Anatomy - Eye Autonomics Flashcards
what is the sensory nerve of the face collectively known as?
trigeminal nerve (CNV) 3 parts
what are the 3 parts of the trigeminal nerve?
ophthalmic nerve (V1) maxillary nerve (V2) mandibular nerve (V3)
what does ophthalmic nerve supply?
upper eyelid
cornea
conjunctiva
skin of root/bridge/tip of nose
what does the maxillary nerve supply?
skin of lower eyelid
skin over maxilla
skin of the ala of the nose
skin/mucosa of the upper lip
what does the mandibular nerve supply?
skin over the mandible and TMJ
what is the only area of the face not supplied by the trigeminal nerve?
jaw line
supplied by C2 and C3 spinal nerves
describe the steps in the blink reflex
sensory (afferent limb):
- action potentials are conducted from the cornea via CNV1 branches
- action potentials travel to trigeminal ganglion then along CNV to the Pons
central CNS connections between CNV and CNVII (facial nerve)
motor efferent limb:
- action potentials conducted via CN VII (facial nerve) to eyelid part of orbicularis oculi
describe the route of sympathetic axons
originate from autonomic centres in the brain
pass down spinal cord
exit spinal cord with T1-L2 spinal nerves (thoracolumbar outflow)
travel to sympathetic chains running down the length of the vertebral column
pass into all spinal nerves (anterior and posterior rami)
pass into splanchnic nerves to eventually supply organs
how does the eye differ?
uses cervical ganglia instead of splanchnic nerves
superior and inferior cervical ganglia relay sympathetic info
describe how sympathetic nerves reach the eye
presynaptic sympathetic axons from the CNS exit spinal cord in T1 spinal nerve and ascend within the synaptic trunk
axons synapse in the superior cervical sympathetic ganglion
post-synaptic sympathetic axons enter internal and external carotid nerves and pass onto the surface of the internal and external carotid arteries - forming peri-arterial sympathetic plexus
these nerves are then carried to the organs of the head on the surface of the branches of these arteries
ophthalmic artery carries sympathetic axons into the orbit
the ophthalmic artery is a terminal branch of which artery?
internal carotid
all parasympathetic axons leave the CNS via which nerves?
cranial nerves - III, VII, IX and X sacral spinal nerves
= craniosacral outflow
how does parasympathetic info from CN III reach the eye and what does it do?
presynaptic fibres synapse at the ciliary ganglion and post synaptic fibres travel to the eye
change shape of eye and iris
what do the parasympathetic ganglia in the head supply?
eye
lacrimal gland
salivary glands
what does the vagus nerve supply?
organs of the neck, chest, abdomen as far as the mid-gut
what do sacral spinal nerves do?
carry parasympathetic axons to the hindgut, pelvis and perineum
what is CN III also known as?
oculomotor
where is CN III found?
connects with the CNS at junction between midline and pons
describe the course of CN III
connects with the CNS at junction between midline and pons
passes through cavernous sinus
exits via superior orbital fissure
what does CNIII supply somatic motor to?
somatic motor to superior, medial and inferior rectus and inferior oblique
levator palpebrae superioris
where does CN III supply presynaptic parasympathetic ganglions to?
ciliary ganglion
what are the ciliary nerves?
supply autonomic axons to control diameter of iris and refractive shape of lens
what does the long ciliary nerve contain?
sympathetic
somatic sensory
what does the short ciliary nerve contain?
sympathetic parasympathetic
how are ciliary nerves involved in the blink reflex?
form the first part of the relfex
what happens at the ciliary ganglion?
ciliary fibres pass through
only important function is the synapse between the pre and post synaptic fibres from CN III
name 6 autonomic reflexes of the eye
maximal eyelid elevation/wide eye opening in fight or flight
pupillary dilation/constriction adjusting light entry (e.g pupillary light reflex)
focussing lens far and near vision (accommodation reflex)
lacrimation reflex (tear production)
vestibulo-ocular reflex
oculocardiac reflex
name 4 sympathetic functions of the eye
opens eyes wider
get more light into eyes
focus on far objects
emotional lacrimation (emotional tears)
name 4 parasympathetic functions of the eye
allows orbicularis oculi to work
get less light into eyes (to protect from bright light or allow sleep)
focus on near objects
reflex lacrimation (to wash away foreign body)
what muscle is responsible for opening the eyes wider and what are it’s components?
