Anatomy Flashcards
What is the white sclera covered by?
conjunctiva
What is it the iris covered by?
cornea
what is the limbus?
the corneoscleral junction
where is the lacrimal gland found in relation to the eye?
ii. why is this important?
the superolateral - found in the fossa for the lacrimal gland
ii. So the lacrimal fluid washes over the eye to the lacrimal lake
what is the dark circle of the eye called?
pupil
the pupils and iris of both eyes should be the same size true or false?
true
What is the orbit?
the bony cavity which houses the eye
How many bones make up the orbit?
7
Names the bones which make up the orbit.
Superficial bones:
Frontal bone (superior)
Zygomatic bone (lateral)
Maxilla bone ( inferior medial)
Deeper bones:
Sphenoid bone
Ethmoid bone
Lacrimal bone
Palatine bone
where are the orbital plates found?
Frontal bone
Ethmoid bone - more susceptible to fractures as they are thin walled plates
Maxilla bone - more susceptible to fractures as they are thin walled plates
Where is the optic canal?
Postero medially in the optic
what is the role of the optic canal?
Gap to allow the optic nerve and opthalmic artery to enter the orbit
Where is the superior orbital fissure located?
ii. what is its role?
between the greater and lesser wings of the sphenoid bones
ii. where cranial nerve 3,4 and 6 pass into the orbit
where is the supraorbital notch/foramen found?
ii. what is its role?
frontal bone
ii. allows supraorbital neurovascular bundle to enter the orbit
where is the infraorbital foramen found?
ii. what is its role?
maxilla bone
ii. allows infraorbital neurovascular bundle to enter the orbit
what cranial nerve is the supraorbital nerve a branch of?
The ophthalmic division of the trigeminal nerve
What cranial nerve is the infraorbital nerve a branch of?
Maxillary division of the trigeminal nerve
What is the shape of the orbit?
pyramidal shape
where is the apex of the orbit located?
posteriorly at the optic canal
where is the base of the orbit located?
anteriorly (superiorly)
what does the base of the orbit consist of?
The orbital rim:
lateral margin
inferior margin
medial margin
superior margin
compare the axis of the eyeball and orbit
eyeball axis - anterior
Orbit axis - anterolateral
what does a blowout fracture refer to?
medial wall and orbital floor fracture
where are the sutures in the orbit found?
frontal and zygomatic bone
zygomatic bone and maxilla bone
frontal bone and maxilla bone
what is the most external structure of the eye lid?
orbicularis oculi muscle
what type of muscle is the orbicularis oculi?
sphincter muscle
what are the two parts of the orbicularis oculi?
Orbital part - responsible for tight squeezing shut of eyes
palpebral part - inner part lies directly on the eye. Responsible for gentle closing of eyes
Which nerve innervates the orbicularis oculi muscle?
CN VII
what do the deeper structures of the eye lid consist of?
Tarsus - eye lid’s fibroskeleton
There is a inferior and superior tarsus
what are the ligaments found in the eye lid?
lateral palpebral
medial palpebral
what is the orbital septum
tough layer of connective tissue that holds the orbit components in place
separates superficial and deep parts of orbit. Thereby preventing spread of infection
where is the tendon of LPS?
found superiorly on the deeper layer of the eyelid
What is the LPS?
Levator palpebrae Superioris muscle
it attaches to the superior tarsus and skin of the eye lid via the tendon of LPS
what is the role of the LPS?
it pulls up the upper eye lid
it is a skeletal muscle
what is the smooth muscle of the LPS called?
ii. how does it carry out its role?
superior tarsus muscle (mueller’s muscle) - helps open eyes really wide when required
ii. It is a smooth muscle so has sympathetic innervation
Where is the tarsal gland found?
tarsus
what is the role of the tarsal glands?
secretes lipids which line the eye lid preventing overflow of tears or lacrimal fluid
which nerve innervates the lacrimal gland to produce lacrimal fluid?
CN VII
what happens to lacrimal fluid as you blink?
pushes lacrimal fluid to medial angle
where does the lacrimal fluid end up in the medial angle?
lacrimal lake
then it is needs to pass into the canaliculi
How does the lacrimal fluid enter the two canaliculi
via the two lacrimal puncta ( one in the upper and one in the lower eyelids)
Where does the lacrimal fluid move to once its entered the canaliculi?
the lacrimal sac - this is this the first part of the nasolacrimal duct
passes down the nasolacrimal duct
eventually ends up at the inferior meatus
what are the 7 extraocular muscles?
