Anatomy Ear
Lateral wall: membranous wall - tympanic membrane
Describe the mechanisms of pitch and volume encoding
Pitch coding: area of basilar membrane distorted by wave at highest amplitude
Volume coding: degree & number of distortion of hair cells
What is the tallest cilia (on a hair cell) called
1 large kinocilium & stereocilia cluster embedded in cupular
How are different smells identified (generally)
Proteins: > 1000 types, encoded by different genes, found in different receptors. Different receptors are more selective to different odorants.
Smell: Unique pattern of activity over receptor population. Projected onto targeted glomeruli in olfactory bulb in odor map → CNS interprets
Where do primary afferent olfactory nerves terminate?
Lateral rostral solitary nucleus of medulla
What is the smallest skeletal muscle in the body and what does it do
Stapedius: supplied by CN VII; attached from temporal bone to neck of stapes. Function = contract with > amplitude sound to reduce ossicles movement. Tympanic/attenuation reflex: protective, prevents excessive oscillation
Define impedance matching in relation to hearing and the mechanisms through which it occurs.
Sound waves converted into fluid pressure waves. Ensuring that input is converted into suitable measurable output.
Impedance matching device: Tympanic membrane & ossicles. Tympanic membrane sound vibrations pressure increased by ossicles > 22x to overcome the inertia of inner ear fluid.
What are the movements/planes associated with each of semicircular canals
Anterior - lateral flexion; Posterior - flexion/extension; Lateral - rotation
Describe the structure and function of olfactory receptors
Olfactory Receptors: bipolar neurons with thin axon & single dendrite; Odorant bind to receptor. Olfactory rod: Short, thick dendrite with expanded end → 5-10 cilia project to surface. Axons: pierce cribriform plate of ethmoid bone, enter olfactory bulb. Cells: continually replaced, lifespan 1-2 months; produce receptor potentials. Trigger AP train; use GPCR transduction
Outline the nerves involved in taste sensation and what their innervate
Taste sensation:
CN VII: taste info from anterior ⅔
CN IX: taste info from posterior ⅓
Vagus X: taste info from epiglottis/throat taste buds
What are the nerves that traverse/supply the middle ear
Tympanic nerve = branch of CN IX, supply mucous membrane inner ear. Form tympanic plexus → lesser petrosal preganglionic PNS. Synapse in otic ganglion → parotid gland.
CN VII from internal acoustic meatus to the stylomastoid foramen protrudes into middle ear chorda tympani leaves CN VII, pieces posterior wall & exits through anterior ear
What are the 3 mechanism of hearing (HINT; Ossicular, Air ...)
Ossicular conduction: tympanic membrane movement displaces auditory ossicles. Stapes movement at oval window establish pressure wave in perilymph
Air conduction: via vibrations of secondary tympanic membrane of round window
Bone conduction: vibration transmission via skull bones to the fluid of inner ear
Describe what movements the utricle and saccule are sensitive to
Utricle: linear acceleration, sensitive to horizontal forces esp. head forward/backward
Saccule: sensitive to vertical forces, but also to movement in all directions
What are the different olfactory epithelial cells?
