Muscle Tissue

Question 1

Comparison of Skeletal, Cardiac, and Smooth muscle

Answer 1

• Skeletal:
  
  • Many nuclei per cell: peripheral
  • Striations
  • Very long
  • Controls movement
• Cardiac:
  
  • 1-2 nuclei per cell: central
  • intercalated disks
  • Found in heart only
• Smooth:
  
  • 1 nucleus/cell: central
  • NO striations
  • Spindle shaped
  • Lines organs and vessels

Question 2

Skeletal Muscle Contraction: Sliding filament theory

Answer 2

• A band has thick filaments I band has thin
• Z line in center of I bands
• H band is zone of no overlap
• Thick and Thin filaments slide across each other
• Filament length does NOT change
• Z to Z gets shorter
• H band and I band get shorter
• A band stays the SAME

Question 3

Skeletal Muscle Contraction: Sarcomere proteins

Answer 3

• Myosin is contractile element of thick filaments
• Actin is contractile element of thin filaments
• Tropomyosin covers the myosin binding groove on actin
  
  • Contains Ca+ dependent troponin molecules
• Actins held together @ Z line by actinin
• Titin attaches actinin to myosin
• Myosin has head and tail

Question 4

Skeletal Muscle Contractile Cycle

Answer 4

Pre: Ca2+ binds troponin c and moves tropomyosin so myosin can bind actin

1. Myosin head is attached to Actin
2. ATP binds to myosin and releases head from actin
3. ATP hydrolysis provides energy for cocking of myosin head: rotates
4. Myosin and Actin rebind & phosphate releases
5. Cocked myosin head rotates moving actin filament
   
   • ADP released and ready for next cycle
     - Continues as long as ATP present, myosin and actin can interact (Ca2+)

Question 5

Calcium Regulation of Skeletal muscle Contraction

Answer 5

• Low Ca2+ levels tropomyosin covers myosin binding site on Actin
• Troponin complex made of TnI, TnC, TnT
• In high Ca2+ levels Ca binds TnC and induces conformational change
  
  • tropomyosin moved and myosin can bind

Question 6

Excitation-Contraction Coupling in Skeletal Muscle

Answer 6

• AP generated in sarcolemma
• Causes conformational change in DHPR
• DHPR linked to RyR in SR
• depolaization opens both and Ca2+ from SR exits via RyR
• No extracellular Ca2+ needed
• Contraction occurs
• Ca2+ATPase (SERCA) activated
  
  • Pumps Ca back into SR: relaxation
• Get stronger contraction by increasing frequency

Question 7

Disorders Affecting Skeletal Muscle E-C coupling

Answer 7

• Myasthenia gravis: blocks NT
  
  • Muscle weakness and paralysis
• Malignant Hyperthermia: spontaneous Ca channel opening
  
  • hypercontractile/stiffness
  • Volitile anesthetics

Question 8

Cardiac Muscle Contraction: Conduction

Answer 8

• Via gap Junctions (NO NMJ)
• Intercalated disks have gap junction
• Made of connexons

Question 9

Cardiac Muscle AP

Answer 9

• Much longer AP than skeletal
• AP plateau
• Ca2+ enters during plateu
• DHPR is true Ca2+ channel here

Question 10

Cardiac Muscle Ca2+ release from SR

Answer 10

• DHPR is gates Ca2+ channel
• NO physical link b/t DHPR and RyR
• Calcium dependent calcium release
• AP open volt-gated DHPR
• Ca enters from ECF
• Ca binds Ca-gated channel in SR (RyR)
• RyR opens and releases Ca2+ for contraction
• Graded contraction

Question 11

Smooth Muscle Contraction basics

Answer 11

• Actin and myosin based
• Actin attached to dense bodies in cytoplasm and PM
• Twisting contraction

Question 12

Smooth Muscle Contraction: mechanism

Answer 12

• Ca2+ dependent modification of THICK filaments
• Ca binds Calmodulin
• Ca/Calmodulin complex interacts w/ Myosin light chain kinase
• MLC is contracted when phosphorylated and relaxed when dephosphorylated
  
  • When P tails active and ready to interact

Question 13

Smooth Muscle Contraction: E-C coupling

Answer 13

• From ECF
  
  • Voltage gated Ca channels
  • Transmitter gated Ca channels
• From SR
  
  • Ca activated Ca release
  • 2nd messengersL IP3

Question 14

Smooth Muscle Relaxation

Answer 14

• Not just Ca2+ removal

- Determined by phosphorylase