Sense Organs Flashcards
What is the vestibulocochlear nerve
Main Nerve supply in the inner ear - 8th cranial nerve
Refers to the two main bones inner ear
Vestibule = involved in balance
Cochlear = involved with hearing
Contains vestibular fibre nerve branches
& cochlear fibres
Nerve is located within the brainstem (space between pons / medulla oblongata)
3 sections of the ear
- Outer
- Middle
- Inner
3 main bones in the middle ear
Smallest in the body
Have tiny symovial joints (which sometimes can degenerate over time)
Malleus (hammer)
Incus (anvil)
Stapes (stirrup) - smallest
() = what they look like
What is the eustachian tube
Connects the middle ear to the nasopharynx
Helps equalise pressure in middle ear
Aka ‘pharyngotympanic’ tube
3 main parts of the outer ear
- Auricle/Pinna
- External auditory canal
- Tympanic membrane (eardrum)
What is the pinna
Aka auricle
Flap of elastic cartilage, visibile part of the ear on side of head
Ridges in the skin helps trap soundwaves & directs them into the auditory canal
What is the tympanic membrane
Ear drum
Thin, semi-transparent partition between external auditory canal & middle ear. Lined with simple cuboidal epithelium, elastic & collagen fibres
Transmits sound from outer ear to the auditory ossicles.
Converts sound waves into mechanical vibration
What is the middle ear
A small air filled cavity in the temporl bor containing 3 main bones
What is the stapedius muscle
Tiny muscle that connects to the stapes to dampen large vibrations & prevent excessive movement
(Supplied/innovated by facial nerve e.g sounds in bells palsey)
Role of the middle ear
3 bones transmit sound in the form of vibration from the tympanic membrane to the oval window which connects to cochlea
What connects the middle ear to inner
Oval window (connected to stapes)
What makes up the inner ear labyrinth
Consists of outer bony labyrinth that encloses inner membranous labyrinth
Contains
3 semicircular canals & vestibule (responsible for balance)
Cochlea (hearing)
What fluid does the labyrinth contain
Perilymph & endolymph
What are stereocilia
Microscopic hair cells in epithelial tissue that give information about sound
Receptors for hearing that extend into the endolymph
(Sensory cells are topped with 40-80 cilia each)
How does the cochlea interpret sound
Waves of fluid move the stereocilia which creates an electrical impulse that sends information into the cochlea nerve
Pitch of soundwaves measured in
Hertz (Hz)
Higher frequency = higher pitch
Volume of sound measured in
Decibels (dB)
Decibel scale
Near total silence = 0dB
10x more = 10dB
100x more = 20dB
1000x more = 30dB
85dB or more prolonged = damage
Around 140 = instant pain
What is white noise
A constant noise that contains all different frequencies of sound (mix of different sound waves)
Background noise the brain ignores
Can be used to mask other sounds (privacy enhancers, sleep aids, tinnitus masking)
White noise with headphones can aid concentration
Role of the esutachian tube
Closed tube but can open for air to equalise pressure between middle ear & atmosphere ‘ear popping’
Also drains mucous & common route for infection
Yawning & swallowing contracts the neck muscles opening the tube
Essential air can escape middle ear otherwise damage would occur with pressure changes
Why are middle ear infections more common inchildren
The eustachian tube is more horizontal & shorter, less distance for virus & bacteria
As age gets longer & more vertical
Which structures provide info on head position aka balance
Semi-circular canals & vestibule
Plus a dense layer of calcium carbonate crystals aka ‘otolithic membrane’
Role of the otolithic membrane
Dense layer of calcium carbonate crystals that extend over & rest on the stereocilia
Any change in head position causes movement in the perilymph & endolymph which causes the membrane to bend hair cells & stimulate sensory nerve endings > action potential is then transmitted to the cerebellum (via CN VIII)
What can cause vertigo
Where calcium carbonate crystals break off from the membrane and land amongst the stereocilia causing nerve signals to be overstimulated»_space; feeling of movement when not
How is balance in the cerebellum regulated
Input from:
- vestibular (from inner ear)
- visual feedback (from eyes)
- proprioceptors in skeletal muscles, joints & surrounding ligaments (dorsal columns heavily myelinated - info travels from feet)
Balance/cerebellar functioning test
- nose to finger test
- clapping hand test
- ataxia (wide leg stance)
What cranial nerve is the eye supplied by
Cranial nerve 2
Optic
Role of the iris
Coloured part of the eye, controls amount of light reaching the retina by adjusting pupil size
Role of the lens
Located behind the pupil & further focuses light (along with the cornea - both bend light rays)
What is the vitreous humour
Area of fluid behind the lens that helps lubricate & keep eye open
Eyebrow function
Prevent sweat/other material from entering eye
Function of eyelashes/eyelids
Help to spread secretions over eye & protect
Conjunctiva function
Thin transparent mucous membrane of columnar epithelial cells lining the internal eyelids & anterior eyeball - protects cornea
Eyelid margins secrete oily material to delay tear evaporation
Lacrimal apparatus function
Tearduct - trigeminal nerve (CN V) controls
Tears protect eye from infection (contain IgA & lysozymes) & lubricate & have an emotional function
What is light
Part of electromagnetic spectrum
Wavelengths are 400-700nanometers (nm) & exhibit colours depending on their length
White light = combination of all
How is light focused onto the retina
- refraction of the light rays
(Images focused on the retina are inverted & left-right reversed too. Brain learns to coordinate this) - accommodation of the eyes