Supporting cell: columnar epithelial cells lined with mucosal microvilli; secretory granules
Basal cell: olfactory epithelium base; undifferentiated stem cell → form receptors - Undergo mitosis
Bowman’s cell: produce mucus - that dissolves odour molecules. Odorant molecules dissolve into mucus → electrical transduction. Bind to odorant receptors in olfactory sensory neurons on cilia
Olfactory receptor
What are the 3 major cell types in taste buds and what is their function
Taste buds & receptors: receptors within taste buds; receptors cells replaced every 10 days
Supporting cells: type 1, may sense Na+ through channels
Basal cells: undifferentiated stem sell - taste receptor precursors
Taste receptor cells: specialised epithelial chemoreceptors. Produce depolarising receptor potentials in response to tastant. Innervated by afferent nerves; type 3 presynaptic (sour) & type 2 receptor cells
Describe the structure of membranous labyrinths and the fluid they contain
Perilymph: fluid in scala vestibuli (superior) & scala tympani (inferior), similar to ECF. Continuous at end
Endolymph: fluid in scala media; ionic composition similar to ICF (> K+, < Na+). Sensory transduction within Organ of Corti
Structure: spiral shaped, 35mm long, 3 tubular canals. Reissner’s/vestibular membrane divides scala vestibuli & media. Basilar membrane divides scala media & tympani - base of Organ of Corti. Scala vestibuli ends at oval window; Scala tympani ends at round window
Describe the auditory transduction pathway
Auditory transduction:
Sound waves oscillate tympanic membrane → vibrate ear ossicles
Displace flood in cochlea → vibrate organ of Corti → bend hair cell cilia
Change K+ conductance → oscillating cochlear microphonic potential
Open voltage gated Ca2+ channels in presynaptic terminals of hair
Intermittent glutamate release → intermittent APs in afferent cochlear nerves
Describe the semicircular canal stimulation
Semicircular Canal Stimulation: detect change in velocity; dynamic equilibrium
Hair cells: 1 large kinocilium & stereocilia cluster embedded in cupular. Bend towards kinocilium → depolarization. Bend away from kinocilium → hyperpolarisation. Afferent nerves carry vestibular info to brain
Endolymph drag: via inertia, bends hair cells in opposite direction to head rotation. Continues rotating after motion stops, returns to rest after delay.
Describe the steps of olfactory transduction
Olfactory transduction: convert chemical signal into electrical signal
Odorant binds to cilia receptor proteins
Olfactory receptor proteins coupled to AC via Golf
AC catalyses ATP → cAMP ⇒ > cAMP gated Na+/Ca2+ channels open
> Ca2+ opens Ca2+ gated Cl- channels → receptor cell depolarises. > Ca2+ also complexes with calmodulin & bind channel → < cAMP affinity. Ca2+ also extruded through Ca2+/Na+ exchanger
Depolarise initial segment of olfactory nerve axon
Outline the 4 papillae and their function
Tongue: covered in projection called papillae → Multicellular protuberances with taste buds
Circumvallate: 9, contain 100-300 taste buds; at rare of tongue; circular
Fungiform: located in posterolateral trenches of tongue; 5 taste buds each
Foliate: posterolateral tongue trenches; taste buds degenerate early childhood
Filiform: cover entire tongue, tactile receptors, no taste buds
Taste buds: small pop. in pharynx, larynx, epiglottis, esophagus
What is the name of each of the walls of the middle ear
Roof: tegmental wall; petrous part of temporal bone, with epitympanic recess
Floor: jugular wall
Lateral wall: membranous wall - tympanic membrane
Medial wall: labyrinthine wall - lateral semicircular canal prominence facial nerve prominence, tympanic plexus on promontory (turn of cochlear)
Posterior wall: mastoid wall - bulging of lateral semicircular;
Anterior wall: carotid wall
Route of auditory information processing
Hair cells --> afferent cochlear nerves --> synapse in superior olivary complex --> inferior colliculus (topographic) --> thalamus MGN --> auditory cortex
Outline the role of the different groups of medulla vestibular nuclei
Medial/superior nuclei: receive input from semicircular canals. Project to nerves to extraocular muscles via medial longitudinal fasciculus
Lateral nuclei: receive input from utricles - project to spinal cord via lateral vestibulospinal tract - postural reflex
Inferior nuclei: utricles, saccules, semicircular canal input
Projections: brain stem & cerebellum via medial longitudinal fasciculus. Sensory cortex S1 area 5 → body orientation
Vestibular dysf(x): manifested by uncontrolled eye movement & nausea/vertigo
Describe the olfactory pathways
Olfractory receptors synapse with mitral cells at glomeruli. Inhibitory granule/periglomerular cells also synapse on mitral cells - sharpen info. Mitral cells travel in olfactory tract --> terminate piriform cortex, amygdala (emotion), hypothalamus, hippocampus (memories)
List one example of a receptor associated with each major flavour type
Salt = amiloride-sensitive Na+ channels; esp. tongue tip
Sour = H+-sensitive TRP channels; esp. tongue sides
Sweet = T1R2 & T1R3 GPCRs transduce stimuli; esp. tongue tip
Umami = T1R1 & T1R3 GPCRs via IP3 → > Ca2+ permeability; esp. tongue top
Bitter = T2R GPCRs; esp. Tongue posterior