Final answer:
Intrinsic control of GI tract motility and secretion is governed by the enteric nervous system, which is made up of the myenteric and submucosal plexuses. These regulate the rhythmic contractions for motility and digestive secretions, respectively, acting independently of the central nervous system.
Step-by-step explanation:
Local/intrinsic control of motility and secretion in the gastrointestinal (GI) tract is mainly managed by the enteric nervous system. The enteric nervous system encompasses around 100 million motor, sensory, and interneurons and operates independently of the central nervous system. This system is found in two primary plexuses within the alimentary canal: the myenteric plexus (plexus of Auerbach) and the submucosal plexus (plexus of Meissner). The myenteric plexus is essential for controlling the rhythmic and forceful contractions of the muscularis, critical for motility. Meanwhile, the submucosal plexus regulates digestive secretions and responds to the presence of food.
Contrary to intrinsic regulation, extrinsic innervation through the autonomic nervous system, comprising both sympathetic and parasympathetic nerves, also influences GI motility and secretion. Sympathetic activation tends to decrease GI motility and secretion, whereas parasympathetic activation increases them, illustrating the balance between the extrinsic and intrinsic control mechanisms within the GI tract.