In cardiac muscle cells, what process links an action potential to muscle contraction?

A. An adolescent who is depressed over not being accepted by peers: Role playing allows adolescents to practice social interactions, develop communication skills, and explore coping strategies in a safe environment. It can help the client gain confidence, improve problem-solving abilities, and prepare for real-life peer situations.

B. Hyperactive 4-year-old who has recently been tested for autism: While play therapy is useful for young children and those with autism spectrum disorder, structured role playing may be too abstract for a 4-year-old. Developmental level and attention span may limit the effectiveness of role playing in this age group.

C. An adult with schizophrenia who often refuses to take prescribed antipsychotic medications: Role playing is generally less effective for clients with active psychotic symptoms such as delusions or hallucinations. Medication adherence issues in schizophrenia are better addressed through psychoeducation, motivational interviewing, and structured support.

D. An older adult resident of a long-term care facility who sometimes takes other residents' belongings: While role playing could be used to teach social norms, behavioral interventions such as redirection, supervision, and environmental modifications are more practical and immediately effective for managing problematic behaviors in older adults with cognitive decline.

A. Potassium efflux and membrane repolarization: Potassium efflux occurs during the repolarization phase of the cardiac action potential, restoring the resting membrane potential. While necessary for resetting the cell electrically, it does not directly trigger the contractile machinery or link the action potential to muscle contraction.

B. Inhibition of myosin heads: Myosin head inhibition occurs when tropomyosin blocks binding sites on actin in relaxed muscle. This is the resting state prior to contraction, not the process that couples the action potential to contraction.

C. Closing of sodium channels: Sodium channels close immediately after depolarization, contributing to the refractory period and preventing further Na+ influx. While important for the timing of action potentials, this does not directly initiate contraction or activate contractile proteins.

D. Calcium entry and activation of contractile proteins: During excitation-contraction coupling in cardiac muscle, calcium ions enter the cell through voltage-gated L-type calcium channels during the plateau phase. This calcium triggers release of Ca2+ from the sarcoplasmic reticulum, allowing calcium to bind to troponin. Troponin undergoes a conformational change, which permits myosin cross-bridge cycling ultimately producing muscle contraction.