What level of the brain stem is the major input to the cerebellum?

Correct Answer: B

Rationale: The pons (B) is the major input to the cerebellum via the middle cerebellar peduncle, relaying cortical signals for coordination. The midbrain (A) and medulla (C) have lesser roles, and spinal cord (D) input is via inferior peduncles. B is correct.

Correct Answer: D

Rationale: The axon is the part of a neuron that transmits an electrical signal (action potential) to a target cell, such as another neuron or muscle cell, via the synapse. Dendrites receive signals, and the soma (cell body) processes them, but the axon is responsible for transmission.

Correct Answer: C

Rationale: Myelin is primarily composed of lipids (e.g., cholesterol) and proteins (e.g., myelin basic protein), which form the insulating sheath around axons. Carbohydrates and nucleic acids are not major components.

Correct Answer: B

Rationale: Ligand-gated channels open when a neurotransmitter (ligand) binds to them, allowing ions to flow. Voltage-gated channels respond to depolarization, not ligand-gated ones.

Correct Answer: D

Rationale: Metabotropic receptors require effector proteins (e.g., G-proteins) to initiate intracellular signaling cascades. Ionotropic receptors are ligand-gated channels that don’t use effector proteins.