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Muscular System ____ Human skeletal

muscles

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Muscular System

• Helps maintain homeostasis by …– _______– __________ – Communication– Control of body openings and passages– _____ production

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Muscle Tissues

• 3 types of muscle tissue– Skeletal muscle– _______ muscle– _____ muscle

• Trivia: about ____% of body mass is skeletal muscle in someone of “normal” height and weight

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Muscles

• A particular muscle, e.g., the biceps brachii, is an organ composed of skeletal muscle tissue, connective tissue, etc.

• “Muscular system” really refers to the ________ muscles

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Skeletal Muscle

• Connective tissues– ____mysium, around individual muscle

cells (muscle cells = muscle fibers)– ____mysium, around fascicles– ____mysium, around entire muscle, blends

into CT sheets called fascia

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Skeletal Muscle• Attachment to bone

– ________ attachment – epimysium blends into periosteum

– __________ attachment – tendoncomposed of dense regular CT

– Aponeurosis – broad, flat tendon connecting muscle to muscle

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Origin & Insertion

• ______ – the muscle attachment at the relatively stationary end

• ________ – the muscle attachment at the more mobile end

• Example, triceps brachii– O: scapula, proximal humerus– I: olecranon

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Skeletal Muscle Histology

• “_____” = flesh, so many terms in this unit have “sarco” in their name

• Sarcoplasm = cytoplasm• _________ reticulum

= modified endoplasmic reticulum• ________ = contractile unit

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Sarcomere

• Functional unit of skeletal muscle• Thick filaments

– ______• Thin filaments

– _____– Troponin– __________

• Transverse tubules (T tubules)

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Thick and Thin Filaments

• Thick:– Myosin sort of looks

like a golf ____• Thin:

– “_____” of g-actin form a twisted pair of strands

– Troponin and tropomyosin attached

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Sarcomere

• A band• I band• H band • Z disc

• Sarcomere = Z disc to Z disc• Myofibril = many sarcomeres,

end to end

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Contraction

• Occurs when myosin head groups pull on actin filaments

• Binding site blocked by _______– Ca+2 ions bind to troponin, troponin

changes shape and pulls tropomyosin out of the way

– Now myosin can get at the actin

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Excitation-Contraction

Action potential hits T tubules and dives down into sarcoplasm

1. Voltage-gated Ca+2 channels open in terminal cisternae of SR, Ca+2 flows out of the SR and into the sarcoplasm

2. Ca+2 binds to troponinTroponin pulls tropomyosin away from

myosin binding sites on actin filaments

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Excitation-ContractionMyosin-ATP complex hydrolyses ATP

to ADP and Pi (activation)

3. Myosin-ADP-Pi complex binds to actin

4. ADP and Pi float away (power stroke)

5. Myosin releases actin when new ATP binds to head group

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Excitation-Contraction

Motor neuron stops releasing ACh

Acetylcholinesterase (AChE) clears ACh from synaptic cleft

Ca+2 pumped back into SR

Tropomyosin moves back to block the binding sites on the actin filaments

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Muscle Metabolism

• Immediate energy sources– Use the O2 that’s already there in the muscle– Use myokinase and creatine kinase to make ATP

• Short-term energy sources– Emergency use only!– Anaerobic glycolysis (glycogen, lactic acid)

• Long-term energy sources– Back to aerobic cellular respiration as the

blood flow to the muscle increases– A marathon runner tries to go from immediate

energy to long-term energy without short-term

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Slow- & Fast-Twitch

• ____-twitch fibers (oxidative)– Endurance fibers, dark meat– Lots of myoglobin, mitochondria, capillaries

• ______-twitch fibers (glycolytic)– Run-away-from-the-tiger fibers, white meat– Low myoglobin and mitochondria,

not so many capillaries, plenty of glycogen

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Skeletal Muscle Shapes 1

Skeletal Muscle Shapes 2• ________ muscles

– thick in middle and tapered at ends– biceps brachii m.

• _________ muscles have parallel fascicles– rectus abdominis m.

• ___________muscle– broad at origin and tapering to a narrower insertion

• Pennate muscles– fascicles insert obliquely on a tendon– unipennate, bipennate or multipennate– palmar interosseus, rectus femoris and deltoid

• ________ muscles– ring around body opening– orbicularis oculi

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Cardiac Muscle

• Striated like skeletal muscle• Shorter cells, often branched• Only one nucleus per cell• ____________ discs between cells

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Smooth Muscle

• One nucleus per cell• No visible _________• Contracts in response to changes

in the local environment– chemical stimuli (hormones, low O2, low pH, etc.)

– stretch (bladder,stomach)

• Or in response to ____________ nerve fibers

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Smooth Muscle

• Still myosin pulling on actin, but not arranged in ______________

• Actin anchors to plasma membrane, twisted Nerf football effect

• Calmodulin: Ca+2 binding protein, sort of equivalent to troponin in skeletal muscle

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