Lecture 13: MUSCLE PHYSIOLOGY Flashcards
Muscle types? 4
- Skeletal muscle
- Cardiac (heart) muscle
- Smooth muscle
- Myoepithelial cells
The structure of skeletal muscle (3)
1 * Composed of muscle fibres:
Each fibre is an elongated cylindrical shaped cell.
2 * 10 – 100 m in diameter and up to 0.75 m long.
3 * Packed with myofibrils (contractile elements).
Skeletal muscle fibres have a striated appearance
Due to the arrangement of the contractile proteins
Skeletal muscle fibres are multinucleate
Skeletal muscle fibers are striated, multinucleated cells ranging from 10 to 100 micrometers in diameter and many centimeters long.
Muscle fibres contain ‘myofibrils’ - what does that mean?
Myofibrils are the contractile elements in skeletal muscle
Structure of the actin (thin) filament (simple 3)
- actin
- troponin complex
- tropomyosin
Structure of the actin (thin) filament:
Actins (2)
- 2 chains (polymers)
of actin molecules intertwined - FORM FILAMENT
Structure of the actin (thin) filament: Tropomyosin
- Helps to stabilise
the actin filaments. - COVERS THE MYOSIN BINDING SITES IN RESTING STATE
Structure of the actin (thin) filament: TROPONIN
- 3 subunits.
- INVOLVED IN CONTROL OF CONTRACTILE ACTIVATION
Structure of the thick (myosin) filament:
- MYOSIN: (heads)
- Actin binding site
- Myosin ATPase site
- Tail and flexible hinge region - THICK FILAMENT
- Myosin molecules
- myosin heads
Structure of the thick (myosin) filament: ACTIVATION
When activated, the myosin heads on each side of the filament move towards the center of the filament.
What is Sarcomere
functional unit of contraction.
The sarcomere is similar in both skeletal and cardiac muscle
Arrangement of the contractile apparatus: The Sarcomere
The contractile proteins located between two Z lines are known as the Sarcomere = functional unit of contraction.
Z disc ….Thin (actin) filament…Thick (myosin) filament…H ZONE (M line)…H Zone..Thick (myosin) filament…Thin (actin) filament…Z disc
Arrangement of the contractile apparatus: The Sarcomere ..
Z disc and M line
Z-disc: Holds actin filaments in place
M-line: Holds myosin filaments in place
Sarcomeres: Light and dark bands
thin filament is light
Z disc is dark
M line is dark
Thick filament is dark
Electron micrograph of a myofibril in C.S.
ACTIN VS MYOSIN
- Each myosin filament can interact with 6 actin filament
- Each actin filament can interact with 2 myosin filaments
The sliding filament mechanism of contraction
INOLVES Thin (actin) filament Thick (myosin) filament
Control of cross bridge cycling: Role of Ca2+
3 (explain process)
- ACTIN
- TROPONIN COMPLEX
- TROPOMYOSIN
- tropomyosin blocking myosin binding site
- Binding site exposed by Ca+2 - mediated tropomyosin movement
Intracellular anatomy of a muscle fibre
- Sarcoplasmic Reticulum (SR) ‘Ca2+ store’
2.SR Ca2+ = release
channels
3.Myofibrils
4.Plasma membrane
5.T-tubule opening
6.Transverse Tubular System (T-tubules)
- Central SR region contains Ca2+ pumps to re-sequester Ca2+ after release finishes)
Summary: Control of skeletal muscle CONTRACTION
- Action potential
- Muscle membrane
- Release channel (RC)
- Voltage sensors (VS)
- T-Tuble
- SR
- Ca+2 IN VIA SR Ca2+ pump - Ca2+ binds to troponin, tropomyosin moves, unmasking myosin binding sites on the actin filament.
- In contractile apparatus
- Crossbridge cycling → CONTRACTION with Ca+2
Summary: Control of skeletal muscle RELAXATION
- Action potential
- in muscle membrane
- Release channels (RC) CLOSE
- Voltage sensors (VS)
- voltage sensors repolarise
- T -tubule
- SR
- Ca +2 in via SR Ca2+ pump - Contractile apparatus: Ca2+ on contraction
The T-tubular network is complex
T-tubular network in a cross section (CS) of a frog sartorius muscle fibre
