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Sympathetic Nervous System (T1-T4)
         ↑           ↓
    Spinal Cord → Sympathetic Chain Ganglia → Cardiac Nerves
                         ↓
                 Release Norepinephrine
                         ↓
                    Increase HR & Force

    Parasympathetic Nervous System (Medulla)
          ↓
    Vagus Nerve (Cranial Nerve X)
          ↓
   Release Acetylcholine
          ↓
  Decrease HR & Force