The Muscular System and Integumentary System

1. The Muscular System and Integumentary System Ms. Hoffman September 13, 2004

2. How do Muscles and Bones Interact? • Skeletal muscles generate force and produce movement by contracting, or pulling on body parts • Skeletal muscles are joined together by tough connective tissues called tendons • Tendons are attached so that they pull on bones and make them work like levers • Most skeletal muscles work in opposing pairs • When one muscle contracts, the other relaxes • Ex. When the biceps muscle contracts, the triceps is relaxed and you can curl your arm • Ex. When the biceps muscle relaxes, the triceps muscle contracts and you can extend your arm

4. What is Muscle Tone? • Skeletal muscles remain in a state of partial contraction • At all times, a few muscle cells are being stimulated while others are not • Limited stimulation causes a tightening of some muscles called resting muscle tone • Resting muscle tone is responsible for keeping the back and legs straight and the head upright, even when you are relaxed • Regular exercise increases muscle tone

5. Muscles • Provide the forces that put the body into motion • More than 40% of the mass of the average human body is muscle • Fxns: regulate blood pressure, move food through the digestive system, power every movement in the body

6. Types of Muscle Tissue • Muscle tissue is found everywhere in the body…from beneath the skin to deep within the body • There are three different types of muscle tissue: skeletal, smooth, and cardiac • Each type of muscle tissue has a different structure and plays a different role in the body

8. Skeletal Muscles • Usually are attached to bones • Responsible for voluntary movements like dancing, running, jumping • Have alternating light and dark bands or stripes called striations when viewed under the microscope • Most skeletal muscles are controlled by the central nervous system • Skeletal muscle cells are large cells, have many nuclei, and vary in length from 1 mm – 30 cm • May be referred to as muscle fibers because these muscle cells are so long and slender • Complete skeletal muscles consists of: muscle fibers, connective tissues, blood vessels, and nerves

9. Skeletal Muscle

11. Smooth Muscles • Usually are not under voluntary control • Spindle-shaped, one nucleus, no striations • Found in hollow structures like the stomach, blood vessels, and small and large intestines • Fxns: move food through your digestive tract, control the way blood flows through your circulatory system, decrease the size of the pupils of your eyes in bright light • May function without nervous stimulation • Connected to one another by gap junctions that allow electrical impulses to travel directly from one muscle cell to a neighboring muscle cell

12. Smooth Muscle

14. Cardiac Muscle • Only found in the heart • Striated like skeletal muscle • Usually only have one nucleus like smooth muscle • Usually not under the direct control of the central nervous system • Cardiac cells are connected to their neighboring cells by gap junctions

15. Cardiac Muscle

16. Muscle Contraction • Muscle fibers in skeletal muscles are made of smaller structures called myofibrils • Each myofibril is made of even smaller structures called filaments • Thick and thin filaments alternate to create the striated appearance of muscle cells • Thick filaments are made of a protein called myosin • Thin filaments are made of a protein called actin

18. Muscle Contraction • Myosin and actin filaments are arranged along a muscle fiber in units called sarcomeres • Sarcomeres are separated from each other by regions called Z discs • During relaxation of a muscle there are no thin actin filaments in the center of a sarcomere

20. Muscle Contraction • Myosin and actin filaments are what cause muscles to contract • A muscle contracts when the thin actin filaments in a muscle fiber slide over the thick myosin filaments • For contraction to occur, the thick myosin filaments must form a cross-bridge with the thin actin filament • The cross-bridge changes shape and pulls on the actin filament which slides toward the center of the sarcomere • The distance between the Z discs decreases • The cross-bridge detaches from the actin filament and the cycle is repeated when the myosin binds to another site on the actin filament

23. What Supplies the Energy for Muscle Contraction? • The energy of muscle contraction is supplied by ATP • One molecule of ATP supplies the energy for one interaction between a myosin cross-bridge and an actin filament • Lots of ATP is needed! • ATP can be produced by cells via cellular respiration

24. Controlling Muscle Contractions • Motor neurons connect the central nervous system (brain and spinal cord) to skeletal muscle cells • Impulses from motor neurons control the contraction of skeletal muscle fibers • Neuromuscular junction- the point of contact between a motor neuron and a skeletal muscle cell

25. Controlling Muscle Contractions • At the neuromuscular junction there are pockets (vesicles) in the terminals of the motor neuron that release a neurotransmitter called acetylcholine • Neurotransmitters are chemicals used by neurons to transmit an impulse across a synapse (space where a message can be relayed) to another cell • Acetylcholine molecules cross the synapse and cause an impulse in the cell membranes of the muscle fiber • This impulse causes calcium ions to be releases within the fiber • The calcium ions affect proteins that regulate how the actin and myosin filaments interact • The contraction of a muscle fiber is an all- or -none process