Ch.6 Muscles
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| Contractility | The ability of skeletal muscle to shorten with force
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| Excitability | The capacity of skeletal muscle to respond to a stimulus
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| Extensibility | The ability to be stretched
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| Elasticity | Ability to recoil to their original resting length after they have been stretched
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| Epimysium | A connective tissue sheath that surrounds each skeletal muscle
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| Fascia | Another connective tissue located outside the epimysium.
Surrounds and separates muscles
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| Perimysium | Loose connective tissue that surrounds muscle fasciculi (fascicle)
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| A muscle is composed of... | Numerous visible bundles known as muscle fasciculi (fascicle)
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| The fasciculi are composed of... | Fibers
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| Fibers | Single muscle cells
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| Endomysium | A connective tissue sheath that surrounds each fiber
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| Myofibrils... | Fill the cytoplasm of each fiber
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| Myofibrils | A threadlike structure that extends from one end of the fiber to the other
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| 2 major kinds of protein fibers that myofibrils consist of | Actin myofilaments, myosin myofilaments
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| Actin myofilaments | Thin myofilaments
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| Myosin myofilaments | Thick myofilaments
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| Form highly ordered units called sarcomeres | Actin and myosin myofilaments
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| Sarcomere is the... | Basic structural & functional unity of the muscle
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| Resting membrane potential | The charge difference across the membrane
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| Action potential | The brief reversal back of the charge
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| Motor neurons | Nerve cells that carry action potentials to skeletal muscle fibers
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| Each branch that connects to the muscle forms a ___________ _________ or ________ near the center of the cell. | Neuromusclular junction or synapse
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| Motor unit | A single motor neuron & all the skeletal muscle fibers it innervates
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| Presynaptic terminal | Enlarged nerve terminal
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| Synaptic cleft | The space between the presynaptic terminal & the muscle cells
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| Postsynaptic terminal | Muscle fiber
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| Each presynaptic terminal contains... | Synaptic vesicles
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| Synaptic vesicles that secrete a neurotransmitter called... | Acetylcholine
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| Every muscle fiber | Cylindrical cell
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| Each muscle fiber... | contains several nuclei
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| Muscles help... | produce heat essential for maintenance of normal body temperature.
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| Action potential reaches nerve terminal | Synaptic vesicles releases acetylcholine into synaptic cleft (by exocytosis)
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| Acetylcholine diffuses across | Synaptic cleft
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| Acetylcholine | binds to receptor molecules in the muscle cell membrane (sarcolemma)
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| Combination of acetylcholine with its receptor | Influx of sodium ions into the muscle fibers
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| The influx of sodium ions into the muscle fibers initiates | Action potential in muscle cell
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| Acetylcholinesterase | The acetylcholine released into the synaptic cleft between the neuron & muscle cell is rapidly broken down by enzymes
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| Name 2 things the enzymatic breakdown ensures | 1. One action potential in the neuron yields only one action potential in the skeletal muscle. 2. Only one contraction of the muscle cell
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| Muscle contraction | Occurs as actin & myosin myofilaments slide past one another causing the sarcomeres to shorten.
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| Sarcomeres shorten | muscle shortens
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| Sliding filament mechanism | Sliding of actin myofilaments past myosin myofilaments during contraction
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| H and I bands | Shorten
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| A bands | Do not change in length
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| Muscle twitch | Contraction of entire muscle
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| Muscle fiber won't respond to stimulus until that stimulus reaches a level called... | Threshold
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| Once the stimulus reaches threshold... | Muscle fiber will contract maximally
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| Reaching threshold and muscles contract maximally known as... | All-or-none response
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| Lag phase | Time between application of a stimulus to a motor neuron & the beginning of contraction
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| Contraction phase | Time of contraction
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| Relaxation phase | Time during which the muscle relaxes
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| Tetany | The muscle remains contracted without relaxing
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| Recruitment | The increase in number of motor units being activated
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| ATP is needed for | Energy for muscle contraction
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| ATP is produced | In mitochondria
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| ATP is | Short-lived and unstable
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| ATP stands for | Adenosine triphosphate
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| Creatine phosphate | When at rest they can't stockpile ATP but they can store another high-energy molecule
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| Anaerobic respiration | Without oxygen
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| Aerobic respiration | With oxygen (more efficient)
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| Oxygen debt | Amount of oxygen needed in chemical reactions to convert lactic acid to glucose & replenish the depleted stores of creatine phosphate stores in muscle cells
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| Muscle fatigue | ATP is used during muscle contraction faster than it can be produced in the muscle cells
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| 2 types of muscle contractions | Isometric & Isotonic
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| Isometric (equal distance) | Length of the muscle does not change, but the amount of tension increases during the contraction process
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| Isotonic (equal tension) | Amount of tension produced by the muscle is constant during contraction, but the length of the muscle changes
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| Muscle tone | Refers to constant tension produced by muscles of the body for long periods of time.
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| Fast- twitch fibers | Contract quickly and fatigue quickly. Well adapted to perform anaerobic metabolism
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| Slow-twitch fibers | contract more slowly & are more resistant to fatigue. Better suited for aerobic metabolism
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| Points of attachment of each muscle | Its origin & insertion
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| At the attachment points the muscle is connected to | Bone by a tendon
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| Origin (head) | Most stationary end of the muscle
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| Insertion | End of the muscle undergoing the greatest movement
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| Belly | Portion of the muscle between the origin and the insertion
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| Some muscles have | Multiple origins or head
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| I band | Light area on each side of Z line. Consists of actin
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| A band | Darker central region in each sarcomere. Extends the length of the myosin
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| H zone | Center of the sarcomere (another light area.) Consist of only myosin
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| M line | Dark staining band. Myosin myofilament are anchored in the center of the sarcomere
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