Muscles
Definition
Muscle: a band or bundle of fibrous tissue in a human or animal body
that has the ability to contract, producing movement in or maintaining
the position of parts of the body.
Cells of Muscular tissue are elongated and that is why they are called
muscle fibers.
Classification/Types of Muscles in our body
• Muscles are classified into three main types
• 1) Skeletal Muscles
• 2) Cardiac Muscles
• 3) Smooth Muscles
Skeletal Muscles
Cardiac Muscle
Smooth Muscle
• Smooth Muscle is called “Smooth” because it looks smooth on
microscopic image.
Let us use Comparison to understand the
difference
• Skeletal Muscle, Smooth Muscle and Cardiac Muscle can be
distinguished based on three main characteristics.
• 1) Histology (how they appear under microscope)
• 2) Location in the body
• 3) If they are under voluntary control or not
Skeletal Muscles
• They constitute almost 40% of our body weight. There are almost 650
named skeletal muscles. Cell Membrane of Skeletal Muscles is called
Sarcolemma(the term “sarco” is used wherever we mean “muscle”
and “lemma” means covering). Cytoplasm of Skeletal Muscle fibres is
called ?????-plasm. This ?????-plasm contains large number of
filaments called myofibrils. They are divided into actin and myosin
filaments. The “Striated” appearance of Skeletal Muscles under
microscope is due to presence of these filaments.
Types of Fibres/Fibers in Skeletal Muscles
• In Sarcoplasm, there is a protein similar to Haemoglobin/Hemoglobin,
called Myoglobin. Based on amount of myoglobin in skeletal muscles,
they can classified into Red, White or Intermediate Skeletal Muscle
fibres.
• Red Fibres have higher amount of Myoglobin and number of
mitochondria. Thus, they are able to contract/twitch for longer
periods, without fatigue. For Example Muscles of Back have more red
fibres.
• White Fibers have lesser amount of Myoglobin, so they can contract
fast but fatigue fast. Example: Muscles of Eye and Hand.
Parts of Muscle
• A Skeletal Muscle consists of a fleshy part and two ends. The Belly or
Fleshy part is made up of muscle fibres while ends are made up of
fibrous tissue.
• “Origin” is that part of the muscle, which is attached to a
structure(bone,cartilage) that remains fixed during muscle
contraction.
• “Insertion” is the other end of the muscle, which is attached to a nonfixed structure that moves during contraction.
• Some books use the term “Proximal Attachment” for Origin and
“Distal Attachment” for Insertion.
Tendon
• a flexible but inelastic cord of strong fibrous collagen tissue attaching
a muscle to a bone.
• Muscles are attached to bones by means of Tendons. Tendons
“connect” Muscles with bones.
• It is a cord-like structure which serves to attach the muscle to a
structure located some distance away from the muscle tissue.
• Usually, attachment of a tendon is restricted to a small area on a
bone. In some cases, the attachment of a muscle is spread over a
larger area, so the connective tissue takes form of a thin-broad sheet,
called “Aponeurosis”.
Skeletal Muscle Tissue
• Skeletal muscles are organs
• Vary in shape and size
• A skeletal muscle is composed of cells
• Each cell is as long as the muscle
• Small muscle: 100 micrometers long; 10 micrometers in
diameter
• Large muscle: 35 centimeters long; 100 micrometers in
diameter
• Skeletal Muscle cells are called MUSCLE FIBERS
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Functions of Skeletal Muscle
• Body Movement
• Maintenance of posture
• Temperature regulation
• Storage and movement of materials
• Support
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Composition of Skeletal Muscle
• Each skeletal muscle is composed of fascicles.
• bundles of muscle fibers
• Muscle fibers contain myofibrils.
• composed of myofilaments
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Endomysium
• Innermost connective tissue layer
• Surrounds each muscle fiber
• Help bind together neighboring muscle fibers and
• Support capillaries near fibers
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Perimysium
• Surrounds the bundles of muscle fibers called fascicles.
• Has a dense irregular connective tissue sheath which contains extensive arrays of
blood vessels and nerves that branch to supply each individual fascicle.
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Connective Tissue Components of Sk. Muscles
• Three layers of CT
• Collagen fibers
• Elastic fibers
• Endomyseium: surrounds each muscle fiber
• Perimysium: surrounds each fascicle
• Epimysium: surrounds entire muscle
• Provide protection, location for blood vessels, nerves
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Epimysium
• A layer of dense irregular connective tissue that surrounds the whole skeletal
muscle.
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Deep Fascia
• An expansive sheet of dense irregular connective tissue
•
•
•
•
separates individual muscles
binds together muscles with similar functions
forms sheaths to help distribute nerves, blood vessels, and lymphatic vessels
fill spaces between muscles
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Classification of Skeletal Muscles
• Skeletal Muscles can be classified on the basis of
• A) Shape and Fibre Architecture
• B) Group Action
Classification on basis of Shape and Structure
1)
2)
3)
4)
5)
Muscles with fibres parallel to line of pull
Muscles with fibres oblique to line of pull
Spiral Muscles
Cruciate Muscles
Circular Muscles
Muscles with fibres parallel to line of pull
• These Muscles have great range of movement but comparatively less
power. They are further sub-classified into
Muscles with Fibres Oblique to the line of Pull
• Further Classified as
• 1) Triangular Muscles( Broad Origin, Narrow Insertion)
• 2) Pennate Muscles (Pennate means feather-like), Uni-pennate are
muscles which are attached to only one side of the tendon. Bipennate are attached to both sides of a tendon.
• 3) Radial/Circumpennate Muscles (Origin from an osteo-facial
compartment, insertion on a central tendon)
Spiral Muscles
• Some flat muscles undergo a twist as they pass from their broad
origin, to relatively narrow insertion. They are called Spiral Muscles.
Cruciate Muscles
• They consist of two planes of fibres arranged in different directions.
Circular Muscles: The Fibres are arranged in a circular pattern and
enclose a body orifice, such as the eye or oral cavity.