Chapter 9 Flashcards
Muscle Tissue and Physiology
Nearly half of body’s mass
Can transform chemical energy into directed mechanical energy
3 types: skeletal, cardiac, smooth
Muscle tissue
Packaged into skeletal muscles
Voluntary muscle (consciously controlled)
Contract rapidly, tire easily, powerful
Made of nerve blood supply, connective tissue sheaths, attachments
KEY WORDS: skeletal, striated, voluntary
Skeletal muscle tissue
Longest of all muscle, have striations
Skeletal muscle fibers
Found only in heart
Striated
Involuntary (not controlled consciously)
KEY WORDS: cardiac, striated, involuntary
Cardiac muscle tissue
Found in walls of hollow organs
Not striated
Involuntary
KEY WORDS: visceral, nonstriated, involuntary
Smooth muscle tissue
Excitable - receive and respond to stimuli
Contractible - shorten forcefully
Extensibility - stretched
Elasticity - recoil to resting strength
4 Main Muscle Characteristics:
- Produce movement
- Maintain posture
- Stabilize joints
- Generate heat when they contract
Skeletal muscle functions
Dense irregular connective tissue surrounding entire muscle; may blend with fascia
Outermost tissue sheath
Epimysium
Fibrous connective tissue surrounding fascicles
Middle tissue sheath
Perimysium
Fine areolar connective tissue surrounding each muscle fiber
Most internal tissue sheath
Endomysium
Epimysium fused to periosteum of bone or perichondrium of cartilage
Direct attachement
Connective tissue wrappings extend beyond muscle as ropelike tendon or sheetlike aponeurosis
Indirect attachment
Long, cylindrical cells that contain multiple nuclei
Sarcolemma - muscle fiber membrane
Sarcoplasm - muscle fiber cytoplasm
Contains glycosomes and myoglobin
Modified organelles: myofibrils, S.R., T tubules
Muscle fiber
Densely packed, rod-like elements that run length of muscle fiber
Features: striations, sarcomeres, myofilaments
Myofibrils
Stripes formed from repeating series of dark and light bands along length of each myofibril
A bands = dark regions
I bands = light regions
Striations
Lighter region in middle of dark A band
Intersected by “M” zone vertically
H zone
Sheet of proteins on midline of light I band
Zigzag pattern
Z disc
Smallest contractile unit (functional unit) of muscle fiber
Consists of area between Z discs
Contains whole A band, 1/2 I band
Align with one another along myofibril
Sarcomere
Thick and thin filaments within sarcomere
2 types: Actin and Myosin
Myofilaments
Extend length of A band
Connected at M line
Myosin band
Thick filaments
2 Heavy polypeptide chains intertwined
Myosin tails
4 Light polypeptide chains combined
Contain actin and ATP binding sites
Myosin globular heads
Extend across I band and partway in A band
Anchored to Z disc
Composed of actin (G actin and F actin)
Thin filaments
Complex of three molecules attached to tropomyosin
Found in groove between actin filaments
Regulatory protein in thin filaments
Troponin
Coiled protein
In relaxed muscle, ____ blocks the myosin attachment sites on actin
Regulatory protein in thin filaments
Tropomyosin
Bind sarcomeres together
Maintain alignment of sarcomere
N, M, C
Nebulin
Myomesin
C proteins
Structural protein that links thin filaments to integral proteins of sarcolemma which are then anchored to the extracellular matrix
Dystrophin
Muscle-destroying diseases
Most common type = Duchenne muscular dystrophy
Muscular dystrophy
Sarcolemma of DMD tears easily, allowing for entry of excess calcium which damages contractile fibers
Disease progresses from extremities upwards
Duchenne Muscular Dystrophy
Nervous system stimulates muscle fiber, myosin heads are allowed to bind to binding sites on actin
Causes sliding (contraction) to begin
Cross bridges
Activation of cross bridges to generate force
Ends when cross bridges are inactive
Contraction
Cross bridges attachments form and break several times
During contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more
