Anatomy of the Nervous System
Cerebral hemispheres are separated by a fissure and falx cerebri but are connected by commissures and other structures. The medial brain surface reveals complex, highly organized, structures of the hemispheres. The spinal cord and the brain (ie, the CNS) merge at the level of the brainstem. The major connection between the 2 hemispheres is the corpus callosum. Important sites of CNS drug effects are in the limbic system— communicating structures involved with smell, memory, and emotion. Four communicating cavities (ventricles) in the brain contain CSF produced by choroid plexuses. CSF circulation— from ventricles to central canal of spinal cord to drainage in venous sinuses—provides protection against trauma and a way to communicate chemically. Structures respond to circulating substances (eg, neurotransmitters, neuropeptides, hormones), as evidenced by introducing substances into CSF. The central action of a drug is studied by direct injection into ventricles.