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Physiology of Cells 2002 > Lecture 13: MUSCLE PHYSIOLOGY > Flashcards

Lecture 13: MUSCLE PHYSIOLOGY Flashcards

1
Q

Muscle types? 4

A
  1. Skeletal muscle
  2. Cardiac (heart) muscle
  3. Smooth muscle
  4. Myoepithelial cells
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2
Q

The structure of skeletal muscle (3)

A

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).

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3
Q

Skeletal muscle fibres have a striated appearance

A

Due to the arrangement of the contractile proteins

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4
Q

Skeletal muscle fibres are multinucleate

A

Skeletal muscle fibers are striated, multinucleated cells ranging from 10 to 100 micrometers in diameter and many centimeters long.

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5
Q

Muscle fibres contain ‘myofibrils’ - what does that mean?

A

Myofibrils are the contractile elements in skeletal muscle

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6
Q

Structure of the actin (thin) filament (simple 3)

A
  1. actin
  2. troponin complex
  3. tropomyosin
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7
Q

Structure of the actin (thin) filament:

Actins (2)

A
  • 2 chains (polymers)
    of actin molecules intertwined
  • FORM FILAMENT
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8
Q

Structure of the actin (thin) filament: Tropomyosin

A
  • Helps to stabilise
    the actin filaments.
  • COVERS THE MYOSIN BINDING SITES IN RESTING STATE
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9
Q

Structure of the actin (thin) filament: TROPONIN

A
  • 3 subunits.
  • INVOLVED IN CONTROL OF CONTRACTILE ACTIVATION
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10
Q

Structure of the thick (myosin) filament:

A
  1. MYOSIN: (heads)
    - Actin binding site
    - Myosin ATPase site
    - Tail and flexible hinge region
  2. THICK FILAMENT
    - Myosin molecules
    - myosin heads
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10
Q

Structure of the thick (myosin) filament: ACTIVATION

A

When activated, the myosin heads on each side of the filament move towards the center of the filament.

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11
Q

What is Sarcomere

A

functional unit of contraction.

The sarcomere is similar in both skeletal and cardiac muscle

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12
Q

Arrangement of the contractile apparatus: The Sarcomere

A

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

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13
Q

Arrangement of the contractile apparatus: The Sarcomere ..

Z disc and M line

A

Z-disc: Holds actin filaments in place

M-line: Holds myosin filaments in place

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14
Q

Sarcomeres: Light and dark bands

A

thin filament is light

Z disc is dark
M line is dark
Thick filament is dark

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15
Q

Electron micrograph of a myofibril in C.S.

ACTIN VS MYOSIN

A
  • Each myosin filament can interact with 6 actin filament
  • Each actin filament can interact with 2 myosin filaments
16
Q

The sliding filament mechanism of contraction

A

INOLVES Thin (actin) filament Thick (myosin) filament

17
Q

Control of cross bridge cycling: Role of Ca2+

3 (explain process)

A
  1. ACTIN
  2. TROPONIN COMPLEX
  3. TROPOMYOSIN
    - tropomyosin blocking myosin binding site
    - Binding site exposed by Ca+2 - mediated tropomyosin movement
18
Q

Intracellular anatomy of a muscle fibre

A
  1. 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)

  1. Central SR region contains Ca2+ pumps to re-sequester Ca2+ after release finishes)
19
Q

Summary: Control of skeletal muscle CONTRACTION

A
  1. Action potential
  2. Muscle membrane
  3. Release channel (RC)
  4. Voltage sensors (VS)
  5. T-Tuble
  6. SR
    - Ca+2 IN VIA SR Ca2+ pump
  7. Ca2+ binds to troponin, tropomyosin moves, unmasking myosin binding sites on the actin filament.
  8. In contractile apparatus
    - Crossbridge cycling → CONTRACTION with Ca+2
20
Q

Summary: Control of skeletal muscle RELAXATION

A
  1. Action potential
  2. in muscle membrane
  3. Release channels (RC) CLOSE
  4. Voltage sensors (VS)
  5. voltage sensors repolarise
  6. T -tubule
  7. SR
    - Ca +2 in via SR Ca2+ pump
  8. Contractile apparatus: Ca2+ on contraction
21
Q

The T-tubular network is complex

A

T-tubular network in a cross section (CS) of a frog sartorius muscle fibre

Physiology of Cells 2002 (24 decks)

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