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MUSCULAR SYSTEM. I. Overview. Muscles – 40-50% of body mass Functions skeletal movement control of organ and vessel size maintain posture and position support soft tissue guard entrances and exits maintain body temperature (85%). 3 Kinds of Muscle Tissue. Skeletal
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I. Overview • Muscles – 40-50% of body mass • Functions • skeletal movement • control of organ and vessel size • maintain posture and position • support soft tissue • guard entrances and exits • maintain body temperature (85%)
3 Kinds of Muscle Tissue • Skeletal • Striated • Voluntary • AKA: Somatic Tissue
C. 3 Kinds of Muscle Tissue 2. Cardiac • Heart muscle • Branched cells • Multinucleiated • Thick striations • Intercalated discs • Increase speed of impulses • Involuntary • AKA Visceral Tissue
3 Kinds of Muscle Tissue • Smooth • Spindle shaped • Nonstriated • Involuntary • Found around hollow organs such as arteries, esophagus, stomach
D. Muscle Characteristics • Contractility Ability to shorten and exert tension • Excitability Ability to respond • Extensibility Ability to contract after being stretched • Elasticity Ability to regain initial length after contraction
I. Overview E. Each muscle is an organ comprised of • Muscle tissue • Connective tissues • Nervous tissue • Blood
II. Anatomy of Skeletal Muscle • Connective Tissue • Superficial Fascia Surround and separate each muscle
A.Connective Tissue 2. Deep • Epimysium - whole muscle • Perimysium - bundles of fibers (fascicles) • Endomysium- single muscle fiber
A.Connective Tissue 3. Tendons • Formed from the union of all three deep fascia • Connect muscle to bone
A.Connective Tissue 4. Aponeurosis – flat sheet
B. Muscle Fibers • Each muscle fiber • is a single, long, cylindrical muscle cell. • Sarcolemma (cell membrane) • Sarcoplasm (cytoplasm) • Many mitochondria • Nuclei • Sarcoplasmic reticulum
B. Muscle Fibers 1. Each muscle fiber • is wrapped in endomysium
1. Each muscle fiber c. is a bundle of myofibrils which is made of a budle of myofilaments
B. Muscle Fibers 2.Fascicles: • a bundle of muscle fibers • wrapped in perimysium
B. Muscle Fibers 3. Myofibrils • made of thin and thick filaments
B. Muscle Fibers 3. Myofibrils • Thick filaments made up of the protein myosin. c. Thin filaments are made up of the protein actin.
Thin filaments Tropomyosin and troponin are regulatory proteins Actin and myosin are contractile proteins.
B. Muscle Fibers 3. Myofibril d. Together, the thick and thin filaments make up the striations
B. Muscle Fibers 4. Sarcomeres • Contractile unit of a muscle • Consists of overlapping thick and thin filaments Sarcomere
B. Muscle Fibers 4. Sarcomere c. Muscle contraction • results from thick and thin filaments sliding past one another.
C. Neuromuscular Junction 1. Where the neuron and muscle fiber meet • The neuron and muscle fibers it controls make up a motor unit (2-2000 fibers/unit)
C. Neuromuscular Junction 3.When stimulated, all of the muscle fibers of a motor unit contract all at once.
C. Neuromuscular Junction 4. Anatomy Axon terminal – nerve end • Produces a neurotransmitter - acetycholine (Ach)
C. Neuromuscular Junction 4. Anatomy Motor end plate – site on muscle with Motor end plate acetycholine receptors Synaptic cleft - space between the nerve & motor end plate
III. Skeletal Muscle Contraction • nerve impulse • ACh released • Ach binds to receptor on muscle • Enzyme (Acetylcholine esterase removes ACh A. Initiation events
III. Skeletal Muscle Contraction • ACh causes to Na+ to diffuse into cell • If threshold is reached, action potential occurs • - impulse travels along membrane resulting in contraction B. Action Potential
III. Skeletal Muscle Contraction C. Sliding Filament Theory • Action potential causes Ca++ release from S.R • Ca++ binds to thin filament • Thin filament rotates exposing binding site for myosin • Myosin binds actin • uses ATP to "rachet" once • releases, "and binds to next actin
Calcium is the "switch" that turns muscle "on and off" (contracting and relaxing).
III. Skeletal Muscle Contraction D. How Neurotoxins Work • cobra toxin and curare • block Ach receptors • cause flaccid paralysis, potentially fatal respiratory arrest • nerve gas and insecticides • inhibit AchE • cause potentially fatal paralytic convulsions
How a Nerve Gas Works Normal Nerve Gas
Effect of Atropine on the Transmission of Acetylcholine in the presence of a nerve agent
III. Skeletal Muscle Contraction D. How Neurotoxins Work • Botulism toxin and curare • block Ach release • cause flaccid paralysis, potentially fatal respiratory arrest • Tetanus toxin • cause excessive Ach release from motor neurons • causes potentially fatal paralytic convulsions (“lock jaw”)
III. Skeletal Muscle Contraction E. Rigor Mortis • Ca++ pumps run out of ATP • Ca++ cannot be removed • continuous contraction • eventually tissues break down
A. Aerobic Respiration IV. Energy Metabolism in Sk.Ms. • Most efficient use of glucose Sources of glucose include blood glucose and stored glycogen • 36ATP/glucose • requires oxygen • occurs in mitochondria • Muscle cells have more mitochondria than any other cell • Require a steady supply of O2
B. Creatine-phosphagen system • During rest, muscles store energy as creatine phosphokinase (CPK or CK) • During intense exercise, ATP is depleted first, then CK is used to convert ADP back to ATP
C. Lactic Acid Pathway • Anaerobic use of glucose • 2 ATP/ glucose • Lactic acid produced as waste product – Oxygen Debt • Is toxic to tissue • Can be recycled in liver
V. Muscle Twitch-cycle of contraction and relaxation A. Reasons for varying degrees 1. The number of muscle fibers innervated by a single neuron varies 2. Some motor units have lower thresholds than others 3. Muscle fibers differ functionally: fast twitch – slow twitch fibers
V. Muscle Twitch B. Fast vs Slow Twitch Fibers 1. Differ in • How they make ATP • Speed of ATP break down • Mitochondria content • How fast they fatigue
B. Fast vs Slow Twitch Fibers 2. Slow Twitch Fibers • Smallest fibers • Fatigue resistant • Aerobic ATP production • Many mitochondria • Slow contractions • Example: uroanal muscles