Autonomics of the Eye Flashcards
What are the three divisions of the facial nerve?
CN VI Ophthalmic nerve
CN VII Maxillary nerve
CN VIII Mandibular nerve
What is innervated by the ophthalmic division of the facial nerve?
Upper Eyelid
Cornea
Conjunctiva
Skin of the root/bridge/tip of the nose
What is innervated by the maxillary division of the facial nerve?
Skin of the lower eyelid
Skin over the maxilla
Skin of the alla of the nose
Skin/mucosa of the upper lip
What is innervated by the mandibular division of the facial nerve?
Skin over the mandible and temporomandibular joint
APART from the angle of the mandible- C2, 3 spinal nerve
Describe the sensory (afferent) limb of the blink reflex?
Action potentials conduced from the cornea via CN VI branches to trigeminal ganglion, along CN V to pons
What is the central connection of the blink reflex?
Central CNS connection between CN V and CN VII
Describe the motor (efferent) limb of the blink reflex?
Action potential conducted in CN VII to eyelid- part of obicularis oculi
Where do sympathetic axons originate?
Autonomic centres in the brain
How to sympathetic axons supply organs?
Travel down spinal cord, exit T1-L2, travel to sympathetic chains, pass into spinal nerves pass into splanchnic nerves
Describe the path of pre-synaptic sympathetic axons to the eye?
Presynaptic axons from CNS exit spinal cord in T1 spinal nerve and synapse in superior cervical ganglion
- superior
- middle
- inferior
Describe the path of post-synaptic sympathetic axons to the eye?
internal and external carotid nerves
Pass onto the surface of internal and internal carotid arteries, carried to organs of the head on the surface of their arteries
What does the ophthalmic artery carry?
Sympathetic axons to the orbit
Describe parasympathetic outflow?
Axons leave CNS in III, VII, IX & X to internal organs (not body wall)
How do parasympathetic axons get to the eye?
Parasympathetic ganglia in head to eye, lacrimal gland and salivary gland
What does the ciliary ganglion carry and supply?
CN III
Eye (Iris, ciliary muscles)
What does the pterygopalatine ganglion carry and supply?
CN VII
Lacrimal Gland
What does the otic ganglion carry and supply?
CN IX
Parotid gland
What does the submandibular ganglion carry and supply?
CN VII
Sublingual and submandibular gland
Where does the oculomotor nerve connect with the CNS?
Junction between midbrain and pons
Describe the path of the oculomotor nerve?
Passes through cavernous sinus and exits via superior orbital fissure
What supplies motor fibres to levator palpebrae superioris?
Oculomotor
What is the superior division of oculomotor supplying?
SR and LPS
What is the inferior division of oculomotor supplying?
MR, IR, IO and ciliary ganglion
What do the ciliary nerves supply?
Autonomic axons to control diameter of iris and refractive shape of lens
What type of nerve fibre is carried by the long ciliary nerve?
Sympathetic
Somatic Sensory
What type of nerve fibre is carried by the short ciliary nerve?
Sympathetic
Parasympathetic
What is the ciliary ganglions purpose?
Allow synapsing of parasympathetics
What are the autonomic reflexes of the eye?
Maximal eyelid elevation/wide eye opening of fight or flight
Pupillary dilatation/constriction adjusting light entry
Accommodation reflex
Lacrimation reflex
Oculo-cardiac reflex
Vestibulo-ocular reflex
What is the vestibulo-ocular reflex?
Turns the eye in the opposite direction to head gaze, allows you to stabilise gaze in head movement
Connections- CN VIII, III, IV & VI
What is the oculo-cardiac reflex?
Reflex bradycardia in response to tension on extra-ocular eye muscles or pressure on eye
Connections- CN CI & CN X
What are the sympathetic functions of the eye?
Open eyes wider
Get more light into eyes
Focus on far objects
Emotional lacrimation
What are the parasympathetic functions of the eye?
Allow obicularis oculi to work
Get less light into eyes (to protect the bright light or when asleep)
Focus on far objects
Reflex lacrimation to clean cornea
What kind of fibres does the levator palpebrae superioris contain?
Skeletal and Smooth Muscle
How do sympathetic fibres reach the levator palpebrae superioris?
- superior cervical sympathetic ganglion
- internal carotid nerve
- internal carotid plexus
-axons carried on ophthalmic artery
and on its branches to the orbital structures
What dilates the pupil?
Sympathetics
What is a mydriatic pupil?
Non-physiologically enlarged pupil
How are dilator pupillae fibres arranged?
Radially
originate around the external circumference of the iris = FIXED
insert around the internal circumference of the iris = MOBILE
What constricts the pupil?
Parasympathetics
What is a mitotic pupil?
Non physiologically constricted pupil
In what syndrome might you find a mitotic pupil?
Horners
What is a fixed pin-point pupil?
Pathological sign- opiate drugs
What is a fixed blown pupil?
CN III pathology
Where are sphincter pupillae fibres?
Encircle pupil
-around internal circumference of iris
Where do connections occur in the pupillary light reflex?
Midbrain
Describe the 1st neurone change in the pupillary light reflex?
1st neurones
-retinal ganglion cells pass via the ipsilateral optic nerve to decussate in the optic chiasm, then synapse in the pretectal nucleus in the midbrain
What connects the lens to the ciliary body?
Suspensory ligaments
Describe the ciliary body
Muscular and vascular
Smooth muscle like a sphincter at circumference
What happens to the ciliary muscle in far vision?
Relaxes
- no parasympathetics
- ligament tightens and lens flattens to focus
What happens to the ciliary muscle in near vision?
Contracts
- parasympathetic
- ligament relaxes and lens becomes spherical to focus on near objects
Are sympathetics involved in changing lens shape?
NO
What are the three components of the accommodation reflex?
- Bilateral pupillary constriction (CN III)
- Bilateral convergence
- Bilateral relaxation of lens
What is the role of bilateral pupillary constriction?
To prevent diverging light rays from hitting the periphery of the retina and causing a blurred image
What is the role of Bilateral convergence ?
Medial rotation of both eyes
Simultaneous movement of both eyes maintains single binocular vision
What causes bilateral relaxation of lens’?
The lens becomes spherical due to contraction of ciliary muscles (CN III)
What are basal tears?
Important in corneal health
Clean/nourish and hydrate the avascular cornea
Contain lysozyme
What is lysozyme
Enzyme that hydrolyses bacterial cell wall
What are reflex tears?
Extra tears in response to mechanical or chemical stimulation
What is the afferent limb involved in reflex tears?
CN VI from cornea/conjunctiva
What is the efferent limb involved in reflex tears?
Parasympathetic axons originating from CN VII
Describe the 2nd neurone change in the pupillary light reflex?
2nd neurones (bilateral) -located entirely within the midbrain and connect the pretectal nucleus to the next synapse in the dinger westphalia nucleus (the location of the cell bodied of the parasympathetic axons of CN III)
Describe the 3rd neurone change in the pupillary light reflex?
3rd neurones
- pass from the EW nucleus, via the CN III then its inferior division to synapse in the ciliary ganglion
Describe the 4th neurone change in the pupillary light reflex?
4th neurones
-short course in the ciliary nerves to sphincter pupillae muscles
What are the two nerves involved in lacrimation?
Facial and trigeminal
