Sense Organs Flashcards
Which cranial nerve supplies the ears?
Vestibulocochler nerve CN8
What are the 3 parts of the ear?
Outer
Middle
Inner
Which part of the ear connects to the nasopharynx and how?
Middle ear via the Eustachian tube
Name the three parts of the outer ear
Auricle / pinna
External auditory canal
Tympanic membrane (ear drum)
What is the auricle / pinnacle made from and what does it do?
Flap of elastic cartilage covered by skin that traps and directs sound waves
What is the tympanic membrane?
Semi-transparent partition between external auditory canal and middle ear
What does the tympanic membrane do?
Converts sound waves into mechanical vibration
What is the middle ear
Small air-filled cavity in the temporal bone
What does stapes attach to?
It attaches to the ‘oval window’ which connects to the cochlea
What is the name of the small muscle in the middle ear and what does it do?
Stapedius
Dampens large vibrations and is inner ages by the facility nerve
What is another name for the inner ear?
Labyrinth
What are the names of the two parts of the inner ear?
Outer bony labyrinth
Inner membranous labyrinth
3 parts of the bony labyrinth and their functions
3 semi-circular canals & vestibule - receptors for balance
Cochlea - heading
What fluids are found in the labyrinth
Perilymph & endolymph
Where is the cochlea and describe its shape
Anterior to the vestibule
Spiralled hollow chamber
What is in the cochlea?
Epithelial cells line with hair cells, topped with 40-80 cilia each called stereocilia
What are stereocilia?
Receptors for hearing that extend into the endolymph
How does hearing in the inner ear work?
Fluid movement (vibration) causes stereocilia movement which initiated and electrical impulse
What does the vestibulocochlear nerve do?
Cranial nerve XIII provides sensory info for hearing and balance
Describe the structure of the vestibulocochlear nerve
2 parts - vestibular fibres and cochlear fibres
Vestibular fibres have nerve branches that synapse with receptors for balance
Cochlear nerve provides hearing
Where in the brain does the vestibulocochlear nerve connect to?
Brainstorm
What are the 4 steps of sound sensation?
Sound wave
Mechanical vibration
Fluid waves
Nerve impulse
Stages of how sound travels (sound physiology)
- The pinna concentrates the waves and directs them along the auditory canal
- Vibrations transmitted though the middle ear by the 4 auditory ossicles
- Stapes rocks the oval window sending fluid waves in the cochlear perilymph
- Pressure waves transmitted to cochlea causing round window to bulge
- Pressure wave into endolymph
- Vibration of hair cells
- Bending stereocilia hair cells generates action potential
- Nerve impulse along vestibulocochlear
- Vestibulocochler impulse to cerebrum
What is pitch and how is it measured?
Frequency of sound waves Hz (hertz)
What is volume and how is it measured?
Amplitude of sound waves (dB) decibels
Prolonged exposure to what sound level causing hearing loss
90dB
What is white noise?
Background noise the brain ignores
Can be used to mask other sounds
Where is the Eustachian tube?
Connects nasopharynx to the middle ear
What are the roles of the Eustachian tube?
Equalise pressure between middle ear and atmosphere
Drain mucus
Why are middle ear infections more common in children?
Eustachian tube is more horizontal in children
Which parts of the inner ear aid balance by providing info about the head position?
Semi-circular canal and vestibules
How is info about head movement relayed for balance
Dense layer of calcium carbonate extends over and rests on the stereocilia called the otolithic memebrane
What is the otolithic memebrane?
Dense layer of calcium carbonate crystals
What causes movement in the perilymph and endolymph?
Change in head position
Bend hair cells and stimulate sensory nerve endings
Which part of the brain makes postural adjustments to maintain balance?
Cerebellum
What feeds back to the cerebellum to make postural adjustments
Vestibular - ear
Visual
Proprioceptors - skeletal muscles
Which nerve supplies the eye
Optic nerve - cranial nerve II
What are the 3 layers of the eyeball?
