of cell bodies of parasympathetic axons of CNIII)
What is the 3rd neurone chain (Bilateral) in the light reflex ?
Pass from EW nucleus, via CNII then its inferior division, to synpase in the ciliary ganglion
What is the 4th neurone chain (Bilateral) in the light reflex ?
Course in the short ciliary nerves to the sphincter pupillae muscles
How is the refractive shape of the lens controlled in far vision?
Ciliary muscle relaxes in far vision, ligament tightens and lens flattens to focus on object in distance
How is the refractive shape of the lens controlled in near vision?
Ciliary muscle contracts in near vision, ligament relaxes and lens becomes spherical to focus on object nearby
What components of the accomodation reflex (response to near) are assessed?
Bilateral pupillary constriction (CNs III), bilateral convergence -medial rotation of both eyes (CNs III), bilateral relaxation of lens-lens becomes spherical due to contraction of ciliary muscles (CNsIII)
What are the 3 types of tears?
Basal, reflex, emotional
What do basal tears do and contain?
Clean/nourish and hydrate avascular cornea. Contains lysozyme (hydrolyse bacterial cell walls)
What are reflex tears?
Extra tears in response to mechanical or chemical stimulatioon
What do postsynaptic sympathetic fibres reach levator palpebrae superioris via?
Superior cervical sympathetic ganglion, internal carotid nerve and plexus, axons are carried on ophthalmic artery and on its branches to orbital structures
Do sympathetics dilate or constrict the pupil?
Dilate
What is a non-physiologically enlarged pupil?
Mydriatic pupil
What do mydriatic drugs do?
Induce dilation of the pupil
Do parasympathetics constrict or dilate the pupil?
Constrict
What is a non-physiologically constricteed pupil?
Miotic pupil
What is a fixed dilated (blown) pupil a sign of?
Pathological injury-CNIII pathology (inhibting the pupillary constriction action of parasympathetic axons in ciliary nerves)
Where is the encircling arrangement of sphincter pupillae fibres?
All around the internal circumference of iris
What are the afferent and efferent limbs of lacrimation of reflex tears?
Afferent is CNV1 from cornea/conjunctiva. Efferent is parasympathetic axons originating from CNVII
The presynaptic parasympathetic axons for what are contained with the chorda tympani?
Submandibular and sublingual glands
Is the intracranial volume constant or varied?
Constant
What 3 membranes make up the meninges?
Dura, arachnoid, pia
What is the space between arachnoid and pia?
Sub-arachnoid space
What are the meninges?
Protective coverings of brain and spinal cord
Describe the dura mater
‘Hard mother’, tough, sensory supply from CNV, encloses dural venous sinuses
Describe the arachnoid mater
‘Spidery mother’, arachnoid granulations
What is within the subarachnoid space?
Circulating CSF and blood vessels
Describe the pia
‘Faithful mother’, adheres to brain (and vessels and nerves entering/leaving)
Where is CSF reabsorbed into?
Into the dural venous sinuses, via arachnoid granulations
