week 12 - special senses Flashcards
structural components of the eye
sclera pupil iris cornea optic nerve
structure of sclera
White of the eye, fibrous and elastic tissue, outer layer of eye - allows for the contrast of the eye to determine where a person/animal is looking
structure of the pupil
middle of the iris
wider in dark
smaller in light
structure of iris
smooth muscle structure which controls the diameter of the pupil via two muscles - sphincter pupillae and dilator pupillae
structure of cornea
avascular
common for use in transplant as it cannot reject the tissue due to blood supply as it does not have one
optic nerve structure
appears as a solid white structure roughly in the middle of the retina
surrounded by the meningeal layers of the brain, any pressure increases intracranially (eg bleed, tumour or other space occupying lesion) will be transmitted along the nerve and causes bulging of the optic disc - This is called papilloedema and requires investigation as to the cause
what is keratoconus
thinning of the cornea resulting in a coning shape and can cause blurring and double vision of the eyes
Surgery may have to be done in more severe cases of a corneal transplant
what is aqueous humour
produced in anterior and posterior chambers of the eye from the ciliary bodies
maintains the pressure inside the eye, provides nutrients to eye and protects the eye
what is vitreous humour
a gel which occupies the space between the lens anteriorly and the retina posteriorly
mainly contains phagocytes to remove cell debris and is mainly water with no blood vessels
describe the retina
the light sensitive layer of tissue of the eye and where the rods and cones are for black and white and colour vision respectively
pathway of nerve fibres in eye
- Visual input comes through pupil -> vitreous humour -> retina -> optic nerves -> optic tract -> optic chiasm -> optic tract -> optic radiation -> occipital lobe
where are tears proudced
lacrimal gland
function of tears
lubricates movement
removes debris - debris moves from lateral to medial direction into nose
why does your nose run when you cry
nasolacrimal duct (in nasolacrimal canal) takes tears from lacrimal gland to nasal cavity
7 bones of the orbit
frontal sphenoid zygomatic palatine ethmoid lacrimal maxilla
where are the paranasal sinuses
maxillary - under eyes
frontal - forehead
ethmoid - posterior to nose
sphenoid - posterior to nose
function of paranasal sinuses
reduces weight of skull
allows circulation of mucous
contributes to resonance of sounds
which cranial nerves control eye movement
III
IV
VI
7 extraocular muscles and their movements
levator palpebrae superioris - keeping upper eyelid open
Superior rectus – elevation of eyeball (also adduction of eyeball and medial rotation)
Inferior rectus – depression of eyeball (adduction and lateral rotation)
Medial rectus – Adducts the eyeball
Lateral rectus – Abducts the eyeball
Superior oblique – depression of eyeball, abduction and medial rotation
Inferior oblique – Elevation, abduction and lateral rotation of the eyeball
which eye nerves supply which muscles
Trochlear nerve only supplies superior oblique
Oculomotor nerve – inferior oblique, superior rectus, medial rectus, inferior rectus
Abducent nerve – lateral rectus
how structure of nose relates to its function
incoming air is warmed, humidified, filtered nose does this best due to: rich, superficial blood supply, mucous provides moisture mucous and hairs trap particles
describe the location of the cribriform plate
The olfactory bulb, part of the brain, lies on the superior surface of the cribriform plate, above the nasal cavity
Branches of the olfactory nerve run through the cribriform plate to provide special sensory innervation to the nose
conchae in the nasal cavity
increase surface area
increase chance of olfactory exposure
innervation to tongue
CN IX - taste and sensation from posterior 1/3
CN XII - motor control of most tongue muscles
lingual nerve - carries axons from CN V and VII for taste and sensation in anterior 2/3
describe the surfaces in the mouth
buccal surface - side of the mouth where the surface is towards the cheeks as a surface of the teeth
lingual surface - faces the tongue as a surface of tongue
floor of mouth - mylohyoid muscle and overlying stratified squamous epithelium
epiglottis
elastic cartilage which helps close over the trachea during swallowing
describe the ossicles in ear
malleus - attached to tympanic membrane
incus
stapes
they transmit vibrations through middle ear
what is the oval/vestibular window
opening into the vestibule of inner ear
closed by base of stapes
what is the cochlear/round window
opening into the cochlear portion of inner ear
tympanic cavity contains…
tympanic membrane
vestibular/oval window
cochlear/round window
what is the helicotrema
the location where the tympanic duct and the vestibular duct merge, at the apex of the cochlea
what is Reissner’s membrane
separates the vestibular duct (scala vestibuli) from the cochlear duct (scala media)
function of cochlea
sound amplification
conversion from vibration to electrical signal
signal transmitted via cochlear part of CN VII
function of semicircular canals
balance
vestibular part of CN VIII
CN in nose
CN I
CN in ears
CN VIII
CN in eyes
CN II for vision
CN III IV VI for eye movements
what is sound
