1/2/2023 0 Comments Autonomic nervous system lensDuring a "fright, flight, or fight" response, vasodilation of certain arterioles supplying skeletal tissue is essential. beta 2 receptors expressed on arterioles in a particular tissue as well as on the concentration of epinephrine in the blood. The degree of vasodilation is dependent on the density of alpha 1 vs. Beta 2 receptors are activated primarily by circulating epinephrine and their stimulation causes relaxation of smooth muscle and vasodilation. Arterioles of certain organs including skeletal muscle and cardiac muscle express beta 2 receptors in addition to alpha 1 receptors. Since arterioles express primarily alpha 1 receptors, you might imagine that an increase in sympathetic nerve firing would result in vasoconstriction of most arterioles. This contraction narrows the diameter of the arteriole lumen thus reducing blood flow. Activating these receptors results in an increase in intracellular calcium causing smooth muscle contraction. Blood VesselsĪrterioles of the body mostly express alpha 1 receptors on their smooth muscle cells. Therefore, beta 1 antagonists such as betaxolol are also often used to treat glaucoma, since they reduce the production of aqueous humor. Stimulation of beta 1 receptors on the ciliary body epithelium increases the production of aqueous humor. This action helps to open up pores in the trabecular network so that aqueous humor can drain into the canal of Schlemm and into the venous circulation.įor this reason, eye drops that are muscarinic agonists, such as pilocarpine, can be used to treat elevated intraocular pressure (glaucoma), lowering intraocular pressure by increasing the outflow of aqueous humor. This tissue has beta - 2 receptors and when stimulated by the sympathetic nervous system, it causes relaxation which helps with far vision and when stimulated by the parasympathetic nervous system on M3 receptors it causes contraction which helps with near vision.Ĭontraction of the ciliary muscle also puts tension on an area calle the trabecular network in the anterior eye. The autonomic nervsous system also innervates the ciliary muscle of the eye which is behind the retina and around the lens. Both are mydriatics and are administered as eye drops to reduce systemic effects. Phenylephrine is an alpha 1 agonist and atropine is a muscarinic antagonist. Ophthalmologists often need to enlarge the diameter of the pupil in order to more easily examine the retina. The inner, sphincter pupillae muscles are innervated by the parasympathetic division, express M3 receptors, and cause miosis when they contract. Outer iris smooth muscles - the dilator pupillae muscles express alpha 1 receptors, cause mydriasis when they contract and are controlled by sympathetic fibers. Among these are the intrinsic muscles of the eye (those controlling the size of the pupil and the shape of the lens) and the secretory epithelium (produces aqueous humor) of the ciliary body.Ĭircular and radial muscles of the iris, named sphincter pupillae and dilator pupillae respectively, control how much light enters the eye. The eye has multiple autonomic functions controlled by several autonomic receptors. Having an understanding of the ANS and its particular receptors located on effectors and the drugs that activate or block these receptors will assist your understanding of the actions of this system. In the following section, some drugs will be presented. Drugs that are agonists, bind to a specific receptor and activate it, while an antagonist binds to a receptor and prevents it from being activated, or inhibits it. Certain drugs exert their effects by binding to cholinergic and adrenergic receptors to increase or decrease the activity of effectors normally controlled by the ANS.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |