MUSCLES-STRUCTURE AND FUNCTION
FUNCTIONS AND PROPERTIES OF MUSCLE TISSUE
Functions of muscle tissue
- Movement: Our body's skeleton gives enough rigidity to our body that skeletal muscles can yank and pull on it, resulting in body movements such as walking, chewing, running, lifting, manipulating objects with our hands, and picking our noses.
- Maintenance of posture: Without much conscious control, our muscles generate a constant contractile force that allows us to maintain an erect or seated position, or posture.
- Respiration: Our muscular system automatically drives movement of air into and out of our body.
- Heat generation: Contraction of muscle tissue generates heat, which is essential for maintenance of temperature homeostasis. For instance, if our core body temperature falls, we shiver to generate more heat.
- Communication: Muscle tissue allows us to talk, gesture, write, and convey our emotional state by doing such things as smiling or frowning.
- Constriction of organs and blood vessels: Nutrients move through our digestive tract, urine is passed out of the body, and secretions are propelled out of glands by contraction of smooth muscle. Constriction or relaxation of blood vessels regulates blood pressure and blood distribution throughout the body.
- Pumping blood: Blood moves through the blood vessels because our heart tirelessly receives blood and delivers it to all body tissues and organs.
- This isn't a complete list. Among the many possible examples are the facts that muscles help protect fragile internal organs by enclosing them, and are also critical in maintaining the integrity of body cavities. For example, fetuses with incompletely formed diaphragms have abdominal contents herniate (protrude) up into the thoracic cavity, which inhibits normal lung growth and development. Even though this is an incomplete list, an appreciation of some of these basic muscle functions will help you as we proceed.
Properties of muscle tissue
All muscle cells share several properties: contractility, excitability, extensibility, and elasticity:
- Contractility is the ability of muscle cells to forcefully shorten. For instance, in order to flex (decrease the angle of a joint) your elbow you need to contract (shorten) the biceps brachii and other elbow flexor muscles in the anterior arm. Notice that in order to extend your elbow, the posterior arm extensor muscles need to contract. Thus, muscles can only pull, never push.
- Excitability is the ability to respond to a stimulus, which may be delivered from a motor neuron or a hormone.
- Extensibility is the ability of a muscle to be stretched. For instance, let's reconsider our elbow flexing motion we discussed earlier. In order to be able to flex the elbow, the elbow extensor muscles must extend in order to allow flexion to occur. Lack of extensibility is known as spasticity.
- Elasticity is the ability to recoil or bounce back to the muscle's original length after being stretched.
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