Anatomy of the Nervous System
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.