Chapter 9 part 1 Flashcards
What is nearly half of the body’s mass and why?
Muscle tissue because it holds a lot of water
What does muscle tissue do for the body?
Converts chemical energy in the form of ATP into directed mechanical energy that exerts a force
What are the three types of muscle tissue?
Skeletal
Cardiac
Smooth
What are three prefixes for muscle?
Myo
Mys
Sarco
What are skeletal muscle cells called?
Muscle fibers (elongated)
Are skeletal muscles striated or smooth? Voluntary or involuntary? Multinucleated or uninucleated?
Striated
Voluntary (require nervous system stimulation)
Multinucleated
Where does nervous system stimulation happen in skeletal muscles?
At the neuromuscular junction
Describe cardiac muscle?
In heart
Involuntary (no nervous system stimulation needed)
Striated
Intercalated discs/branched
Where do you find smooth muscle?
walls of hollow organs
Bladder
Stomach
airways
Spindle shaped and uninucleated
What are the 4 special characteristics of muscle tissue?
Excitability
Contractility
Extensibility
Elasticity
What is excitability?
The ability to receive and respond to stimuli
What is contractility?
The ability to shorten forcibly when stimulated
What is extensibility?
Ability to be stretched
What is elasticity?
Ability to recoil to resting length
What are the 4 important functions of muscles?
Movement
Maintaining posture and body position
Stabilizing joints
Heat generation
What do nerve endings do for skeletal muscles?
They regulate contraction (requires stimulation from nervous system)
What do arteries and veins do for the skeletal muscles?
Deliver nutrients and oxygen, remove waste
What is the epimysium?
Dense irregular connective tissue that surrounds entire muscles
What is the perimysium?
Fibrous connective tissue surrounding fascicles (group of muscle fibers)
What is the endomysium?
Areolar connective tissue surrounding each muscle fiber
Where do skeletal muscles attach?
To the insertion (movable bone) and the origin (immovable bone)
What is direct attachment of skeletal muscles?
Where the epimysium is fused to periosteum of bone or perichondrium of cartilage
What is indirect attachment of skeletal muscle?
The connective tissue wrappings extend beyond muscle as ropelike tendon or sheet like aponeurosis (on front of skull)
What is the sarcolemma?
The plasma membrane of skeletal muscle
What is the sarcoplasm?
The cytoplasm of skeletal muscle fibers
What do glycosomes do?
They store glycogen in the skeletal muscle fibers
What does myoglobin do?
They store oxygen in the skeletal muscle fibers
What do myofibrils contain?
Sarcomeres (contractile unit)
What are myofibrils?
Densely packed rodlike elements
What are striations of skeletal muscle fiber?
Repeating series of dark A bands and light I bands
What is the H zone of striations?
Lighter region in midsections of dark A band where filaments do not overlap
What is the M line?
Line of protein myomesin that bisects the H zone
What is the Z disc?
Sheet of protein on midline of light I band
Anchors thin filaments and connects myofibrils to one another
What runs the entire length of an A band?
Thick filaments
What runs the entire length of the I band and partway into A band?
Thin filaments
What runs from the z disc to z disc?
Sarcomere
What are thin filaments made up of?
Actin myofilaments
What are thin filaments anchored to?
Zdiscs
What are thick filaments made up of?
Myosin myofilaments
Where are thick filaments connected?
At the M line
What do myosin tails contain?
2 interwoven, heavy polypeptide chains
What is contained in the myosin heads?
2 smaller, light polypeptide chains that act as CROSS BRIDGES during contraction
What do myosin heads act as?
Binding sites for actin of thin filaments
Binding sites for ATP
ATPase enzymes
Where are the active sites for myosin head attachments during contraction?
Actin
What regulates actin binding to myosin heads?
Tropomyosin and troponin
What are elastic filaments of myofibrils made up of?
The protein titin
What do the elastic filaments of myofibrils do?
Hold the thick filaments in place
Helps recoil after stretch
Resist excessive stretching
What does dystrophin do?
Links the filaments to proteins of the sarcolemma (plasma membrane of the muscle cell)
What 3 proteins bind filaments together and maintain alignment?
Nebulin
Myomesin
C proteins
What kind of ER is the sarcoplasmic reticulum?
Smooth ER
What is the function of the sarcoplasmic reticulum?
Regulation of intracellular Ca2+ levels (stores and releases calcium)
What forms perpendicular cross channels in the SR?
