Week 8- Visual, Auditory and Vestibular Sensory Systems Flashcards
Describe the “travel” of sound
Longitudinal waves that move in a back-forth motion
What is high pressure?
Compression
What is low pressure?
Rarefaction
What is a period?
The time for a particle to move 1 cycle
What does frequency refer to and what is its units?
= 1/Period (seconds) and is measured in Hz
What is a wave length?
The distance particles travel
What constitutes a louder sound on a graph depicting sound frequency?
greater amounts of pressure between peaks
What is the normal human range of hearing?
20Hz to 20kHz
What is sound pressure level?
Conversion of pascals
What is a decibel equal to?
20*log10(X)
What dB range to humans hear over
120dB SPL range
Name the basic features of outer ear anatomy
- Pinna (auricle)
- External auditory meatus
- temporal bone
Name the basic features of the middle ear
- Tympanic membrane
- Ossicles (malleus, incus and stapes)
Name the basic features of the inner ear
- Cochlea
- Vestibular systems (semicircular canals and otoliths)
What are the components of the pinna?
Helix Antihelix Lobule Concha Tragus Antitragus Intertragical notch Triangular fossa Scapha Darwins tubercle (not everyone has one)
What is the pinna made up of?
Elastic cartilage covered by stratified squamous epithelium
- hair follicles
- sebaceous glands
- ceruminous glands (modified sweat glands)
How does the outer ear contribute to the generation of ear wax?
Via the ceruminous glands
Modified sweat glands
What is the function of the pinna?
- Funnels sound into the ear canal
- 2-fold increase (6dB) increase in pressure at typmanum
- PInna fold alter the characteristics of sound
What are pinna cues?
When the pinna folds deflect the sound to change the spectrum slightly
What are the spectral features of sound?
Interaural timing difference (ITD)
Interaural level difference (ILD)
Describe the physical features of the middle ear
- Temporal bone (aerated, mastoid)
- tympanic membrane (eardrum)
- ossicles (malleus, incus and stapes)
- Eustachian tube
describe the nerve distribution across the tympanic membrane
Does not have many nerve endings, most sensitive around the outer edges (very painful)
What is the name of the head of the malleus?
Umbo
How does the ear equalise air pressure?
Pulls open the eustatian tube when the levator and tensor palati pull the soft palate up during swallowing
What can occur in the petrous bone cavities of the middle ear?
Mucous filling cavity, causing the formation of infection
What are the functions of the middle ear?
- Ossicles transmit vibrations to inner ear
- Tympanum: stapes foot plate provides 3-fold gain (10dB)
- @ low-frequencies, middle-ear pressure acts on both windows, limiting gain
- Tensor tympani and stapedius muscles suppress middle ear gain
Total = 26dB gain
Describe the features of the inner ear
Cochlea
- Oval window (stapes footplate)
- round window (clear membrane)
- Bony Labyrinth (perilymph)
- Membranous labyrinth (endolymph)
Vestibular System
- Otoliths (Saccule and utricle)
- Semicircular canals (lateral, posterior, anterior)
Why is the cochlear in a spiral shape?
A long membrane needing to fit in a small space. Became spiralled throughout evolution and development
What fluid is found within the scala vestibuli and scala tympani?
Perilymph (high [Na+])
What components make up the bony labyrinth?
Scala vestibuli and scala tympani
What fluid is associated with the scala media?
Endolymph (high [K+])
What is the name given to the very apex of the cochlea, where the scala vestibuli and scala tympani join?
Helicotrema
Where does the organ of corti sit?
Basilar membrane
Describe the basilar membrane
trampoline like structure. transfers fluid pressure changes (waves) between SV and ST. Organ of Corti moves with the membrane
Describe Cochlear Tonotopy
- Stapes vibrations cause increased pressure in SV than ST, displacing the organ of Corti
- Fluid pressure wave generates OoC wave that travels along the partition towards the apex
What is the Travelling wave?
organ of corti wave generated by fluid pressure wave that travels towards the apex of the cochlear
Describe the mechanical properties of the basilar membrane
Varies along its length
Describe the difference between the base and apex of the cochlear
Base- narrow & stiff, has high-frequency resonance
Apex- broad and floppy, has a low-frequency resonance
How many rows of outer hair cells are there and what are their role?
