The purpose of this study was to explore students' knowledge and learning of the human nervous system (HNS) in an introductory undergraduate Human Anatomy and Physiology course. Classroom observations, demographic data, a preinstructional unit test with drawings, and a postinstructional unit test with drawings were used to identify students' overall knowledge and learning during the unit of study. Quantitative and qualitative analysis indicate that students have an initially poor understanding of the nervous system with many prevailing alternative conceptions. These alternative conceptions include both structural and functional components and often incorporate colloquial use of language. Findings reveal students include the heart as a major component of the HNS, a reflex arc illustrated by the action rather than structure, and types of neurons (unipolar, bipolar, or multipolar) differentiated by charge or number of cell bodies rather than structural arrangement. Classroom instruction coupled with concurrent laboratory participation provided experiences for students to overcome some of their alternative conceptions. The finding of this research suggest that instructors should be aware of the students' prevailing alternative conceptions prior to instruction and that use of drawings as a formative assessment tool is an excellent way to collect such information. (Contains 3 tables and 6 figures.)