The term afferent refers to neural pathways carrying action potentials to the brain. These include those pathways associated with either conscious senses (e.g. vision) or unconscious senses (e.g., blood pressure).  In general we call this system the Sensory Nervous System (SNS)

The term efferent refers to neural pathways carrying action potential commands away from the brain centers to structures that will carry out the commands. These structures are known in general as effectors.  The majority of effectors in the human body are either muscles or glands.  Muscles include voluntary (e.g., skeletal) and involuntary types (e.g., smooth and cardiac). Glands include exocrine (e.g., salivary) or endocrine (e.g., pituitary).

The efferent pathways are divided into two systems based primarily on their effector type.  The somatic nervous system (SomNS) carries efferent commands to skeletal muscle.  The autonomic nervous system (ANS) carries efferent commands to involuntary muscles and glands.

By studing the SomNS and ANS we will also begin to explore their effectors.
By studying the SNS we will learn about the various sensory cells used by the nervous system throughout our body.  In subsequent trimesters sensors and effectors will be explored in greater detail.