Effector organs

Name the two types of effector organs that execute the body's responses and give a specific example of how each acts in the same dangerous situation.

State whether these structures are muscles, bones, or endocrine glands, and what effector function each performs: biceps, femur, thyroid, diaphragm, adrenal glands.

Explain the difference between voluntary and involuntary muscles, and give an example of each type.

When it is very cold, we shiver without deciding to. Explain what type of response this is, which effector organs act, and why these contractions help to maintain body temperature.

In a test on the function of interaction, the response time of two people to the sudden sound of an evacuation siren is measured:

• Person A (first day at work, has never heard the siren nor knows the evacuation routes): takes 4.2 seconds to interpret the signal and decide which door to start running towards.

• Person B (has participated in four emergency drills): takes 0.6 seconds to start running towards the correct exit.

1. a) Identify and arrange chronologically the components of the interaction circuit (receptor, sensory pathways, integration centre, motor pathways, and effector organs) involved from the moment the siren sounds until the person takes the first stride.
2. b) Explain biologically why Person B reacts seven times faster. Is it because their effector muscles contract at a higher speed or due to a change in the processing of their nerve centres? Justify your answer by distinguishing between an untrained conscious response and a motor pattern automated by learning.

Explain what hormones are, which organs produce them, and how they reach the target cells they act upon.

Explain what an endocrine gland is and name two examples, indicating the hormone each one produces and its main effect.

Compare the body's muscular response and hormonal response: which is faster, which lasts longer, how the signal arrives in each case, and give an everyday example of each type.

A child grows several centimetres over a few months without noticing it, whereas standing up from a chair happens instantly. Compare the action of growth hormone with that of a skeletal muscle in terms of speed, duration and the way the order arrives.

In an experiment, a laboratory animal is given a drug that specifically blocks adrenaline receptors in liver and bronchial cells, but does not affect its heart or nervous system. In the sudden presence of a predator:

1. a) Predict what difficulties its skeletal muscles will have in sustaining an intense and prolonged run, justifying your answer based on cellular respiration and the substances it requires.
2. b) A researcher states: "Since motor nerves continue to order the muscles to contract, the animal will run just as fast and for the same amount of time." Refute this statement, explaining why the alarm response to a danger requires the coordinated action of the endocrine system and not just the nervous system.

In a medical laboratory, the blood glucose level (blood glucose concentration) of two patients is analyzed while fasting and two hours after eating an identical breakfast rich in carbohydrates:

• Patient A: 0.9 g/L fasting → 1.1 g/L after two hours.

• Patient B: 1.4 g/L fasting → 2.4 g/L after two hours.

1. a) Interpret these results and identify, justifying your deduction, which of the two patients has a failure in the functioning of the pancreas as an endocrine effector.
2. b) A classmate claims: "The patient with higher values has more glucose in their blood, so their muscle cells will have much more energy available to exercise." Reasonably refute their statement, explaining what insulin actually does in target cells and what real cellular consequence occurs if this hormone is not administered.

In the human body, the hypothalamus-pituitary axis detects testosterone levels in the blood: if the concentration is high, it stops sending stimulating signals to the testes so that they cease their own production (negative feedback). A bodybuilder injects high doses of synthetic testosterone for six months and then abruptly stops taking it.

1. a) Predict what will have happened to the mass and glandular activity of his own testes after those six months. Justify your prediction based on the described hormonal control mechanism.
2. b) Predict what serious hormonal imbalance this athlete will suffer during the weeks immediately following the sudden cessation of treatment, and justify why he will not be able to regain a normal hormone level the day after stopping it.

Thyroxine, produced by the thyroid gland, is the hormone that regulates basal metabolism, that is, the rate at which cells consume nutrients and oxygen to obtain energy (cellular respiration). In hypothyroidism, thyroxine production is insufficient.

1. a) The three classic symptoms of hypothyroidism are generalised fatigue, body weight gain (even without eating more), and constant cold intolerance. Justify the biological origin of each of these three symptoms by directly relating them to cellular respiration.
2. b) A patient tells the doctor: "Since I lack energy and feel cold, instead of taking the daily thyroxine pill, I am going to eat twice as much sugar and use an electric blanket." Refute the patient's idea by explaining why increasing nutrients is useless if the effector hormonal order is missing.

Unit challenge. Design your own neuroscience lab at home to test how your body responds to different stimuli. Your final product will be a short report that includes a data table, the biological analysis of the process, and your conclusions.

