Cranial nerves Flashcards
where does the efferent system go from and to?
CNS to muscles / glands
where does the afferent nervous system go from and to
sensory nerve endings to CNS
what type are each of the cranial nerves?
III - oculomotor
IV - trochlear
V - trigeminal
VI - abducens
VII - facial
what are the muscles that are around the eyeball?
(check screenshots and be able to label the diagram)
what does cranial nerve IV do?
causes abduction to the lateral rectus muscle
what is the annulus of zinn
a tendonous ring that surrounds the optic foramen
what extraocular muscle is cranial nerve IV and what is it for
the superior oblique muscle of the contralateral orbit
-depression
-abduction
-intorsion
where is the origin of CN IV? what muscle is it’s final innervation?
the midbrain, superior oblique muscle
what are the two components to CN IIIs mechanism
somatic motor and visceral motor
what is the somatic motor component of CN III
supplies the SR MR IR and IO extraocular muscles of the eye and the levator palpebrae superiosis muscle of the upper eyelid
what is the visceral motor component of CN III
parasympathetic innervation of the constrictor pupillae and ciliary muscles part of the pupillary light reflex and accommodation reflex
what is different about the superior rectus muscle with cranial nerve III
its nucleus is on the contralateral side of the brain while the 3 other muscles that are innervated are ipsilateral
what four muscles does CN III innervate and what side of the brain?
ipsilateral inferior rectus muscle
ipsilateral inferior oblique muscle
ipsilateral medial rectus muscle
contralateral superior rectus muscle
how does CN III innervate the iris and cillary muscles parasympathetically
-innervates the constrictor pupillae to trigger pupillary light reflex
-innervates ciliary muscles to trigger accomodation reflexes
give the parasympathetic pathway to the iris sphincter
- preganglionic cells in the nucleus of edinger westphal
- axons exit through CN III
- synapse in ciliary ganglion
- iris constrictor via short ciliary nerves
what happens when the eye is exposed to light?
- CN III triggers pupillary light reflex
- light entering eye causes signals sent to pretectal nuclei in the midbrain via the optic nerve of CN II
- the pretectal nucleus of the midbrain in turn projects bilaterally to the edinger-westphal nucleus’
- preganglionic parasympathetic fibres from each half of the edinger westphal nucleus project to the ciliary ganglion of the ipsilateral orbit
- post ganglionic parasympathetic fibres exit the ciliary ganglion to innervate the constrictor pupillae muscle of the ipsilateral eye
why can people who are completely blind retain a pupillary light reflex?
as in humans, ipRGCs account for only ~0.2% of all RGCs
give the sympathetic pathway to the iris dilator
hypothalamus
preganglionic cells in spinal cord
superior cervical ganglion
iris dilator
what three muscles make up the accommodation reflex and what happens to them?
-ciliary muscle increases in curvature of the lens and hence increases the refractive power of the lens
-iris sphincter causes pupil to constrict to help sharpen the image on the retina
-medial rectus causes the eyes to converge so they can fixate on the target object
what eye movement do each of the following cause:
-adduction
-abduction
-depression
-elevation
-intorsion
-extorsion
-dextrocycloduction
-levocycloduction
-nasal rotation
-temporal rotation
-downward rotation
-upward rotation
-upper corneal pole rotates inwards
-upper corneal pole rotates outwards
-upper corneal pole rotates rightward
-upper corneal pole rotates leftward
name each of the eye muscles, their origins and their insertions
-medial rectus: common ring tendon: anterior globe
-lateral rectus: common ring tendon and greater wing of sphenoid: anterior globe
-superior rectus: common ring tendon and optic nerve sheath: superior anterior globe
-inferior rectus: common ring tendon: inferior anterior glove
-superior oblique anatomic: lesser wing of sphenoid: superior posterior lateral globe
-inferior oblique: medial maxillary bone: posterior lateral globe
where in the brain is the origin of CN VI?
pons
whats the final innervation of CN VI
the lateral rectus muscle
where is the origin of the cranial nerve III
the midbrain
for the medial rectus
what’s its primary (2ndary and tertiary if they have it) action and what CN is it’s innervation?
adduction and inferior III
for the lateral rectus,
what’s its primary (2ndary and tertiary if they have it) action and what CN is it’s innervation?
abduction and VI
for the superior rectus
what’s its primary (2ndary and tertiary if they have it) action and what CN is it’s innervation?
1.elevation
2. incyclotorsion
3. adduction
superior III
for the inferior rectus
what’s its primary (2ndary and tertiary if they have it) action and what CN is it’s innervation?
- depression
- excylotorsion
- adduction
inferior III
for superior oblique
what’s its primary (2ndary and tertiary if they have it) action and what CN is it’s innervation?
1.incyclotorsion
2.depression
3.abduction
IV
for inferior oblique muscle
what’s its primary (2ndary and tertiary if they have it) action and what CN is it’s innervation?
