Anatomy Flashcards
Insert diagram of surface anatomy
Iris is covered by the cornea
While sclera is covered by conjunctiva
Lacrimal lake is the most medial structure
Lacrimal papilla and puncture can be found medially on both eyelids
Pupil is at the centre of the iris
What is the name of the corneoscelral junction
Limbus
Where is the lacrimal gland located?
Superolateral to the eye
What is the name for the loose arching folds connecting conjunctival membrane to the eyelid?
Conjunctival formix
What part of the eye has the most refractive power?
Cornea
Name the six bones that make up the orbit
- frontal
- zygomatic
- maxilla
- sphenoid
- lacrimal
- ethmoid
Which bones have orbital plates?
Frontal, maxilla and ethmoid
Name two bones that are thin and fracture easily
Maxilla and ethmoid
What travels in the optic canal and where does it pass through?
Optic nerve and ophthalmic artery through the sphenoid bone
Which cranial nerves pass through the superior orbital fissure?
CN III, IV, VI
What passes through the infraorbital foramen
Infraorbital neurovascular bundle
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Describe a blow out fracture
Bones surrounding the orbit can withstand high amounts of pressure but this pressure can be transferred to thinner bones - maxilla and ethmoid
Name the type of fracture where contents of the orbit pass through the fracture
Trap door fracture
If the stronger bones do fracture where does it tend to occur?
Sutures
What muscle makes up the eyelid?
Orbicularis oculi
Name the two parts of the orbicularis oculi and what they are responsible for
- palpebral (gentle closure of the eye)
- orbital (tight closure of the eye)
What nerve innervates the orbicularis oculi?
CN VII
Other than the orbicularis oculi what else is the eyelid made of?
Tarsus - fibrous skeleton, thick bands of connective tissue superiorly and inferiorly with a palpebral ligament at either side
Name the muscle that elevates the upper eyelid
Levator Palpebrae Superioris
Where does the LPS attach?
To the tarsus and skin
Which nerve supplies the LPS?
CN III
What is the additional slit of smooth muscle attached to the LPS?
Mueller’s/superior tarsus
What is special about Mueller’s muscle?
It has sympathetic supply to aid eye widening
What do tarsal glands secrete?
Lipids to line the eyelid
Name the three layers of the eye
- Fibrous outer layer
- Vascular Layer (Uvea)
- Retina (photosensitive inner layer)
What are the two parts of the fibrous outer layer?
Sclera and cornea
What makes up the vascular layer?
Iris
Ciliary body
Choroid
Where is the anterior segment?
Found in front of the lens and is made of two chambers
- anterior (between cornea and iris)
- posterior (between iris and suspensory ligaments)
Where is the posterior segment?
Behind the lens, 2/3rds of the eye and contains vitreous humour
What makes people see floaters?
Clumps of collagen
Where is aqueous humour secreted from?
Ciliary processes
Describe the pathway of aqueous humour
Circulates in posterior chamber then passes through the pupil to the anterior chamber to nourish the cornea
Where is aqueous humour reabsorbed?
Scleral venous sinus at the iridocorneal angle
Describe the arterial supply to the orbit
- ICA
- Carotid canal
- Ophthalmic Artery (close to optic nerve in canal)
Name the branches of the ophthalmic artery
- ciliary arteries
- nasal cavity branches (littles area)
- forehead (scalp branches)
- central artery of the retina
Describe the venous drainage of the orbit
Forehead vein, superior ophthalmic vein, inferior ophthalmic vein, central vein mainly drain into the cavernous sinus via the superior orbital fissure
What is special about the facial vein?
It is thought to be valveless
Where does light focus in the retina?
Posterior area called the fundus
What are the different parts of the retina?
Optic Disc, Macula, Fovea
What happens at the optic disc?
Entry/exit of blood vessels and CN II axons
What is the macula?
Central portion of the retina that has the greatest density of cones
What is the fovea?
Centre of the macula, area of most acute vision
In which direction do the retinal arteries, veins and ganglion axons lie relative to the retina?
Anterior
What is the blind spot?
There are no photoreceptors in the optic disc so light cannot be processed at this area
Where is the optic disc in relation to the eye?
Nasal aspect
What will interruption of the retinal artery branch result in?
