1. Which of the following structures is not part of the central nervous system? A. Brain B. Spinal Cord C. Sciatic Nerve D. Brainstem Answer: C. Sciatic Nerve Rationale: The central nervous system consists of the brain and spinal cord. The sciatic nerve is part of the peripheral nervous system, which connects the CNS to the limbs and organs. 2. The blood-brain barrier is impermeable to many substances to protect the brain. Which substance can pass freely through this barrier? A. Glucose B. Red blood cells C. Bacteria D. Antibodies Answer: A. Glucose Rationale: The blood-brain barrier allows glucose to pass because it is the brain's primary source of energy. Other substances like red blood cells, bacteria, and antibodies are generally blocked to protect the CNS from pathogens and toxins. 3. During an action potential, the rapid influx of which ion into the neuron is responsible for depolarization? A. Calcium B. Sodium C. Potassium D. Chloride Answer: B. Sodium Rationale: During an action potential, sodium ions rush into the neuron, causing depolarization. This change in electrical charge transmits the nerve impulse along the neuron. 4. What is the primary function of the myelin sheath in a neuron? A. To produce neurotransmitters B. To facilitate rapid signal transmission