- excyclotorsion
2.elevation - abduction
inferior III
why is it when light is shined onto one eye, there is pupillary constriction in both eyes?
because of the bilateral projections from the eye to the pretectal nuclei and then from each pretectal nucleus to both endinger-westphal nuclei
Which cranial nerves innervate the iris constrictor?
-cranial nerve III = oculomotor
action of which muscles will be affected as a result of damage to the left oculomotor nucleus?
-left inferior rectus
-left inferior oblique
-left medial rectus
-right superior rectus
which cranial nerves provide an afferent pathway for sensory perception in the eye?
-cranial nerve II
-cranial nerve V
What are the different branches of cranial nerve VII
-branchial motor: innervates voluntary muscles in the face -sympathetic
-visceral motor: innervates lacrimal gland in eyes and nose - parasympathetic
-special sensory: taste
-general sensory: touch
What muscles lift the eyelid?
-levator muscle
-mullers muscle
-frontalis muscle
What muscle is used to close the eye
Orbiculares oculi muscle
Where is the frontalis muscle? What exactly does it do?
It starts at the top of the head and attaches to the eyebrow skin. It lifts the eyebrow and controls facial expression
What nervous system controls mullers muscle, how is it affected by being awake or being tired?
-sympathetic nerves
-when you’re awake it is contracted so lifts the eyelids
-when you’re tired or asleep, it sags letting the eyelid droop
Where is the orbicularis oculi?
Circles the eye, located just under the skin
What cranial nerve causes Bell’s palsy? What’s another name for it?
What are the four main features of Bell’s palsy?
Cranial nerve VII, lower motor neurone lesion (LMN)
-ipsilateral upper and lower facial asymmetry
-eyebrow droop
-uncontrolled tearing
-loss of the efferent limb of the conjunctival reflex so cannot close the eye
What’s the origin of CNVII?
Pons
What’s the function for CNVII to innervate the sphenopalatine ganglion?
Secretomotor to lacrimal glands for lacrimation via parasympathetic pathway
What does the ganglion of cranial nerve V (trigeminal innervate)?
Cornea and the conjunctiva
Where do nerves enter the cornea?
They enter through the edges via the limbus and then travel towards the centre branching off towards the epithelium
Where in the cornea is the nerve ending density the highest?
In the central 5mm of corneal surface
Give a feature of neurones in the cornea
They are unmyelinated
Give the three nerve networks in the cornea
-plexus in the epithelium (very dense)
-subepithelial plexus under bowman’s layer in the anterior stroma
-plexus in the middle of the stroma
What parts of the cornea are not really innervated
Posterior stroma and endothelium
What are c fibres in the cornea sensitive to? How are they arranged
Temperature specifically cold, parallel to the surface
What are the A delta fibres in the cornea sensitive to and how are they arranged
Touch, vertically within the epithelium
What is the pathway for the tearing reflex?
- Cornea is stimulated
- Sensory axons in CN V
- Trigeminal ganglion
- Sensory nuclei of CN V in pons
- Thalamus
- Superior salivatory nucleus in pons
- Axons project out through CN VII
- Pterygooalatine ganglion
- Lacrimal nerve
- Lacrimal gland
Axons on the temporal side of the retina go to which side of the brain?
The ipsilateral side
Axons on the nasal part of the retina go to which side of the brain?
The contra lateral side
What is the pathway for CNII (optic nerve) from the retina to the striate cortex?
- Retinas
- Optic nerves
- Optic chiasmata
- Optic tracks
- Lateral geniculate nuclei
- Neurones carry info via Optic radiations
- Striate cortex
What does mapping of the visual pathway allow for?
Visual prosthesis
What does damage to the optic nerve cause?
Ipsilateral blindness
What does damage to the lateral aspect of the optic chiasm cause?
Ipsilateral temporal hemianopia
What does damage to the medial aspect of the optic chiasm cause? What could it be caused by?
Bilateral hemianopia, could be caused by a tumour in the pituitary gland
In terms of optic radiation, why can damage only normally occur to a portion of the geniculocalcarine tracts?
Because fibres if the optic radiation are much more spread out than those of the optic tract
What could damage to the fibres of meyers loop and/ or damage to the temporal love portion of the optic radiation cause?
Loss of input from the inferior half (which would be the superior visual field) of both contra lateral hemiretinas
What could damage to the fibres of the parietal lobe portion of the geniculocalcarine tract result in?
A loss of input from the superior half (which would be the inferior visual field) of both contra lateral hemiretinas
what is a consequence on vision of the damage to the left optic tract?
loss of right visual field in the right eye only
which are the functions of the opthalmic division of the trigeminal nerve?
-sensory innervation of the conjunctiva
-sensory innervation of the cornea
-sensory innervation of the choroid
which sheaths surround the axons of the retinal ganglion cells in the optic nerve or the whole optic nerve?
-myelin sheath
-pia matter
-dura matter
-arachnoid matter
which cranial nerves play a sensory function in the eye and adnexa?
-II
-V
which muscles of the eyelid are innervated by cranial nerve VII?
-frontalis muscle
-orbicularis oculi
