| MadSci Network: Anatomy |
General reference: Human Biology by George B. Johnson, 1994, WC Brown Publ
The submitted questions really are a matter of definitions and nervous system vocabulary:
1) Sympathetic nervous system: One of two divisions of the autonomic (involuntary) nervous system; this division controls the "fight or flight" responses of the individual, such as INCREASING the heart rate, the respiratory rate, the blood pressure, and the blood flow to the skeletal muscles.
2) Parasympathetic nervous system: The other division of the autonomic system; this division in general counteracts or inhibits or acts to produce the opposite effect as that of the sympathetic system; i.e., it will DECREASE the heart, respiratory, and blood pressure responses summarized above (see #1), as well as promote digestion and bowel/urine elimination.
3) Somatic: An adjective derived from the noun, "soma" or body; used to describe nervous system responses that are associated with the trunk, arms, legs, head and neck and their musculature; somatic is the opposite of another adjective, visceral, which describes body ORGAN (VISCERA) nervous system responses.
4) Autonomic: An adjective meaning involuntary or automatic nervous system reactions; i.e., those that are not regularly influenced by conscious choice or a voluntary decision to act. Thus the parasympathetic and sympathetic systems are designted as autonomic in nature. The opposite term is voluntary.
5) Motor: An adjective meaning motion or movement; in the case of the skeletal muscles of the limbs, their innervation is volunary motor in type; while the control of the bowel smooth muscle and the heart muscle is described as being involuntary motor in type. Motor control involves nervous OUTPUT impulses, which are sent AWAY from the brain and spinal cord (called the central nervous system). The opposite adjective is sensory (see below).
6) Sensory: An adjective meaning sensation or feeling and defines the second type of nervous system information, which is information INPUT TOWARD the brain and spinal cord from the various sensory receptors (i.e., pain, heat, cold, touch) responding to stimuli from outside the nervous system (and often from the environment outside the individual).
7) Efferent: Another adjective that means nerve impulse transmission AWAY from the central nervous system. Thus motor control is efferent control, because it involves the movement of nerve information away from the center and toward the periphery.
8) Afferent (added as afterthought): The opposite of efferent; thus sensory information is by definition afferent in nature because the impulses travel toward the center; this is considered input to the central nervous system.
COMMENT: The excercise in preparing these definitions shows that a major concept in neuroscience is the careful balance and interplay of opposites; a concept shared by the endocrine system in which negative feedback maintains homeostasis.