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-Rods

Single sensory nerve fiber

Single sensory nerve fiber

-Cones

-Cones

(j Many sensory lerve fibers

Cone

Cone

(a) A single sensory nerve fiber transmits impulses from several rods to the brain. (b) Separate sensory nerve fibers transmit impulses from cones to the brain. (c) A scanning electron micrograph of rods and cones (1,350x).

of rods increases in these areas. Also, the degree of convergence among the rods and cones increases toward the periphery of the retina. As a result, the visual sensations from images focused on the sides of the retina tend to be blurred compared with those focused on the central portion of the retina.

The bony orbit usually protects the eye, but a forceful blow can displace structures within and around the eye. The suspensory ligaments may tear and the lens dislocated into the posterior cavity, or the retina may pull away from the underlying vascular choroid coat. Once the retina is detached, photoreceptor cells may die because of lack of oxygen and nutrients. Unless such a detached retina is repaired surgically, this injury may cause visual loss or blindness.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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