Anatomy Flashcards
Which bones make up the orbital rim?
Maxilla
Zygomatic
Frontal
Apart from the bony orbit, what other structures protect the eyeball?
Eyelids
Eyelashes
Lacrimal glands + ducts
Conjunctiva
What is the name of the slightly thickened are of connective tissue which contains glands, and sits on the inside of the eyelid?
Tarsal plate
Which nerve supplies orbicularis oculi?
CN VII - facial
Which three nerves supply the skeletal muscles of the eye?
CN III - oculomotor
IV - trochlear
VI - abducens
Which muscle works to elevate the eyelid?
Which nerve supplies this muscle?
Levator palpebrae superioris
CN III - oculomotor
Give two functions of tears
Keeps eyes moist, helps to supply the cornea with oxygen
Describe the pathway of tears starting from lacrimal gland
Lacrimal gland
- > across cornea
- > puncta lacrimalia
- > canaliculi
- > lacrimal sac
- > nasolacrimal duct
- > into nose through inferior meatus of lateral wall of nasal cavity
Which nerve innervates the lacrimal gland?
CN VII - facial
Which cranial nerves have a parasympathetic component?
CN III - oculomotor
CN VII - facial
CN IX - glossopharyngeal
CN X - vagus
Why can the trigeminal nerve not supply the lacrimal gland?
Trigeminal has no parasympathetic component so cannot supply a gland
What are the two broad types of conjunctivitis?
How do they present?
Bacterial - tends to present with pus
Allergic - tends to present with erythema
What are the three layers of the eye ball and which structures do each contain?
Outer fibrous: - Sclera - Cornea Middle vascular - Pigmented choroid - Ciliary body - Iris Inner nervous - Retina
What is the ciliary body made up of?
How does the lens move if the muscles are relaxed/tensed?
Ciliary muscles + suspensory ligament of lens
When the muscles relax, the ligaments are pulled and put tension on the lens to thin it
When the muscles contract they relax the suspensory ligaments, allowing the lens to become fatter
Which type of muscle is found in the iris?
What are the two muscles?
- Nervous innervation?
- Under what circumstances do they move?
Ssmooth muscle fibres
- Sphincter (constrictor) pupillae (concentric)
- Parasympathetic control from CN III
- Bright light, accommodation - Dilator pupillae (radial)
- Sympathetic
- Dim light, fright
Name each of the extrinsic muscles of the eye and the direction in which they move the eye
Superior rectus - elevates and adducts Inferior rectus - depresses and adducts Lateral rectus - abducts Medial rectus - adducts Inferior oblique - up and out Superior oblique - down and out
Which nerves supply the extrinsic muscles of the eye?
All are supplied by CN III except:
- Lateral rectus which is supplied by CN VI (abducens)
- Superior oblique which is supplied by CN IV (trochlear)
Give some features of the superior oblique muscle
- Passes through the trochlea
- Attaches to sclera
- Supplied by trochlear nerve
- Tramp muscle – down and out
- Makes the eyeball go down and out
Revise testing of the eye muscles
Revise testing of the eye muscles
What is the suspensory ligament of the eye?
A thick fascial sling that holds the eye just above the floor of the orbit
What can happen to the suspensory ligament if the zygoma is #?
If trauma occurs to the cheek and the zygoma is #, the zygoma rotates medially in towards the floor of the orbit – suspensory ligament will be displaced and move inferiorly – eye will also descend within the orbit
Double vision results as eyes are in different orientations
What runs along the floor of the orbit?
What can displacement of the zygoma do to this?
Running along floor of orbit is the infraorbital canal/groove
- Contains NV bundle – nerve, artery, vein
- Infraorbital nerve, artery and vein
Displacement of zygoma can impinge upon this canal and cause damage to the NVB – can result in sensory loss to the mid face region
In terms of general sensory supply to the face, what areas do the branches of the trigeminal nerve supply?
Which nerve supplies the angle of the mandible?
CN V1 (ophthalmic nerve) supplies:
- Upper eyelid
- Cornea
- All the conjunctiva
- Skin of the root/bridge/tip of the nose
CN V2 (maxillary nerve) supplies: - Skin of the lower eyelid
- Skin over the maxilla
- Skin of the ala of the nose
- Skin/mucosa of the upper lip
CN V3 (mandibular nerve) supplies: - Skin over the mandible and temporomandibular joint (apart from the angle of the mandible – supplied by C2,3 spinal nerves)
Which reflex prevents damage from foreign bodies striking the anterior surface of the eye?
How does it work?
The blink (corneal) reflex APs travels centrally along divisions of CN V1 from the cornea to the trigeminal ganglion, then in CN V to the pons APs are conducted peripherally in CN VII to the eyelid part of orbicularis oculi
What are the functions of the two parts of orbicularis oculi?
Palpebral part allows us to close our eyes gently i.e. blink
Orbital muscles cause us to scrunch up our eyes
How do sympathetic axons course from the CNS to the organs of the head region?
The presynaptic axon extends from CNS to synapse with a ganglion – associated with the sympathetic chain in the sympathetic nervous system
AC is the neurotransmitter here
Postsynaptic axon extends from the ganglion towards the organ
Noradrenaline is the neurotransmitter here
The effect is smooth muscle contraction or glandular secretion?
