Electrical slow waves in the small intestine. A, No action potentials appear at the crests of the slow waves, and the muscle contractions associated with each slow wave are small. B, Muscle action potentials appear as sharp upward-downward deflections at the crests of the slow waves. Large-amplitude muscle contractions are associated with each slow wave when action potentials are present. Electrical slow waves trigger action potentials, and action potentials trigger contractions.
thetic signals to the digestive tract originate at levels 3 and 4 (central sympathetic and parasympathetic centers) in the medulla oblongata and represent the final common pathways for the outflow of information from the brain to the gut. Level 5 includes higher brain centers that provide input for integrative functions at levels 3 and 4.
Autonomic signals to the gut are carried from the brain and spinal cord by sympathetic and parasympathetic nervous pathways that represent the extrinsic component of innervation. Neurons of the enteric division form the local intramural control networks that make up the intrinsic component of the autonomic innervation. The parasympa-thetic and sympathetic subdivisions are identified by the positions of the ganglia containing the cell bodies of the postganglionic neurons and by the point of outflow from the CNS. Comprehensive autonomic innervation of the di-
Interstitial cells of Cajal. ICCs form networks that contact the GI musculature.
Electrical slow waves originate in the networks of ICCs. ICCs are the generators (pacemaker sites) of the slow waves. Gap junctions connect the ICCs to the circular muscle. Ionic current flows across the gap junctions to depolarize the membrane potential of the circular muscle fibers to the threshold for the discharge of action potentials.
gestive tract consists of interconnections between the brain, the spinal cord, and the ENS.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.