The nervous and endocrine systems

Compare nerve and hormonal signals in terms of their speed, duration, transmission pathway and destination precision, and give an example of a typical response for each.

In the medical treatment of children with central precocious puberty (abnormal pubertal development before age 8 due to premature activation of the hypothalamic axis), a potent gonadotropin-releasing hormone (GnRH) agonist administered via a continuous-release subcutaneous implant is used as a drug.

1. a) Knowing that under normal physiological conditions the hypothalamus secretes GnRH in intermittent pulses every 60 to 90 minutes to induce the synthesis of LH and FSH in the anterior pituitary, explain the apparent contradiction: why does the uninterrupted and constant administration of a GnRH activator (agonist) halt puberty instead of accelerating it? Justify the cellular mechanism undergone by the anterior pituitary receptors.
2. b) In recent decades, the age of pubertal onset has significantly advanced in populations with high-calorie diets and higher rates of childhood obesity. Formulate a biological hypothesis relating body adipose tissue mass, the hormone leptin, and the GnRH pulse generator, and predict why a youth athlete with an extremely low body fat percentage may present with amenorrhea or delayed puberty.

Describe the parts of a neuron (dendrites, cell body or soma, axon, and axon terminals) and explain the function of each in receiving, conducting, and transmitting nerve impulses.

What is a synapse? Explain why the signal does not pass electrically from one neuron to another in most of them and what advantage using a chemical messenger can have (modulation, amplification).

Explain what negative feedback is in hormonal regulation, describing a specific example: the regulation of blood glucose by insulin and glucagon, or that of the thyroid axis.

Distinguish between the central and the peripheral nervous systems: which organs each includes, what general function it fulfils and how they communicate with each other.

Goitre is the growth of the thyroid due to lack of iodine. Explain, using the negative feedback of the pituitary-thyroid axis, why the gland grows when it cannot make thyroid hormone, and why iodised salt almost eradicated this problem.

During an acute stress response experiment, two groups of individuals are subjected to an unexpected 30-minute stress test:

• Control Group: experiences an immediate increase in heart rate (from 70 to 135 bpm in just 6 seconds), pupillary dilation, and an early spike in blood glucose, followed from 15-20 minutes onward by a sustained increase in hepatic gluconeogenesis and a decrease in protein synthesis.

• Treated Group: has previously received a specific beta-adrenergic receptor-blocking drug.

1. a) Predict with justification what differences the Treated Group will show compared to the Control Group in heart rate, blood pressure, and blood glucose during the first 60 seconds after stimulus onset.
2. b) Explain why the adrenaline-mediated response (sympathetic nervous system and adrenal medulla) triggers cellular effects within seconds, whereas the response coordinated by cortisol (hypothalamic-pituitary-adrenal cortex axis) takes tens of minutes to establish itself. Base your reasoning on the chemical nature of each hormone and their respective cellular transduction mechanisms.

What is a hormone and where is it produced? Name two human endocrine glands, the hormone secreted by each, and its main effect.

When you touch a very hot object, you pull your hand away before feeling pain. Describe the pathway of the nerve impulse in this reflex arc, naming the neurons involved and explaining why the response does not pass through the brain first.

In a study on the mesocorticolimbic reward circuit in laboratory rodents, microdialysis is used to measure dopamine concentrations in the nucleus accumbens, and autoradiography techniques are used to assess the density of D2 receptors in postsynaptic neurons under three conditions:

• Condition 1 (natural appetitive stimulus: sugar solution): dopamine increases by 45% above baseline for 20 minutes; D2 receptor density remains unchanged (100%).

• Condition 2 (acute amphetamine injection): plasma dopamine at the synapse spikes by 650% for more than 90 minutes.

• Condition 3 (after 4 weeks of daily amphetamine use, following 24 hours of deprivation): baseline dopamine levels drop 35% below normal, and the density of active D2 receptors falls to 40% of the initial level.

1. a) Interpret the data from Condition 3 to explain the molecular mechanisms of drug tolerance and anhedonia (the inability to experience pleasure from natural stimuli). What adaptive synaptic plasticity phenomenon explains the reduction in D2 receptors?
2. b) Based on these biological data, refute the claim of someone who argues that "overcoming an addiction requires no medical or pharmacological support, but merely a firm act of willpower."