The nervous system begins prenatally and develops into the spinal cord and brainstem. The brainstem further develops into the cerebellum and cerebral hemispheres. The central nervous system comprises the brain and spinal cord, encased in bone and protected by cerebrospinal fluid. The brain directly controls thoughts, emotions, and motivations while the spinal cord carries information between the brain and body. The peripheral nervous system relays information between the central nervous system and receptors and effectors throughout the body. It connects the brain to sensory organs and muscles via the somatic and autonomic nervous systems.