Lif

In bright light

Figure 12.32

Sympathetic motor nerve fiber

Radially arranged smooth muscle fibers of the iris

Circularly arranged smooth muscle fibers of the iris

Pupil

Parasympathetic ganglion ire

In dim light, the radial muscles of the iris are stimulated to contract, and the pupil dilates. In bright light, the circular muscles of the iris are stimulated to contract, and the pupil constricts.

Sclera

Pigmented choroid coat

Retina

-—- _ . * Pigmented •(•1*1 ™ .1—epithelium

Impulses to optic nerve

Figure

Sclera

Pigmented choroid coat

Retina

Impulses to optic nerve

Horizontal cell Bipolar neuron Amacrine cell

Ganglion cell

Nerve fibers

Receptor cells

Horizontal cell Bipolar neuron Amacrine cell fc t f Light waves

Ganglion cell

Nerve fibers

Vitreous humor

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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