Introduction
• Muscle cells – strong, concerted contraction to produce INTERGRATED MOVEMENT
• Muscle tissue – composed of cells containing contractile protiens → necessary for cellular contration
• Muscle arises from mesoderm
• Types of Musscle tissue - Skeletal, striated muscle because of striped appearance
- cardiac,
- smooth
SKELETAL MUSCLE
➔ Myocytes/muscle fibres => very long, multinucleated cells (syncytial cells)
➔ Myocytes derived from → prenatal fusion of many mononuclear myoblasts
→ Result of fusion – single monocyte contains multiple oval nuclei, peripherally
located.
➔ Myofibrils – run parallel to long axis of
myocytes
- Composed off thick and thin
myofilaments
- Myofilaments → responsible for
contraction!
➔ T-Tube: finger like invagination of the
sarcolemma → forms a complex network that
encircles the myofibrils
➔ A wave of impulses spreads across membrane
and extends into the T Tubuli
➔ The impulse travels deeper into the myocyte
through T-Tubuli and reaches the
sarcoplasmic reticulum
➔ Ca2+ diffuses from SR --> into sarcoplasm
, ➔ Dark A-Band → thin and think myofilaments overlap
→ within each is a central zone called → H-Band
➔ Lighter I-Band → only think myofilaments present
→ bisected by dark line → Z-Line
➔ Thick myofilaments → several hundred myosin molecules
➔ Myosin → small globular projections/heads → ATP binding sites AND actin binding sites.
➔ Troponin → runs over the actin subunits
→ complect of three subunits → TnT, TnC, Tnl
-TnT: strongly attaches to tropomyosin
-TnC: Binds calcium ions
-Tnl: inhibits the actin-myosin interaction
➔ Actin – filamentous polymer
- consists of globular monomers (G-Actin)
- each monomer contains a binding site for MYOSIN
➔ RELAXATION → MYOSIN – heads have binding site for ATP and ACTIN
→in a resting muscle => cannot be associated with acting, because the binding sites for
myosin heads are covered by TROPONIN-TROPOMYOSIN COMPLEX
➔ CONTRACTION → Ca2+ bind to troponin (TnC) → tropomyosin molecule is shifted deeper into the groove of
the actin and MYOSIN-BINDING SITE on the ACTIN is EXPOSED
→ actin and myosin interact
→ ATP split into ADP, energy is released
→ this activity leads to deformation/bending of the myosin head
→ this movement of myosin heads = pulls the actin towards the center of sarcomere,
therefore, shortening the sarcomere
➔ Contraction isn’t caused by a shortening of individual myofilaments; it is a result of an increase in the AMT of
OVERLAP between myofilaments
➔ During contraction, the I-band decreased in size
➔ H-Band diminishes in width
• Muscle cells – strong, concerted contraction to produce INTERGRATED MOVEMENT
• Muscle tissue – composed of cells containing contractile protiens → necessary for cellular contration
• Muscle arises from mesoderm
• Types of Musscle tissue - Skeletal, striated muscle because of striped appearance
- cardiac,
- smooth
SKELETAL MUSCLE
➔ Myocytes/muscle fibres => very long, multinucleated cells (syncytial cells)
➔ Myocytes derived from → prenatal fusion of many mononuclear myoblasts
→ Result of fusion – single monocyte contains multiple oval nuclei, peripherally
located.
➔ Myofibrils – run parallel to long axis of
myocytes
- Composed off thick and thin
myofilaments
- Myofilaments → responsible for
contraction!
➔ T-Tube: finger like invagination of the
sarcolemma → forms a complex network that
encircles the myofibrils
➔ A wave of impulses spreads across membrane
and extends into the T Tubuli
➔ The impulse travels deeper into the myocyte
through T-Tubuli and reaches the
sarcoplasmic reticulum
➔ Ca2+ diffuses from SR --> into sarcoplasm
, ➔ Dark A-Band → thin and think myofilaments overlap
→ within each is a central zone called → H-Band
➔ Lighter I-Band → only think myofilaments present
→ bisected by dark line → Z-Line
➔ Thick myofilaments → several hundred myosin molecules
➔ Myosin → small globular projections/heads → ATP binding sites AND actin binding sites.
➔ Troponin → runs over the actin subunits
→ complect of three subunits → TnT, TnC, Tnl
-TnT: strongly attaches to tropomyosin
-TnC: Binds calcium ions
-Tnl: inhibits the actin-myosin interaction
➔ Actin – filamentous polymer
- consists of globular monomers (G-Actin)
- each monomer contains a binding site for MYOSIN
➔ RELAXATION → MYOSIN – heads have binding site for ATP and ACTIN
→in a resting muscle => cannot be associated with acting, because the binding sites for
myosin heads are covered by TROPONIN-TROPOMYOSIN COMPLEX
➔ CONTRACTION → Ca2+ bind to troponin (TnC) → tropomyosin molecule is shifted deeper into the groove of
the actin and MYOSIN-BINDING SITE on the ACTIN is EXPOSED
→ actin and myosin interact
→ ATP split into ADP, energy is released
→ this activity leads to deformation/bending of the myosin head
→ this movement of myosin heads = pulls the actin towards the center of sarcomere,
therefore, shortening the sarcomere
➔ Contraction isn’t caused by a shortening of individual myofilaments; it is a result of an increase in the AMT of
OVERLAP between myofilaments
➔ During contraction, the I-band decreased in size
➔ H-Band diminishes in width
