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Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in controlling hemorrhage and reducing acute blood loss.
The activation of these receptors by acetylcholine will activate an intracellular G protein, that in turn will activate the phospholipase C pathway, that will end in an increase of intracellular calcium concentrations and therefore contraction of the smooth muscle cell. The muscle contraction will cause the diameter of the bronchus to decrease ...
The middle pharyngeal constrictor is a sheet-like, fan-shaped muscle. [1]The muscle's fibers diverge from their origin: the more inferior fibres descend deep to the inferior pharyngeal constrictor muscle; the middle portion of fibres pass transversely; the more superior fibers ascend and overlap the superior pharyngeal constrictor muscle.
Middle constrictor muscle; Inferior constrictor muscle; During swallowing, these muscles constrict to propel a bolus downwards (an involuntary process). The inner longitudinal layer includes: Stylopharyngeus muscle; Salpingopharyngeus muscle; Palatopharyngeus muscle; During swallowing, these muscles act to shorten and widen the pharynx.
The origin of a muscle is the bone, typically proximal, which has greater mass and is more stable during a contraction than a muscle's insertion. [14] For example, with the latissimus dorsi muscle, the origin site is the torso, and the insertion is the arm. When this muscle contracts, normally the arm moves due to having less mass than the torso.
An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, such as the muscle contractions that result from tetanus. Also, a loss of function at the junction can produce paralysis. [5]
When blood pressure is increased in the blood vessels and the blood vessels distend, they react with a constriction; this is the Bayliss effect. Stretch of the muscle membrane opens a stretch-activated ion channel. The cells then become depolarized and this results in a Ca 2+ signal and triggers muscle contraction. No action potential is ...
The iris dilator and sphincter muscles are contained in the iris and contract in order to dilate or constrict the pupils. The ciliary muscles change the shape of the lens to focus on objects in accommodation. In the skin, smooth muscle cells such as those of the arrector pili cause hair to stand erect in response to cold temperature and fear. [1]