3 rows of outer hair cells
Acts as the cochlear amplifier
How many rows of inner hair cells are there and what are their role?
1 row of inner hair cells
Transduction to action potentials- transmit the sensation of sound
What sits on the basilar membrane of the organ of Corti
supporting cells
Where is the techtorial membrane?
overhangs over the organ of Corti
Where is the Stria Vascularis and what does it do in the organ of Corti?
Located on the lateral wall
Actively pumps K+ into endolymph
has the highest metabolic rate of any tissue in the human body
Where are nerves located in the cochlea?
the cochlear nerve and the spiral ganglion are located in the Modiolus
Where do neurons synapse in the cochlea?
Neurons synapse with the basal surface of hair cells
What is a MET channel?
Mechano-Electrical Transduction Channel
What is found on the tops of the hair cells and how are they linked?
Stereocillia is found on top of hair cells. Tip links connect the two neighbouring cilia of each hair cell, from the tallest to the K+ channel on the shortest.
How do K+ channels open?
With the movement of the basilar membrane, causing the taller stereocilia to bend and mechanically pull open the channel. Being surrounded by endolymph means that K+ is readily moved into the hair cell, depolarising them.
What happens when OHCs depolarise?
OHCs contract when they depolarise. This leads to the pumping of the vibration, triggering the release of glutamate from IHCs onto the afferent neuron
Where does active amplification increase the vibration of the travelling wave?
At the tip of the travelling wave
Describe non-linear amplification
OHC amplification doesnt work well for loud sound
- Increases frequency sensitivity
- Increases dynamic range
What does loss of OHC gain result in?
Poor hearing and poor discrimination
Describe endocochelar potential (EP)
- Stria Vascularis pumps K+ into 150mM K+ fluid @90mV
- MET channels open, K+ flows into hair cells, down EC gradient
Describe the effect on hearing if stria is dysfunctional
The OHC gain doesn’t work, resulting in a 40dB hearing loss
- Most common form of hearing loss
- High frequency hearing loss
- Blood supply begins to drop off with age, resulting in less vibrations
Describe the segmentation of auditory processing
Cochlea
Cochlear Nucleus (brainstem; midbrain) - spectral and temporal coding
Superior Olivary Complex (MSO, LSO)
- ILF and ITD coding
Inferior Colliculus (midbrain) - Integration with other senses
Medial Geniculate Nucleus (thalamus)
- Attentional Filter
Auditory Cortex
- Perception and recognition
What are the basic functions of the vestibular system?
Integrating data storage system
- Eye
- Cortex cerebellum
- cortical awareness of body/head/motion
- eye movement
- control of posture
- control of motor skills
- joint position
List the components of motion measurement
Position Velocity Acceleration Jerk (vestibular neurons fire off at jerk) Rotation and translation gravity
What are the 3 directions of the semicircular canals?
Superior
Posterior
Horizontal
Left and right of each, resulting in 6 total
What is the ampulla of the semicircular canals?
The enlarged part of the semi.circ.canals
What are the cristae of the vestibular system?
Sensory epithelium- hair cells
What is the cupula?
gelatinous cap that overlies hair cells in the vestibular system
What is the vestibule?
perilymph space
What are the otoliths?
Saccule (saccular macula) –> cochlea
Utricle (utricular macula) –> semi. c.
What layer lays over the neuroepithelium?
Otoconial layer
- Crystals that are denser than water
- tugs on gelatinous mass when head is tilted
Describe the anatomy and function of the otoliths
- Hair bundles move with body
- otoconial layer lags behind
- Hair bundles (tip links and MET) face in a particular direction
- Responds to translation n all directions
- MET open= depolarisation= glutamate release
- No active amplification
Describe the difference in positions of the utricular and saccular maculas
Utricular: vertical
Saccular: horizontal
Both sensitive to movements in most linear directions (not so sensitive to rotations)
Describe the anatomy and function of the semicircular canals
- Left-right posterior and anterior canals align so that geometry allows for sensitivity in all head planes
- Hair cells rotate with head
- Endolymph lags, moving Cupula due to inertia
Describe the function of the vestibular ocular reflex
VOR keeps eyes focused forward during head rotation
when the head turns left, canal fluid doesnt as much
eyes rotate right due to excitation and inhibition
Describe the differences between the posterior and anterior cavities of the eye
PC: filled with vitreous humour (gel)
AC: filled with aqueous humour, produced by ciliary epithelium and reabsorbed by sclera venous sinus
Why is light required to be refracted in the eye?
