Effector Organs
You're walking down the street in Mexico City when a bus suddenly honks its horn very close by. You jump onto the sidewalk, and even though you're already safe, your heart pounds hard for several minutes. The nervous system decides the response, but it doesn't carry it out: that's the job of the effector organs. Why does your body respond at two such different speeds to the same scare?
Two types of effector organs
The nervous system receives information from the environment and sends out commands. The ones that carry out those commands are the effectors. Some act in a fraction of a second; others act over minutes, days, or years.
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.
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.
State whether these structures are muscles, bones, or endocrine glands, and what effector function each performs: biceps, femur, thyroid, diaphragm, adrenal glands.
Hormones: messengers in the blood
During puberty, your height, your voice, and your body change over the course of months, without a nerve wire connected to every cell. How does the body deliver chemical messages that are slow, yet able to act on very specific areas?
Hormones also regulate sexual maturation and reproduction. During puberty, hormones produced by the testes and the ovaries bring about the body's changes and cause the gametes to form; later, other hormones regulate the menstrual cycle and pregnancy.
| Nervous response (muscle) | Hormonal response (gland) | |
|---|---|---|
| How the command arrives | Nerve impulse through the neurons | Hormone through the blood |
| Speed | Very fast (milliseconds) | Slower (seconds to months) |
| Duration | Brief | Long-lasting |
| Example | Pulling your hand away from a hot pot | Changes of puberty |
Adrenaline and glucose: two hormones with measurable effects
A single hormone can act on several organs, and in each one it produces a different effect, because only the cells that have its receptors respond.
Adrenaline (adrenal glands) prepares the body to flee or fight. It acts on the heart, which beats faster; on the bronchi, which widen so more air can enter; and on the liver, which releases glucose into the blood. This way, the muscles receive more oxygen and more glucose for cellular respiration, which gives them the energy for a long run.
If the adrenaline receptors in the liver and bronchi were blocked, less glucose and less oxygen would reach the muscles. Even if the motor nerves keep ordering them to contract, the muscles would soon run out of energy: the nerve command isn't enough if there's no fuel.
Insulin (pancreas) lowers blood glucose: it helps glucose enter the cells, and the excess is stored in the liver. After eating, blood glucose rises a little and insulin brings it back to its usual level. If the pancreas fails, blood glucose stays very high after eating: this is diabetes.
Explain what hormones are, which organs produce them, and how they reach the target cells they act upon.
Explain what hormones are, which organs produce them, and how they reach the target cells they act upon.
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…
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.
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…
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:
- 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.
- 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…
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.
- 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.
- 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.
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…
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:
- 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.
- 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.
Bones, joints, and muscles: the locomotor system
If you try to bend a rigid bar, it snaps. Your leg, on the other hand, flexes with strength and smoothness as you walk while supporting all your weight. How do hard pieces, like bones, work together with soft tissues to allow movement without breaking?
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.
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…
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.
Taking care of muscles and bones
Go back to the beginning: when you heard the horn, your muscles jumped instantly thanks to the nerve command, and the adrenaline from the adrenal glands kept your heart racing for several minutes. Two effectors, two speeds.