- changes lens size & pupil size (contraction & relaxation of iris)
What is refraction
Describes the bending of light rays
Occurs when light moves from one substance to another which have a different density
What is ‘accomodation’
Changing the diameter of the lens
What perception needs greater refraction
Close percpetion - tires the eyes
Ciliary muscle contracts, reducing suspensory ligament tension & lens becomes more convex
What perception needs lesser refraction
Distant perception
Ciliary muscle relaxes, increasing tension on suspensory ligaments & lens gets flatter
What are the circular muscles of the iris
Smooth muscle that constricts the pupil
Parasympathetic stimulates these fibres
What are the radial muscle fibres of the iris
Smooth muscle that dilates the pupil
Sympathetic stimulates the fibres contraction
What is eyeball convergence
Medial movement of two eyeballs so that both are directed towards the object
Extra-ocular muscles move the eyes in coordination under autonomic control
Closer the object, greater the eye rotation (cross-eyes eventually)
What is diplopia
Double vision caused by incomplete convergence of the eyeballs (2 images sent to brain)
What is the optic chiasma & where is it located
Where the optic nerve switches sides/crosses over in the brain
Is located next to the pituitary gland - hence tumours can cause ‘tunnel vision’
What is the retina
Inner layer of the eye, lining 3/4 of posterior of the eyeball
Beginning of visual pathway
What is used to view optic nerve & blood vessels
Ophthalmoscope
Can identify pathologies/nerve damage/brain tumour
Eg MS, diabetes
What is the optic disc
Location where the optic nerve exits the eyeball & blood vessels enter/exit
‘Blind spot’ (no cone or rod cells)
What 2 cells are found in the retina
Rod cells (120 million)
Cone cells (60 million)
What are rod cells
Allow us to see in dim light but dont provide colour
Provide black, white & greyscale
What are cone cells
Produce colour vision through combinations
3 types:
Blue, red, green
What is the macula lutea
Yellowish spot at exact centre of retina
With fovea in the centre
What is the fovea centralis
Small depression in centre of the macula lutea that contains only cone cells
Is the area of highest visual activity
What are photopigments
Transmembrane proteins within the discs of rod and cone cells
When light hits the photopigment it changes shape initiating an action potential
Once activated, a photopigment must then be regenerated/restored
What vitamin are photopigments derived from
Vitamin A in the form of retinal which binds to protein ‘opsin’
Pigmented layer of the retina stores a large quanitity of vitamin A which contributes to the regeneration of rod cells
Dietary forms of vitamin A
Preformed = animal origin eg liver, egg yolk (excess can be toxic)
Precursors (metabolised to retinal in the intestines aka regulated absorption) = carotenoids (also powerful antioxidants) eg carrots, sweet potato, squash, mango, leafy greens
Light adaptation
Emerging from dark to light, eyes adjust quite quickly
Adapts in seconds by decreasing sensitivity
Cones must regenerate photopigments, this can happen as quick as within first 8 minutes
Dark adaptation
Moving from light to dark sensitivity takes eyes longer to adjust, increasing slowly
Rods must regenerate photopigments which takes much longer than cones
What is the olfactory epithelium
Nose contains over 10-100 million receptors for olfaction within a tiny area (5cm2)
What is in the olfactory epithelium
- Olfactory receptors: neurons attached to cilia. Respond to chemical stimulus of odorants by producing an action potential (up CN 1)
- Supporting cells: provide physical support, nourishment & help detoxify chemicals
& olfactory glands that secrete mucous to trap odorants - Basal cells: stem cells that continually divide to produce new receptors
How long do olfactory recptors live
Around 1 month
What nerve involved in smell
CN 1
Olfactory nerve
How do olfactory receptors extend to cranial nerve
Nerve axons extend Through the cribriform plate of the ethmoid bone which then extends into the temporal lobe of the brain
Some axons project into the limbic system (emotion)
Olfactory adaptation
Has a low threshold and only a few molecules need to be present to detect smell
Decreased sensitivity to odours occurs rapidly - adapt by 50% in first second - odours can seem 80% less powerful after a few minutes of exposure
Aim of adaptation is to protect from danger if harmful scent
Cells involved in gustation
Chemicals are dissolved in saliva which stimulates chemoreceptors
Formed of 8 muscles controlled by CN 12 - hypoglossal (purely motor)
- Gustatory receptor cells
- Basal cells
- Supporting cells
Lifespan of gustatory receptor cells
Live around 10 days
How many taste buds in an adult
10,00 taste buds in adult, most on tongue but some on soft palate, pharynx & epiglottis
types of tongue papillae
- Circumvallate papillae - largest, V-shaped found at back of tongue
- Fungiform - mushroom shaped, present all over tongue, contain about 5 taste buds each
- Foliate papillae - located in small trenches at lateral margins of tongue, most degenerate in childhood (used for breastfeeding/process of)
- Filiform papillae - tactile receptors help tongue move food/feel textures
5 tastes
Sour, sweet, salty, bitter, umami
Taste impaired when dry mouth
Sense of taste triggers salivation & gastric juices
Responsiveness to taste is present in all areas of tongue
Area of brain taste information goes
Gustatory nucleus in the medulla oblongata & some into the limbic system
Nerves involving taste
Facial nerve (CN 7)
Glossopharyngeal nerve (CN 9)
Nerves involving tongue sensation/movement
Trigeminal nerve
Glossopharyngeal nerve
Vagus nerve