Light entering the pupil is refracted to focus the image on the retina
How is refraction achieved (%)
Achieved by the cornea (75% and the lens (25%)
What does the amount of refraction in the eye depend on?
The amount of refraction that occurs depends on the distance of the object
Describe the process of accommodation in the refraction of light
- Ciliary muscles (oculomotor nerve)
- Ciliary processes
- Suspensory ligaments
- Lens stretched
What does the retina consist of?
- pigmented layer of melanin containing cells
- neural layer containing neurons
- retinal blood vessels
- optic nerve
What are the sublayers of the neural layer of the retina? (from where light is received first)
Ganglion cell layer
bipolar cell layer
photoreceptor layer (cones and rods)
What are photoreceptors?
- located in the deepest layer of the retina
- transduce light energy into a receptor potential
- contain photopigments that absorb light
Describe the workings of rods as photoreceptors
- Respond to low levels of light
- Decreased visual acuity
- sensitive to light but not so much features of light
- contain rhodopsin, forming when light levels decrease (slow process, hence why it takes a while to see clearly in the dark)
Describe the workings of cones as photoreceptors
- respond to high levels of light
- increased visual acuity
- 3 different cone types
- Blue, red and green absorbing the same colour of light
- we have colour vision due to different wavelengths of light activating different photopigments of different cone types
What is the central fovea?
only cones present allowing increased visual acuity
What is the optic disc?
Also known as the blind spot, does not have rods, nor cones present. Arteries and veins emerge from here
Describe the basics of how visual pathways work
- lens produces an inverted laterally reversed image (upside down, back to front)
- each eye has a right and left visual field
- Temporal side and nasal side
What is meant by the binocular field?
overlap occurs between what the left and right eyes see in their visual fields, forming the central binocular field.
Which visual field corresponds to what side of the brain?
LVF: right brain
RVF: left brain
Describe the end location of the visual pathway
Visual pathway ends in he visual cortex above and below calcarine sulci
- Lower VF= above
- Upper VF= below
- Central VF= posterior
- Peripheral VF= anterior
What is the effect of a lesion on the visual pathway?
Lesions in particular parts of the brain cause predictive visual field losses
What are the classifications of vision loss?
Hemianopia: loss of half a visual field
Bilateral: both eyes
Quadrantanopia: loss of 1/4 visual field
Homonymous: same visual field in both eyes
SLIDE 60
STREAMS OF VISUAL PROCESSING
What nucleus receives retinal and visual cortex inputs?
Edinger-Westphal nucleus
If light was shone in the left eye, what response would be expected?
- Contraction of left pupil (direct response)
- Contraction of right pupil (consensual response)
What occurs in the eyes when an object is closer
Edinger-Westphal adjusts ciliary muscle and medial rectus muscle to focus on the closer object
What fluid is contained in the anterior and posterior cavities of the eye?
Anterior: aqueous humour
Posterior: vitreous humour (gel)
Under what circumstances do the ciliary muscles contract?
High frequencies/amounts of light
What cranial nerve innervates the ciliary muscle?
Oculomotor nerve
Where is the optic chiasm located in relation to the hypothalamus?
Located in the forebrain, directly in front of the hypothalamus
Which parts of the visual fields are directed to the visual cortex above and below the calcarine sulcus in the occipital lobe?
Lower visual fields = above
upper visual fields= below
What is the difference in the ear lobe compared to the rest of the pinna? (think piercing)
Does not contain cartilage
What is the different innervations of the auricle?
Anterior= trigeminal (V) Posterior= Facial (VII)
What do the ceruminous glands of the subcutaneous tissue secrete?
Cerumen (ear wax)
What innervates the EAM?
Vagus (X)
State the order of the ossicles including their attachments (if applicable)
Malleus (tympanum), incus, stapes (oval window)
Name the location of receptors, gelatinous material and stimulus of the semicircular canals
Crista, cupula, rotation of the head
Name the location of receptors, gelatinous material and stimulus of the utricle/saccule
Macular, otalithic membrane and acceleration