changes in pressure over time - spreads out as a wave of pressure from the source
Sound will dissipate through any medium as long as the particles in that medium can vibrate
high pitch
high frequency low wavelength
intensity/loudness
amount of energy/strength of vibrations - height of wave
range of hearing for a young human adult
20-20,0000 Hz
inner ear parts
cochlea and vestibule
middle ear parts
tympanic membrane
ossicles
eustachian tube
outer ear parts
pinna - amplifies and filters incoming sounds
ear canal - has hairs and wax on outer third
mechanisms that amplify sound in middle ear
difference in size between tympanic membrane and oval window
lever action - ossicles act as little levers adding a small amount of amplification
why does the middle ear amplify sound
transmission of sound from air to fluid-filled inner ear is inefficient due to impedance mismatch
branchial arches in ear
First arch turns into mandible which gives rise to malleus and incus
Second arch gives rise to stapes
describe the protective muscles in the middle ear
stapedius reflex and tensor tympani
they contract when ear is exposed to very loud sounds - there to stiffen the stapes so it does not vibrate and damage cochlea
structure of eustachian tube
connects nasopharynx to middle ear
lined with mucosa
function of eustachian tube
Keeps the air pressure in the middle ear space the same as the ambient atmospheric pressure - This is important to enable the tympanic membrane to vibrate
describe conductive hearing loss
sound does not reach cochlea - inner ear still working but sound does not reach there
caused by:
• Ear canal – wax, foreign body, congenital atresia
• Tympanic membrane – perforation
• Ossicles – congenital fusion, damage from infection
• Middle ear space – fluid instead of air
describe the vestibular apparatus
contains sensory structures for balance and head movements
utricle and saccule which are there for static position
semicircular canals are there for rotatory acceleration in three planes
describe the scala media
contains endolymph
where is perilymph
scala vestibuli and scala tympani
structure of organ of corti
has a basilar membrane which the the hair cells sit on
tectorial membrane covers the hair cells
one row of inner hair cells and 3 rows of outer hair cells
how does the organ of corti work
sound vibrations in scala vestibuli and scala tympani set up vibrations in basilar membrane
inner hair cells pick up vibrations on basilar membrane and send neural impulses along auditory nerve
outer hair cells are motile and change shape and stiffness when stimulated by the vibrations - acts as an amplifier to increase amount of vibration
as BM vibrates, stereocilia are bet against tectorial membrane - opens an ion channel - hair cell membrane is depolarised and NTs are released
describe hair cell depolarisation and hyperpolarisation
tallest cilium is the kinocilium on hair cell
kinocilium moves away from sterocilia causing depolarisation
kinocilium moves towards sterocilium causing hyperpolarisation
describe sensorineural hearing loss
the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve
loss of inner hair cells
no signal to brain
loss of hearing
loss of outer hair cells
basilar vibration is insufficiently amplified
some loss of hearing
loss of discrimination - can hear speech but not understand it
describe the travel of an impulse generated by a sound wave
first order neurons in spiral ganglion of the cochlea -> CN VIII -> synapse on juction of medulla and pons -> pons -> midbrain -> thalamus -> cortex -> temporal lobe
what is the auditory nerve
one of two parts of CN VIII
describe the anterior 2/3 of tongue
innervated by CN V and VII
tuberculum impar is the midline
describe the tongue muscles
genioglossus, hyoglossus and styloglossus
suspended from mandible, hyoid and styloid bones
muscles work with palatoglossus to move tongue
function of filiform papillae
rough surface of tongue for manipulation of food
where are taste buds
scattered across tongue in fungiform papillae
5 tastes and where they come from
sour (acid, H+) salty (Na+) sweet (glucose) bitter (coffee, beer, quinine, blue cheese, olives) savoury/umami (glutamate)
chorda tympani in tongue
branch of the facial nerve that originates from the taste buds in the front of the tongue, runs through the middle ear, and carries taste messages to the brain
pathway of nerve impulses caused by taste
taste runs along lingual nerve and leave in chorda tympani which runs through middle ear to join facial nerve - runs with facial nerve to brainstem
lingual nerve
branch of CN V (trigeminal)
turbinates on nose
projections from either side of the nose with thick vascular mucosa to warm and humidify the air
pathway of smell
odorant molecules in air dissolve in nasal mucus
odour receptor cells are then stimulated and axons pass through the little holes in cribiform plate up into olphactory bulb
describe olfactory receptors
exist on dendrites of receptor cells
each receptor responds to more than one odourant and each odourant stimulates more than one receptor
where does CN I project to
amygdala, hippocampus, parahippocampal gyrus
what is congenital anosmia
lifelong inability to smell
can be assoicated with kallmans syndrome
causes of anosmia
base of skull fracture covid 19 brain tumour early sign of Alzheimer’s, Parkinson’s, MS rhinosinusitis
