Muscle Tissue Flashcards
Muscle tissue
Muscle tissue
- optimize property of contractility
- actin microfilaments- generate forces necessary for muscle contraction
- mesodermal origin
3 types of muscle tissue
3 types of muscle tissue:
-
Skeletal muscle
- long, multinucleated cells with cross striations (muscle fibers)
- contraction is quick, forceful, & voluntary
- contraction is caused by the sliding interactions of thick myosin filaments along thin actin filaments
- embryonic development:
- Mesenchymal myoblasts fuse->
- Myotubules with many nuclei
- Myofilaments->
- Striated muscle fibers (location of elongated multinuclei- periphery under sarcolemma)
-
Cardiac muscle
- has cross-striations, elongated, branched cells bond to intercalated discs
- contraction is vigorous, rhythmic, & involuntary
- One or two Centered nuclei with glycogen
-
Smooth muscle
- fusiform cells, lack striations
- contraction is slow & involuntary
- Single Centered nuclei

Satellite cells
Satellite cells
- inactive reserve myoblasts
- Progenitor cells produce new muscle fiber following injury

Sarcoplasm, Sarcoplasmic reticulum, Sarcolemma
Sarcoplasm- cytoplasm of muscle cell
Sarcoplasmic reticulum- Smooth ER of muscle cell
Sarcolemma- muscle cell membrane & external lamina

Hypertrophy & Hyperplasia
Hypertrophy-
- increased cell volume (BIG TROPHY :)
- as in exercise that enlarges skeletal musculature by stimulating formation of new myofibrils & growth in the diameter of individual muscle fiber
Hyperplasia-
- increase in # of cells (I’ve been to MANY PLACES:)
- Smooth muscles able to renew continually
Identify


Organization of skeletal muscle
Epimysium
- surrounds skeletal muscle
- dense irregular connective tissue
- present only in skeletal muscle
Perimysium
- surrounds fascicle
- functional unit in which fibers work together
- Present in all muscle types
Endomysium
- surrounds muscle fibers (has sarcolemma, mitochondria, sarcoplasmic reticulum)
- with reticular fiber & scattered fibroblast
- capillaries bring O2 to the muscle fibers
- Present in all muscle types
Myofibrils-> A bands (dArk bands) & I bands (lIght bands)
Myofilaments (actin & myosin) in sarcomere-> extends from Z disc to Z disc (2.5um resting)

Structure of a myofibril & proteins that make the parts
A band- location of thick myosin filament
H band- center of A band, NO actin
M band- ties myosin bundle together
I band- actin without myosin
Z line- ties actin filaments
Force is generated in A but not in H band!
A-actinin
- protein in Z-discs
- connectin filaments
Titin
- protein in I band and Z discs
- largest protein in the body
Nebulin
- binds thin myofilaments
- helps anchor to a-actinin
Creatine kinase
- found in M line
- phosphocreatine-> phosphate-> ADP (help supply ATP)
Myomesium
- found in M line
- holds thick filaments in place

Myosin and Actin
&
Tropomyosin and Troponin
Myosin
- thick filament
- has heavy (twisted tails) and light chain (2 heads)
- heads have actin & ATP binding sites
Actin
- thIn filament (acTHIN :)
- 2 regulatory proteins:
-
Tropomyosin
- 2 polypeptide chains located in the groove between 2 twisted actin strands
- covers the myosin binding site on actin
-
Troponin
- 3 subunits: TnT(attaches to tropomyosin), TnC(binds calcium), TnI(regulates actin-myosin interaction)
- after binding to calcium will change its shape & move tropomyosin to expose myosin-binding active sites
-
Tropomyosin

Sarcoplasmic reticulum, Tranverse tubule & Terminal cisternae system of 3 muscle types
Sarcoplasmic reticulum
- contains pumps & other proteins for Ca2+ sequestration
- well developed in skeletal muscle, less developed in cardiac, & irregular smooth ER without distinctive organization in smooth muscle
Transverse tubule
- tubular infoldings that penetrate into the sarcoplasm and encircle each myofibril near the aligned A & I bands
- Ca2+ gets distributed simultaneously to produce uniform contraction of all myofibrils
Terninal cisternae
- adjacent to T-tubule
- allows depolarization of sarcolemma in a T-tubule-> release Ca2+-> contraction of sarcomere
- 2 terminal cisterns per sarcomere in triads with T-tubule in skeletal muscle
- 1 small terminal cistern per sarcomere in dyad with T-tubule in cardiac muscle