No change in length
Sliding filament model of contraction
Thin and thick filaments overlap only at ends of A band
Relaxed state
Z discs are pulled towards M line (Z discs get closer)
I bands shorten
H zones disappear
A bands move closer to each other
Myofibril state:
Contracted state
Network of smooth endoplasmic reticulum tubules surrounding each myofibril
Regulates intracellular Ca2+ levels
Runs longitudinally
Terminal cisterns: Thicker areas with lots of calcium
Sarcoplasmic reticulum (SR)
Tubes formed by protrusion of sarcolemma deep into cell interior
Lumen continuous with extracellular space
Tubules penetrate cell’s interior at each A-I band junction between terminal cisterns
Increase muscle fiber’s surface area
T tubules
Area formed from terminal cisterns of two sarcoplasmic reticulums and a T tubule
Triad
Events at neuromuscular junction
Muscle fiber excitation (shortening and developing tension)
Excitation-Contraction coupling
Cross bridge cycling
Skeletal muscle contraction
Low Ca2+ = Tropomyosin blocks active sites on actin; Myosin heads cannot attach to actin
High Ca2+ = Ca2+ binds to troponin; Troponin changes shape and moves tropomyosin away from myosin-binding sites; Myosin heads allowed to bind to actin, forming bridge
Sarcomere shortening
Cross Bridge Cycling
Myosin heads bind to active sites of actin, forming ____
Cross bridges
Part one of CBC
Myosin binds to actin
Cross bridge formation
Part two of CBC
ADP and P are released, myosin head pivots and bends, changing shape
Pulls filament toward M line
Power stroke
Part three of CBC
Cross bridge breaks
Cross bridge detachment
Part four of CBC
ATP is hydrolyzed to ADP and P
Myosin head returns to high energy position
Binds to new binding site on actin
Cocking myosin head
- Activation by brain
- Transmission down spinal cord
- Motor neurons activate muscle
Muscle movement process
Electrical signals that are created by a depolarizing current
Occurs along the cell membrane in adjacent sarcolemma
Short term
Action potential
Open by chemical messengers binding such as neurotransmitters
Ex. ACh
Chemically gated ion channels
Open or close in response to voltage changes
Ex. K+ channels
Voltage-gated channels
Stimulate skeletal muscles
Somatic motor neurons
Long, threadlike extensions of motor neurons
Axon
Region where motor neuron hovers over skeletal muscle
Contains: axon terminal, synaptic cleft, junctional folds
Neuromuscular junction
End of axon
Axon terminal
Gel-filled space separating muscle fiber and axon terminal
Synaptic cleft
Membrane pockets filled with neurotransmitters and stored in axon terminal
Commonly holding acetylcholine
Synaptic vesicles
ACh broken down into ____
Acetylcholinesterase
Infoldings of sarcolemma, containing ACh receptors (ion channels)
Junctional folds
Flip in polarity; (Inside + Outside -)
Na+ rushes into muscle fiber, K+ rushes out
Depolarization
Difference in electrical potential between inside and outside of membrane
Resting sarcolemma is polarized (Inside - Outside +)
Membrane potential
Local depolarization occurring at the neuromuscular junction
End plate potential (EPP)
Restoring sarcolemma to its initial polarized state (- inside, + outside)
Repolarization
Muscle fiber cannot be stimulated for a specific amount of time, until repolarization is complete
Refractory period
Events that transmit AP along sarcolemma (excitation) are coupled to sliding myofilaments (contraction)
AP is propagated along sarcolemma and down into T-tubules
AP is very brief
Excitation-contraction (EC) coupling
T-tubule proteins change shape –> calcium release channels in SR –> release calcium into cytoplasm
Part of EC coupling
Tropomyosin blocks actin binding site, Ca2+ levels low
End of muscle contraction
3-4 hours after death, muscles stiffen
Intracellular calcium levels increase because ATP is no longer being synthesized
Rigor mortis