Pairs of terminal cisterns
Label the SR, Terminal Cisterna, and sarcolemma
What are T Tubules?
Continuations of sarcolemma in which its lumen (inside) is continuous with the Extracellular space
What do T tubules do for the muscle fiber’s surface area?
Increase the surface area
Where do T tubules penetrate the cell’s interior?
At each A band - I band junction
What are the triads of muscle fibers?
Paired terminal cisterns and T tubule
What do the T Tubules do for muscle action potential?
They bring action potentials into the interior of muscle fiber (they must be stimulated by nervous system)
What happens to the lengths of individual thick and thin filaments in the sliding filament model of contraction?
They do not change in length (does not necessarily cause shortening of fiber)
When does shortening occur of the muscle fiber?
When tension generated by cross bridges on think filaments exceeds forces opposing shortening (not isometric)
In what state do thin and thick filaments only overlap at ends of A band?
Relaxed state
What happens during the sliding filament model of contraction?
Thin filaments slide past thick filaments (actin and myosin overlap more)
When does contraction occur?
When myosin heads bind to actin (cross bridges are formed)
How does sliding begin in the sliding filament model of contraction?
Myosin heads bind to actin and sliding begins
How does ratcheting thin filaments toward center of sarcomere work?
Cross bridges form and break several times (this causes shortening of the muscle fiber)
Z discs are pulled toward the M line
What happens when the intracellular Ca2+ concentration is low?
Tropomyosin (blocker) blocks active sites on actin so that myosin heads cannot attach to actin
(muscle fibers relax)
What happens at higher intracellular Ca2+ concentrations?
Troponin changes shape when Calcium binds to it and moves tropomyosin out of the way so that myosin heads bind to actin
(causes sarcomere shortening and muscle contraction)
How does muscle contraction end?
When nervous stimulation ceases, Calcium ions are pumped back into the sarcoplasmic reticulum and contraction ends
How are cross-bridges formed?
High-energy myosin heads attach to thin filaments (actin)
What happens during a working (power) stroke?
Myosin head pivots and pulls thin filament toward M line
What happens during cross bridge detachment?
ATP attaches to myosin head and cross bridges detaches
What is meant by “cocking” of myosin head?
Energy from hydrolysis of ATP cocks myosin head into high energy state (resets itself)
What happens during rigor mortis?
Cross bridges do not detach because it requires ATP so the body stays contracted
(dying cells take in calcium and cross bridges are formed)
What is needed for activation of skeletal muscles?
Nervous system stimulation
Action potential must be generated in sarcolemma
What is EC coupling?
Excitation-contraction coupling is when action potentials propagate along the sarcolemma and intracellular calcium levels must rise briefly
What are the two layers of smooth muscle?
Longitudinal (fibers parallel to long axis of organ- contraction leads to shortening)
Circular (fibers in circumference of organ- contraction leads to elongation)
What is peristalsis?
Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through lumen of hollow organs
What type of cells are seen in smooth muscle fibers?
Thin and short, only one nucleus, no striations
What connective sheaths are seen in smooth muscle?
It lacks connective tissue sheaths it only contains endomysium only
How is the sarcoplasmic reticulum in smooth muscle related to the SR in skeletal muscle?
It is less developed in smooth muscle because it does not depend on nervous system stimulation
What binds to calcium ions in smooth muscle?
Calmodulin
There are no sarcomeres, myofibrils, or T tubules
What are dense bodies in smooth muscle?
Proteins that anchor non-contractile intermediate filaments to sarcolemma at regular intervals
What type of junctions are in smooth muscle?
Gap junctions
We want smooth muscle to contract in synchronicity (peristalsis)
What type of movement do smooth muscle fibers contract?
Corkscrew manner
What energizes the sliding process in the contraction of smooth muscle?
ATP
actin and myosin interact by sliding filament mechanism
Where is calcium obtained in smooth muscle for smooth muscle contraction?
From the SR and extracellular space (mainly extracellular space because SR is underdeveloped)
How are smooth muscle contracted?
Calcium binds to and activates calmodulin
Activated calmodulin activates myosin kinase
Myosin kinase Phosphorylates and activates myosin
Cross bridges interact with actin and contraction occurs
What does smooth muscle relaxation require?
Active transport of calcium into SR and ECF to decreasing intracellular calcium (dephosphorylation of myosin to reduce myosin ATPase activity)`
