muscle Flashcards
muscle cells are
muscle fibres
myofilaments
actin and myosin
muscle cells contain myoglobin:
- structured related to hemoglobin
- O2 storage and release to working muscle
specialized muscle terms for cytoplasm, endoplasmic reticulum, plasma membrane
- sarcoplasm
- sarcoplasmic reticulum
- sarcolemma
3 types of muscle
skeletal, smooth, cardiac
skeletal muscle
- voluntary
- striated
- movement of skeleton, eye, tongue, etc
- sphincters of digestive and urinary tracts
- maintains body temp
smooth muscle
- visceral muscle
- main component of viscera
- controlled by autonomic NS and endocrine system
cardiac muscle
- heart
- contraction inherent
skeletal muscle cells are what type in terms of nucleus
multinucleate
skeletal muscle fibres surrounded by reticular connective tissue
endomysium
skeletal muscle;
groups of fibres (fascicles) are separated by dense connective tissue called
perimysium
skeletal muscle
enveloping the entire muscle is a thick layer of dense connective tissue
epimysium (fascia)
endomysium:
perimysium:
epimysium:
- surrounds fibers
- surrounds fascicles
- surroundeds entire muscle, continues as tendon
in transverse section skeletal muscles
- fibres appear roundish in transverse section
- flattened peripheral nuclei (remember multinucleate within the fibre)
striations of skeletal muscle
caused by organizations of actin and myosin
satellite cells/ Stem cells; likely mesenchymal stem/ stromal cells
Differentiate into muscle cells in response to damage
embryological development of skeletal muscle; fibers develop from chains of
myoblasts
embryological development of skeletal muscle; chains of myoblasts fuse end to end to form multinucleate syncytia called
myotubes
steps of embryological development of skeletal muscle
- Fibres develop from chains of myoblasts
- Fuse end to end to form multinucleate syncytia: myotubes
- Lay down actin & myosin
- Nuclei become displaced to periphery
once myoblasts have fused to form a fiber, their nuclei can no longer
synthesize DNA and so they cannot divide (so can’t create new muscle fibres but they can grow bigger)
skeletal muscle grows via
hypertrophy (so they can’t grow new fibers, but they can grow bigger)
- Increase in sarcoplasm
- Number of myofibrils
what inhibits muscle growth
gene myostatin;
so if mutation of myostatin can grow huge muscles
Satellite cells (MSCs)
- Mesenchymal stem cells
- for Growth in the young
- for Repair in adults
3 types of skeletal muscle fibers
- Red fibers (type I: slow oxidative fibers) endurance
- White fibers (Type IIX; fast glycolytic fibers) sprint
- Intermediate fibers (Type IIA; fast ox/ glyx fibers), mix of red and white
Red fibers (type I: slow oxidative fibers) endurance
(skeletal muscle)
- Fewer myofibrils, rich in myoglobin and mitochondria
- Extensive blood supply
- Aerobic
- Slow, powerful and sustained (tonic) contractions
White fibers (Type IIX; fast glycolytic fibers) sprint
(skeletal muscle)
- Less myoglobin and sarcoplasm, simple mitochondria
- Relatively poor blood supply; why they are white
- Rich in glycogen
- Anaerobic
- Rapid (twitch) contractions, easily exhausted
Intermediate fibers (Type IIA; fast ox/ glyx fibers), mix of red and white
- Properties intermediate between red and white fibers
- Rich in myoglobin and mitochondria
- Rich in glycogen
- extensive blood supply
Example; breast meat on roast chicken;
what fibers is is dominated by
flap wings briefly to escape; short burst of flight powered by white (fast) fibers, white meat
(vs in ducks Long flights so meat tends to be darker red than chicken breast meat)
aerobic muscle fibers:
anaerobic muscle fibers:
- red, slow
- white, fast
Striations
- Each fiber (muscle cell): myofibrils in parallel
- Each myofibril; myosin and actin laid down in an orderly pattern, in register with each other, forming A and I bands
A bands
- dark
- anisotropic, means they stay constant length
- made up of myosin
- Pale central H band within, bisected by dark M line where myosin filaments joint
I bands
- light
- isotropic; means they change their length, do this when muscle contracts
- made up of actin
- Bisected by a dark Z line; where actin filaments join
Sarcomere;
regions between Z lines
Myofibrils during contractions (sliding filament theory)
- Actin filaments (thin, attached to Z line) slide over the myosin filaments (thick, attached to M line)
- Shortening of the sarcomere (and also the I band)
sliding filament theory where myofibrils move during contraction is dependent on
ATP and CA2+
Sarcolemma
- Aka plasmalemmal/ membrane
- Sends tubular extensions into muscle fiber called T tubules
