midterm exam Flashcards
muscle tissue is nearly ___ the body’s mass
1/2
what can muscle tissue do?
transform chemical energy (ATP) into directed mechanical energy
prefixes for muscle
Myo, mys, and sarco
Three types of muscle tissue
Skeletal
Cardiac
Smooth
Skeletal muscle tissue is packaged into?
skeletal muscles
What are skeletal muscles?
organs that are attached to bones and skin
Characteristics of skeletal muscle fibers
- longest of all muscle
- striations (stripes)
- voluntary
- Contract rapidly
- tire easily
- powerful
characteristics of cardiac muscle tissue
- found only in heart
- Makes up bulk of heart walls
- Striated
- Involuntary; Contracts at steady rate due to the heart’s own pacemaker,
nervous system can increase rate
Characteristics of smooth muscle tissue
- found in walls of hollow organs
- Examples: stomach, urinary bladder, and airways
- Not striated
- Involuntary: cannot be controlled consciously
- Key words for smooth muscle: visceral, nonstriated and involuntary
4 main characteristics of all muscles
Excitability
Contractility
Extensibility
Elasticity
Excitability
(responsiveness) - ability to receive and respond to stimuli
Contractility
ability to shorten forcibly when stimulated
Extensibility
The ability to be stretched
Elasticity
The ability to recoil to resting length
4 important functions of muscles
- Produce movement: responsible for all locomotion and manipulation
- Maintain posture and body position
- Stabilize joints
- Generate heat as they contract
Skeletal muscles 3 features
- nerve and blood supply
- connective tissue sheaths
- attachments
3 things each muscle recieves
- nerve
- artery
- veins
skeletal muscle has _____ supplying every ______
nerves, fiber
Contracting muscle fibers require huge amounts of ______ & ______
oxygen & nutrients
what do muscles need to be removed quickly?
waste products
Each skeletal muscle & each muscle fiber, is covered in _______
connective tissue
connective tissue sheaths do what?
Support cells and reinforce whole muscle
Epimysium
dense irregular connective tissue surrounding entire muscle
Perimysium
fibrous connective tissue surrounding fascicles
fascicles
groups of muscle fibers
Endomysium
fine areolar connective tissue surrounding each muscle fiber
Muscles span _____ and attach to _____
joints, bones
in how many places must muscles attach to bone?
at least 2 places
Insertion
attachment to movable bone
Origin
attachment to immovable or less movable bone
Skeletal muscle fibers
long, cylindrical cells that contain multiple nuclei
Sarcolemma
muscle fiber plasma membrane
Sarcoplasm
muscle fiber cytoplasm
muscle fibers contain many ______
glycosomes
what do glycosomes do?
used for glycogen storage, as well as myoglobin for O2 storage
Myofibrils
densely packed, rodlike elements that makeup 80% of muscle cell volume
how many myofibrils can be in a single muscle fiber?
thousands (1000s)
myofibrils characteristics
- Striations
- Sarcomeres
- Myofilaments
- Molecular composition of
myofilaments
Striations
stripes formed from repeating series of dark and light bands along length of each myofibril
what are A bands?
dark regions
H zone
lighter region in middle of dark A band
I bands
lighter regions
sarcomere
Smallest contractile unit (functional unit) of muscle fiber
Individual ________ align end to end along myofibril, like boxcars of train
sarcomeres
myofilaments
Orderly arrangement of actin and myosin myofilaments within sarcomere
Actin myofilaments
- thin filaments
- Extend across I band and partway in A band
- Anchored to Z discs
myosin myofilaments
- thick filaments
- Extend the length of A band
- Connected at M line
how are cross bridges formed?
During contraction, heads link thick and thin filaments together
actin - thin filaments
bears active sites for myosin head attachment during contraction
Tropomyosin and troponin
regulatory proteins bound to actin
what does the sarcoplasmic reticulum regulate?
intracellular Ca2+ levels by storing and releasing Ca2+
Sarcoplasmic reticulum
network of smooth endoplasmic reticulum tubules surrounding each myofibril
T tubules
- A tube formed by protrusion of the sarcolemma deep into cell interior
- Increase muscle fiber’s surface area greatly
- Allow electrical nerve transmissions to reach deep into the interior of each muscle fiber
what happens during muscle contraction?
- thin filaments slide past thick filaments, causing actin and myosin to overlap more
Four steps that must occur for skeletal muscle to contract
- Events at neuromuscular junction
- Muscle fiber excitation
- Excitation-contraction coupling
- Cross bridge cycling
steps for a muscle to contract/ send a signal
- Action potential goes down the nerve and reaches the terminal
- calcium channels open calcium into terminal
- calcium causes the release of ACH (acetylcholine)
- ACH binds to receptors on muscle membrane
- opens sodium channels and NA+ rushes in
- depolarizes the muscle membrane (sarcolemma)
- ends when AcetylcholineSTERASE is gone
-new action potential
3 steps to action potential
- Generation of end plate potential
- Depolarization
- Repolarization
end plate potential
- ACh released from motor neuron binds to ACh receptors on sarcolemma
- Opens chemically gated ion channels
- Na+ diffuses into muscle fiber
- Some K+ diffuses outward, but not much
- Because Na+ diffuses in, interior of sarcolemma becomes less negative (more positive)
- Results in local depolarization called end plate potential
Depolarization
generation and propagation of an action potential (AP)
when voltage membrane reaches its threshold, what happens?
Na+ channels will open
Large influx of Na+ through channels into cell triggers AP that is unstoppable and will lead to ________________
muscle fiber contraction
Repolarization
restoration of resting conditions
what happens during repolarization?
- Na+ voltage-gated channels close, and voltage-gated K+ channels open
- K+ efflux out of cell rapidly brings cell back to initial resting membrane voltage
Refractory period
muscle fiber cannot be stimulated for a specific amount of time, until repolarization is complete
Excitation-contraction (E-C) coupling
events that transmit action potential along sarcolemma (excitation) are coupled to sliding of myofilaments (contraction)
At low intracellular Ca2+ concentration…
- Tropomyosin blocks active sites on actin
- Myosin heads cannot attach to actin
- Muscle fiber remains relaxed
what is released when calcium is too high?
calcitonin
what is released when calcium is too low?
parathyroid
what happens when calcium is too high
-calcitonin
-gut lets calcium go
-kidneys excrete calcium
-bones dont put calcium in blood
what happens when calcium is too low
- parathyroid
- gut puts calcium into blood
- kidney holds onto calcium
-bone puts calcium into blood