levator palpebrae superioris
contains skeletal plus smooth muscle
post-synaptic sympathetic fibres reach levator palpebrae superioris via which 5 structures?
superior cervical sympathetic ganglion internal carotid nerve internal carotid plexus axons carried on the ophthalmic artery and on its own branches to the orbital structures
do sympathetics dilate or constrict the pupil?
dilate the pupil in dim light and in the fight or flight response
what is a mydriatic pupil?
a non-pathologically enlarged pupil
can be caused by mydriatic drugs
what structures are responsible for pupillary dilation?
dilator pupillae fibres
where do dilator pupillae fibres originate and insert?
radically arranged
originate around the external circumference of the iris (fixed)
insert around the internal circumference of the iris (mobile)
do parasympatheics dilate or constrict the pupil?
constrict the pupil in bright light and “rest and digest”
what is a miotic pupil?
non-physiologically constricted pupil
e.g = horner’s synrome
what is the significance of a fixed dilated/constricted pupil?
fixed pin point pupil can indicate opiate use
fixed dilated pupil can indicate a serious pathology (e.g CN III pathology)
what fibres are responsible for constricting the pupil and how are they organised?
sphincter pupillae fibres encircle pupil around the internal circumference of iris
describe the steps in the pupillary light reflex
special sensory (afferent) limb of the reflex (CNII/optic nerve) senses light
CNS connections occur in the midbrain
motor (efferent) limb of the reflex (CN III/oculomotor nerve) is bilateral
direct light reflex occurs in the stimulated eye (one where light is shone on)
a consensual light reflex occurs in the non-stimulated eye
how many groups of neurones are involved in the pupillary light reflex?
4
what are the 1st neurones in the papillary light reflex?
retinal ganglion cells
pass through via the ipsilateral optic nerve to decussate (cross over) in the optic chiasm, then synapse in the pretectal nucleus in the midbrain
what are the 2nd neurones in the papillary light reflex?
bilateral neurones
located entirely in the midbrain and connect the pretectal nucleus to the next synapse in the Edinger Westphal nucleus
what is present in the Edinger Westphal nucleus?
cell bodies of the parasympathetic axons on CN III
what are the 3rd neurones of the pupillary light reflex?
pass from the EW nucleus via CN III then its inferior division to synapse in the ciliary ganglion
what are the 4th neurones in the pupillary light reflex?
course in the short ciliary nerves to the sphincter pupillae muscles
what is the ciliary body?
smooth muscle which acts like a sphincter around the circumference of the lens
muscular and vascular
what does the ciliary body/muscle do?
relaxes in far vision
- ligament tightens and lens flattens to focus on an object in the distance
- no parasympathetics
contracts in near vision
- ligament relaxes and lens becomes spherical to focus on near objects
- parasympathetic
what are the 3 components of the accommodation reflex?
bilateral pupillary constriction (CN III)
bilateral convergence - medial rotation of both eyes (AKA going cross eyed to look at something on nose etc) (CN III)
bilateral relaxation of the lens
what are the 3 types of tears?
basal tears
reflex tears
emotional tears
what are basal tears?
important in corneal health
clean/nourish and hydrate the avascular cornea
contain lysozyme which hydrolyses bacterial cell walls
what are reflex tears?
extra tears in response to mechanical or chemical stimulation
afferent limb = CN V1 from conjunctiva/cornea
efferent limb = parasympathetic axons originating from CN VII
what are emotional tears?
happy
sad
frightened
what does the superior division of CN III supply?
superior rectus
levator palpebrae superioris
what does the inferior division of CN III supply?
medial rectus
inferior rectus
inferior oblique
ciliary ganglion
what is the vestibulo-ocular reflex?
turns the eyes in the opposite direction to a head movement
stabilises gaze on an object during head movement
CNS connections between CN VIII and CN III, IV and VI
what is the oculocardiac reflex?
reflex bradycardia in response to tension on extraocular muscles or pressure on eye
CNS connections between CN V1 and CN X
