Muscle Tissue Flashcards
Skeletal Muscle
(S, F, L)
Structure: composed of long, striated multinucleated muscle fibers; limited ability to renew
Function: production of major movements of the body
Location: all over the body; most are attached to bones
Cardiac muscle
(S, F, L)
Structure: composed of short, striated, uninucleate cardiomyocytes with branched cytoplasm, firmly attached to each other via intercalated discs; inability to renew, contains glycogen storage
Function: coordinated contraction and relaxation fills and pumps blood; glycogen stores for energy
Location: heart
Smooth muscle
(S, F, L)
Structure: composed of short, fusiform, uninucleate smooth muscle cells staggered in parallel; able to renew continually; homogenous eosinophilic cytoplasm (no striations or bands)
Function: coordinated contraction of the visceral organs
Location: visceral organs; gastrointestinal tract (GI blood vessels, exocrine glands, etc.)
Regeneration in skeletal muscle
Satellite cells in skeletal muscles have limited ability to proliferate and differentiate into skeletal muscle cells; as a result, extensive injury and destruction of muscle tissues cannot be fully repaired; muscle building exercises causes muscle fibers to grow, not to increase in number
Skeletal muscle fiber
(S, F, L)
Structure: striated, multinucleated muscle cell
Function: individual contractile cell
Location: throughout the muscle
Endomysium
(S, F, L)
Structure: thin reticular fibers
Function: structural support for each cell and delivery of small vessels and nerves
Location: surrounds each muscle fiber
Fascicle
(S, F, L)
Structure: A bundle of muscle fibers
Function: functional unit that works together
Location: throughout the muscle
Perimysium
(S, F, L)
Structure: connective tissue
Function: bind together fascicles and help it function as a unit, deliver larger vessels and nerves
Location: surround each fascicle
Named muscles
(S, F, L)
Structure: formed from a collection of fascicles
Function: work in a coordinated manner to create movements
Location: throughout the body
Epimysium
(S, F, L)
Structure: dense connective tissue
Function: sheath the muscle, help transmit contractile force of the muscle, deliver major vessels and nerves
Location: surround each muscle
Myofibril
(S, F, L)
Structure: thin and long bundles that fill the muscle fiber
Function: contractile structure as long as the muscle cell
Location: throughout sarcoplasm
Sarcomere
(S, F, L)
Structure: contractile unit of the myofibril
Function: line up back to back to form a myofibril
Location: length of the myofibril
Myofilaments
(S, F, L)
Structure: strands of protein polymers; myosin (thick filaments) and actin (thin filaments)
Function: Interaction between thick and thin filaments produces contraction; overlap between the two filaments creates a banding pattern (striations)
Location: within each sarcomere
Sarcoplasmic reticulum
(S, F, L)
Structure: network of specialized sER surrounds each myofibril. Terminal cisternae are dilated portions of the sarcoplasmic reticulum
Function: store, release, and reuptake Ca++
Location: throughout the sarcoplasm surrounding each myofibril; terminal cisternae are located between A and I bands
Transverse tubules (T-tubules)
(S, F, L)
Structure: invagination of the sarcoplasmic reticulum (sarcoplasm??)