Mechanism of contraction
Mechanism of contraction- occurs as the overlapping thin and thick filaments of each sarcomere slide past one another
Action potential at NMJ->
T-tubules->
Terninal cisternae of sarcoplasmic reticulum trigger Ca2+ release->
Ca2+ bind to Troponin->
Troponin changes its shape & moves Tropomyosin on the F-actin to expose the myosin-binding active sites & allow cross bridges to form->
Binding actin produces a pivot in the myosin toward the Z disc. Thin filaments move into the A band (energy through ATP is used)->
Myosin binds another ATP & detaches from actin->
Neural impulse stops & levels of free Ca2+ diminish. Tropomyosin again covers the myosin binding sites on actin->
Filaments passively slide back. Sarcomeres return to relaxed state.
Rigor mortis
Rigor mortis
- absence of ATP
- actin-myosin cross bridges stabilize
- skeletal muscle become rigid when mitochondrial activity stops after death
Innervation of action potential
At MEP (motor end plate) or NMJ, acetylcholine gets released at synaptic cleft->
ACh binds to the receptors in the junctional folds of sarcolemma. ACh receptors contain a nonselective cation channel->
Muscle action potential->
ACh gets removed by acetylcholinesterase
Motor unit
Motor unit
- 1 axon + all the muscle fibers it innervates
- finer movements (example: ocular)- innervates few muscles
- coarser movements (example: gluteus)- innvervates many muscles (100)
Myasthenia gravis
Myasthenia gravis
- autoimmune disorder that involves circulating anitbodies against proteins of ACh receptors
- skeletal muscle weakness
- extraocular muscle of eyes are commonly affected first
Muscle spindles and Golgi tendon organs
Sensory receptors associated with skeletal muscles:
Muscle spindles
- stretch detectors in muscle fascicles
- encapsulated by modified perimysium (cells, fluid, muscle fibers)
Golgi tendon organs
- enclose sensory axon penetrating among the collagen bundles at the myotendinous junction
- detect changes in tension

Duschenne muscle dystrophy
Duschenne muscle dystrophy
- mutation of dystrophin gene
- defective linkages between the cytoskeleton & the ECM
- muscle contractions disrupt weak linkages to atrophy
- large actin-binding protein inside sarcolemma or skeletal muscle
Skeletal muscle fiber types
Skeletal muscle fiber types:
- Slow oxidative muscle fibers
- slow contractions over long periods without fatigue
- red fibers d/t:
- many mitochondria
- many surrounding capillaries
- much myoglobin
- Fast glycolytic fibers
- specialized for rapid short-term contraction
- white fibers d/t:
- few mitochondria or capillaries
- anaerobic metabolism of glucose-derived from stored glycogen
- Fast oxidative-glycolytic fibers
- intermediate

Myoglobin
Myoglobin
- globular sarcoplasmic protein similar to hemoglobin which contains iron atoms and allow for O2 storage
Cardiac muscle
Cardiac muscle
- embryonic development: mesenchymal cells align in chainlike arrays-> form complex junction between interdigitating process
- Intercalated discs:
- abundant of desmosomes & fascia adherens junctions (tranverse)- provide strong intercellular adhesion during the cells’ constant contractile activity
- gap junction (longitudinal)
- provide ionic continuity between the cells
- serve as electrical synapse promoting rapid impulse conduction through many cardiac muscle cells simultaneously & contraction of many adjacent cells as a unit
- Secretory granules:
- found near atrial muscle nuclei
- associated with small golgi complexes
- release peptide hormone (atrial natriuretic factor ANF)
- target cells of kidneys to affect Na+ secretion
- natriuresis and diuresis
- Fatty acids
- major fuel of the heart
- stored in triglycerides in small lipid droplets
- Also present: glycogen granules, perinuclear lipofucsin pigment granules
- Ischemia- tissue damage d/t lack of O2
Smooth muscle
Smooth muscle (visceral muscle)
- Fibers are enclosed by an external lamina & network of type I & type III collagen fibers comprising the endomysium
- linked by numerous gap junctions (coordinate contractions)
- concnetrated near the nucleus are mitochondria, polyribosomes, RER, vesicles of golgi
- calveolae- contain major ion channels that control Ca2+ release from sarcoplasmic cisternae at myofibrils which initiates contraction
- myosin phosphorylation by MLCK (myosin light chain kinase) when calmodulin binds Ca2+-> actin-myosin binding
- Dense bodies
- contains a-actinin
- functionally similar to Z disc
- Intermediate filaments composed of desmin- attach to dense bodies
- Cadherins of desmosomes (submembranous dense bodies)- links adjacent smooth muscle cells
- Synaptic vesicles in varicosites release neurotransmitter: ACh or NE
- Reticulin fibers with the basal lamina of smooth muscle cells help hold the cells together as a functionla unit during the slow rhythmic contraction of this tissue
- support fibroblast activity synthesizing collagen, elastin, & proteoglycans
- Leiomyomas
- benign tumor that develop from smooth muscle fibers- walls of uterus
- aka fibroids
- Visceral (single unit):
- connected by gap junctions
- visceral organs
- stress-relaxation-contraction method
- Multi-unit
- NOT connected by gap junction but adherens & desmosomes
- Arteries, airways, eyes
- nerve or hormones
- nerve stimulated bu stretching