4 rectus muscles -all originate from common tendinous ring. all then insert onto sclera
- superior rectus
- Inferior rectus
- Medial rectus
- Lateral rectus
2 oblique muscles: both insert onto sclera
- Superior oblique - passes through the trochlea
- Inferior oblique
- Levator palpebrae superioris
Where does the superior oblique originate from?
sphenoid bone
where does the inferior oblique originate from?
orbital plate of maxilla
Where does the LPS originate from ?
lesser wing of sphenoid
where does the LPS attach to?
skin and tarsus of superior eyelid
What is the innervation of the Extraocular muscles?
THINK: LR6 SO4 AO3
LR6:
Lateral rectus - CN VI (abducent nerve)
SO4:
Superior oblique - CN IV ( trochlear nerve)
AO3:
All others - CN III (oculomotor nerve)
what is the cornea?
clear part of the anterior eye
it is continuous with the sclera. However it is more convex
The cornea is avascular true or false?
true
what are the three layers of the eye?
- Outer - fibrous layer- has 2 parts
the sclera - muscle attachment
Cornea - 2/3 of refractive power
- middle layer - Uvea (vascular layer) - has 3 parts
iris - pupil diameter
Ciliary body - controls iris, shape of lens and secretion of aqueous humour
Choroid - nutrition and gas exchange. Darky reddy brown layer which makes up most of the vascular layer
- Inner layer - retina (photosensitive) - many parts
- main layers of retina:
- Photoreceptors - most posterior section
- Ganglion - where there is a synapse between photoreceptors and axons of the ganglion cells
- Axons of the ganglion cells - most anterior section
What does the anterior segment of the eye consist of?
Everything in front of the lens
It is divided into:
Anterior chamber - between cornea and iris
and
Posterior chamber - between iris and suspensory ligaments
What does the posterior segment of the eye consist of?
Behind lens - makes up 2/3 of the eye
Contains the vitreous body;
vitreous humour
vitreous body common location for floaters
what is the iridocorneal angle?
angle between the iris and cornea
this is the angle which is referred to in “open angle” and closed angle” glaucoma
Discuss the circulation of the aqueous humour
- Ciliary body consists of smooth muscle and blood vessels. It is here where the ciliary processes secrete aqueous
- Aqueous circulates within the posterior chamber and nourishes the lens
- The Aqueous then passes through the pupil into the anterior chamber and nourishes the cornea.
- The Aqueous reabsorbed into scleral venous sinus (canal of schlemm) at the iridocorneal angle
What is the arterial supply of the eye?
ophthalmic artery - branch of the internal carotid - supplies most of the anatomical structures in the eye
Infraorbital artery - branch of the external carotid - supplies some structures in the floor of the orbit
How does the internal carotid artery enter the cranial cavity?
passes through the cranial canal
it is here where it ophthalmic artery branches off
How does the ophthalmic artery enter the orbital cavity?
via the optic canal
what are the branches of ophthalmic artery?
ciliary arteries - long and short
central artery of the retina
what do ciliary arteries supply blood to?
main supply to choroid
what does the central artery of the retina supply blood to
pierces through the optic sheath and travels with optic nerve to reach retina
Only arterial supply for retina - it is an end artery
What is an end artery?
An artery with insufficient anastomoses to maintain viability of the tissue supplied if arterial occlusion occurs.
what is the name of the only vein which drains the retina?
central vein of the retina
what are the main veins of the eye?
superior ophthalmic vein
Inferior ophthalmic vein - drains mainly into superior ophthalmic vein. Does drain into pterygoid plexus too
Facial vein - orbit also drains anteriorly into it
where does the superior ophthalmic vein end up at?
Cavernous sinus via the superior orbital fissure
what is the route of the central vein of the retina?
it either directly enters cavernous sinus or the superior ophthalmic nerve and then the cavernous sinus
What does the danger triangle of the face refer to?
corners of the mouth to the bridge of the nose, including the nose and maxilla
many links of Superficial veins means spread of infection can be deadly
what is the conjunctival fornix?
loose soft tissue lying at the junction between the palpebral conjunctiva (covering the inner surface of the eyelid) and the bulbar conjunctiva (covering the globe)
Discuss how light is picked up in the retina.
Light hits the axons of the ganglion cells
passes through the axons and then the ganglion cells themselves
Light picked up by photoreceptors
Discuss the structures of the Retina.