1. Experimentation: Ask a family member for help with the ruler drop test. Your helper will hold a $30\text{ cm}$ ruler by the top end. Place your fingers at the base ($0\text{ cm}$) without touching it. When they release it without warning, catch it as quickly as possible. Do $5$ attempts with a visual stimulus (looking at the ruler) and another $5$ with an auditory stimulus (eyes closed, reacting to the command "now!", which your helper says at the exact moment of releasing the ruler).

2. Data collection: Record in a table the distance at which you catch it (in $\text{cm}$) and calculate the mean for each condition, expressing it with a decimal comma (for example, $15.4\text{ cm}$).

3. Biological analysis: Describe the complete pathway of information in both cases: identify the activated sensory receptor, transmission through the nervous system, and the acting effector organ. Provide a reasoned justification of which of the two stimuli produced a faster response.

Assessment criteria:

• Thoroughness in data collection and correct calculation of means.

• Accurate identification of sensory receptors, nerve centers, and effectors.

• Clear scientific justification of the differences observed between both stimuli.

Explain what a joint is and cite two examples of joints in the human body, indicating which movements each one allows.

Name the three parts of the musculoskeletal system and state the general function of each one in movement.

State whether these statements are true or false and justify your answer: a) skeletal muscles move bones by pushing them; b) the skeleton also protects delicate organs; c) hormones reach the organs they act on through the blood.

Describe how bones, joints, and muscles work together when you bend your arm to lift a bottle of water, indicating what each element contributes to the movement.

Diagrams A and B represent the same arm with the two muscles that move the forearm, marked with ?: in each case, one appears thickened (contracted) and the other stretched (relaxed). State which muscle (biceps or triceps) is contracted in each diagram and, taking into account that skeletal muscles can only pull and not push, explain why bending and straightening the forearm requires the coordinated action of both and what this type of muscle pair is called.

During intense exercise, the heart beats faster and breathing speeds up. Explain why the work of the muscles requires the collaboration of the circulatory and respiratory systems.

An athlete suffers a complete rupture of the Achilles tendon, the structure that connects the gastrocnemius (calf) muscle to the calcaneus (heel bone). When trying to stand on tiptoe:

1. a) The gastrocnemius muscle receives the motor command, shortens, and bulges visibly, but the heel does not lift off the ground at all. Justify this biomechanical fact by explaining which link in the transmission chain has failed and what happens to the force generated by the muscular contraction.
2. b) A friend of the athlete proposes: "So that they can walk while recovering, let's lock their ankle with a rigid plaster cast; that way the calf muscle can lean on the cast and lift the heel." Refute this proposal biomechanically, explaining the essential role that both the tendon and the movable joint play in the lever system of the musculoskeletal system.

In an ankle sprain, the joint swells and hurts. Explain which structures of the joint can be damaged when the foot twists and why inflammation appears in the area.

Children's bones bend more before breaking than those of older people. Relate this difference to the composition of bone at each age, and explain which habits in youth help to have strong bones in old age.

Bone tissue is not inert: it is continuously destroyed and formed. Bone mass reaches its maximum value ("peak bone mass") around age 25 and, starting at age 45, it naturally decreases at an approximate rate of 1.0 % per year. If bone mass drops below 60 units, the risk of fracture from minor trauma skyrockets.

• Person A (exercised regularly and had a calcium-rich diet in their youth): reaches a peak of 100 units at age 25.

• Person B (sedentary and with a calcium deficit in youth): only reaches a peak of 75 units at age 25.

1. a) Assuming that both lose 1.0 % of their maximum mass each year starting at age 45, calculate the bone mass of each at age 65 (after 20 years of loss). Based on the results, justify why it is said that youth habits are an "investment" for old age.
2. b) If both people suffer a fracture at age 65, why will it take them much longer to heal the bone than a 10-year-old child? Justify your answer by comparing bone cell activity and vascularisation in both stages of life.

To study how the nervous system and the musculoskeletal system interact, three patients with different conditions in one leg are analysed after one month of progression:

• Patient A: has a leg immobilised by a cast following an ankle fracture (the motor nerves and muscles are intact, but the joint does not move).

• Patient B: has suffered a complete severing of the sciatic nerve that innervates the leg muscles (the muscles are disconnected from the spinal cord).

• Patient C: has the same nerve injury as Patient B, but receives daily sessions of external electrical stimulation applied directly to the skin over the muscle, causing it to contract.

1. a) Predict in which of the three patients the most severe and rapid muscle atrophy will occur, and justify why Patient C better preserves muscle mass than Patient B despite having the same neurological injury.
2. b) A student suggests: "To prevent Patient B's atrophy, it would be enough to stimulate the motor area of their brain with electrodes so that it sends stronger commands." Refute this statement by justifying the anatomical pathway of the motor response from the nerve centre to the muscle effector.