The most likely mode of transmission for Hepatitis B is

A. node - SA node - bundle of His - right & left bundle branches - Purkinje fibers. : This sequence begins with a vague term and misplaces the primary pacemaker. The sinoatrial node must initiate the impulse before reaching the atrioventricular node. This lacks the correct hierarchical flow of electrical depolarization.

B. Purkinje fibers - right & left bundle branches - bundle of His - AV node - SA node. : This represents a retrograde conduction pattern rather than the physiological anterograde pathway. Normal cardiac activation proceeds from the atria down to the ventricular apex. It is not the standard functional order of conduction.

C. SA node - AV node - bundle of His - right & left bundle branches - Purkinje fibers. : The impulse begins at the sinoatrial node, pauses at the atrioventricular node, and travels through the ventricular septum. It then distributes via the bundle branches to the terminal Purkinje network. This is the anatomical route for ventricular systole.

D. SA node - AV node - Purkinje fibers - right & left bundle branches - bundle of His. : This choice incorrectly places the terminal Purkinje fibers before the bundle of His and its branches. The electrical signal must pass through the specialized septal conduction tissues first. It does not follow the correct physiological progression.

A. Resting tremors and muscle rigidity. : These extrapyramidal signs result from the specific loss of dopaminergic neurons in the substantia nigra. The lead-pipe or cogwheel rigidity and rhythmic tremors at rest are pathognomonic findings. They distinguish it from primary cortical or demyelinating diseases.

B. Early cognitive decline. : Memory loss and disorientation at the onset of illness are characteristic of Alzheimer's disease or Frontotemporal dementia. In Parkinson's, cognitive impairment typically occurs much later in the disease progression. Motor symptoms almost always precede significant dementia.

C. Peripheral nerve demyelination. : This describes pathologies like Guillain-Barre syndrome or chronic inflammatory demyelinating polyneuropathy. Parkinson's is a central nervous system disorder involving deep gray matter nuclei. It does not involve the destruction of peripheral myelin sheaths.

D. Excess dopamine in the brain. : Parkinson's is characterized by a profound deficiency of dopamine, not an excess. Excess dopamine is sometimes associated with schizophrenia or the side effects of levodopa therapy. The disease itself is a hypodopaminergic state.