Senses Flashcards
senses can be categorised in the context of the type of input they receive, outline the different categories and their unput
1) touch = pressure/stretching
2) nociception = pain
3) electroception = electric current
4) taste/olfaction/vomerolfation = chemicals
5) hearing = sound waves
6) vision/thermoception/dermal photorecpetion = radiation
outline why sensory infomation is most concentrated around the head
1) sensory inputs are kept close to the brain, reducing delays in processing
2) most spp movement takes place on an axis which puts the head in contact with the environment first so having it concentrated in direction of travel prioritises the most immediatley relevant information
outline how touch works
= the sensation of movement perceived via more mobile, thin areas of skin which respond to pressure and active nerve signals either directly or via hair cells
= thicker skin = bad as less movement so less responce from nerves beneath skins
outline touch in aquatic spp
. Some aquatic vertebrates (fishes and amphibians) have a specialised group of mechanoreceptors called the ‘lateral line system’, which respond to water movement and are found along the sides of the body and (particularly) around the head.
= fine hairs called kineocilia attach to sensory cells, covered by a cupula to stop collapse in wtaer, when something pumps into cilia it moves nerve cells and cell bodies attached to them
outline how nociception works
‘Pain’ is actually a set of distinct sensations with sensory nerves that respond directly to the different types, these 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.
what are the different nerves invloved in nociception
Ab fibre = non-noxious mechanical stimuli (non painful)
Ad fibre = noxious mechanical stimuli ( painful such as hit with hammer)
c fibre = noxious heat and chemical stimuli (such as spicy food or heat)
outline electroreception
As electrical signals travel far better through water than air, electroreception is 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.
outline taste
One of three chemical senses, located on the tongue of almost all tetrapods in the form of ‘broccoli-shaped’ taste buds, which contain receptors that recognise particular chemical structures and bind to them which are then perceived as the tastes we recognise
=perception of taste from food combines input from taste buds with olfactory cues (smells) and nociceptive cues (e.g. the C fibers that sense heat and ‘spice’).
outline olfaction
Olfaction (smell) is a chemical sense specialised for detecting highly volatile (airborne) molecules, but like taste the sensory input is received by specific chemical receptors that bind to odorants.
what is vomerolfaction
The third chemical sense is vomerolfaction, which is similar in many ways to the olfactory (and taste) system in that is senses chemicals via specific receptors. However, the vomeronasal system is specialised for less volatile chemicals, often sensing pheromones, and the information is both received and processed in separate locations from the olfactory system.
outline hearing
Hearing is fundamentally the perception of vibrations, predominantly (and conventionally) airborne vibrations in the form of sound. Sound reception essentially works via a 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 information to the brain
outline hearing in reptiles vs mammals
In reptiles there is a much simpler system with one (relatively thick) bone which does most of the transmission of vibrations to the inner ear (stapes), but mammals evolutionarily modified two bones from the reptilian jaw (quadrate and articular) to create a ‘jointed’ system that helps to amplify vibrations and provide more sensitive hearing.
outline vision
The most common form of radiation sensing in animals (with the possible exception of the nociceptive heat receptors) is vision. Eyes are one type of visual photoreceptor system, and they are constructed to filter the quality and quantity of light entering the eyeball (via the cornea, anterior chamber, and pupil), then focus that light (via the lens) on the retina at the back of the eye. The retina contains light sensitive (photoreceptive) cells which come in various forms, at the broad level rods (which are more sensitive to light and so are better in low-light conditions, but in most species can’t differentiate colours) and cones (need more light to operate but provide colour vision – some rare examples noted of functioning cones in nocturnal animals
outline how snake eyes evolved differently to other eyes
At some point in the early history of snakes, likely as a result of a fossorial lifestyle, they lost their eyes and subsequently ‘re-evolved’ them. The result is a unique eye structure in which focussing of the lens is done by moving the (spherical) lens back and forth rather than stretching the lens to change it’s shape as is the case in all other tetrapods.
outline how cutaneous photoreceptos detect non-visual light in a species example
Sea snakes have evolved a separate photoreceptor system on the skin of the tail. That detects light shining on that part of the body and results in the snake moving it’s tail away from the light (presumably to rduce detectability by ensuring the snake is hiding adequately). The precise mechanisms behind this system are still poorly known.