Loss of an area of visual field corresponding to the area of ischaemia
What will interruption of the central artery/vein result in?
Monocular blindness
What happens to light that hits the nasal retina?
It crosses over at the optic chiasm to the opposite side of the brain
What happens to light that hits the temporal retina?
It stays on the same side
What eye movements occur in the vertical axis?
Abduction and adduction
What eye movements occur in the transverse axis?
Elevation and depression
What eye movements occur in the anteroposterior axis?
Intorsion and extorsion
Name the seven extra ocular muscles
- Lateral rectus
- Medial rectus
- Superior rectus
- Inferior rectus
- Inferior oblique
- Superior oblique
- LPS
Where do the recuts muscle come from and attach onto?
From the annulus to the sclera
Where does the superior oblique originate?
Sphenoid
Where does the inferior oblique originate?
Orbital plate of the maxilla
What is the way to remember the nerve supply to the extra-ocular muscles?
LR6 SO4 AO3
Lateral rectus 6
Superior oblique 4
All others 3
What is special about the superior oblique?
It passes through the trochlea
Describe the relationship between superior rectus and inferior oblique
Synergistically elevate but are antagonists as rotators
Describe the relationship between superior oblique and inferior rectus
Synergistically depress but are antagonists as ab/adductors
Where does the LPS originate and insert?
Originates form the lesser ring of sphenoid bone and inserts onto skin and tarsus of superior eyelid
Describe the sensory innervation to the face
CN V1 - upper eyelid, cornea, conjunctiva to top of the nose
CN V2 - skin over maxilla and lower eyelid
CN V3 - skin over mandible and TMJ (except angle of mandible)
Which nerves originate from CN V1?
Supraorbital and nasal skin branches
Which nerve originates from CNV2?
Infraorbital nerve
Describe the sensory component of the corneal reflex
APs from the cornea via CNV1 go to the trigeminal ganglion then CN V in the pons
Describe the motor component of the corneal reflex
APs from CNVII go to the palpebral part of the orbicularis oculi
What is the purpose of the corneal reflex?
Acts as a protective measure to clear the eye and stop anything getting into it
What nerves are involved in the vestibule-ocular reflex?
CN VIII, CN III, CN IV and CN VI
What is the oculocardiac reflex?
Reflex bradycardia in response to tension on extra ocular muscles/pressure on eye involves connections between CN V1 and CN X
What is the sympathetic effect on the eye?
Opens eyes wider to let more light in and focus on further objects
What is the parasympathetic effect on the eye?
Less light in to protect the retina, focus on near objects and reflex lacrimation to clean cornea
How do eyes open wider?
Muellers muscle has sympathetic innervation and works with LPS
Describe the pathway of postsynaptic fibres that supply the Muellers muscle
- Superior cervical ganglion
- Internal carotid nerve
- Internal carotid plexus
- Axons on ophthalmic artery
- Branches on orbital structures
What muscle is responsible for pupil constriction?
Sphincter pupillae
What muscle is responsible for pupil dilation?
Dilator pupillae
Name the afferent limb of the pupillary light reflex
Ipsilateral CN II
Name the efferent limb of the pupillary light reflex
Bilateral CN III
What are the four parts of the neurone chain in the pupillary light reflex?
- Retinal ganglion
- Midbrain synapse between CN II and CN III
- CN III to Ciliary Ganglion
- Short ciliary nerves to sphincter papillae
How does the signal pass from one side to the other?
Ipsilateral signal passed to the ipsilateral pretectal nucleus but then passed to bilateral Ediger Westphal Nuceli
What connects the lens to ciliary body?
Suspensory ligaments
Describe how the lens changes shape
Ciliary muscles relax and ligaments tighten to flatten the lens
Ciliary muscles contract and ligaments relax to spherical and focus on near objects
What is the innervation to stimulate contraction?
Parasympathetic - CN III
What are the three rules regarding accommodation reflex?
- Lens is more optically powerful when spherical
- Lens naturally wants to relax into spherical shape
- Ciliary muscle is like a sphincter - small when contracted
Name three types of tears
Basal, reflex and emotional
Describe basal tears
Clean/nourish/hydrate the avascular cornea, contain lysozyme to hydrolyse the bacterial cell wall
Describe reflex tears and the nerve pathway
Extra tears in response to stimuli
Afferent - CN V1
Efferent - CN VII
What is the sensory innervation to the cornea?
