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Figure 22A

Computer analysis improves the consistency and accuracy of describing sperm motility, morphology, and abundance.

Emission (e-mish'un) is the movement of sperm cells from the testes and secretions from the prostate gland and seminal vesicles into the urethra, where they mix to form semen. Emission occurs in response to sympathetic nerve impulses from the spinal cord, which stimulate peristaltic contractions in smooth muscles within the walls of the testicular ducts, epididymides, vasa deferentia, and ejaculatory ducts. At the same time, other sympathetic impulses stimulate rhythmic contractions of the seminal vesicles and prostate gland.

As the urethra fills with semen, sensory impulses are stimulated and pass into the sacral portion of the spinal cord. In response, motor impulses are transmitted from the cord to certain skeletal muscles at the base of the erectile columns of the penis, causing them to contract rhythmically. This increases the pressure within the erectile tissues and aids in forcing the semen through the urethra to the outside—a process called ejaculation (e-jak"u-la'shun).

The sequence of events during emission and ejaculation is coordinated so that the fluid from the bulbourethral

Shier-Butler-Lewis: I VI. The Human Life Cycle I 22. Reproductive Systems I I © The McGraw-Hill

Human Anatomy and Companies, 2001

Physiology, Ninth Edition sends an image to a videocassette recorder, which projects a live or digitized image. The camera also sends the image to a computer, which traces sperm trajectories and displays them on a monitor or prints a hard copy (Figure 22A). Figure 22B shows a CASA of normal sperm, depicting how the swimming pattern alters as they travel.

CASA systems are also helpful in studies that use sperm as "bio-markers" of exposure to toxins. For example, the sperm of men who work in the dry cleaning industry and are exposed to the solvent per-chloroethylene (believed to damage sperm) were compared with sperm from men who work in the laundry industry and are exposed to many of the same chemicals except this one. CASA showed a difference in sperm motility that was directly related to level of exposure, as measured by exhalation of the chemical. This result supported the reproductive evidence: Although the men in both groups had the same num bers of children, the dry cleaners' partners took much longer to conceive than did the launderers' partners. Table 22B lists the components of a sperm analysis. ■


Normal Value


2-6 milliliters/ejaculate

Sperm density

120 million cells/milliliter

Percent motile

> 40%

Motile sperm density

> 8 million/milliliter

Average velocity

> 20 micrometers/second


> 8 micrometers/second

Percent abnormal morphology

> 40%

White blood cells

> 5 million/milliliter

(a) (b) (c) (d)

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