Outer - sclera
Middle - uvea
Inner - retina
What is the coloured portion of the eye called and what does it do?
Iris. Controls the amount of light reaching the retina by adjusting the pupil size
What is behind the pupil and why does it do
Lens - further focused light along the cornea
5 eye accessory structures
Eyebrows
Eyelids / lashes
Conjunctive
Lacrimal apparatus - produces tears
Blinking
What do tears do
Protect the eye from infection and lubricate movements of the eye
Which cranial nerve controls tears
Trigeminal nerve - CNV
What do tears contain
IgA and lysozymes
Which gland produces tears
Lacrimal gland
3 steps to achieve clear vision
- refraction of light rays
- accomodation
- changing size of pupils
What is refraction
Bending light rays
The cornea and lens refract light rays helping to focus the image on the retina
What distance do objects need to be refracted from?
Closer than 6m
What is accommodation
As lens curvature becomes greater its focusing power increases
What happens to the lens when an object is close and what is this called
Ciliary muscle contracts - lens becomes more convex - greater refraction\
Called ‘accommodation’
What happens to the lens when an object is far away and what is this called
Ciliary muscle relaxes - flattens the less - less refraction
Called ‘accommodation’
What does the sympathetic nervous system do to pupil size
Dilates the pupil
What does the parasympathetic nervous system do to pupil size
Constricts the pupil
What is eyeball convergence
MEdial movement of two eyeballs so they are both directed towards the same object
What happens if convergence is not complete
Double vision - diplopia
What is binocular vision?
Both eyes focus on one object which allows for perception of depth and 3D nature
What is the part of the brain where images cross over
Optic chiasma
Why is tunnel vision more common in pituitary tumours
As the optic chiasma sits next to the pituitary gland
Where is the retina and what does it do?
Inner layer of the line
Beginning of the visual pathway
What’s special about viewing the retina
It’s the only place where a nerve can be viewed
What is the optic disc
Where the optic nerve exits the eyeball and causes a blind spot
It doesn’t contain any rod or cone cells
2 layers of the retina
Pigmented layer
Photoreceptors
2 types of photoreceptors
Rod cells and cone cells
Difference between rod cells and cone cells
Rod cells - 120mil
See in dim light, no colour
Cone cells - 6 mil
Three types -blue, red and green
Cones regenerate quickly, rods take longer
What is the macula lutea
Yellow spot at the centre of the retina
What is the favea centralis
Small depression in the macula lutea that has only cone cells
Area of highest visual acuity
What are photo-pigments and what are they derived from
Transmembrane proteins
Vitamin A
Where is the most vitamin A stored
In the pigmented layer of the retina
What is vitamin A derived from?
Retinoids
3 types of retionoids
Retinol
Retinal
Retinoic acid
What happens to vitamin A in the retina
Vitamin A in the form of retinal blinds to a protein called opsin to produce photopigments
What are carotenoids
Precursors to vitamin A
How many smell receptors are there and what are they contains in?
10-100 million
olfactory epithelium
3 parts of the olfactory epithelium
- olfactory receptors - neurons attached to olfactory hairs
- supporting cells - physical support
- basal cells - stems cells that produce olfactory receptors
How is smell processed
Chemical sense
Olfactory glands produce mucus
Secretion helps dissolve the odorant
Which nerve is involved in smell
Olfactory nerve - CN1
What is the connection between smell and emotion
Some of the axons in the olfactory tract project into the limbic system
When it comes to smell what does adaptation mean
Decreased sensitivity to odours is rapid
Prevents us smelling bad odours
What is another name for taste
Gustation
Which cranial nerve is connected to the tongue
Hypoglossal nerve CNXII
What do taste buds contain x 3
Gustatory receptor cells - detect taste
Basel cells - stem cells
Supporting cells
4 nerves invloved in taste
Facial nerve - anterior 2/3 tongue
Glassopharyngeal nerve - taste and sensation
Trigemial nerve - tongue
Vagud nerve - throat and epiglottis
