freewheel. 1  a device in the transmission of a motor vehicle that automatically disengages the drive shaft whenever it begins to turn more rapidly than the engine. 2  a form of rear bicycle wheel that has a device freeing it from the driving mechanism, as when the pedals are stopped in coasting.
Ampullae are an important part of the water vascular system of starfish, which is the responsible for the animal's locomotion. The only function of the ampullae is to store the water that enters the vascular system and send it to the minuscule tube feet, located in the ventral side of the starfish's arms.he contraction of the muscles also causes the water stored in the ampullae to move to the tube feet, which are the locomotion organs of the starfish. Nerve cells connected to the ampullae and other parts of the vascular water system control the relaxation and contraction of the ampullae's muscle fibers.
Autonomic outflow from the medulla is divided principally into sympathetic and parasympathetic (vagal) branches. Efferent fibers of these autonomic nerves travel to the heart and blood vessels where they modulate the activity of these target organs.The heart is innervated by vagal and sympathetic fibers.utonomic Innervation of the Heart and Vasculature. The medulla, located in the brainstem above the spinal cord, is a major site in the brain for regulating outflow outflow to the heart and blood vessels, and is particularly important for short-term feedback regulation of arterial pressure.