The Muscular System
Introduction to Muscles 600 muscles in the body Connected to bone by tendons Function: Primary: movement Heat production Three types: Skeletal Cardiac Smooth
Structure Muscle cells specialized for contraction Units of contraction: Sarcomeres Muscles composed of muscle cells or fibers The harder the work, the greater the number of muscle fibers engaged Muscles anchored to bones by tendons
Tendons Most rope-like Some flat: aponuerosis Fibrous connective tissue Merges with the fascia covering the muscle and with the periosteum Each muscle has 2 tendons connecting it to 2 bones Origin Insertion
Arrangement Antagonist: muscles work in opposition to one another. Antagonistic muscles are found on opposite sides of a joint. When one contracts, the other relaxes. Synergistic: cooperate in the same function Muscles always pull; never push
Flexion of the thigh means to pull it forward and up. Where are the muscles that do this? Where are the extensor muscles of the thigh What is meant by synergistic muscles?
Flexion of the thigh means to pull it forward and up. Where are the muscles that do this? On the front of the thigh crossing the groin, Where are the extensor muscles of the thigh? On the back of the thigh crossing the hip joint. What is meant by synergistic muscles? Muscles with the same function or that work together to perform a function.
Muscle Fiber Microscopic Structure
Sarcomere is the contractile unit Structure
Microscopic Structure Muscle fiber = muscle cell Thousands of cells in each muscle Each fiber has its own motor nerve ending Neuromuscular junction
Where Does Movement Begin? Nerve impulses for movement Begin in the frontal lobe of the cerebrum Coordinated in the cerebellum
Of Neurons, Chemicals and Neurotransmitter: acetylcholine Potentials Muscle fiber membrane: sarcolemma Location sites for acetylcholine Contains acetyl cholinesterase Electrolytes Calcium Potassium Sodium Energy source ATP Oxygen Binds to both hemoglobin and myoglobin
Muscle Fiber Each muscle fiber has its own nervous enervation Neuromuscular junction: where muscle cell and nerve cell meet In the axon terminal contains sacs of Ach Individual contracting units: sarcomeres Each muscle fiber has thousands of sarcomeres Sarcomeres are arranged end to end in cylinders called myofibrils
Muscle Fibers Z lines are the end boundaries of sarcomeres Protein filaments of myosin are in the center of the sarcomere Protein filaments of actin are at the ends of the sarcomere attached to the Z line Myosin filaments are attached to Z lines by the protein titin Myosin and actin interact to produce muscle contraction Troponin and tropomyosin are inhibitory proteins; they prevent sliding of myosin and actin during relaxation
Let s put it together Impulse for movement from cerebrum travels down motor neuron several muscle cells stimulated by release of Ach into the synaptic gap receptors on the sarcolemma bind with ACh
Chemically gated ion channels open Na+ rushes through channels Goes into muscle fiber causing an action potential to form on muscle membrane Action potential spreads Eventually involves entire muscle Muscle contracts
Tone At rest most muscles are in a slight state of contractions: Tone For slight contraction, only a few muscle fibers are involved Fatigue of muscle fibers is avoided by alternating individual muscle fibers Regulated by cerebellum Requires energy: ATP Good muscle tone improves coordination Maintains posture Is increased by exercise Normal muscle tone generates 25% of body s heat at rest
Exercise Isometric Contraction without movement Increase muscle tone, strength Not aerobic Isotonic Result in movement Increase muscle tone, strength and size Improves CV, Resp efficiency Aerobic if sustained >30 minutes
Exercise: Maintaining Homeostasis Exercise = physiologic stress Physiologic balance must be maintained Respiratory response Cardiovascular response Integumentary response Nervous system response Heat control
Muscle Sense Proprioception Brain s ability to know location and activity of muscles Stretch receptors
Major Muscles of the Body Name of a muscle is related its function or location
Head and Neck