Question

if one nerve stimulus arrives at a muscle fiber so soon that the fiber has only partially relaxed from the previous twitch, the most likely result will be________.
fatigue
spasm
incomplete tetanus
complete tetanus
flaccid paralysis
question 16 (1.7 points) saved
why is the contraction strength of smooth muscle relatively independent of its resting length?
it gets nearly all of its ca²+ from the extracellular fluid.
it does not have intercalated discs.
it does not have sarcomeres.

Explanation:

• Fatigue: Fatigue occurs when muscle is unable to contract due to lack of energy (like ATP depletion), not directly due to the described stimulus - relaxation pattern.
• Spasm: A spasm is a sudden, involuntary contraction, often due to nerve irritation, not related to the described sequential nerve - muscle interaction.
• Incomplete tetanus: In incomplete tetanus, nerve stimuli arrive at a muscle fiber before it has fully relaxed from the previous twitch. This causes a sustained but partially relaxed contraction (a "bumpy" contraction).
• Complete tetanus: In complete tetanus, stimuli are so frequent that there is no relaxation between contractions. But the question states "partially relaxed", so it's not complete tetanus.
• Flaccid paralysis: Flaccid paralysis is a loss of muscle tone and the ability to contract, usually due to nerve damage or certain diseases, not related to the described stimulus - relaxation pattern.

For the second question:

• Smooth muscle contraction and resting length:
• Smooth muscle does not have sarcomeres (the contractile units with a strict overlap - based length - tension relationship like in skeletal muscle). In skeletal muscle (with sarcomeres), optimal overlap of actin and myosin (determined by resting length) is crucial for maximum contraction strength. Since smooth muscle lacks sarcomeres, its contraction strength is relatively independent of resting length.
• The source of \(Ca^{2 +}\) (from extracellular fluid) is related to the initiation of contraction, not the length - strength relationship.
• Intercalated discs are cell - to - cell junctions in cardiac muscle, not relevant to the length - strength relationship of smooth muscle.

Answer:

• First question: C. incomplete tetanus
• Second question: It does not have sarcomeres.