Reflexes of the Eye Flashcards
What division of the trigeminal nerve does the supraorbital nerve belong to?
CN V1 = ophthalmic
Where does CN V1 supply on the face?
Upper eyelid, cornea, conjunctiva
Where does CN V2 supply on the face?
Skin of lower eyelid and over the maxilla
Where does CN V3 supply on the face?
Skin over mandible and TMJ (except the angle of the mandible)
What is the sensory limb of the blink reflex?
Action potentials conducted from the cornea via CN V1 branches to the trigeminal ganglion, then along CN V to pons
What nerves are the central CNS connections between in the blink reflex?
CN V and CN VII
What is the motor limb of the blink reflex?
Action potentials conducted via CN VII to eyelid part of orbicularis oculi
What are the autonomic reflexes of the eye?
Wide eye opening of fight/flight, pupillary light reflex, accommodation reflex, lacrimation reflex, vestibulo-ocular reflex, oculocardiac reflex
What is the vestibulo-ocular reflex?
Turns eye in opposite direction to head movement and stabilises gaze on object during head movement
What nerves are involved in the vestibulo-ocular reflex?
CNS connections between CN VII and CN III/IV/VI
What is the oculocardiac reflex?
Reflex bradycardia in response to tension on extra-ocular muscles or pressure on eye
What nerves are involved in the oculocardiac reflex?
CNS connections between CN V1 and CN X
What are the sympathetic reflexes of the eye?
Opens eyes wider, get more light in, focus on far objects, emotional lacrimation
What are the parasympathetic reflexes of the eye?
Get less light in (protect retina from bright light/when asleep), focus on near objects, reflex lacrimation (to clean eye)
Which muscles opens the eye wider?
Levator palpebrae superioris = contains skeletal and smooth muscle, Mueller’s muscle, sympathetic innervation
What do post-synaptic sympathetic fibres travel via to open the eyes wider?
Superior cervical sympathetic ganglion, internal carotid nerve, internal acoustic meatus, axons carried on ophthlamic artery and on its branches to orbital structures
What nerves modality constricts the pupils during rest and digest, and in bright light?
Parasympathetic system
What is a non-physiologically constricted pupil classed as?
A miotic pupil (e.g Horner’s syndrome)
Are fixed pin point or dilated pupils normal?
No = are often serious pathological signs (ie of opiates or CN III pathology respectively)
Which structure is responsible for constricting the pupils?
Sphincter pupillae fibres = encircle pupil around the internal circumference of the iris
Which nerve modality is responsible for pupillary dilation?
Sympathetic system
What is a non-physiologically dilated pupil classed as?
A mydriatic pupil (e.g mydriatic drugs)
What structure is responsible for dilating the pupils?
Dilator pupillae fibres = radially arranged, originate around external circumference of iris (fixed) amd insert around internal circumference of iris (mobile)
What is the special sensory limb of the pupillary light reflex?
Ipsilateral CN II
Where do the CNS connections for the pupillary light reflex occur?
In the midbrain
What is the motor limb of the pupillary light reflex?
Bilateral CN III
How does the stimulation of the eye affect the pupillary light reflex?
Direct light reflex occurs in stimulated eye
Consensual light reflex occurs in non-stimulated eye
How many neurons make up the chain in the pupillary light reflex?
4
What is the first neuron in the pupillary light reflex?
Retinal ganglion cell = pass via ipsilateral optic nerve, decussate in optic chiasm, synapse in pretectal nucleus in midbrain
What is the second neuron in the pupillary light reflex?
Bilateral = located entirely in midbrain and connect pretectal nucleus to next synapse in Edinger-Westphal nucleus
What is the Edinger-Westphal nucleus?
Location of cell bodies of parasympathetic axons of CN III
What is the third neuron in the pupillary light reflex?
Bilateral = pass from Edinger-Westphal nucleus via CN III then its inferior division to synapse in ciliary ganglion
What is the fourth neuron of the pupillary light reflex?
Bilateral = course in short ciliary nerves to sphincter pupillae muscles
What do the suspensory ligaments of the lens connect?
The circumference of the lens and the ciliary body
What is the ciliary body?
Both muscular and vascular = smooth muscle like sphincter around circumference
What happens to the ciliary muscle during far vision?
Relaxes = no parasympathetics, ligament tightens and lens flattens to focus on object in distance
What happens to the ciliary muscle during near vision?
Contracts = parasympathetic control, ligament relaxes and lens becomes spherical to focus on near objects
What does the lens accommodation reflex occur in response to?
Near vision
What are the three elements of the lens accommodation reflex?
Bilateral pupillary constriction
Bilateral convergence of both eyes towards midline
Bilateral relaxation of lens
What nerve innervates all three aspects of the lens accommodation reflex?
CN III
What causes bilateral pupillary constriction during the lens accommodation reflex?
Parasympathetic constrictor of sphincter pupillae
What causes the bilateral convergence of both eyes towards the midline during the lens accommodation reflex?
Medial rectus muscle
What causes the bilateral relaxation of the lens during the lens accommodation reflex?
Contraction of ciliary muscles
What is the purpose of basal tears?
Corneal health = cleans/nourishes and hydrates avascular cornea, contains lysozyme (hydrolyses bacterial cell walls)
What causes reflex tears?
Chemical or mechanical stimulation
What is the sensory limb of reflex tears?
CN V1 from the cornea and conjunctiva
What is the motor limb of reflex tears?
Parasympathetic axons from CN VII
What emotions can cause lacrimation?
Happiness, fear or sadness
