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Understanding Skeletal Muscle Structure
Feb 15, 2025
Lecture Notes on Skeletal Muscle Structure and Function
Overview of Skeletal Muscles
Total number of skeletal muscles: 75 pairs
Functions:
Responsible for posture
Movements of limbs
Other functions include swallowing and eye movement
Key Topics Covered
Muscle Fibers
Motor Units
Types of Fiber
Fiber Architecture
Muscle Fibers
Definition: Muscle fibers are the cells that make up skeletal muscle.
Characteristics:
Thread-like appearance
Each fiber has a membrane called
sacrolemma
.
Contains
sarcoplasm
(similar to cytoplasm) that includes nutrients and mitochondria.
Myofibrils
Definition: Myofibrils are structures within muscle fibers.
Contain proteins responsible for muscle striations.
Types of proteins:
Actin
(thin filaments)
Myosin
(thick filaments)
Organization of Muscle Fibers
Muscle fibers are surrounded by membranes:
Endomysium:
Covers individual muscle fibers.
Perimysium:
Covers bundles of muscle fibers called fascicles.
Epimysium:
Covers the entire muscle.
Sarcomeres
Definition: The functional units of muscle contraction within myofibrils.
Structure:
Composed of
Z-lines
,
A-band
,
I-band
,
M-band
, and
H-zone
.
I-band:
Isotropic, contains actin (thin filaments).
A-band:
Anisotropic, contains myosin (thick filaments).
M-band:
Intermediate disc located between I-band and A-band.
H-zone:
Hollow space in the center of the A-band.
Muscle Contraction Mechanism
During contraction:
Z-lines move toward the H-zone.
Actin filaments slide over myosin filaments.
Muscle shortens, leading to contraction.
Additional Structures
Sarcoplasmic Reticulum:
Stores calcium ions needed for contraction.
Transverse Tubules:
Provide channels for the movement of electrolytes, generating action potential for muscle activation.
Muscle Fiber Count
Determined at birth and remains consistent throughout life.
Muscle growth primarily involves increasing the diameter of fibers, not the number of fibers.
Summary
Covered the structure and function of skeletal muscle fibers, myofibrils, sarcomeres, and their role in muscle contraction.
Emphasized the importance of certain membranes and additional structures in muscle function.
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