muscles Chapter 8

3 types of muscles: skeletal: attached to bones, cylindrical, multinucleated, striated, voluntary Cardiac: only in heart, branches, uninucleated, striations, involuntary Smooth: hollow visceral organs, uninucleated, no striations, involuntary

Muscle functions Produces movement Maintains posture Stabilizes joints Generates heat

Skeletal muscle activity Skeletal muscles must be stimulated by nerve impulses to contract One nerve cell can stimulate a few muscle cells or hundreds. The area where nerve cells branch into the muscle is called the neuromuscular junction.

Muscle activity continued……. When a nerve transmitter reaches a muscle, it releases a chemical-acetylcholine Sodiim ions rush into the muscle cell allowing it to contract—called action potential Potassium ions will rush out of the cell to return cells to normal

Contraction of a muscle as a whole “all or none” law applies to muscle contractions. A muscle cell will contract to its fullest when stimulated adequately. It will never partially contract. Muscle twitches--- single brief, jerky contractions. Most muscle activity requires the nerve impulse to be sent rapidly and does not have a chance to rest.

Energy for muscle contractions *ATP is the only energy source that can be directly used for muscle power. There are 3 ways to generate ATP: Creatine phosphate + ADP=ATP Aerobic respiration-glucose is broken down to co2 + h2o with oxygen Anaerobic glycolysis-without oxygen when activity is intense and oxygen is low, lactic acid will collect in muscles. --causes soreness in muscles

Skeletal muscles Organ composed of several different types of tissues (vascular, nervous, connective tissues) They pull on tendons, which in return pull on bones Origen: the attachment of muscle (by means of tendon) to the stationary bone Insertion: the other end of the muscle is attached to the movable bone. Belly: fleshy portion of the muscle between the origin an insertion Example: spring on a screen door-----Origen/door frame, insertion/door, spring/belly

Isotonic Muscle shortens and movement occurs. Most familiar type of contraction Example: arm curl, lifting a box

Isometric Muscles do not shorten, but tension increases Example: lifting a heavy weight and it doesn’t move/holding it in place, pushing on a wall

Effect of muscles on exercise: Endurance-jogging, biking, aerobics that result in stronger, more flexible muscles with greater resistance to fatigue Resistance- enlargement of individual muscle cells by making more contractile filaments

5 rules of muscle activity Cross at least 1 joint The bulk of muscle lies proximal to joint that is crossed All have at least 2 attachments They pull only---never push Insertion moves toward origin during contraction