• myofibrils containing myofilaments
• from mesoderm
• cells=fibers
• numerous mitochondria

• myoblasts from myotome region of somites
• fuse end to end=myotubules
• nuclei pushed to periphery
  

• myblasts from splanchnopleuric mesoderm
• elongate into contractile proteins
  

• myoblasts from splanchnopleuric mesoderm around heart
• adhere, but don't fuse-->intercalated discs
• purkinje fibers form
  

B=Motor End Plate

A=Axon

C=Skeletal muscles

Myosin

rod like tail

2 globular heads

heads=ATP binding site

Actin

twisted double strand

active sites myosin binding

tropomyosin and troponin=regulatory proteins

• 3 polypeptides
• TnI-binds to actin
• TnT-binds to tropomyosin
• TnC-binds to Ca++
  

• nerve impulse reaches axon end, voltage-gate channels release Ca++
• Ca++ flows in from extracell space
• some synaptic vesicles fuse with axon membrane
• ACh released by exocytosis
• ACh diffuses across synaptic cleft, attatches to receptors
  

modified ER, tubules surround each myofibril

role=regulate intercell Ca++

Perpendicular cross channels at A-Band-I-Band junction

SR tubules

form at A Band-I Band junction

sarcolemma penetrates cell interior

1. action potential progresses along sarcolemma-->T-tubules
2. AP causes terminal cisternae to release Ca++
3. Ca++ binds to troponin (TnC), removes block of tropomyosin
4. myosin heads attach to actin, pull to center

• Ca++ signal ends, removed by active transport to SR
• tropomyosin restored

• cells spindle shaped and uninucleate
• where=walls of hollow organs (stomach, intestines)
• what=involuntary movement
  

SR poorly developed

T-Tubules ABSENT

NO STRIATIONS

thick and thin filaments

Tropomyosin only

No sarcomeres

protein plaques, dense bodies

smooth muscle=2 sheets at right angles

• longitudinal-long axis
• circumferential-circles around

smooth muscle nerve fibers have bulbous endings=varicosities

neurotransmitters released in wide cleft, general area

Autonomic-ACh or norepineph

slow, synchronized

whole sheet

gap junctions

pacemaker cells

some, self excitatory

• Ca++ activates calmodulin
• activates kinase enzyme
• kinase tranfers phosphate from ATP to myosin head
• activates myosin ATPase
• myosin+actin
• pulls on actin-->plaques-->dense bodies