| Term | Definition |
|---|
| What are the 5 categories of tastants? | Sweet (carbs), salty (minerals), umami (savoury), sour, bitter |
| How do we sense sweet tastes? | G-protein/cAMP --> close K+ channels --> depolarisation --> Ca2+ in --> glutamate released onto nerve terminals |
| How do we sense salty tastes? | Receptors are ion channels for Na+...direct depolarisation |
| How do we sense savoury ("umami") tastes? | Glutamate is the main tastant, binds with and opens ligand-gated Na+ channels |
| How do we sense sour tastes? | 2 mechanisms: Na+ channel allows H+ to enter cell; K+ channel closes when H+ binds with it |
| How do we sense bitter tastes? | 2 possible ways: calcium/quinine block K+ channels and cause depolarisation; or there are specific membrane receptor proteins which use a 2nd messenger to release internal Ca2+ and activate synaptic vesicle machinery |
| Which cranial nerves are involved in taste? | Facial (#7) - anterior 2/3 of tongue, glossopharangeal (#9) - posterior 1/3 tongue, vagus (#10) - epiglottus/pharynx |
| Describe the gustatory pathway to the brain | Primary gustatory afferents --> medulla --> 2nd order fibres to thalamus --> primary gustatory cortex in postcentral gyrus/insula |
| What are the receptors for smell? | Bipolar neurons in olfactory epithelium (roof of nose) |
| Describe the olfactory pathway to the brain | Olfactory nerve fibres path through cribiform plate, terminate in olfactory bulb. From here the nerves for a tract to the primary olfactory cortex in temporal lobe. |
| Describe the mechanism through which an odorant initiates an AP | Odorant binds with receptors --> G-protein activated, cAMP produced --> cAMP-gated ion channels open --> depolarising receptor potential --> AP travels down olfactory nerve to brain |
| The external ear is made up of the ______ and the ______ | Pinna, external ear canal |
| The middle ear consists of | Tympanic membrane, ossicles, eustachian tube |
| What is the function of the middle ear? | Converts pressure waves in air into vibrations of fluid of the cochlea |
| Which bone is attached to the tympanic membrane? | Malleus |
| The 3 bones in the middle ear, in order from the tympanic membrane to the cochlea, are: | Malleus, incus, stapes |
| What are the structures in the inner ear? | Cochlea, cochlear nerve, semicircular ducts |
| What is the lowest intensity of sound a healthy ear can perceive? | 0dB |
| The (healthy, young) ear is sensitive to what range of frequencies? | 20Hz - 20kHz |
| What does the stapes connect with? | Oval window |
| What is the function of the Eustachian tube? | Connects middle ear with nasal cavities, normally closed but opens with yawning/swallowing, which equalises pressure in external and middle ear (optimising TM function) |
| What is the organ of Corti? | In middle of cochlea, has hair cells that convert vibrations into nerve signals |
| What is glaucoma? | Drainage is impaired: excess aqueous humour pushes lens backwards into vitreous humour which in turn compresses the retina |
| When looking at an object which is close by, your lens is _____ because the ciliary muscle is _____ | flattened, relaxed |
| Presbyopia | Lens hardens and becomes less elastic; happens with old age |
| Are rods for daytime or nighttime vision? | Night - "scotopic" ("C is for colour", so cones are for day time) |
| Retinal molecules in rhodopsin absorb light and change shape from ___ to ____ | cis, trans (it's alphabetical order = easy to remember) |
| In the retina, is glutamate inhibitory or excitatory? | Inhibitory |
| The fovea has ___ rods but ___ cones | no, many |
| Retinal changes shape, activates G-proteins which catalyse production of phosphodiesterase and leads to breakdown of cGMPs which then _____Na+ channels and ____ release of glutamate | close, stop (NB: when glutamate is inhibitory) |
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