Why is convergence reflex important

The complexity of the circuitry the chain or network of neurons controlling a ocular motor response increases with the level of processing involved in initiating, monitoring, and guiding the response. In this chapter we will start at the level of reflex responses and move onto more complex voluntary responses in the following lecture.

The eye blink reflex is the simplest response and does not require the involvement of cortical structures. In contrast, voluntary eye movements i. The ocular reflexes are the simplest ocular motor responses. Ocular reflexes compensate for the condition of the cornea and for changes in the visual stimulus. For example, the eye blink reflex protects the cornea from drying out and from contact with foreign objects. The pupillary light reflex compensates for changes in illumination level, whereas the accommodation responses compensate for changes in eye-to-object-viewed distance.

Note that reflex responses are initiated by sensory stimuli that activate afferent neurons e. In general, ocular reflexes are consensual i.

Consequently, a light directed in one eye elicits responses, pupillary constriction, in both eyes. In this chapter you will learn of the structures normally involved in performing these ocular responses and the disorders that result from damage to components of neural circuit controlling these responses.

Tactile stimulation of the cornea results in an irritating sensation that normally evokes eyelid closure an eye blink. The response is consensual i.

The corneal eye blink reflex neural circuit: This neural circuit Figure 7. Figure 7. As the afferent information from each cornea is distributed bilaterally to facial motor neurons by the reticular formation interneurons, the eye blink response is consensual, that is, both eye lids will close to stimulation of the cornea of either eye. The pupillary light reflex involves adjustments in pupil size with changes in light levels.

The pupillary light reflex allows the eye to adjust the amount of light reaching the retina and protects the photoreceptors from bright lights. The iris contains two sets of smooth muscles that control the size of the pupil Figure 7. Both muscles act to control the amount of light entering the eye and the depth of field of the eye 1. The pupillary light reflex neural circuit : The pathway controlling pupillary light reflex Figure 7.

The lines ending with an arrow indicate axons terminating in the structure at the tip of the arrow. The lines beginning with a dot indicate axons originating in the structure containing the dot.

Bilateral damage to pretectal area neurons e. Recall that the optic tract carries visual information from both eyes and the pretectal area projects bilaterally to both Edinger-Westphal nuclei: Consequently, the normal pupillary response to light is consensual.

That is, a light directed in one eye results in constriction of the pupils of both eyes. Pupillary Dark Response. The pupils normally dilate increase in size when it is dark i. This response involves the relaxation of the iris sphincter and contraction of the iris dilator. The iris dilator is controlled by the sympathetic nervous system.

The pupillary dark reflex neural circuit : The pathway controlling pupil dilation involves the. Axons from the superior cervical ganglion also innervate the face vasculature, sweat and lachrymal glands and the eyelid tarsal muscles. When the superior cervical ganglion or its axons are damaged, a constellation of symptoms, known as Horner's syndrome , result.

This syndrome is characterized by miosis pupil constriction , anhidrosis loss of sweating , pseudoptosis mild eyelid droop , enopthalmosis sunken eye and flushing of the face. The accommodation response is elicited when the viewer directs his eyes from a distant greater than 30 ft. The accommodation near point response is consensual i. The accommodation response involves three actions:. Pupil accommodation: The action of the iris sphincter was covered in the section on the pupillary light reflex.

During accommodation, pupil constriction utilizes the "pin-hole" effect and increases the depth of focus of the eye by blocking the light scattered by the periphery of the cornea Nolte, Figure , Pg. The iris sphincter is innervated by the postganglionic parasympathetic axons short ciliary nerve fibers of the ciliary ganglion Figure 7. Lens accommodation: Lens accommodation increases the curvature of the lens, which increases its refractive focusing power.

The ciliary muscles are responsible for the lens accommodation response. They control the tension on the zonules, which are attached to the elastic lens capsule at one end and anchored to the ciliary body at the other end Figure 7.

The ciliary muscles function as a sphincter and when contracted pull the ciliary body toward the lens to decrease tension on the zonules see Figure 7. The decreased tension allows the lens to increase its curvature and refractive focusing power. When the ciliary muscle is relaxed, the ciliary body is not pulled toward the lens, and the tension on the zonules is higher. High tension on the zonules pulls radially on the lens capsule and flattens the lens for distance vision.

The ciliary muscles are innervated by the postganglionic parasympathetic axons short ciliary nerve fibers of the ciliary ganglion. Convergence in accommodation: When shifting one's view from a distant object to a nearby object, the eyes converge are directed nasally to keep the object's image focused on the foveae of the two eyes.

This action involves the contraction of the medial rectus muscles of the two eyes and relaxation of the lateral rectus muscles. The medial rectus attaches to the medial aspect of the eye and its contraction directs the eye nasally adducts the eye. The medial rectus is innervated by motor neurons in the oculomotor nucleus and nerve.

The accommodation neural circuit : The circuitry of the accommodation response is more complex than that of the pupillary light reflex Figure 7. Ocular motor control neurons are interposed between the afferent and efferent limbs of this circuit and include the.

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Q: What is the importance of the convergence reflex? Write your answer Related questions. What is the value of the convergence reflex of the eyes?

What extrinsic eye muscles are controlled during the convergence reflex? What is convergence reflex? What extrinsic eye muscles control the movement of the eyes during convergence reflex? In the experiment on the convergence reflex what happened to the position of the eyeballs as the object was moved closer to the subject's eyes? What is the value of the convergence reflex in the eye? What is the importance of reflex hammer?

What are two example of reflex actions and their importance? What happened to the position of the eyeballs as the object was moved closer to the subjects eye? What is the importance of a reflex action? What has the author Edwin Forbes Tait written? What is the importance of reflex action? What is the importance of cat righting reflex?

Importance of reflex action? What is the importance of reflex reactions? What part of speech is convergence? What is another word for convergence?

What is a example of convergence? Is the knee-jerk reflex a simple reflex stretch reflex or a spinal reflex? Three reactions occur simultaneously; the eyes adduct, the ciliary muscles contract, and the pupils become smaller. What is the process of accommodation? Accommodation: In medicine, the ability of the eye to change its focus from distant to near objects and vice versa. This process is achieved by the lens changing its shape. Accommodation is the adjustment of the optics of the eye to keep an object in focus on the retina as its distance from the eye varies.

Which cranial nerve is responsible for accommodation? What is meant by accommodation of eye How is it helpful? The process by which the ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina is called the accommodation of the eye.

What is an accommodation disorder? Accommodation disorders have a variety of causes. Visual symptoms include light sensitivity, nystagmus, blurred vision, vision loss and strabismus. What does Perla stand for? Pupils Equal and Reactive to Light and. What is near point of accommodation? Medical Definition of near point : the point nearest the eye at which an object is accurately focused on the retina when the maximum degree of accommodation is employed — compare far point — see range of accommodation.