1. Department of Human Morphology and Developmental Biology
Muscle tissue
Agnes Nemeskeri
2013
Department of Human Morphology and Developmental Biology

2. A/ Smooth muscle tissue
Types of muscle tissue
- muscle cells (myocytes)
-energy from the hydrolysis of ATP (converting chemical energy into mechanical work)
A/ Smooth muscle tissue
-no cross-striations
B/ Striated muscle tissue
-repeating elements give
cross-striated appearance

3. Striated muscle

4. Striated muscle SKELETAL b) VISCERAL c) CARDIAC
-histological unit: multinucleated muscle fiber grouped in bundles
-originating and inserting on skeletal elements
-contraction needs nervous stimulus
b) VISCERAL
-histological unit: multinucleated muscle fiber grouped in bundles
-independent of bones (intrinsic muscles of tongue, upper third of
esophagus
-contraction needs nervous stimulus
c) CARDIAC
-histological unit: cardiac muscle cell (mono- or binucleated
-branching network of individual cells – functions as a unit
-intrinsically capable of rhythmic contraction

5. Size of muscle cells Striated muscle fiber Cardiac muscle cell
Smooth muscle cell in uterine wall at the end of gestation
Smooth muscle cell in blood vessel wall

6. Light microscopy of skeletal and visceral striated muscle
esophagus

7. Skeletal and visceral striated muscle
Myofibrils are composed of repeated sections of sarcomeres
muscle fiber
thin
thick
line
sarcomere
A muscle cell from a biceps may contain 100,000 sarcomeres

8. Striated muscle fiber- myofibrillum
Sarcomere =
myofibrillum
Sarcomeres are composed of regularly aligned thin and thick filaments

9. Cross striation at molecular level
thin filament
thick filament

10. Thin filament F-actin resembles a two-stranded cable
Thin filament
F-actin resembles a two-stranded cable
Thin filament – 6-9 nm
-pointed end – actin capping protein: tropomodulin
-barbed ends of actin filaments are anchored to the Z-bands
Actin
-2 actin filaments are coiled on eachother – filamentous
linear polymer (G- actin globular subunits –
polymerization)
Tropomyosin – filamentous protein
-blocking the myosin binding site on actin
Troponin complex - TnT is a tropomyosin-binding subunit regulates
interaction of troponin complex with thin filamentum
TnC is a Ca2+ - binding subunit
TnI inhibits ATP-ase activity of actin-myosin (binding)

11. Thick filament
Each head cycles approximately five times per second with a movement of 110 Å per cycle.
However, because hundreds of heads are interacting with the same actin filament, the overall rate of movement of myosin relative to the actin filament may reach 80,000 Å per second
Thick filament – nm
-myosin: ATP dependent motor protein
-one myosin molecule is composed of 4 chains
- 2 heavy chains - coiled heavy chain: tail - N terminal globular head,
- 2 light chains - neck region between the head and tail creates angle
-hundreds of myosin molecules form a thick filament

12. Structural and mechanical integrity of the sarcomeric elements
Desmin - forms a scaffold around the Z-disk of the sarcomere
-connects the Z-disk to the subsarcolemmal cytoskeleton
-it links the myofibrils laterally by connecting the Z-disks
-desmin may also connect the sarcomere to the extracellular matrix (ECM) through desmosomes which could be
important in signalling between the ECM and the sarcomere which could regulate contraction and movement desmin links the mitochondria to the sarcomere 
Desminopathy
J Clin Invest. 2009;119(7):1806–1813. doi: /JCI38027.
Desmin related cardiomyopathy

13. Structural and mechanical integrity of the sarcomeric elements
Titin molecule – extends from Z-disc to M-line
- large protein
- associates with thick filament
-maintains central position of thick filaments
Nebulin – extends from Z-disc along the length of actin filament
- template for the regulation of thin filament length
Alpha actinin- component of Z-disc
- anchors the barbed end of of actin filaments to Z-disc
Myomesin + M-protein
- involved in anchoring the myosin filaments to other filaments (titin)
- myomesin protects sarcomere, keeps it stable during intense or sustained
stretching

14. Resting muscle at molecular level
ATP binding – weakens the actin-myosin cross-bridge – without nerve stimulus – no Ca++ around the myofilaments
-myosin head detaches – myosin binding actin spots are covered by tropomyosin
ATP
relaxation
myosin head detaches

15. Contraction at molecular level „Sliding filament model”
-nervous stimulus – Ca++ release
-activation of a myosin light chain ATP-ase enzym regulatory part
-ATP hydrolysis starts
-myosin cocks – the head moves the + end of actin filament
-az aktin myosinkötőhelye szabaddá válik,
a foszfát ion leválik, a myosin aktinkötő helye aktívvá válik
myosin fej erősen kötődik a G aktin monomerhez
-ez görbült helyzetbe kényszeríti a fejet, elhúzva az aktin szálat
-leválik az ADP is
-újra üres az ATP kötő hely
-a myosin fej görbült helyzetben marad míg nem kötődik egy ATP

16. Sarcoplasmic reticulum + T-tubule system
-major role in excitation-contraction coupling
-sarcoplasmic reticulum
- stores and pumps calcium ions
-smooth endoplasmic reticulum
T-tubule
- deep invagination of the sarcolemma
TRIAD=T-tubule + terminal cistern
sarcoplasmic reticulum releases calcium ions during muscle contraction and absorb them during relaxation

17. Ca++ in contraction
muscle contractions are caused by calcium's bonding to troponin
unmasking the binding sites covered by the troponin-tropomyosin complex on the actin myofilament
allows the myosin cross-bridges to connect with the actin

18. Structure of the palindromic titin–telethonin–titin complex
Palindromic assembly of the giant muscle protein titin in the sarcomeric Z-disk
Peijian Zou, Nikos Pinotsis, Stephan Lange, Young-Hwa Song, Alexander Popov, Irene Mavridis, Olga M. Mayans, Mathias Gautel & Matthias Wilmanns
Nature 439, (12 January 2006)

19. Cardiac muscle

20. Light microscopy of the cardiac muscle

21. EM of cardiac muscle Eberth’s line = intercalated disc
fascia adherens - anchoring sites for actin, connect to sarcomere
desmosoma - stop separation during contraction by binding 
intermediate filaments, joining the cells together
nexus - allow action potentials to spread between cardiac cells by permitting the passage of ions between cells producing depolarization of heart muscle
-cardiomyocytes connected
by intercalated discs to work as a syntitium

22. Sarcoplasmic reticulum and T-tubule system
DIAD
-at the sarcomere Z-line
-a single T-tubule paired with a terminal cisterna of the sarcoplasmic reticulum
-juxtaposing an inlet for the action potential near a source of Ca2+ ions

23. Smooth Muscle

24. Smooth muscle – light microscopy

25. Smooth muscle - EM
plaque
thin
thick filaments
dense body
dense bodies
nucleus
plaques
Dense bodies - actin filaments of contractile units are attached to dense bodies
Dense bands  (or dense subsarcolemmal plaques) - are circumfering the smooth muscle cell in a rib-like pattern
areas alternate with regions of membrane containing numerous caveolae

26. Contraction of smooth muscle cells
Unlike cardiac and skeletal muscle, smooth muscle does not contain the calcium-binding protein troponin

27. Myofascial integration
Color code: connective tissue
muscle fiber

28. REFERENCES