Cardiac accelerator fibers originate from which spinal segments?

Cardiac accelerator fibers originate from which spinal segments?

• A. C3-C5
• B. T1-T4
• C. T5-T12
• D. T10-L1

Answer: (B)

Cardiac accelerator fibers are part of the sympathetic nervous system that speeds up the heart and strengthens its contractions. These preganglionic neurons sit in the spinal cord's intermediolateral cell column from the upper thoracic levels and send their fibers out through the ventral roots. They then travel in the sympathetic chain to the upper thoracic and cervical ganglia, where they synapse on postganglionic neurons that reach the SA node, AV node, and myocardium. That pathway is why increasing sympathetic activity raises heart rate and contractility. The upper thoracic region, specifically around T1 to T4, is the source of these cardiac accelerator fibers. Choices referring to C3-C5 point to the phrenic nerve, not cardiac acceleration. Lower thoracic or lumbar levels like T5-T12 or T10-L1 are associated with other thoracic or abdominal innervations and don’t provide the primary input to the heart’s acceleration.

Cardiac accelerator fibers are part of the sympathetic nervous system that speeds up the heart and strengthens its contractions. These preganglionic neurons sit in the spinal cord's intermediolateral cell column from the upper thoracic levels and send their fibers out through the ventral roots. They then travel in the sympathetic chain to the upper thoracic and cervical ganglia, where they synapse on postganglionic neurons that reach the SA node, AV node, and myocardium. That pathway is why increasing sympathetic activity raises heart rate and contractility.

The upper thoracic region, specifically around T1 to T4, is the source of these cardiac accelerator fibers. Choices referring to C3-C5 point to the phrenic nerve, not cardiac acceleration. Lower thoracic or lumbar levels like T5-T12 or T10-L1 are associated with other thoracic or abdominal innervations and don’t provide the primary input to the heart’s acceleration.