- Surround each myofibril at junction of the A and I bands
- Continuous with extracellular environment
Sarcoplasmic reticulum
- Aka endoplasmic reticulum
- Network that encircles myofibrils between T tubules
- Form flattened cisternae on either side of T tubules
- Triad; cisternae, T tubule, cisternae
Ca2+ stored in
sarcoplasmic reticulum
During nervous stimulation sarcolemma becomes
depolarized, transmitted throughout entire fiber via T tubule system
depolarization of sarcolemma causes
release of Ca2+ form the sarcoplasmic reticulum; flows into sarcoplasm that surrounds the actin and myosin filaments; causes their contraction
Triad
cisternae, T tubule, cisternae
what provides energy for contraction
Mitochondria located within I bands
Innervation of skeletal muscle via
motor nerves from CNS
Each motor nerve divides within the muscle, branches supply separate groups of fibers and the branches end in
specialized synapses called neuromuscular junctions (motor end plates)
motor unit=
Nerve and fibers it innervates
Sensory nerve endings =
- neuromuscular spindles
- Convey info to CNS
- Rate and extent of muscle stretch
- Tendo-muscular junction
Least specialized of the 3 muscle types
smooth muscle
smooth muscle fibers have how many nuclei
one, central, oval/round
smooth muscle fibres may be found
- Singly
- Groups: Sheets or layers
Fasciculi
many smooth muscle fibers form
irregular branching fasciculi ; fasciculi function as contractile units
Fibers within a fasciculus are roughly
parallel
does smooth muscle have myofibrils/ sarcomeres?
No myofibrils, no sarcomeres
3 types of myofilaments in smooth muscle
- Actin (thin)
- Myosin (thick)
- Intermediate filaments
in smooth muscle actin anchored at
dense bodies: connect to intermediate filaments
how do smooth muscle contract
also sliding filament theory
in smooth muscle _______ spread the force of contraction throughout cell
Intermediate filaments
Innervation of smooth muscle
- Contraction is inherent
- Coordinated via gap junctions between adjacent cells
- Rate of contraction modulated by the ANS and hormones
- Smooth muscles surrounding blood vessels regulated by vasomotor nerves
Cardiac muscle made up of chains of branching cells with how many nuclei
1-2 central nuclei
form a 3D branching network
cardiac muscle cells joined at specialized junctions=
intercalated discs
Intercalated discs;
- specialized junction where cardiac muscle cells joined
- allow cells to be linked physiologically and mechanically, rapid spread of contraction and anchorage of myofilaments
are cardiac muscle striated
- yes, arrangement of myofilaments similar to skeletal muscles
- Cross striation present
(Not as distinct as skeletal muscles) - Longitudinal striations
(Due to rows of mitochondria)
Each cardiac muscle cell contacts other via
intercalated discs
cardiac muscle , how its different to skeletal muscle
- while actin and myosin are arranged into myofibrils, they have fan-like arrays rather than cylindrical structures
- Separated by sarcoplasm containing many mitochondria; aerobic metabolism
- T tubules are larger; penetrate myofilaments at Z lines, all parts of fiber no more than 2 microns from sarcolemma, no triads
4 types of cardiac muscle
- Ventricular muscle (described above)
- Atrial muscle; cells have a smaller diameter, T tubules absent
- Conducting fibers; smaller than contractile cells, embedded in dense connective tissue to form nodes, intercalated discs and myofilaments not well developed, coordinate electrical events
- Purkinje fibers; modified conducting fibers in ventricle, not purkinje neurons!
Innervation of cardiac muscle
- Contraction is inherent; independent of neural control
- No neuromuscular junctions
- No sensory endings
- However it is modulated by neural signals
- ANS
- Nerves terminate in nodes formed by conducting fibers
Which of the following statements about muscle is INCORRECT?
The contraction of cardiac muscle is dependent on neural control and so it is extensively supplied with neuromuscular junctions and sensory nerve endings
In skeletal muscle cells, depolarisation of the sarcolemma is transmitted throughout the fibre via the organisation of T-tubules
In skeletal muscle, neuromuscular spindles convey information to the central nervous system about the rate and extent of muscle stretch
The contraction of smooth muscle is inherent and is coordinated by gap junctions between adjacent cells
The contraction of cardiac muscle is dependent on neural control and so it is extensively supplied with neuromuscular junctions and sensory nerve endings
