The orbit, eye and ear Flashcards
what muscle does the trochlear nerve supply?
superior oblique
which number cranial nerve is the trochlear nerve?
CN IV
list the muscles involved in eye movement
lateral rectus, superior rectus, inferior rectus, medial rectus, superior oblique inferior oblique muscles
which nerve supplies the lateral rectus muscle?
CN VI - abducens nerve
which cranial nerve has three divisions (name and number)?
CN V - trigeminal nerve
what are the divisions of the trigeminal nerve?
- opthalmic nerve
- maxillary nerve
- mandibular nerve
what is CN II called?
optic nerve
which muscles does the oculomotor nerve (CN III) supply?
medial rectus
superior rectus
inferior rectus
inferior oblique
nasociliary branch is part of which Cranial nerve?
it is part of the ophthalmic division of the 5th Cranial nerve (CN V)
what nerve supplies the lateral rectus muscle?
abducent nerve (it is a motor nerve)
what do lesions to the sympathetic fibres cause?
pupil to not dilate, remaining small and constricted
What does compression to the parasympathtic neurones in the oculomotor nerve do?
pupil remains dilated!
compression ca occur due to swelling and oedema of the brain due to increased intracranial pressure.
what is the blood supply to the eye and orbit?
ophthalmic artery
what are the branches of the ophthalmic artery?
- anterior and posterior Ethmoidal arteries - supply the ethmoid air sinuses (medially)
- central artery of the retina - travels in the nerve to the retina.
contraction of the medial rectus muscles does what?
adducts the eye
contraction of the lateral rectus muscle does what?
abducts the eye
If you look to your left, which muscles are contracting?
in the left eye - lateral rectus is contracting
in the right eye - medial rectus muscle is contracting
when in the orbital axis (abduct) what do the superior and inferior recti muscle do?
these muscles only elevate and depress the abducted eye
when do the superior and inferior oblique muscles raise/lower the eye?
when the eye is adducted (to the midline)
what is the middle ear also known as?
the tympanic cavity
what forms the medial wall of the middle ear?
- the promontory which is an elevation in the wall produced by the cochlea (in the inner ear)
- the fenestra vestibuli (oval window) closed by the middle ear ossicle, the stapes.
- fenestra cochlea (round window) which is closed by a second tympanic membrane
what is the auditory tube also known as?
the pharyngotympanic tube
which cranial nerve is the mucous membrane of the auditory tube supplied by?
the IXth cranial nerve - glossopharyngeal nerve
What is the function of the auditory tube?
to equalise the pressure on either side of the tympanic membrane
what forms the lateral wall of the middle ear?
the tympanic membrane
what forms the roof of the middle ear (tympanic cavity)?
a thin part of the petrous temporal bone
directly above lies the temporal lobe of the brain
What forms the anterior wall of the middle ear?
formed by two canals/tubes:
- the auditory canal
- the tensor tympanic muscle
Describe the course of the tensor tympanic muscle?
lies above the auditory (pharyngotympanic) tube.
forms a tendon that inserts into the handle of the malleus (one of the ossicle bones)
What lies in the posterior wall of the middle ear (tympanic cavity)?
An opening known as the aditus that connects the epitympanic recess to the mastoid antrum
The stapedius muscle that inserts into the stapes (one of the ossicle bones)
What forms the floor of the middle ear (tympanic cavity)?
it is related to the jugular foramen and the internal jugulart artery!
describe the malleus?
It is one of the ossicles of the middle ear
It is shaped like a hammer with its head articulating via a saddle shaped synovial joint to the incus
The handle of the malleus articulates to the inner side of the tympanic membrane.
Describe the incus?
It is the middle ossicle of the middle ear.
It has a short process that attaches to the epitympanic recess
It has a long process that runs parralel to the handle of the malleus to then attach via a ball and socket synovial joint to the stape.
Describe the stape?
This fits into the oval window AKA fenestra vestibuli
The stapedius muscle tendon attaches to the neck of the stape.
DID YOU KNOW - the stapedius muscle is the smallest skeletal muscle in the body… WOWZA!
what is the difference between membranous and bony labyrinths?
The membranous labyrinth lies with the bony labyrinth.
The membranous labyrinth has semicircular DUCTS that lie within the semicircular CANALs of the bony labyrinth.
The bony labyrinth has the cochlear CANAL, which inside lies the cochlear DUCT
What are the divisions inside the cochlear?
these are:
- scala tympani
- canal of cochlear
- scala vistibuli
how do vibrations travel in the cochlear?
They are created by the movement of the footplate of the stape.
They then travel along the scala vestibuli, to the apex of the cochlear, where they pass through the HELICOTREMA into the scala tympani.
They travel down the scala tympani to the fenestra cochlea that is covered by the second tympanic membrane.
name the three semicircular canals in the inner ear?
Posterior, anterior and lateral semicircular canals
the anterior is often know as superior too
What is the ampulla in the inner ear?
There is an ampulla at one end of each semicircular canal, the ampulla contains the organs sensitive to body movement
What are the names of the two sacs in the membranous labyrinth?
They are the utricle (behind) and the saccule (in front)
Describe the layout of membranous labyrinth?
There are the semicircular DUCTS that like within the semicircular canals (bony labyrinth). These arise from the sac of endolymph called the utricle.
The utricle joins to another sac called the saccule, by forming a endolymphatic duct.
The saccule gives rise to the cochlear duct that travels within the cochlear canal.
What links the saccule to the cochlear duct?
The ductus reuniens
what are afferent nerve fibres?
carry impulses from the receptor to the central nervous system
What are efferent nerve fibres?
these carry impulses from the CNS to the muscle (or organ etc). they cause and EFfect!
What are the two branches of the vestibulocochlear nerve?
vestibular nerve
cochlear nerve
Which cranial nerve is the vestibulocochlear nerve?
8th cranial nerve (CN VIII)
Describe the organ of corti?
location: located on the basilar membrane in the cochlear DUCT.
structure:
formed of inner and outer stereocilia ‘hair’ cells. These form pillars that sweep towards each other and form a triangular shaped tunnel of corti.
The stereocilia on the outer hair cells are attached to a fibrogellatinous membrane called the TECTORIAL membrane. the inner hair cells are not attached to this!
