Which of the following minerals is essential for the formation of thyroid hormone?

A. leukocytosis: Leukocytosis refers to an increase in the number of white blood cells, most commonly seen with infection, inflammation, or stress responses.

B. leukopenia: Leukopenia is defined as a decrease in the total white blood cell count, which may result from bone marrow suppression, chemotherapy, viral infections, or certain autoimmune conditions.

C. differential white blood cell count: A differential white blood cell count measures the percentage of each type of white blood cell present in the blood, rather than the total number.

D. hemostasis: Hemostasis refers to the process of blood clot formation to stop bleeding and is unrelated to white blood cell levels.

A. Brain, spinal cord, and autonomic nerves: The autonomic nerves are part of the peripheral nervous system (PNS), not the central nervous system. The CNS is anatomically confined to structures housed within the cranial cavity and vertebral canal. Inclusion of autonomic nerves extends beyond the CNS classification.

B. Brain, spinal cord, and peripheral nerves: Peripheral nerves consist of cranial and spinal nerves that extend outside the brain and spinal cord. These nerves form the peripheral nervous system and serve as communication pathways rather than central processing structures. Therefore, they are not considered part of the CNS.

C. Brain and spinal cord: The central nervous system is composed exclusively of the brain and spinal cord. These structures are enclosed by the skull and vertebral column, protected by meninges and cerebrospinal fluid, and function as the primary centers for integration, processing, and coordination of neural activity.

D. Sensory division and motor division: The sensory (afferent) and motor (efferent) divisions describe functional subdivisions of the peripheral nervous system. They classify nerve pathways based on direction of impulse transmission rather than anatomical CNS structures.