Function: Transmit membrane depolarization throughout the sarcoplasm; trigger Ca++ release from terminal cisternae
Location: travel through the muscle fiber at A and I junctions
Triad
(S, F, L)
Structure: Unit of two terminal cisternae with a T Tubule in the middle
Function: effective depolarization wave transmission and release of Ca++
Location: A and I junctions
A band
(S, F, L)
Structure: dark band
Function: span of thick filaments; areas of overlap with thin filaments on either side
Location: middle portion of sarcomere
H band
(S, F, L)
Structure: less dark band in the middle of the A bad
Function: portion of A band with only thick filaments
Location: middle portion of the A band
M line
(S, F, L)
Structure: Faint, thin line in the middle of the A band
Function: Anchor thick filaments in place
Location: middle of A band
I band
(S, F, L)
Structure: light band
Function: area with only thin filaments
Location: lateral portion spanning two sarcomeres
Z line (Z disc)
(S, F, L)
Structure: dense line in the middle of the I band
Function: Anchor thin filaments and mark the boundary of the sarcomere
Location: end margin of each sarcomere; midline of the I band
Neuromuscular junction
(S, F, L)
Structure: Site of interaction between the motor axon terminal (highly branched, contains numerous ACh filled vesicles) and receptor region on sarcolemma (shallow depression with many membrane folds and junctional folds expressing receptors for ACh)
Function: In response to action poetical the motor axon terminal releases ACh into the synaptic cleft; the ACh receptors bind ACh and initiate membrane depolarization wave throughout the muscle fiber
Location: Usually in the middle of the muscle fiber but may vary
Motor Units
A group of skeletal muscle fibers innervated by a single motor neuron that contract together
Small motor unit
A small group of muscle fibers innervated by a single motor neuron that generates fine, delicate movements quickly. Includes extrinsic eye muscles and muscles that control the fingers
Large motor units
A large group of muscle fibers innervated by a single motor neuron that generates a large contractile force but is relatively slow to respond as a whole. Includes the muscles of the back, thighs, and buttocks.
Muscle contraction process
Action potential travels down the axon –> triggers release of Ach at a neuromuscular junction –> Ach binds receptors on the sarcolemma at NMJ –> Sarcolemma depolarization wave travels through the rest of the cell and T-tubules –> terminal cisternae release Ca++ –> Ca++ allows interaction of myosin and actin by binding to troponin and releasing tropomyosin from the actin —> ATP is used to slide the filaments on each other —-> Shortens sarcomere, shortening myofibril and resulting in muscle contraction
Muscle fiber types
Type I - red, slow twitch fibers
Type Ila - intermediate fibers
Type IIb - white, fast-twitch fibers
Type I Muscle fibers (Slow twitch)
(S, F, L)
Structure: small diameter, red appearance in vivo due to high myoglobin content; many mitochondria
Function: slow to contract but resistant to fatigue; undergo oxidative phosphorylation to produce maximum ATP
Location: postural muscles; large amount in muscles of endurance athletes
Type IIa Muscle fibers (Intermediate)
(S, F, L)
Structure: Medium-sized diameter; slightly red due to a good amount of myoglobin; many mitochondria; glycogen storage
Function: faster to contract and fairly resistant to fatigue; generate ATP by both oxidative phosphorylation and glycolysis
Location: Large amount in mid-distance runners and swimmers
Type IIb Muscle Fibers (fast twitch)
(S, F, L)
Structure: Large diameter; light pink in vivo due to less myoglobin; fewer mitochondria; large glycogen storage
Function: Fast to contract and prone to fatigue; generate ATP rapidly by anaerobic glycolysis. Lactic acid by-products cause fatigue
Location: Extraocular muscles, muscles of the fingers; large amount in short distance runner and weight lifters
Intercalated discs
(S, F, L)
Structure: dark bands between cardiomyocytes
Function: create cardiomyocytes syncytium; allows for the chemical and electrical communication between cells
Location: in between cardiomyocytes
Transverse portion of cardiomyocytes
(S, F, L)
Structure: contains adhesion junctions and desmosomes
Function: adheres cardiomyocytes end to end
Location: portions of the disc perpendicular to the long axis of the cell (filaments)
Lateral portion of cardiomyocytes
(S, F, L)
Structure: contains gap junctions
Function: transmission of macromolecules and ions between cells
Location: portions of the intercalated disc parallel to the long axis of the cell
Diad
S, F, L
Structure: a unit of one terminal cisternae and one T-tubule
Function: effective depolarization wave transmission and release of Ca++
Location: level of Z-lines
Dense bodies
(S, F, L)
Structure: A group of proteins on the cytoplasmic side of sarcolemma
Function: attach and anchor thin filaments to sarcolemma
Location: scattered throughout the cytoplasmic side of sarcolemma
