Section IV.
PROPERTIES OF MUSCLES. A difficulty arises in examining the physical properties, due to the close connection between the muscular fibre and the cellular membrane. It is probable that most of the properties should be referred to the cellular membrane rather than the pure fibre itself; but for practical purposes, we regard the properties exhibited in any muscle as being exercised in the entire organ. It is well known that human muscles are reddish-brown. However, this color can nearly disappear with repeated washing without altering the proper fiber structure. Some animals have white muscles despite their rapid movements. The pectoral muscles of black game birds are deep red while internal ones are pale. Exercise influences muscle color significantly; it's deeper in wild than tame animals. Muscle cohesion varies but is generally less than that of membranous structures. It diminishes when the fibers lose vitality, making them easily torn in a dead body. Muscular extensibility is considerable, especially for involuntary muscles like those covering hollow organs such as stomach and bladder. Voluntary muscles contract causing others to extend; this extension concerns only the fleshy part since tendons are unyielding. Extensibility increases with muscle length. Diseases often provide striking examples of muscular extensibility, e.g., in eyelids or mouth due to swelling. The most important property is tonic contraction, which occurs independently of vital contraction and depends on cellular tissue elasticity. This property continues after death but ceases during decomposition. Vital properties include sensibility and contractility; the latter gives muscles their unique characteristics. Muscle sensibility informs us about muscle condition and warns when rest is needed to prevent overexertion. Some modern writers attribute a 'muscular sense' to muscles, which allows us to feel limb position without external senses. This property is distinct from Haller's described 'rumerrea'. The most important property of muscles is their ability to contract on stimulus application, producing animal movements essential for survival functions. Modern physiologists call this irritability or contractility. <Callout type="important" title="Key Property">Tonic contraction and contractility are crucial muscle properties that enable movement and survival.</Callout> The examples of tonic contraction include muscles recovering their original state after being distended by any cause, leaving a space between the ends proportioned to the extent of separation. Division of a living muscle produces two phenomena: retraction at both ends and antagonistic contraction. Tonic contraction is weakened but not destroyed by death; it continues for some time post-mortem causing stiffness in corpses until decomposition begins.
Key Takeaways
- Muscles exhibit various physical properties such as color, cohesion, and extensibility which are influenced by factors like exercise and death.
- Tonic contraction is a significant property of muscles that occurs independently of vital activity and depends on cellular tissue elasticity.
- Contractility enables muscles to contract upon stimulus application, producing essential animal movements.
Practical Tips
- Understanding muscle properties can help in assessing the condition of an injured person or animal during triage.
- Recognize signs of muscle fatigue as a warning for rest and recovery to prevent overexertion injuries.
Warnings & Risks
- Ignoring signs of muscle fatigue can lead to severe injury or death due to prolonged exertion beyond physical limits.
- Muscle stiffness after death is not an indicator of continued life but rather the result of tonic contraction weakening post-mortem.
Modern Application
While this chapter focuses on historical anatomical observations, understanding muscle properties and their reactions under stress remains crucial for modern survival scenarios. Knowledge of how muscles behave during exertion or injury can aid in effective first aid and triage decisions.
Frequently Asked Questions
Q: What is the significance of tonic contraction?
Tonic contraction is a significant property of muscles that occurs independently of vital activity, depending on cellular tissue elasticity. It allows muscles to recover their original state after being distended.
Q: How does muscle color change with exercise and environment?
Muscle color changes significantly due to exercise; it is deeper in wild animals than tame ones of the same species, influenced by factors such as blood circulation and a peculiar substance possibly osmazome.
Q: What happens when muscles are divided during life?
When a living muscle is divided, two phenomena occur: retraction at both ends proportioned to the extent of separation and antagonistic contraction due to elasticity.