① A small amount of connective tissue, blood vessels, lymphatic vessels and nerves, etc. ②Parallel arrangement, long fiber shape

A. structure and function

B. controlled nerves

C. cell structure

①Shrink ② Provide casual exercise ③Maintain posture ④Heat production ⑤Maintain blood flow ⑥Maintain visceral movement

·Muscle fiber = muscle cell ·sarcolemma = cell membrane ·Sarcoplasm=cytoplasm ·Sarcoplasmic reticulum=smooth endoplasmic reticulum

Protein → myofilament → myofibril → muscle fiber (endomysium) → muscle bundle (perimysium) → muscle (epimysium)

1. Sarcomere

2. myofibrils

3. Transverse tubule (T tubule)

4. sarcoplasmic reticulum

5. Triplet: transverse tubule, cisterna terminalis, sarcoplasmic reticulum

Step 1: Calcium ions trigger myosin heads to attach to actin Step 2: The myosin head rotates and bends, pulling actin toward the M line Step 3: Myosin detaches from actin as new ATP attaches

Slow-twitch fibers: red muscle fibers, rich in myoglobin and mitochondria

Fast-twitch fibers: white muscle fibers, mainly rely on anaerobic glycolysis

Same point

difference

working myocardial fibers

conductive myocardial fibers

endocrine myocardial fiber

body segments

Visceral mesoderm: the smooth muscle and connective tissue on the wall of the digestive tract and the visceral layers of the peritoneum, pleura, and pericardium

Body wall mesoderm: parietal layer of bones, cartilage, dermis and subcutaneous connective tissue, muscles, peritoneum, pleura, and pericardium of the abdominal wall and limbs

Heart zone: Heart plate: Myocardium

*Precursor cells *Produce satellite cells or differentiated skeletal muscle cells