Muscles & M Tissue Slides Flashcards
Skeletal muscle tissue is
Attached to bones Striated Voluntary Powerful Cylinder shape Multi- nucleited
Cardiac muscle tissue
Only in the heart Intercalated discs Striated Involuntary 1 nucleus
Smooth muscle tissue
Not striated
In walls of hollow ograns; stomach bladder, airways
Involuntary
Spindleshaped
Excitability
Receive/respond to stimuli
Electrical current
Extensibility
Normal to larger size
Contractility
Normal to 1/3 of size
Elasticity
Back to normal size
Muscle functions
Generate heat
Stabilize joints
Movement of bones/fluids
Posture/position
Skeletal muscle
Each muscle is served by one nerve, one artery, 1+ veins
Epimysium
Surrounds entire muscle; belly CT
Perimysium
surrounds fascicles Ct
Endomysium
surrounds each muscle fiber/ areolar ct
Anatomy of skeletal muscle fiber
Cylindrical, up to 30 cm Multiple peripheral nuclei Many mitchondria Glycosomes Myioglobin- takes O2 to cells Myofibrils, SR, T-tubules
Myofibrils
Dense, 80% of cell volume
Sarcomere features
Thick filaments: Myosin (A Band)
Thin filaments: Actin (I band and partially to A band)
Zdisc: Anchors thin filaments
Hzone: Lighter midregion where there is no overlap
Mline: Holds adjacent thick filaments together
Myosin Tails
Two interwomen polypeptide chains
Myosin Heads
2 smaller polypeptide chains; crossbridges
Binding sites for actin filaments
Binding sites for ATP
ATPase enzymes
Sarcoplasmic Reticulum
Stores Calcium Ions
T-tubules
Continuous with the sarcolemma
Pentrates cell’s interior at each A/I band junction
During contraction…
myosin heads bind to actin, detach, and bind again to propel thin myofilaments toward the M-line. Zlines move together.. A band doesn’t move.
Requirements for skeletal muscle contraction
Activation: neural stimulation at neuromuscular junction
Excitation: Generation and propagation of an action potential along the sarcolemma
Trigger; rise of intracellular Ca levels
Events at neuromuscular junction
Axons of motor neurons go from CNS—> skeletal muscles via nerves. Each axon ending forms neuromuscular junction with a single muscle fiber
Neuromuscular junction
Midway along length of a muscle fiber.
Axon terminal and muscle fiber separated by synaptic cleft. Synaptic vessicles contain neurotransmitter Ach.
Sarcolemma contain Ach receptors
Events
Nerve impulse arrives at axon terminal.
ACh is released and binds with receptors on the motorr end plate of the sarcolemma. Electrical events lead to a generation of an action potential.
Depolarization
ACh opens chemically ligand gated ion channels. There’s diffusion of Na in and K out. More Na is diffused so the sarcolemmma’s interior becomes less negative.
Generation and Propagation of an action potential
End plate potential spreads to adjacent membrane areas. Voltage gated Na+ channels open. Na influx decreases membrane voltage towards a critical threshold. If the threshold is reached, an action potential is generated.
Repolarization
Na channels close and voltage gated K channels open. K efflux rapidly restores the resting polarity.
Ionic conditions of resting state restored by calcium potassium pump.
What happens at the peak of an action potential?
Na gates will close and K gates will open.
E-C Coupling (excitation-contraction)
Sequence of events of an action potential leading to sliding of the myofilaments
Latent period
lag time; time between initiation and contraction
Events of EC
Action potential is propagted along sarcomere to t-tubules
Voltage sensitive proteins stimulate release of Calcium ions from SR.
Role of calcium in contraction
Calcium binds to troponin, troponin moves tropomyiosin away from active sites on actin. Cross bridge occurs, when Nervous stimulation ceases, ca pumped back into SR and end of contraction.
Cross bridge detachment
ATP attaches to myosin head and the cross bridge detaches.
Cocking of myosin head
Energy from hydrolysis of ATP cocks myosin head into high energy state.
