Receptors and effectors

Classify sensory receptors according to the type of stimulus they detect (photoreceptors, mechanoreceptors, chemoreceptors, thermoreceptors and nociceptors) and give a body example of each.

Differentiate between exteroceptors, interoceptors and proprioceptors, indicating where they are located and what information each type provides.

Name the three types of effector organs involved in the interaction function and give an example of a coordinated response for each.

The fingertips distinguish two pinpricks one millimetre apart; the back, only if they are several centimetres apart. Explain the two-point discrimination test, what determines it (receptor density and cortical territory) and what it says about the sensitivity of each area.

Explain the path of light through the eye (cornea, pupil, lens, vitreous humour, retina) and the function of each element, indicating where the image is formed and where it is transformed into a nerve signal.

Compare the compound eye of an insect with the eye of a vertebrate: basic structure of each, the type of image they form, and the advantage each design offers to the animal possessing it.

The normal trichromatic human retina has three types of cones whose photopigments (opsins) exhibit absorption peaks at different wavelengths: S (blue, ~420 nm), M (green, ~530 nm), and L (red, ~560 nm). The genes encoding the M and L opsins are located in tandem on the X chromosome.

1. a) An individual with deuteranopia completely lacks the functional M opsin. If two beams of light of equal radiance are projected onto them, one at 540 nm and the other at 565 nm, deduce and justify whether their visual cortex will be able to discriminate both stimuli as different colors by comparing signals between cones, or if they will perceive them as indistinguishable shades.
2. b) In a population in genetic equilibrium, the prevalence of X-linked color blindness among males is 6,0% (0,06). Reasonably calculate the expected allele frequency, the percentage of color-blind females, and the percentage of carrier females with phenotypically normal vision.
3. c) A woman with normal vision whose father is color-blind has offspring with a man with normal vision. Justify the probability that their sons and daughters will suffer from color blindness. Why, due to the process of stochastic X-chromosome inactivation (lyonization), can carrier females present a cellular mosaic in the retina without clinically manifesting color blindness?

The inner ear is also the organ of balance. Explain what the semicircular canals and the utricle detect (turns and accelerations, the position of the head) and why getting seasick on a boat is a conflict between what the eyes say and what the inner ear says (motion sickness).

An ethology team studies the sensory mechanisms of two predators using experimental setups:

• Experiment 1: A shark swims in a sandy tank. It attacks with precision a live flatfish buried in the bottom. If the fish is replaced with pieces of fresh meat wrapped in insulating plastic impermeable to water and electricity, the shark swims past it. However, if an electric dipole emitting a continuous microcurrent of 5 nV/cm (similar to the branchial neuromuscular activity of the prey) is buried under the sand without any chemical trace of food, the shark lunges to bite the electrodes.

• Experiment 2: Insectivorous bats are recorded capturing moths in the dark. Upon introducing moths of the family Erebidae, it is observed that they emit trains of ultrasonic clicks when they detect that the bat accelerates its echolocation calls; faced with this, the bat's capture rate drops by 80%.

1. a) Based on Experiment 1, deduce which sensory receptor guides the shark's final attack (ampullae of Lorenzini versus olfactory chemoreceptors) and justify why the plastic barrier prevented detection despite the smell of meat.
2. b) Based on Experiment 2, formulate a neurophysiological hypothesis about how the ultrasound emitted by the moth disrupts the bat's echolocation system and interpret this interaction as a case of sensory predator-prey coevolution.
3. c) Use both examples to argue Jakob von Uexküll's concept of "Umwelt" and justify why designing a pest trap based exclusively on human sensory capabilities is usually ineffective.