Problem 9 - Campbell Biology Concepts & Connections

Question

Muscle A and muscle B have the same number of fibers, but muscle A is capable of more precise control than muscle B. Which of the following is likely to be true of muscle A? (Explain your answer.) a. It is controlled by more neurons than muscle B. b. It contains fewer motor units than muscle B. c. It is controlled by fewer neurons than muscle B. d. It has larger sarcomeres than muscle B.

Step-by-Step Solution

Answer

a. It is controlled by more neurons than muscle B.

Step 1 - Understanding Muscle Control

Precision in muscle control is often related to the number of motor units. A motor unit consists of a motor neuron and the muscle fibers it innervates. More neurons mean more motor units, which allows for finer control.

Step 2 - Analyze the Options

Review the provided options and relate them to the understanding of muscle control: a. More neurons -> more motor unitsb. Fewer motor units -> less precise controlc. Fewer neurons -> fewer motor units d. Larger sarcomeres -> not related to precision control

Step 3 - Identify the Correct Statement

Muscle A has more precise control, which implies a higher number of motor units compared to Muscle B. This would be achieved by having more motor neurons controlling the muscle fibers.

Key Concepts

Motor Units

Understanding motor units is key to grasping muscle control precision. A motor unit consists of a single motor neuron and all the muscle fibers it activates. When we need precise movements, like typing on a keyboard, many small motor units are required. This allows for fine-tuned control as fewer muscle fibers are activated by each neuron.

For example:

• Muscle A, capable of precise movements, has many motor units. Each neuron controls a few muscle fibers.
• Muscle B, which is less precise, has fewer, larger motor units. Each neuron controls many muscle fibers.

More motor units mean the muscle can be controlled very precisely, allowing for delicate movements.

Motor Neurons

Motor neurons are essential in controlling muscle activity. They transmit signals from the brain and spinal cord to muscles, dictating when and how muscles contract.

More motor neurons equate to more detailed commands, resulting in finer control over muscle movements. Hence, Muscle A's enhanced precision is due to:

• Having more motor neurons.
• Each neuron forming a smaller motor unit by controlling fewer muscle fibers.

In summary, more motor neurons mean more motor units, providing the capacity for intricate and precise muscle actions.

Muscle Fibers

Muscle fibers are the individual contractile units within a muscle. When considering control and precision, it's crucial to look at how these fibers are organized and controlled.

In Muscle A, each motor neuron governs a small number of muscle fibers. This setup allows for detailed control because:

• Each signal can specifically target smaller groups of fibers.
• Movements can be finely tuned and adjusted.

Conversely, Muscle B, with each motor neuron overseeing more fibers, has broader, less precise control.
The key takeaway is that finer muscle control is all about having more specific relationships between neurons and muscle fibers.