Exercises: 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 skin contains several types of receptors (touch, pressure, temperature and pain). Explain the advantage of this sensory integration and describe what happens when you touch something that is cold, rough and sharp all at the same time.

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.

In response to a sudden loud noise, the pupils dilate and the heart rate accelerates, as summarized in the diagram. Indicate which element of the pathway (receptor, nervous center, or effector) each numbered box (1 to 4) represents, and which part of the nervous system (voluntary or autonomic) controls each step.

A research team records the electrical activity of two distinct sensory neurons in response to a continuous mechanical stimulus of constant intensity applied for 10 seconds:

• In Neuron A, the action potential frequency rapidly drops to zero at 0.8 seconds, even though the stimulus remains active.

• In Neuron B, the action potential frequency decreases slightly at the beginning, but remains elevated and constant throughout the entire 10 seconds.

1. a) Deduce with reasoning which of these recordings corresponds to a rapidly adapting (phasic) receptor and which to a slowly adapting (tonic) receptor. Associate each behavior with a functional example in the human body: the perception of clothing brushing against the skin versus the detection of pain from an ongoing burn (nociception).
2. b) Justify, from an evolutionary and survival perspective, why it would be maladaptive or lethal for an animal if nociceptors exhibited the same sensory adaptation pattern as olfactory or tactile receptors in the presence of a constant noxious stimulus.

In a medical clinic, the balance of two patients is assessed using the Romberg test (standing upright with feet together and arms at the sides, first with eyes open and then with eyes closed):

• Patient 1 remains stable with eyes open, but immediately loses balance and sways with a risk of falling as soon as they close their eyes.

• Patient 2 exhibits instability and an unsteady gait both with eyes open and closed, with virtually no visual improvement.

1. a) Knowing that one of the patients suffers from degeneration of the proprioceptive pathways of the posterior columns of the spinal cord and the other has cerebellar atrophy, deduce with justification which diagnosis corresponds to each patient based on the multisensory integration of balance.
2. b) A healthy person can maintain balance on a moving bicycle with their eyes closed for a few seconds, but fails if they try to do so with the bicycle completely stationary without putting their feet down. Explain what dynamic sensory information the semicircular canals of the inner ear and the pedaling motion provide compared to purely static balance.

In a neurophysiology laboratory, the effects of two toxins are analyzed:

• Toxin X specifically blocks nicotinic acetylcholine receptors at the skeletal muscle motor endplate, without altering muscarinic receptors.

• Toxin Y acts as a potent competitive antagonist of muscarinic acetylcholine receptors in viscera and glands.

1. a) Predict with reasoning the immediate effects that Toxin X poisoning will cause on pulmonary ventilation (diaphragm), intestinal peristalsis, and pupil diameter.
2. b) A student claims: "Since the somatic system controls voluntary actions and the autonomic system controls involuntary ones, Toxin X will not affect any spinal reflex, whereas Toxin Y will paralyze all automatic movements of the body." Refute their claim by analyzing what happens to the patellar reflex under the effect of Toxin X and to heart rate under Toxin Y.
3. c) Which of the two poisonings will urgently require intubation with mechanical assisted ventilation to prevent death from asphyxiation? Justify your answer based on the type of motor innervation of the diaphragm.