CN V2
Though which ganglion do axons to the lacrimal gland come from?
CN VII at internal acoustic meatus, to pterygopalatine ganglion travel on branches of V2 then V1 to the lacrimal gland
Why do you get a runny nose when you cry?
Lacrimal lake connects to the canaliculi which leads to the lacrimal sac which drains into the nasolacrimal duct which connects to the inferior nasal meatus
Describe the course of sympathetic nerves
Originate from the autonomic centres and passes down the spinal cord exiting at T1-L2 to the sympathetic chain
Where do sympathetic nerves for the head and neck leave the spinal cord and where do they go?
T1, through the sympathetic chain to superior cervical ganglion
After sympathetic nerves synapse at the ganglion where do the post-synaptic axons go on the way to the eye?
Enter the internal and external carotid nerves and pass onto the peri-arterial plexus on the surface of the internal carotid artery and then the ophthalmic artery
Describe the course of parasympathetic nerves
Leave the CNS via cranial nerves III, VII, IX and X or sacral spinal nerves
Name four parasympathetic ganglia in the head and neck
- ciliary
- pterygopalatine
- otic
- submandibular
Where is the ciliary ganglion?
Just anterior to optic canal, superior to the orbital tissue with close relation to CNIII
What is the only nerve to synapse at the ciliary ganglion?
CN III synapses to the short ciliary nerve
Which division of CN III supplies the somatic motor innervation to the extra-ocular muscles?
Superior
How does CN III enter the orbit?
Travels from the between the midbrain and pons to the cavernous sinus and then through the superior orbital fissure
Describe normal light reflex
Symmetrical and displaced slighty nasally to the centre of the pupils
What is the name for the displacement of the light reflex temporally/nasally?
Esotropia - temporally
Exotropia - nasally
What is the name for the displacement of the light reflex inferiorly/superiorly?
Hypertropia - inferiorly
Hypotropia - superiorly
If sclera can be seen superiorly to the iris what does that usually indicate?
Something is pushing the eye forward - proptosis in TED
What is the clinical name for a droopy eye?
Ptosis
Describe the histology of the cornea
Stroma (collagen based) with epithelium on either side which helps to keep it clear and dry
Why is the sclera white?
Different arrangement of collagen compared to the sclera
Describe the swinging light test
light is shone into one eye and they both constrict
light is moved quickly to the other and both remain constricted
light is moved back to the first eye again and it will dilate
What does the swinging light test indicate?
An afferent problem
What conditions cause afferent problems?
Infection, MS, vision threatening
Describe the pathway of light from the upper field of vision
Upper visual field hits the inferior retina and travels along the lower retinal neurones which travel round the ventricle in the temporal lobe to the occipital cortex
Describe the pathway of light from the lower field of vision
Lower visual field hits the superior retina and travel along the upper retinal neurones which jump over the ventricle and in the parietal lobe to the occipital cortex
Name the condition where a patient cannot see anything in the peripheral field of vision
Bitemporal hemianopia - problem at the optic chiasm
If a problem presents after the chiasm how will it present and what is it called?
Patient is unable to see things coming from one side
- contralateral homonymous hemianopia
What is the purpose of the meninges?
Protective coverings of the brain and spinal cord
Name the three layers of meninges
- dura mater
- arachnoid mater
- pia mater
Describe the dura mater, what is its innervation?
Hard, tough covering with sensory supply from CN V made of two layers periosteal and meningeal
What happens when the dura mater splits into two layers?
It encloses the dural sinuses which are venous channels that drain deoxygenated blood from the brain
Describe the arachnoid mater
Trabeculae extending down towards the pia
What is found between the arachnoid mater and the pia mater?
Subarachnoid space
What is in the subarachnoid space?
CSF and blood vessels
Describe the pia mater
Completely adheres to the brain and nerves/vessels that enter or leave
Where does the subarachnoid space end?
S2
Where does the spinal cord end?
L2/L3
Where is a lumbar puncture performed?
After the spinal cord has ended L3-L5