Muscular Tissue

General description 1) components: ---cell: muscle fiber--myofiber elongated thread-liked sarcolemma sarcoplasm SER : sarcoplasmic reticulum ---extracellular G.S: CT with BV, LV and N

According to the structure and function 2) classification According to the structure and function skeletal muscle: striated voluntary m. cardiac muscle: striated involuntary m. smooth muscle: unstriated involuntary m. smooth muscle skeletal muscle cardiac muscle

Skeletal muscle

Often called Striated or Voluntary Muscle Has striations that are visible under light microscopy Under voluntary control Attached to skeleton ( skeletal)

Characteristics of Skeletal Muscles Muscle cells are elongated fibers with many peripheral nuclei Each muscle fiber contains many myofibrils Each myofibril contains many microfilaments

Connective tissue coverings (responsible for force transduction): Epimysium: surround collection of fascicles Perimysium: surround fascicle Endomysium: surround individual fibers

Entire muscle A muscle fibre epimysium Perimysium Endomysium Fasciculus of muscle fibres Endomysium A muscle fibre

1) microstructure of skeletal muscle fiber ① long cylindrical 10-100um in diameter,1-40mm long ② multinucleate, nuclei are ovoid, distributed under sarcolemma ③ filled with longitudinal parallel-arranged myofibrils

Longitudinal section Transverse section

muscle fiber myofibril Thin Filaments Thick Filaments

myofibril: 1-2um in diameter cross striation: light band -I band, dark band- A band

--A band: M-line, H-band --I band: Z-line

--A band (except H band): Thin Filaments Thick Filaments H band: only Thick Filaments --I band: only Thin Filaments

sacromere:1/2 I band, A band ,1/2 I band the smallest structural and functional unit of myofibril

---thick myofilament: composed of myosin: ---thin myofilament: 2) Ultrastructure of myofiber myofibril: ---thick myofilament: composed of myosin: ---thin myofilament: Compose of A. actin B. tropomyosin C. troponin:

Transverse tubule (T tubule): ---definition: sarcolemma and basement membrane invaginate into sarcoplasm to form a transverse distributed tubular system ---location: A-I junctional part ---function: transfer the information into cytoplasm

③ Sarcoplasmic reticulum: ---definition: A longitudinal distributed tubular system formed by smooth endoplasmic reticulum Sarcoplasmic reticulum

H-A band: longitudinal enclose myofibril-- longitudinal tubule ---structure: H-A band: longitudinal enclose myofibril-- longitudinal tubule A-I junction: enlarge to form flattened sac —terminal cisternae triad: one T-tubule + two terminal cisternae ---function: there are calcium pump proteins (ATPase) on membrane, so it can store and release calcium ions triad

Cardiac muscle

1) Microstructure of cardiac muscle ① short column in shaped, 100um long,15um in diameter, with branches, the branches associated with each other to form a network ②  1-2 ovoid nuclei, centrally-located ③  striated, but no very clear ④  intercalated disc: junctional part LM: dark striation across the cardiac fibers

Cardiac muscle

Cardiac muscle: show intercalated disc

2) Ultrastructure of cardiac muscle similar to skeletal muscle, composed of thick, thin filament and have sarcomere ①     myofibril have different diameter, the boundary of myofibril is not very clear

(skeletal muscle : A-I junctional part) ② transverse tubule are thicker, located at Z-line level (skeletal muscle : A-I junctional part) ③ sarcoplasmic reticulum is not well-developed, form less terminal cisternae ④diad: one T-tubule + one terminal cisternae (skeletal muscle : triad) diad cardiac muscle triad skeletal muscle

④ intercalated discs

transverse portion longitudinal portion transverse portion : connection -intermediate junction -desmosome longitudinal portion: communication -gap junction transverse portion longitudinal portion

Smooth muscle

microstructure of smooth muscle ①     elongated, spindle-shaped cells, 8um in diameter, 200( 20-500)um long ②     rob-liked or ovoid nucleus ③     no striation, no myofibril

① caveola on sarcolemme invaginate into cytoplasm 2) ultrastructure of smooth muscle ①     caveola on sarcolemme invaginate into cytoplasm ②  dense patch: under sarcolemma dense body: in sarcoplasm ③     intermediate filament: caveola dense body dense pach

smooth muscle under SEM

Compare with three muscle tissues

1. The location of T tubules of cardiac muscle differ from those of skeletal muscle, the former lie at the A. A-I junctions B.I bands C. A bands D.M lines E. Z lines √

√ 2. Sarcoplasmic reticulum of muscle fiber is composed of A. lysosome B. mitochondria C. microsome D. RER E. SER √

3.The cell junction which transmit rapidly an electrical impulse between adjacent smooth muscle cells is A. tight junction B. intermediate junction C. gap junction D. desmosome E. semidesmosome √

Questions: Describe the characteristics of muscle tissue. Compare the similar with the difference for three kinds of muscle cells according to their fine structure and ultrastructure.