Download thin (actin)

II. Skeletal Muscle Overview
A. Skeletal Muscle Distinguishing Characteristics
•
Striated
•
Voluntary
•
Multi-nucleated
B. Functions
•
Movement
•
Maintain Posture
•
Stabilize Joints
•
Generate Heat
III. Skeletal Muscle Anatomy
Macroscopic Anatomy
•
Figure 8.1
Fascia surrounds each muscle.
Deep layer called epimysium.
•
Bundles of muscle cells (fascicles)are
surrounded by perimysium
•
Each muscle cell (fiber)
surrounded by endomysium
These connective tissues allow each
structure to remain separate and move
independently. Blood vessels and nerves pass through these tissues.
III. Skeletal Muscle Anatomy
A. Microscopic Anatomy
Each muscle cell has:
- membrane (sarcolemma)
- cytoplasm (sarcoplasm)
- many nuclei
- mitochondria
- many myofibrils made of thick
(myosin) and thin (actin) protein
filaments. Myofibrils are organized
in repeating units called
sarcomeres: these are the units that
contract.
Figure 8.1
III. Skeletal Muscle Anatomy
B. Microscopic Anatomy
•
Surrounding each myofibril is a network of channels called
the sarcoplasmic reticulum and transverse tubules.
Figure 8.4
III. Skeletal Muscle Anatomy
C. Sarcomere Anatomy
•
Sarcomeres consists of 2 overlapping myofilaments with a
repeated pattern.
•
Thin filament-actin
•
Thick filament-myosin
Figure 8.2
Muscle contraction video
II. Skeletal Muscle Anatomy
C. Sarcomere Anatomy
Figure 8.3
III. Skeletal Muscle Anatomy
D. Anatomy of Filaments
1. Myosin
• Myosin molecules have long, rod-shaped tails with globular
heads.
• The heads form cross bridges between myosin and actin.
III. Skeletal Muscle Anatomy
D. Anatomy of Filaments
2. Actin
• 2 proteins, troponin and tropomyosin, help to control the
myosin-actin interactions in muscle contraction.
Troponin
Tropomyosin
III. Skeletal Muscle Anatomy
D. Anatomy of Filaments
II. Skeletal Muscle Anatomy
E. Summary
Muscle
Fascicle
Muscle Cell/Fiber
Myofibril
Myofilament(actin/myosin)
Summary Animation
IIII. Skeletal Muscle Contraction
A. Overview of the Sliding Filament Theory
1. When a muscle cell contracts,
individual sarcomeres shorten.
2. Thin filaments slide past
thick filaments, so that they
overlap to a greater degree.
3. I bands shorten,
H zones disappears,
and A bands
move closer together.
Simplified Animation
Figure 8.8
IIII. Skeletal Muscle Contraction
B. ATP Background Information
1. ATP consists of an adenine nucleotide attached by high-energy
bonds to three phosphate groups.
2. When the terminal phosphate group is off, energy is released.
3. ATP ADP + Pi + energy
4. This energy is available to
perform cellular work.
III. Skeletal Muscle Contraction
C. Detailed Sequence of Events
1. Cross bridge attachment
•
Myosin heads bind to actin
2. The working stroke
•
Myosin head pivots, propelling the actin
Figure 8.7
IIII. Skeletal Muscle Contraction
C. Detailed Sequence of Events
3. Cross bridge detachment
•
ATP binds to myosin head,
allowing it to release actin
4. Cocking of myosin head
•
Breakdown of
ATP ADP + Pi provides
energy to cock myosin head
Myosin Head Animation
Figure 8.7
IIII. Skeletal Muscle Contraction
D. Role of Calcium in Muscle Contraction
1. A nervous impulse triggers the release of Ca2+ from the
sarcoplasmic reticulum.
2. Ca2+ binds to troponin, altering the shape and position of
troponin.
3. This causes movement of the attached tropomyosin molecules,
exposing the myosin binding site.
4. When calcium levels drop, the tropomyosin blockade is
reestablished and contraction ends.
Cross Bridge/ATP Animation
III. Skeletal Muscle Contraction
Summary
Figure 8.7
Summary Animation