Vertebrates 17 - Sense Organs Flashcards
General properties for sensing
Receptor cells to afferent neurons to CNS. External: olfactory, hair cells, taste buds. photoreceptors; internal: baroreceptors, proprioceptors
Receptor types
Chemical: olfactory, taste; Mechanical: touch, pressure, sound waves; electrical: electric fields; Thermal: temp, infrared; Light: photoreceptors
Receptor properties
Selective:have selective receptor proteins; Sensitive: can respond to very small stimuli; Threshold of detection; receptor potential: latency; amplification; adaptation
Adaptation
Rapid and slow??? stops sending stimulus if it doesn’t change
Phasic and tonic
Phasic respond only when stimulus comes; tonic always fire, but can change with stimulus
Taste receptors (gustation)
taste buds are receptor cells (1-2 wks) and sustentacular cells and basal cells (stem cells). Mucous cells, chemicals dissolve in the mucous
Taste bud location
Papillae: folds containing taste buds. Circumvallate: larger, back of tongue; foliate: side of tongue; fungiform: tip, sparse cells
5 tastes
Sweet, salt, bitter, sour, umami (savoury - MSG - glutamate). ALL regions of tongue respond to same stimuli, only in the regions where there are taste buds (front, back, sides)
Taste mechanisms: Salt
Receptor proteins: sodium channels (not voltage gated!); causes depolarization.
Taste mechanisms: Sour
H from acid blocks potassium channels from flowing out, positive charge builds up, depolarizes
Taste mechanisms: Sweet, Bitter, Umami
Sugar binds to sugar receptor, starts signal transduction, blocks K channels, depolarizes. These are tonic receptors, so signal increases when sugar binds. (Bitter and umami same, just different receptor)
Taste receptors in aquatic animals
Buds less developed in agnathans. In fish that can be found in mouth, pharynx, fins, skin, barbels. Most don’t have good taste of salt. Some have some simple chemoreceptors for chemicals, they can “taste” pollution and avoid that.
Minnow taste receptors
500X grater sensitivity to sweet, 200X less to salt
Barbels
Found in sturgeon, catfish. Usually in muddier waters, bottom feeders. Taste with barbels then vacuum the fish in.
Evolution of taste
Used to detect what is nutritious and what is toxic. Salt taste in terrestrial animals evolved because we need to consume salt to replenish electrolytes
Taste receptors in birds
Generally many less taste buds (chicken has 25, human has 10000). Birds have fairly particular diets, so it doesn’t have the concern of finding toxic food since they aren’t generalists.
Taste: short or long distance?
Vertebrates use taste as short-distance info. You can’t taste from far away durr
Olfactory receptors
Majority in nasal cavity in turbinates in the nasal epithelia. Long cells to brain with projections with cilia on the outside.
Nasal epithelia
Many mucous cells. Traps particles, warm and humidify air as it passes through. Support cells next to receptor cells secrete GFs, maintain ions around cells, etc. Basal cells = stem cells
Turbinate bones in different vertebrates.
Dogs have more turbinate bones and all is covered in olfactory epithelia. Humans have very small epithelia, weaker smell. Mouse has a bit more than humans.
Odorant receptor proteins
Many types, each cell has one type. 1000s of genes (2-4% genome). Shape fits a certain type of molecule
Transduction mechanism
When odorants bind, they activate a pathway: G protein is phosphorylated, adenylate cyclase converts ATP to cAMP, which open cAMP-gated channels, allow Na in and membrane depolarizes.
Difference b/w taste and smell
Both need chemicals, but smell is more sensitive so it can be used as long-distance info.
Smell transmitted to brain pathway
Info passed to olfactory bulb right above the epithelia for processing. Then sent to cortex regions of brain (olfactory cortex). Some smells can trigger epilepsy in some people.
Odor and memory
Purpose to prevent eating noxious food. Highly associated with memory (remember smell a year later, specific pictures only a few months). LTP stimulated in olfactory cortex, memory stored in prefrontal cortex.
Odor and aquatic vertebrates
Well developed in agnathans. Shark olfactory sacs highly folded, lots of surface area. Dominant sensory apparatus.
Nares of shark
Open to the olfactory sacs. Incurrent and excurrent are the same opening (in eel it enters one and exits another).
Snake smell
Snakes use forked tongue to catch molecules and bring them in to their olfactory epithelia
Pheromones
Detected by mid-ventral part of olfactory epithelia called the vomeronasal organs. Usually detected by only animals of same species. Mostly ungulates, cats, not in aquatic tetrapods, bids, bats, primates.
Flehmen response
In cats. Raise upper lips, look like they are smiling but they are actually opening a small duct in palate into vomeronasal organ.
Innervation of pheromones
Separate from normal olfactory, processes in accessory olfactory bulb.
Birds and smell
Minimal, not very useful since they are generally far away so there are less olfactory trails. Exception is the vulture. They look for dead food, which is generally smelly. Able to find hidden dead animals (but that’s hard to study in natural environment!)
T-Rex and smell
Olfactory bulb was very large (from fossilized brain case made into brain cast). Possible that T-Rex was a scavenger and was able to smell decay.
Arterial chemoreceptors
Carotid and aortic bodies (innervated by carotid sinus and the vagus nerves), and medullary receptors. Sense changes in O2, CO2, pH in blood. They control respiration.
