Senses Flashcards
Pressure
Stretching
Touch
Pain
Noiception
Electric current
Electroreception
Chemicals
Taste
Olfaction
Vomerolfaction
Sound waves
Hearing
Radiation
Vision
Thermoception
Dermal photorecepetion
Why are most senses concentrated around the head?
- sensory inputs are kept close to brain (which processes these inputs) which reduces delays in processing and the (nerve) tissue required to maintain sensory stimuation
- most species movement takes place on an axis that puts head in contact with environment first, so having sensory input concentrated in the direction of travel prioritises the most immediately relevant information
Touch (mechanoreception)
- what is touch?
- where is it perceived?
- aquatic vertebrate?
- snake?
- sensation of movement (including pressure)
movement perceived via more mobile areas of skin which are free to respond to pressure and active nerve signals either directly or via hair cells
Landmann 1975:
aquatic vertebrates (fishes and amphibians) have specialised group of mechanoreceptors called ‘lateral line system’ - respond to water movement and found along sides of body + around head
snakes have set of unique structures around their head, function of which is unknown, h/e due to well developed in aquatic species, been proposed as a sensory system with some functional similarities to lateral line systems
Nociception
- what is nociception?
- pain - set of distinct sensations with sensory nerves that respond directly to the different types, include mild (non-painful) sensations, painful sensations resulting from mechanical impacts, and painful sensations resulting from chemical stimuli (such as spicy food) or physical heat
pain = poorly understood in many animal groups
Aδ fibres (non-painful mechanical stimuli and painful mechanical stimuli) found in snakes - likely present throughout reptiles and similarly function as nociceptors to register painful mechanical stimuli
Electroreception
- what is it? what groups can detect it?
- what is it used for?
- electrical current
- ability to detect electric current = known from aquatic caudates and caeilians, but doesn’t seem to occur in frogs
- used to assist in foraging by detecting electric current in prey
- e.g. Olm (Proteus anguinus)
- e.g. Typhlonectes natans
- electrical signals travel better through water than air - limited to aquatic animals
- electrical signals are generated by living organisms due to nerve firing and so are impossible to avoid emitting, making them good signals for aquatic predators to use in finding prey that may be hidden under the substrate or in murky water
Taste
1/3 chemical senses on tongue of almost all tetrapods
‘broccoli-shaped’ taste buds - contain receptors that recognise particular chemical structures which are then perceived as taste
actual perception of taste = combines input from taste buds w/ olfactory cues and nociceptive cues (spices - C fibres)
Olfaction
- smell - chemical sense specialised for detecting highly volatile (airborne) molecules, but sensory input = received by specific chemical receptors that bind to odorants
- main chemical sense available at distance as it deals with smaller molecules (called ‘odorants’) that are far more volatile than processed by other chemoreceptor systems
Vomerolfaction
3rd chemical sense - similar to olfactory (and taste) - senses chemicals via specific receptors
vomeronasal system = specialised for less volatile chemicals, often sensing pheromones, + info is both received and processed in separate locations from the olfactory system
many reptiles, esp snakes, have highly developed vomerolfactory systems - fundamentally similar in structure to other animals
vomeronasal system = targeted towards heavier, less volatile chemical cues than the olfactory system
Hearing
- perception of vibrations; airborne vibrations in the form of sound
- sound reception works via membrane which moves in response to vibrations, to which is connected bone(s) which transmit the vibrations to the inner ear which receives the pressure changes and generates nerve signals to pass the info to the brain
- reptiles - simpler system w/ one (relatively thick) bone which does most of transmission of vibrations to inner ear (stapes), but mammals evolutionarily modified two bones from the reptilian jaw (quadrate and articular) to create ‘jointed’ system that helps to amplify vibrations and provide more sensitive hearing
- Pinnae (ears in humans) = variably present + help to channel sound from particular directions, increasing both the sensitivity and ability to localise sounds
- snakes can hear airborne sounds - only at low frequencies, but they predominantly use same structures to sense ground-borne vibrations in same way as many other species sense airborne vibrations
Vision - Eyes
radiation sensing = vision
eyes = one type of visual photoreceptor system, + are constructed to filter the quality and quantity of light entering the eyeball (via cornea, anterior chamber and pupil), then focus that light (via lens) on retina at back of the eye
retina contains light sensitive (photoreceptive) cells - various forms - rods (more sensitive to light, better at lo light conditions, no colour vision) + cones (need more light to operate but provide colour vision)
cones may be single of double cones - may or may not have oil droplets which alter colour vision by narrowing spectrum of light being perceived by cone cells
number and type of photoreceptor cells generate differences in vision between species