Fundus - posterior area where light is focused
it includes:
Optic disc - point of CN II formation.
only point of entry/exit for blood vessels and axons of CN II
called the blind spot - no photoreceptors at the optic disc
Macula
small oval type part of retina which has the greatest density of cones
Lateral to optic disc
Fovea
it is a depression which is the Centre of the macula
area of most acute vision
What parts of the retina does light from the left visual field hit?
Nasal retina (inner side) of the Left eye
Temporal retina ( outer side) of the right eye
basically the right side of both eyes
what parts of the retina does the light from the right visual field hit?
Temporal retina ( outer side) of the left eye
Nasal retina ( inner side) of the right eye
Basically the left side of both eyes
which nerve receives information from the retina?
optic nerve (CN II)
what occurs a the optic chiasma?
There is a crossover in information
All light from right visual field (temporal retina of the left eye and nasal retina of the right eye) meet and then are processed together at the LEFT primary visual cortex
All light from left visual field (temporal retina of the right eye and nasal retina of the left eye) meet and then are processed together at the RIGHT primary visual cortex
Think:
Light from temporal side stays on same side e.g. temporal retina of right eye has information processed at right primary visual cortex
where is the light from objects in the lower visual field processed by?
upper part of the primary visual cortex
Where is the light from objects in the upper visual field processed by?
Lower part of the primary visual cortex
What is the lateral geniculate nucleus (LGN)
a relay centre in the thalamus for the visual pathway
what are the axis of the eye?
- Vertical axis:
Abduction/adduction
- Transverse axis:
elevation/depression
- Anteroposterior axis:
Intorsion/extorsion
Which extraocular muscles do not have secondary movements?
Medial rectus
Lateral rectus
what are the primary movements of the extraocular muscles?
Superior rectus - contraction = elevation
Inferior rectus - contraction = depression
Superior oblique - contraction = depression
Inferior oblique - contraction = elevation
Lateral rectus - contraction = abduction
Medial rectus - contraction = adduction
How do you test movements of individual muscles of the eye?
Line up the gaze to plane of muscles being tested
this isolates muscle movement
when the eye has abducted what is the only movement the eye can do when the superior rectus contracts?
elevate
Innervated by CN III
when the eye has abducted what is the only movement the eye can do when the inferior rectus contracts?
depress
innervated by CN III
when the eye has adducted what is the only movement the eye can do when the superior oblique contracts?
Depress
Innervated by CN III
when the eye has adducted what is the only movement the eye can do when the inferior oblique contracts?
Elevate
innervated by CN IV
What does Pure elevation refer to?
both Superior rectus and inferior oblique contract to elevate eyes
However they are antagonists as rotators - they cancel each other out so only elevation occurs
What does pure depression refer to?
Superior oblique and inferior rectus contract to depress eyes
However they are antagonists as adductors/abductors- they cancel each other out so only depression occurs
What are the yoke muscles?
contralaterally paired extraocular muscles that work synergistically to direct the gaze in a given direction. For example, in directing the gaze to the right, the right lateral rectus and left medial rectus operate together as yoke muscles
Give examples of organs in the head and neck which have autonomic innervation.
- Skin - sympathetic innervation of arterioles, sweat glands and arrector muscles
- Eyes - smooth muscle of iris (pupil diameter
smooth muscle of ciliary body associated with
the lens - Lacrimal glands - lacrimal fluid production
- Salivary glands - saliva production
what is the sympathetic innervation route for orbit and eyeball?
presynaptic
- originates from autonomic centres in the brain
- Passes down spinal cord
- Exits spinal cord with T1 spinal nerve
- Travel up within the sympathetic chain where it synapses in superior cervical sympathetic ganglion
postsynaptic
- Enters internal and external carotid nerves
- Pass onto surface of the internal and external carotid arteries
- Carried to the organs of the had of the surface of the branches of these arteries
- Ophthalmic artery carries sympathetic axons into the orbit
what is the common sympathetic innervation route for all organs?
- originates from autonomic centres in the brain
- Passes down spinal cord
- Exits spinal cord with T1- L2 spinal nerves
- travel to sympathetic chains running the length of vertebral column
- Pass into all spinal nerves (anterior and posterior rami)
- Pass into splanchnic nerves to eventually supply organs
what is the common parasympathetic innervation route for all organs?
