Question

Which of the following statement is correct? (a) A motor neuron along with the muscles fibres connected to it constitute a motor unit. (b) The reaction time of the fibres can vary in different muscles. (c) Muscle fatigue is due to lactic acid formation due to anaerobic respiration. (d) All the above

Short answer

The correct answer is (d) All the above. Each of the provided statements is correct according to the understanding of muscle physiology and nervous system.

Step-by-step solution

Verify Statement (a)

This statement is indeed correct. A motor unit consists of one motor neuron and the multiple muscle fibres it innervates or is connected to. When the motor neuron is activated, all muscles fibres in the motor unit contract.

Verify Statement (b)

This statement is also correct. The reaction time, or the time it takes the muscle fibre to respond to the neural stimulus, of fibres can vary in different muscles. This is due to a number of factors, including the type of muscle fibre, the intensity of the stimulus, etc.

Verify Statement (c)

The third statement is correct too. Muscle fatigue often results from lactic acid build-up in the muscles during intense exercise when oxygen levels are low, causing anaerobic respiration. As a result, muscle contractions become more difficult and muscles feel fatigue.

Choose the correct answer

Based on the verifications of statements (a), (b), and (c), it is confirmed that all these statements are correct according to biological understanding of muscle physiology and nervous system. Therefore, the correct answer is (d) All the above.

Key concepts

Motor Units

Understanding the structure and function of motor units is crucial for students studying NEET Biology's muscular system.

A motor unit consists of a single motor neuron and all the muscle fibers it controls. The connection between these two components is a biological marvel - when the motor neuron receives a signal from the central nervous system, it, in turn, activates all the muscle fibers attached to it, leading to muscle contraction.

The size of a motor unit can greatly affect the control we have over muscle movements. Smaller motor units, which are found in muscles that require precise control like those controlling the eyes, contain fewer muscle fibers. Larger motor units, which are more common in muscles used for power like the calf muscle, have thousands of fibers being controlled by a single neuron.

This precise assembly of motor units plays a critical role in our daily tasks, from gently gripping a pencil to running at full speed.

Muscle Reaction Time

Muscle reaction time, a term often mentioned in NEET Biology, refers to the duration it takes for a muscle to respond after it has received a signal to contract.

Various factors influence reaction time, including the type of muscle fiber, the strength of the neural stimulus, and the current state of the muscle (whether it is fatigued or well-rested). Fast-twitch fibers, for example, react more quickly than slow-twitch fibers, providing the rapid contractions needed for explosive movements.

It's also interesting to note that reaction time isn't uniform across our bodies. Muscles involved in reflex actions, like the ones responsible for pulling our hand away from a hot surface, have a much faster reaction time compared to those used for conscious, deliberate movements, such as lifting weights. This variability is an adaptation that is critical for our survival and physical performance.

Muscle Fatigue and Anaerobic Respiration

Muscle fatigue is a common experience during rigorous physical activities and is a topic of importance in NEET Biology.

When muscles are used extensively, they may not receive enough oxygen to perform aerobic respiration, which is their preferred method of generating energy. Instead, they switch to anaerobic respiration, a process that can function without oxygen but produces lactic acid as a byproduct. Accumulation of lactic acid can lead to a burning sensation and the gradual decline in muscle efficiency and strength, a phenomenon known as muscle fatigue.

While the process of anaerobic respiration is a clever workaround, allowing us to continue intense activities for a little while longer, it's not sustainable. As a result, it's crucial for muscles to have rest periods to clear out the lactic acid, recover, and ultimately return to the state of homeostasis.