Muscular System Honors Biology Facilitator: Mr. Lee Room 320
Objectives Describe the three types of muscle tissue Explain how muscles contract
Introduction More than 40% of the mass of an average human is muscle Three types of muscle tissue: Skeletal Smooth Cardiac
Skeletal Muscle Skeletal muscles are normally attached to bones Skeletal muscles are responsible for voluntary movements Most skeletal muscles are controlled by the central nervous system
Skeletal Muscle Complete skeletal muscles have: Muscle fibers Connective tissue Blood vessels Nerves
Skeletal Muscle Skeletal Muscle Structure: Skeletal muscle cells are large (up to 30 cm) and are long and slender Sometimes called striated muscles (light and dark bands called striations) Skeletal muscles are made of bundles of muscle fibers
Skeletal Muscle The muscle fibers are made up of myofibrils The myofibrils are made up of thin filaments called actin and thick filaments called myosin Muscle fibers are divided into functional groups called sarcomeres
Smooth Muscles Smooth muscles are normally not under voluntary control Smooth muscle cells are spindle-shaped, have a nucleus, and are not striated Found in hollow structures like the stomach, blood vessels, and intestines
Smooth Muscles Most smooth muscle cells can function without nervous stimulation They are connected by gap junctions that allow impulses to go directly from one muscle cell to the next connect them to each other
Cardiac Muscle Cardiac muscle is only found in the heart Cardiac muscles have features from both skeletal and smooth muscles It is striated (but smaller cells) Usually have one nucleus
Cardiac Muscle Usually not under direct control of the central nervous system Cardiac muscles are connected to neighbors by gap junctions
Muscle Contractions The functional unit of contraction is called the sarcomere Consists of the region from one Z line to the next Consist of myofibril (made of filaments) Thick filaments have a protein called myosin Thin filaments have a protein called actin Use ATP for contraction vamuscl1.mov
Muscle Contractions Muscle contracts when the thin filaments in the muscle fiber slide over the thick filaments ATP provides the energy for muscle contraction vamuscl2.mov
Control of Muscle Contractions Neuromuscular junction- the point of contact between a motor neuron and a skeleton muscle Vesicles (pockets) in axon terminals release a neurotransmitter called acetylcholine, which cause a nerve impulse This causes release on calcium ions The muscle cell remains contracted until the release of acetylcholine stops
Muscular Movement of Bones Skeletal muscles are normally attached to one end of a bone, stretch across a joint, and attach to the end of another bone Tendon- connective tissue that attaches muscle to bone
Muscular Movement of Bones Origin- point where the muscle attaches to the stationary bone Insertion- point where the muscle attaches to the moving bone Most skeletal muscles are arranged in pairs. Flexor- muscle that bends a joint Extensor- muscle that straightens a joint
Muscle Fatigue Glycogen is stored in muscle cells as a backup energy source for when blood-delivered glucose is used up Next, fat molecules are used When there is no more energy available, Muscle Fatigue sets in Oxygen Debt- after a few minutes of vigorous activity, the body cannot supply enough O 2
Review Describe the three types of muscle tissue Skeletal: Controls voluntary movement Have striations Many nuclei Smooth: Controls involuntary movement No striations One nucleus Cardiac: Controls contractions of the heart Have striations Usually one nucleus
Review Explain how muscles contract: Muscles contract when the thin filaments (actin) in the muscle fiber slide over the thick filaments (myosin)
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