Anatomy + Physiology 2 Flashcards
Describe the sensory innervation of the face?
CN V1 (ophthalmic nerve)
- upper eyelid
- cornea
- conjunctiva
CN V2 (maxillary nerve)
- skin of lower eyelid
- skin over the maxilla
CN V3 (mandibular nerve)
- skin over mandible and TMJ
- except angle of mandible
Which nerve is responsible for the sensory (afferent) limb of the corneal blink reflex?
CN V1 (ophthalmic branch of trigeminal)
Which nerve is responsible for the motor (efferent) limb of the corneal blink reflex?
CN VII (facial) - eyelid part of orbicularis oculi
What is the function of the vestibulo-ocular reflex?
Turns the eyes in the opposite direction to a head movement
Stabilises gaze on an object during head movement
Which nerves are involved in the vestibulo-ocular reflex?
CNS connection between CNVIII + CNs III, IV + VI
What is the oculocardiac reflex?
Reflex bradycardia in response to tension on extra ocular muscles or pressure on eye
Which nerves are involved in the oculocardiac reflex?
CNS connections between CN V1 + CN X
Which structures of the eye have an autonomic nerve supply?
Smooth muscle of iris (pupil diameter)
Smooth muscle of ciliary body associated with lens (focussing)
Lacrimal glands
What is the affect of sympathetic supply to the eye?
Eyes open wider
Pupils increased in diameter (let more light in)
Focus on far objects
What is the affect of parasympathetic supply to the eye?
Pupils narrow (less light into eyes) Focus on near objects
How is a non-physiological constricted pupil described?
Miotic pupil (miosis)
Pathology affecting which nerve might cause a fixed-dilated (blown) pupil?
CNIII (oculomotor)
Which muscle fibres constrict the pupil?
Sphincter pupillae
How is a non-physiological enlarged pupil described?
Mydriatic pupil
Which muscle fibres dilate the pupil?
Dilator pupillae
Describe the afferent and efferent limbs of the pupillary light reflex
Afferent (special sensory) - ipsilateral CN II
CNS connections in midbrain
Efferent (motor) - bilateral CNs III
What is the difference between the direct light reflex and the consensual light reflex?
Direct - occurs in stimulated eye
Consensual - occurs in the other (non-stimulated) eye
What is the function of the suspensory ligament?
Connects the circumference of the lens and the ciliary body to facilitate the accommodation reflex
Describe the mechanism of accommodation for far vision?
Ciliary muscle relaxes (no parasympathetics)
Suspensory ligament tightens + lens flattens to focus on an object in the distance
Describe the mechanism of accommodation for near vision?
Ciliary muscle contracts (parasympathetic)
Ligament relaxes + lens becomes spherical to focus on near objects
What are you assessing when checking the lens accommodation reflex?
Response to ‘near’ - 3 components:
- bilateral pupillary constriction (parasympathetic constriction of sphincter pupillae)
- bilateral convergence of both eyes towards midline (medial rectus)
- bilateral relaxation of the lens (lens becomes spherical due to contraction of ciliary muscles)
–> All CN III
Why does a raised ICP cause papilloedema?
Optic nerve is covered by meninges so raised ICP will be transmitted along the subarachnoid space in the optic nerve sheath
–> compression of optic nerve (and central artery and vein of retina)
Why might CNIII be affected in raised ICP?
Susceptible to damage due to compression from tentorial herniation –> medial temporal lobe herniates through tentorial notch
What would be the effect of a damaged/compressed CN III?
Paralysis of 4 extra-ocular muscles + parasympathetic innervation of sphincter pupillae
How would CN III damage present clinically?
Loss/slowness of pupillary light reflex
Dilated pupil
Ptosis
Eye turned inferolaterally –> down and out
What would be the effect of CN IV damage/compression?
Paralysis of superior oblique –> inferior oblique unopposed
- eye cannot move inferomedially
- diplopia when looking down
What would be the effect of CN VI damage/compression?
Paralysis of lateral rectus –> eye cannot mover laterally in horizontal plane
- medial deviation of the eye
