Biomedical Engineering Reference
In-Depth Information
A
Anatomy and Physiology
of Human Muscle
In order to reproduce similar properties of biological muscles in artificial counter-
parts, one must fully understand mechanism, behavior, and properties of natural
muscles. This section will provide a brief summary of anatomical and physiological
characteristics of human muscles. For the latest techniques for measurement and
characterization of these biological tissues, refer to appendix B.
Muscles provide the movement capability of the human body and form 40-45%
of body weight. They provide a means of direct conversion of chemical (ATP break-
down) to mechanical (movement, work, and force) energy. Myology deals with scientific
study of muscle. There are three distinct types of muscle tissues, which vary in micro-
scopic anatomy and nervous controls. These are skeletal, cardiac, and smooth muscles.
Skeletal muscle tissues are primarily attached to bones and provide for movement
of the skeleton. They are striated because alternating light and dark bands are visible
when the tissue is examined under a microscope. They are also classified as voluntary
muscle tissue since they are under conscious control.
Cardiac muscle tissue is found in the heart only. It is also striated, but involun-
tarily—that is, its contraction is usually not under conscious control and uses a
pacemaker included in the muscle to produce a heartbeat.
Smooth muscle tissue is found in the walls of hollow internal structures such as
blood vessels, the stomach, the intestines, and most abdominal organs. It is nonstri-
ated and involuntary.
There are three basic functions of muscle tissues by contraction or alternating con-
traction and relaxation: producing motion, providing stabilization, and generating heat.
It is thought that as much as 85% of body heat is generated by muscle tissue contraction.
There are four functional characteristics of the muscle:
Excitability, or the ability to respond to certain stimuli by producing action
potentials or impulses of electrical signal: The stimuli triggering action
potentials are chemical, such as neurotransmitters released by neurons or
hormones distributed by the blood.
Contractility, or the ability to contract and generating force to do work:
Contraction is in response to one or more muscle action potentials.
Extensibility, or the ability of the muscle to be extended (stretched) without
damaging the tissue: Most skeletal muscles are arranged in opposing or
antagonistic pairs in which one muscle tissue contracts while the other is
relaxed or even stretched.
Elasticity, or the ability of the muscle tissue to return to its original shape
after stimulation.
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