Exam 4 Review:  Chapter 15:  Tunics of the Eye

Diagram of the Eyeball	Ciliary Body, Suspensory Ligament, and Lens

tunics - The three coats which form the wall of the eyeball, one inside the other, the outer fibrous, the middle vascular, and the inner sensory layers/coats/tunics.

fibrous tunic - The outermost coat of the eyeball consisting of dense collagenous tissue and divided into an anterior transparent cornea and a posterior opaque (white) sclera; this layer provides support, protection and determines the shape of the eye.

sclera - White opaque portion of the fibrous tunic of the eyeball, composed of a dense irregular fibrous connective tissue; it is the site of attachment for the extrinsic eye muscles which rotate the eyeball.

cornea - Transparent dome-shaped anterior portion of the eyeball; part of the fibrous tunic, composed of a specially formed dense regular fibrous connective tissue covered by a nonkeratinized stratified squamous epithelium; it is a powerful refracting surface, providing 2/3 of the eye's focusing power.

vascular tunic - The middle coat of the eyeball consisting of highly vascular and heavily pigmented connective tissue consisting of a posterior choroid layer and an anterior ciliary body and the iris.

choroid - The posterior portion of the vascular middle tunic of the eyeball, lined on the inside by a layer of darkly pigmented cells; it provides the main blood supply to the back of the eye and gives rise to the ciliary body and the iris anteriorly.

ciliary body - The thickened portion of the vascular tunic of the eye located between the choroid and the iris which contains a circular layer of ciliary muscles whose contraction causes the lens to thicken, increasing its ability to focus at near objects.

ciliary muscles - The circular layer of smooth muscle within the ciliary body of the vascular tunic of the eyeball whose contraction causes the lens to thicken, increasing its ability to focus at near objects; they are regulated by visceral motor commands from the Autonomic Nervous System.

suspensory ligament - The delicate fibrous membrane, composed of collagen fibers, which holds the lens of the eye in place; it is anchored to the ciliary process/body.

iris - The pigmented, round, contractile membrane of the eye, the anterior portion of the vascular tunic of the eyeball, suspended between the cornea and lens and perforated by the pupil; it contains a radial and a circular layer of smooth muscle innervated by the ANS to regulate the amount of light entering the eye by adjusting the diameter of the pupil.

pupil - Opening in the center of the iris through which light enters the eye; it is opened or closed by autonomic reflexes in order to regulate the amount of light entering the eyeball.

sensory tunic = retina - Neural tunic of the eyeball; the innermost of the three tunics of the eye; contains photoreceptors (rods, cones) in the deepest layer, bipolar neurons, amacrine cells and horizontal cells in the middle layer, and ganglion cells in the superficial layer.

Sketch and label:

3. a reflex arc for the accommodation (pupillary) reflex.

Note:  Cameras which have two sequential flashes to eliminate "red-eye" make use of the pupillary refles.  See below.   The diagram below is the model for your answer on the exam.  The parasympathetic part of the reflex causes the pupil to constrict when the retina is exposed to bright light.  A similar diagram could be drawn from the more complete diagram at the bottom to illustrate the sympathetic part of the reflex. The parasympathetic part of the reflex: 1.  The oculomotor nucleus contains the cell body for the preganglionic neuron. 2.  The preganglionic neuron synapses with the postganglionic neuron in the ciliary ganglion. 3.  The postganglionic neuron stimulates the circular muscle in the iris to contract, constricting the pupil. The diagram at the bottom illustrates both pathways.