muscles Flashcards
Types of Muscle
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
Skeletal muscle tissue
- attached to bones and skin
- striated
- voluntary
- powerful
- multinucleate
Cardiac muscle tissue
- only in heart
- striated
- involuntary
- uni or binucleate
Smooth muscle tissue
in walls of hollow organs(stomach, urinary bladder, airways
- not striated
- not uninucleate
- involuntary
Common Features
- Elongated cells
- myofilaments
- —actin
- –myosin
- Terminology
- –myo and sacro
Special characteristics of muscle
- Excitability
- –ability to receive and respond to stimuli
- Contractility: ability to shorten when stimulated
- extensibility: ability to be stretched
- Extensibility: ability to be stretched
- Elasticity: ability to recoil to resting length
Muscle Functions
- Movement of bones or fluids (e.g. blood)
- Maintaining posture and body position
- Stabilizing joints
- Heat generation (especially skeletal muscle)
How many arteries and nerves are in each muscle?
Each muscle is served by one artery, one nerve, and one or more veins
What is connective tissue sheaths called?
PICTURE BECCA
- Epimysium:
- —dense regular connective tissue surrounding entire muscle (groups of perimysium)
- Perimysium
- —fibrous connective tissue surrounding fascicles (groups of muscle fibers)groups of endomysium
- Endomysium: fine areolar connective tissue surrounding each muscle fiber
Muscles attach 2 ways. What are they?
PICTURE 9.1
- Directly
- —epimysium of muscle is fused to periosteum of bone or perichondrium of cartilage
- Indirectly
- —connective tissue wrappings extend beyond the muscle as a replica tendon or sheetlike aponeurosis
What is Sarcolemma?
plasma membrane surface
What is sarcoplasm?
cytoplasm of muscle cells
What is myofibrils?
contractile elements of skeletal muscle
What is in s skeletal muscle fiber (cell)
- cylindrical cell 10 to 100 in diameter up to 30 cm long
- multiple peripheral nuclei
- many mitochondria
- numerous glycosomes for glycogen storage and myoglobin for 02 storage
- also contain highly specialized organelles: myofibrils, sarcoplasmic reticulum, and T tubules
Myofibrils
PICTURE OF Myofibril
- Densely packed, rodlike elements
- –80%of cell volume
- Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands
- Composed of contractile proteins
- —Thick filaments - myosin
- —Thin filaments - actin
Sarcomere
- Smallest contractile unit (functional unit) of muscle fiber
- Region of myofibril between two successive Z discs
- Composed of thick and thin myofilaments made of contractile proteins
Features of a Sarcomere
PICTURE OF A SARCOMERE
- Thick filaments: run the entire length of A band
- Thin filaments: run the length of I band and partway into the A band
- Z disc: coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another
- H zone: lighter mid region where filaments do NOT overlap
- M line: line of protein myosin that holds adjacent thick filaments together
Ultrastructure of thick filament
Composed of the protein myosin
- –1. myosin tail forms central part of dark band
- –2. myosin heads contain:
- —–binding sites for actin of thin filaments
- —–during contraction forms a cross bridge with actin
- —-binding sites for ATP
- —-ATPase enzymes
Regulatory Proteins of Actin
- Tropomyosin
2. Troponin - polypeptide complex
What does tropomyosin do?
- Spirals around actin
- Block myosin head binding sites during relaxed state
What is troponin?
- binds Ca2
- binds tropomyosin (TnT)
- Inhibitory protein that binds actin (Tnl)
Elastic filament
PICTURE 9.3
- composed of protein Titin
- Extends from Z disk to the run within the thick filament to the M line
- Helps to resist excessive stretching
Intracellular tubules in muscles
- sarcoplasmic reticulum
- T-tubules
Sarcoplasmic Reticulum (SR)
- Network of smooth endoplasmic reticulum surrounding each myofibril
- Pairs of terminal cistern form perpendicular cross channels
- Stores Ca2+
- Functions in the regulation of intracellular Ca2+levels
T Tubules
PICTURE OF TUBULES WITH SARCOLEMMA
- Continuous with the sarcolemma
- Penetrate the cell’s interior at each A band - I band junction
- Associate with the paired terminal cistern to form triads that encircle each sarcomere
Triad Relationship
- T tubules conduct impulses deep into muscle fiber
- Integral proteins protrude into the inter membrane space from T tubule and SR cisternae membranes
- T tubule proteins: voltage sensors
- SR foot proteins: gated channels that regulate Ca2+ release from the SR cisternae
Contraction
- The generation of force
- Does not necessarily cause shortening
- Shortening occurs when tension generated by cross bridges on the thin filaments exceed forces opposing shortening
What is the sliding filament model of contraction?
PICTURE 9.6
States that during contraction, the thin filaments slide past the thick filaments. Overlap between myofilaments increases and the sarcomere shortens
- –in the relaxed state, thin and thick filaments overlap only slightly
- –during contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line and the H zone to shorten as well as each sarcomere
Events at the neuromuscular junction
- Skeletal muscles are stimulated by somatic motor neurons
- Axons of motor neurons travel from the central nervous system via nerves to skeletal muscles
- Each axon forms several branches as it enters a muscle
- Each axon ending forms a neuromuscular junction with a single muscle fiber
What is in the Neuromuscular Junction
- synaptic cleft-gell filled space that separates axon terminal and muscle fiber
- synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (ACh)
- Junctional worlds of the sarcolemma contain ACh receptors
Events at the Neuromuscular Junction
PICTURE 9.8
- Nerve impulses arrive at axon terminal
- ACh is released and binds with receptors on the sarcolemma
- Electrical events lead to the generation of the action potential
Destruction of ACh
- ACh effects are quickly terminated by enzyme acetychonineterase
- Prevents continued muscle fiber contraction in the absence of additional stimulation
Events in generation of action potential
- local depolarization (end plate potential)
- Generation and propagation of an action potential
- Repolarization
What is Local depolarization?
- ACh binding opens chemically (ligand) gated ion channels
- Simulataneous diffusion of Na+ inward and K+ outward
- More NA+ diffuses, so the interior of the sarcolemma becomes less negative
- Local depolarization - end plate potential
Events in Generation of Action Potential
- Local depolarization wave continues to spread, changing permeability of the sarcolemma
- Voltage-regulated Na+ channels open in adjacent patch, causing it to depolarize to threshold