- All parasympathetic axons leave the CNS via cranial nerves III, VII, IX and X and via sacral spinal nerves
- Craniosacral outflow
- Internal organs, not body wall:
i. Parasympathetic ganglia in head - to eye, lacrimal gland salivary glands
ii. Vagus nerve supplies rgans of the neck, chest and abdomen as far as the
iii. Sacral spinal nerves supply parasympathetic axons to the hindgut, pelvis and perineum
where is the ciliary ganglion found?
in the bony orbit
what is the ciliary ganglion?
parasympathetic ganglion - carries fibres from CN III
what is the parasympathetic route of CNIII to the eye?
- connects with CNS at junction of midbrain and pons
- Passes through cavernous sinus
- exits via superior orbital fissure
- Somatic motor to majority of extraocular muscles
- Presynaptic parasympathetic axons to the ciliary ganglion
- splits into 2 divisions: superior and inferior
what is the meninges?
protective coverings of the brain and spinal cord?
What are the three layers of the meninges?
- Dura mater - sensory supply from CN V
encloses dural venous sinuses via its two layers
the two layers:
i. Periosteum layer
ii. Meningeal layer
2. Arachnoid mater - contains arachnoid granulations
subarachnoid space - contains CSF and blood vessels
- Pia mater - adheres to brain ( follows the grooves of the brain)
where is the subarachnoid space?
between the arachnoid mater and pia mater
how do you access the CSF?
lumbar puncture at L3/4 disc level
or
Lumbar puncture at L4/5 IV disc levels
When does the subarachnoid space end?
inferiorly at vertebral space level S2
How many ventricles in the brain are there?
4
Left lateral ventricle
right lateral ventricle
Midline 3rd ventricle
midline 4th ventricle
what is the circulation of CSF?
- secreted by the choroid plexus
- the CFS passes into the right and left lateral ventricles
- and then passes down into the 3rd ventricle
- then through the cerebral aqueduct it enters the 4th ventricle
- The CSF passes mainly into the subarachnoid space but some passes into the central canal of the spinal cord
- It is then reabsorbed into the dural venous sinuses via the arachnoid granulations
what is the choroid plexus?
epithelium/ modified pia located in the lateral and third ventricles where CSF is produced
in which ganglion do sympathetic fibres traveling to the head and neck synapse?
superior cervical ganglion
postsynaptic sympathetic fibres reach the orbit by travelling on the surface of which artery?
ophthalmic
which parasympathetic ganglia are associated with the orbit?
Ciliary - more associated with the eyeball
pterygopalatine - more associated with the lacrimal gland
which parts of the face does the CN V1 innervate? (ophthalmic)
ii. which type of innervation is this?
upper eyelid
cornea
conjunctiva
ii. sensory
Which parts of the face does CN V2 innervate?
(maxillary)
ii. which type of innervation is this?
Skin of the lower eyelid
skin over the maxilla
ii. Sensory
which parts of the face does CN V3 innervate? (mandibular)
ii. which type of innervation is this?
skin over the mandible and TMJ - except for the angle of mandible
ii. mainly sensory but some motor - motor mainly for muscles involved in mastication
Discuss the corneal reflex (blink)
sensory (afferent) limb:
action potentials conducted from cornea via CN V1 branches to the trigeminal nerve then along the CN V to the pons
Central:
Central CNS connections between CNV and CNVII act as synapse
motor (efferent) limb:
Action potentials conducted via CN VII to the eyelid part of the orbicularis oculi
what are the 6 main autonomic reflexes of the eye?
Wide eye opening of fight or flight
Pupillary light reflex
Accommodation reflex
Lacrimation reflex
vestibulo-ocular reflex
Oculocardiac reflex
What is the vestibulo-ocular reflex?
Turns the eyes in the opposite direction to a head movement
this stabilises gaze on an object while the head moves
what CNS connections are involved in the vestibulo-ocular reflex?
connections occur between:
CN III
CN IV
CN VI
CN VIII
What is the oculocardiac reflex?
Reflex bradycardia in response to tension on extraocular muscles or pressure on eyes
what CNS connections are involved in the oculocardiac reflex?
connections occur between:
CN V1
CN X
Give example of Sympathetic autonomic reflexes.
Eyes open wider
Get more light into eyes
focus on far objects
more emotional - more lacrimation
Give example of parasympathetic autonomic reflexes.
Get less light into eye - when asleep
focus on near objects
reflex lacrimation - if foreign body is on eye
what is Mueller’s muscle?
it is the superior tarsal muscle which is a part of the LPS
it is a smooth muscle which innervated by the sympathetic pathway
it helps elevate the eyelid by 2mm - it is involve in the autonomic reflex to open the eyelid
