Miller-Tendon/muscle Flashcards
Review skeletal muscle architecture
Review the sarcomere
A band: Contains actin and myosin
I band: Contains actin only
H band: Contains myosin only
M line: Interconnecting site of the thick filaments
Z line: Anchors the thin filaments
Review muscle anatomy
Sarcolemma: plasma membrane surrounding cell
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Extends into cell surrounding myofibrils
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Forms the transverse tubules (Fig. 1.41).
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Multiple nuclei: typically located adjacent to sarcolemma
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Sarcoplasmic reticulum (SR)
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Smooth endoplasmic reticulum that surrounds the individual myofibrils
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Stores calcium in intracellular membrane–bound channels.
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Ryanodine receptors (e.g., RYR-1) regulate the release of calcium from the SR and serve as a connection between the SR and sarcolemma-derived transverse tubule.
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Abnormality of ryanodine receptors is implicated in persons susceptible to malignant hyperthermia.
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Dantrolene decreases loss of calcium from the SR.
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Contractile elements
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Sarcomere: basic functional unit of muscle contraction
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Myofibrils
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Set of sarcomeres parallel to axis of cell
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(1–3 μm in diameter and 1μ2 cm long)
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Sarcomere organization causes the banding pattern (striations) seen in skeletal muscle (Table 1.23; see Fig. 1.40).
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Costamere connects the sarcomere to the sarcolemma at the Z disc.
What is the sarcoplasmic reticulum?
Sarcoplasmic reticulum. Action potentials travel down the transverse tubules, causing release of calcium from the outer vesicles.
review muscle contracture
Contractile elements
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Sarcomere: basic functional unit of muscle contraction
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Myofibrils
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Set of sarcomeres parallel to axis of cell
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(1–3 μm in diameter and 1μ2 cm long)
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Sarcomere organization causes the banding pattern (striations) seen in skeletal muscle (Table 1.23; see Fig. 1.40).
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Costamere connects the sarcomere to the sarcolemma at the Z disc.
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Z disc (or line) represents terminus of sarcomere
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Contains desmin, α-actinin, and filamin
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A-band (or dark band) represents thick filaments.
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Thick filaments composed of myosin
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Also contains myosin [H-band], M protein, C protein, titin, and creatine kinase
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I-band represents thin filaments.
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Primarily composed of actin
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Also contains
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Troponin: has binding site for Ca
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Tropomyosin: prevents myosin-actin interaction
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Attach to Z disc
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Involved in delayed-onset muscle soreness (DOMS)
review the gross anatomy of muscle:
Contractile elements
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Sarcomere: basic functional unit of muscle contraction
•
Myofibrils
•
Set of sarcomeres parallel to axis of cell
•
(1–3 μm in diameter and 1μ2 cm long)
•
Sarcomere organization causes the banding pattern (striations) seen in skeletal muscle (Table 1.23; see Fig. 1.40).
•
Costamere connects the sarcomere to the sarcolemma at the Z disc.
•
Z disc (or line) represents terminus of sarcomere
•
Contains desmin, α-actinin, and filamin
•
A-band (or dark band) represents thick filaments.
•
Thick filaments composed of myosin
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Also contains myosin [H-band], M protein, C protein, titin, and creatine kinase
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I-band represents thin filaments.
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Primarily composed of actin
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Also contains
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Troponin: has binding site for Ca
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Tropomyosin: prevents myosin-actin interaction
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Attach to Z disc
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Involved in delayed-onset muscle soreness (DOMS)
review the motor endplate
The α-motoneuron and the myofibers it innervates
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Each myofiber is innervated by a single axon but an axon can innervate multiple myofibers
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Smaller and more delicate muscles have fewer myofibers per motor unit (<5 fibers per unit in extraocular muscles but as many as 1800 fibers per unit in gastrocnemius muscle)
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Contraction
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Response to mechanical or electrochemical stimuli generated at the motor end plate (neuromuscular junction) where the axon contacts an individual myofiber (Fig. 1.42).
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Depolarization reaches motor neuron axon terminal, and acetylcholine (ACh) is released from presynaptic vesicles.
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ACh diffuses across the synaptic cleft (50 nm) and binds to postsynaptic receptors on sarcolemma, which begin depolarization.
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Myasthenia gravis is due to IgG antibodies to the Ach receptor. Manifests initially as ptosis and diplopia. Weakness worse with muscle use.
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Botulinum A injections reduce spasticity by blocking presynaptic acetylcholine release. Commonly used for spastic muscles in cerebral palsy.
Sarcoplasmic reticulum releases calcium.
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Ca binds to troponin and causes conformational change, which stops tropomyosin inhibition of myosin-actin cross-bridges.
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Myosin binds to actin, hydrolyzes ATP, and “pushes” actin on thin filament, leading to muscle contraction
isometric
muscle length remains unchanged
planks
isokinetic
Muscle tension is generated as muscle maximally contracts at a constant velocity over a full ROM.
best for maximizing strength
isotonic
Muscle tension is constant
i.e biceps curls
what is the cause of myathenia gravis?
Myasthenia gravis is due to IgG antibodies to the Ach receptor. Manifests initially as ptosis and diplopia. Weakness worse with muscle use.
Type 1 muscle fibers
Type I
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Slow-twitch, oxidative, “red” fibers (mnemonic: “slow red ox”)
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Aerobic
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Have more mitochondria, enzymes, and triglycerides (energy source) than type II fibers
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Low concentrations of glycogen and glycolytic enzymes (ATPase)
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Enable performing endurance activities, posture, balance
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Are the first lost without rehabilitation
type II muscle fibers
Fast-twitch, glycolytic, “white” fibers
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Anaerobic
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Contract more quickly and have larger, stronger motor units (increased ATPase) than type I fibers
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Less efficient than type I but with large amount of force per cross-sectional area, high contraction speeds, and quick relaxation times
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Well suited for high-intensity, short-duration activities (e.g., sprinting)
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Rapid fatigue
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Low intramuscular triglyceride stores
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Two subtypes:
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Type IIA is intermediate.
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Type IIB is most fatigable and has highest anaerobic capacity.
review the energy source for muscle
review strength training
Strength training—increased tension and decreased repetitions
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Induces hypertrophy (increased cross-sectional area) of fast-twitch (type II) fibers
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Induces myofibrillar muscle protein synthesis (MPS)
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Improves neural activation
review nerve architecture
