When Ciliary Muscles Contract

Parasympathetic tone is dominant when a higher degree of lens adjustment is required, such as . B reading a book. [9] The muscle bundles of the radial part of the ciliary muscle and the internal bundles of its longitudinal part form tendons in the area of their anterior insertion, which are continuous with the extracellular matrix of trabecular mesh rays (Fig. 5-11A, B). The tendons of the internal muscle bundles of the longitudinal part pass through the spur of the sclerus at its internal appearance to continue towards the trabecular network (Fig. 5-11B). The same banded material that forms the sheaths of the elastic fibers in the central area of the trabecular beams is the main structural element of the tendons. The banded material comes into direct contact with the cell membrane of the muscle cell, which forms dense ligaments at the cytoplasmic site (Fig. 5-11C). In the area of contact with the tendons, the muscle bundles rejuvenate and form deep grooves filled with bandaged tissue. The external muscle bundles of the longitudinal part of the ciliary muscle also form tendons, but connect to the fibers of the extracellular matrix of the scleral spur. The scleral spur contains collagen and elastic fibers that are arranged all around (Fig.

5-12A). The elastic fibers are continuous with those of the core of the corneoscleral mesh rays or the cribriform plexus in the adjacent tissue. The outermost muscle bundles of the longitudinal part of the ciliary muscle bend clockwise or counterclockwise before attaching to the scleral spur (Fig. 5-12B).38 They do not bend further inwards, but settle into continuous elastic fibers with the elastic fibers of the scleral spur arranged circumferentially (Fig. 5-12C). Due to the structural connections between the ciliary muscle and the spur of the sclerus, the contraction of the ciliary muscle pulls the spur backwards and widens the trabecular spaces,14 thus inducing changes in the geometry of the trabecular mesh that lead to a reduction in drainage resistance. The tone of the ciliary muscle affects the uveoscleral flow, contraction reduces it and relaxation increases it, probably by its influence on the volume of the extracellular space between the muscle bundles. Thus, atropine increases and pilocarpine reduces uveoscleral flow (see below). The effect was mainly studied in short-term experiments, but studies in monkeys with or without pre-treatment with pilocarpine provided the initial support that prostaglandins decreased IOP by increasing flow through the ciliary muscle (see below).

In addition, the age-related changes in ciliary muscle morphology and uveoscleral flow mentioned above support the general hypothesis that ciliary muscle permeability is an important determinant of uveoscleral flow rate. Viewing nearby objects requires greater focusing power. Light from nearby objects diverges as it enters the eye; Therefore, it needs to be more focused to form an image on the retina. However, there is a limit to the focusing performance of the crystal lens. With the maximum contraction of the ciliary muscle, a normal eye of a young adult can focus on objects about 15 cm from the eye. Closer objects appear blurred. The minimum distance of sharp focus is called the point close to the eye. The main effect of the ciliary muscle is the change in the shape of the lens, which occurs during the accommodation reflex. In addition, during contraction, the longitudinal fibers of the ciliary muscle widen the iridocorneal space and the schlemm canal, which facilitates the drainage of ocular fluid. The word ciliary has its origins around 1685-1695.

[15] The term eyelashes originated a few years later in the years 1705-1715 and is the neo-Latin plural of cilium, which means eyelashes. In Latin, eyelashes means upper eyelid and is perhaps a dorsal formation of supercilium, which means eyebrow. The suffix -ary originally appeared in borrowings from Middle English (-aria), Old French (-er, -eer, -ier, -aire, -er) and Latin (-ārius); It can generally mean “in connection with, associated with”, “contribution to” and “for the purposes of”. [16] Taken together, cili(a)-ary refers to various anatomical structures in and around the eye, namely the ciliary body and the ring-shaped suspension of the lens. [17] The focus of the eye is controlled by the ciliary muscle, which can change the thickness and curvature of the lens. This process of concentration is called accommodation. When the ciliary muscle is relaxed, the lens is quite flat and the focusing force of the eye is at a minimum. Under these conditions, a parallel beam of light is focused on the retina. As the light from distant objects is almost parallel, the relaxed eye is focused on looking at distant objects. In this context, “removed” is about 6 m and more (see exercise 15-1). Presynaptic parasympathetic signals from the Edinger-Westphal nucleus are transported by the cranial nerve III (the oculomotor nerve) and pass through the ciliary ganglion via the postnodal parasympathetic fibers that migrate into the short ciliary nerves and supply the ciliary body and iris.

Parasympathetic activation of muscarinic M3 receptors causes contraction of the ciliary muscles. The effect of contraction is to reduce the diameter of the ciliary muscle ring, which leads to the relaxation of zozonule fibers, the lens becomes more spherical and increases its power to refract light for near vision. [Citation needed] Conversely, the relaxation of the ciliary muscle causes the zonal fibers to tighten, the lens to flatten and increase long-range focus. Aqueous humor is a transparent fluid in the eye that provides internal structures with nutrients and maintains intraocular pressure. It is secreted by the cells of the ciliary body in the posterior chamber of the eye. It circulates through the pupil and enters the anterior chamber. From there, the liquid leaves the eye through the small kanas located on the limb of the eye (the schlemm channels). The process of secretion of aqueous humor must be in synergy with drainage.

If this is not the case, the accumulation of this fluid can lead to an increase in intraocular pressure, which is the main risk factor for glaucoma. The cell membrane of the nerve endings is in direct contact with the elastic fibers of the scleral spur. The contact between the nerve end and the fibers of the connective tissue is a very characteristic feature of mechanosensors, since it is necessary to measure the tone of extracellular fibers. The mechanosensors of the scleral spur can act as proprioreceptive tendon organs for the ciliary muscle or modulate the tone of the cells of the scleral spur. Alternatively, the scleral spur mechanosensors could perform a baroreceptor-like function in response to changes in IOP. In fact, physiological studies suggest that such sensors may exist, as sensory discharges in laboratory animals have been recorded in response to changes in IOP. Ciliary muscle affects the zonal fibers of the eye (fibers that hold the lens in place during housing) and allows lens shape changes for light focus. When the ciliary muscle contracts, it releases the tension on the lens caused by the zonal fibers (fibers that hold or flatten the lens). This tension relief of the zonal fibers makes the lens more spherical and adapts to focus with a short range.

The appendages of the ciliary muscle have not yet been determined. According to some authors, the ciliary muscle comes from a protrusion of the sclera in the anterior chamber of the eye, also known as the scleral spur. .