How do sympathetic axons course from the CNS to the eye?
Presynaptic axons descend through the spinal cord and exit in the T1 spinal nerve, then ascend within the cervical chain
They then synapse in the superior cervical sympathetic ganglion, then fibres either travel in the internal or external carotid nerve – both contain synaptic sympathetic axons
The fibres then pass onto a plexus which is an intertwining of nerves – found near the internal or external carotid artery depending on which nerve we’re talking about
The plexus associated with the internal carotid artery – ophthalmic artery – sympathetic axons are carried by the artery to the eye
Which cranial nerves carry parasympathetic axons?
CN III - oculomotor
CN VII - facial
CN IX - glossopharyngeal
CN X - vagus
How do parasympathetic axons course from the CNS to the organs of the head region?
Presynaptic axon leaves the CNS in CN III, VII, IX or X
The presynaptic axon releases acetylcholine at the synapse in the parasympathetic ganglion to stimulate the cell body of the postsynaptic axon
The postsynaptic axon releases acetylcholine at the organ to stimulate the organ to respond (smooth muscle contraction or glandular secretion)
What is the main difference between sympathetic and parasympathetic nervous systems?
The positioning of the ganglia – in parasympathetic NS the ganglia tend to be isolated within the head and neck, or associated with the surfaces of the organs themselves
How do parasympathetic presynaptic axons leave the CNS?
All presynaptic parasympathetic axons leave the CNS in
- Cranial nerves III, VII, IX & X
- Plus sacral spinal nerves - “carry” parasympathetic axons to the hindgut, pelvis & perineum
How many parasympathetic ganglions are in the head?
Four
Which parasympathetic ganlgion is associated with the eye?
Ciliary ganglion in the orbit
How many ganglia are associated with the facial nerve?
Two
What is the fourth parasympathetic ganglion in the head?
Otic ganglion – associated with CN IX – to parotid for secretion of saliva
What is the function of the vagus nerves?
The vagus nerves supply parasympathetic axons to the organs of the neck/chest & abdomen as far as the midgut
Give three functions of the oculomotor nerve
- (somatic) motor to superior (SR), medial (MR) & inferior rectus (IR) and inferior oblique (IO)
- (somatic) motor to levator palpebrae superioris (LPS)
- Presynaptic parasympathetic axons to the ciliary ganglion
Describe the path of the oculomotor nerves to the orbit from the CNS
Connects with brain at junction between midbrain and pons
After leaving the brain it leaves the cranial cavity via superior orbital fissure - enters the orbit
What are the two branches of the oculomotor nerve?
What are the functions of the two parts?
Superior and inferior
- Superior supplies superior rectus and LPS
- Inferior branch supplies medial rectus, inferior rectus and inferior oblique – motor
- Inferior also conveys presynaptic parasypmpathetics to the ciliar ganglion
- Superior is ONLY MOTOR
- Inferior is motor and presynaptic parasympathetic
Which four structures pass through the superior orbital fissure?
CN III - oculomotor
CN IV - trochlear
CN VI - abducens
CN V1
What are the two types of ciliary nerve?
What are the components of each?
Long ciliary nerve - Sympathetic - Somatic sensory Short ciliary nerve - Somatic sensory - Parasympathetic - Sensory
Which fibres pass through the ciliary ganglion?
- General sensory fibres from the cornea and conjunctiva
- Post synaptic sympathetic fibres from the superior cervical ganglion (don’t synapse here, just pass through)
- Presynaptic parasympathetic fibres from CN III, which synapse with:
- Postsynaptic parasypathetic fibres
Which nerves does the vestibulo-ocular reflex require?
CN VIII & CNs III, IV & VI
What is the oculocardiac reflex?
Which nerves are required for it?
- Reflex bradycardia in response to tension on the extraocular muscles or pressure on the eye
- CNS connections between CN V1 & CN X
Give three effects the sympathetic NS has in the eye
- Open eyes wider to let more light in
- Focus on far objects
- Emotional lacrimation
Give four effects the parasympathetic NS has in the eye
- Allow orbicularis oculi to work
- Get less light into eyes (to protect the retina from bright light or when asleep)
- Focus on near objects
- Reflex lacrimation (to wash away the stimulant foreign body & clean the cornea)
What type of muscle does the LPS contain?
What is the function?
SKELETAL
- Voluntary from oculomotor
SMOOTH
- Sympathetic - not voluntary
What do sympathetics do to the pupil?
Which muscle?
Ssympathetics dilate the pupil
Dilator pupillae muscle is responsible for this – arranged radially around the pupil
Has a fixed origin around the external surface of the iris
Mobile insertion is around the internal bit of the iris
Which muscle constricts the pupil?
Which NS?
Sphincter/contrictor pupillae
Parasympathetic
What is a fixed pin point pupil associated with?
Opiate drugs
What is a fixed dilated pupil associated with?
Serious pathological sign of oculomotor nerve dysfunction
inhibiting the pupillary constricting action of parasympathetic axons in the ciliary nerves
Which eye is the stimulated eye and which is the non-stimulated eye?
