Iris dilator muscle "musculus dilator pupillae", The "Nomina Anatomica" as authorized in 1895 in Basle and in 1935 in Jena used the full Latin expression. Iris dilator muscle The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system. When stimulated, the cells contract, widening the pupil and allowing for more light to pass through the eye.
Skeletal muscle in the rectus femoris. Convergent arrangements are triangle or fan shaped, with wide origins and more narrow insertions. The wide variation of pennation angles in this architecture can actually allow for multiple functions. For instance, the trapezius, a prototypical convergent muscle, can aid in both shoulder elevation and depression. Multipennate arrangements are not limited to a particular arrangement, but—when used specifically—commonly refer to what is essentially a combination of bipennate or unipennate arrangements with convergent arrangements. An example of this architecture would be the human deltoid muscle. Many muscles are named by the action the muscle performs. These include: The