The eye with the light being shone = directed light reflex
Other eye = consensual light reflex
What is the pathway of APs when light is shone in the eye?
- The (special) sensory (afferent) limb of the reflex is the ipsilateral CN II (the optic nerve)
- CNS connections in the thalamus
- The motor limb of the reflex is bilateral via CNs III (the oculomotor nerves)
Describe the events that take place related to the lens when looking at a distant object
The ciliary muscle relaxes in “far vision” (no parasympathetics) the ligament tightens & the lens flattens to focus on distant objects
Describe the events that take place related to the lens when looking at a near object
the ciliary muscle contracts in “near vision” (parasympathetic) the ligament relaxes & the lens becomes spherical to focus on close objects
What are the three components of the accommodation reflex which need to be assessed?
- Bilateral pupillary constriction (CNs III)
to prevent diverging light rays from hitting the periphery of the retina and resulting in a blurred image. - Bilateral convergence - medial rotation of both eyes (CNs III)
simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision - Bilateral relaxation of the lens
the lens becomes spherical due to contraction of the ciliary muscles (CNs III)
Name and describe the three types of lacrimation
- Basal tears (important in corneal health)
- Clean/nourish & hydrate the avascular cornea
- Contain lysozyme (an enzyme that can hydrolyse bacterial cell walls) - Reflex tears (extra tears in response to mechanical or chemical stimulation)
- The afferent limb of the reflex is CN V1 (the ophthalmic nerve) from the cornea/conjunctiva
- The efferent limb is parasympathetic axons originating from CN VII (the facial nerve) - Emotional tears (happy, sad or frightened tears)
What are the two types of humour found in the eye and where is each found?
- Aqueous humour
- Fills up anterior portion of eye
- Divided into posterior – behind iris
- Anterior – in front of the iris - Vitreous humour presses up on the outside of the eyeball and helps to maintain its shape
Describe the pathway of aqueous humour from secretion to absorption.
Blockage of this pathway can lead to which condition?
- Ciliary processes secrete aqueous humour
- Floats into posterior chamber (behind iris)
- Circulates between lens and iris, then through pupil
- Passes into anterior chamber
- Absorbed at irido-corneal junction
Any blockage to this area which prevents circulation of aqueous humour may lead to glaucoma
What is the Munro-Kellie hypothesis?
If one increases, then something else must have to give way – Munro-Kellie hypothesis
Describes relationship between volume and pressure in the skull
What is the Sunset sign?
Which condition is it seen in?
Whites of eyes showing above iris
Hydrocephalus
What are the three layers of the meninges?
Briefly describe each.
Outer = dura mater = stiff, fibrous, doesn’t expand – end osteal and meningeal layers
Middle – thin membrane which looks like a spider web – very thin + see-through
Inner – unicellular thick layer which surrounds the brain itself
Name and describe the two layers of the dura mater
The dura mater has two layers
- Falx cerebri – separates the cerebral hemispheres, bends of over to form a fold
- Tentorium – second fold that holds the cerebrum up off of the cerebellum
What is the function of:
- Tentorium cerebelli
- Falx cerebelli
Tentorium cerebelli - separates cerebellum from hemispheres
Falx cerebelli - separates the two hemispheres of the cerebellum
What is the tentorial notch?
Tentorial notch = space in tentorium – with raised ICP the brain can be forced into this space
What is the name given to the space between two layers of the meninges through which venous blood flows?
Dural venous sinuses
Name each of the ventricles found in the brain
Lateral ventricles (two) - Body - Frontal (anterior) horns - Occipital (posterior) horns - Temporal (inferior) horns Third ventricle - Between thalami - Very flat Fourth ventricle - Between pons/medulla and cerebellum
Where is CSF produced?
CSF is produced in the choroid plexus – layer which surrounds all of the ventricles, but most in the fourth ventricles
Describe the steps in CSF circulation from production to reabsorption
- CSF is produced in the choroid plexus – layer which surrounds all of the ventricles, but most in the fourth ventricles
- Two lateral ventricles
- Interventricular foramen
- Third ventricle
- Cerebral aqueduct
- Fourth ventricle
- -> some to central canal of spinal cord
- Median or two lateral apertures
- Subarachnoid space
- Arachnoid villi
- Superior sagittal sinus
- Reabsorption into venous system
What causes a pupil to dilate in terms of raised ICP?
Pressure on CN III – unopposed sympathetic action of the dilator pupillae
How does raised ICP affect the optic nerve?
Optic ‘nerves’ are actually CNS tracts
- Covered by meninges
Raised ICP increases pressure in the sub-arachnoid space - affects the optic nerve
Also compresses the central artery and vein of the retina
What is the name given to swelling of the optic disc?
Papilloedema
Describe the grades of papilloedema
Grade I - C shaped halo, blurring of edge of disc
Grade II - Circumferential halo with blurred edges
Grade III - Vessels on EDGE of disc disappear
Grade IV - Loss of major vessels ON disc
Grade V - Extremely blurred edges and total or partial obscuring of vessels on disc
