Skeletal muscle
Structure and Function of Skeletal Muscle
Cardiac and skeletal muscle are both striated.
Skeletal: both voluntary and involuntary movement.
Skeletal muscle disorders - rare
The primary cause of disorder is not always within skeletal muscle. It could be
with the neuromuscular junction or within a component of the nervous system.
The disease will eventually manifest itself within skeletal muscle system.
During the early years of life, our muscle mass increases as we develop and
grow. It reaches a plateua. From the age of 50, there is a natual decrease of
muscle mass between a half and 1% per year. (Sarcopenia)
Structure of skeletal muslce
660 skeletal muscles in humans
vary in shape and size
constitutes approx 45% of our body weight
lower in individuals with anorexia
higher in body builders
Skeletal muscle 1
, Functions of skeletal muscle
1. Converts chemical energy into force and mechanical work (Movement and
locomotion)
2. Maintains posture & body position
3. Support soft tissues (abdominal wall, floor of the pelvis cavity)
4. Encircle openings of the digestive and urinary tracts
5. Heat production (in humans, most important thermogenic organ)
6. Reservoir for protein storage - produce energy during starvation
Skeletal muscle naming and Shapes
Naming of skeletal muscle:
Direction - orientation of the muscle
fascicles relative to the body’s
midline eg rectus abdominus -
parallel to the midline of the body
Size - relative size of the muscle eg
gluteus maximus and gluteus
minimus
Shape - shape of the muscle eg
deloid and trapezium muscles
Action - principle action of the
muscle eg those muscles that
increase or decrease the angle of a
joint eg extensors or flexors in the
hand
Number of origins - number or
tendons at origin eg biceps or
triceps
Location - structure near which a
muscle is found
Origin and insertion - sites where
muscle originations and inserts
Skeletal muscle 2
, Musculotendinous Unit (MTU)
Most muscles cross atleast one joint and are attached at the articulating bones
via a tendon
When a muscle contracts, tension is placed on the tendon and bone, resulting in
movement
The musculotendinous unit (MTU) draws one articulating bone toward the other
Origin - the attachment to the stationary bone (or the bone that moves the least)
Insertion - the attachment to the moveable bone (or the bone that moves the
most
Skeletal Muscle Actions
When we use agonist and antagonist, we are describing the primary movement
of a skeletal portion. For eg, if we are describing the movement around the knee
and at particular, increasing the angle at the knee joint, then the quadraceps →
agonist and antagonist (muscle that opposes that movement) → hamstring.
However, if the primary skeletal movement that we want to describe is
decreasing the angle at the knee, then the hamstring would be the agonist and
the quadraceps would be the antagonist.
Muscle Architecture
1. Muscle
2. Muscle fascicle
Skeletal muscle 3
, 3. Muscle fibre
4. Myofibrils
5. Sarcomeres
6. Myofilaments
Skeletal muscle has a hierarchical structure.
Muscle fascicle (cylinders) - collection of individual muscle cells/fibres/myofibres
Myofibrils - long thin-like structures (strawlike) which runs from one end of the
muscle to the other end of the muscle cell. Cell is packed with myofibrils.
Each myofibril is made up of sarcameres (one sarcomere thick)
Sarcomeres are made up of filaments → myofilaments
Myofilaments = Thicker filaments → myosin;
thinner filaments → actin
Muscle Fibres Arrangement
Muscle fibres can be parallel to the force-generating axis of the muscle.
Skeletal muscle 4
Structure and Function of Skeletal Muscle
Cardiac and skeletal muscle are both striated.
Skeletal: both voluntary and involuntary movement.
Skeletal muscle disorders - rare
The primary cause of disorder is not always within skeletal muscle. It could be
with the neuromuscular junction or within a component of the nervous system.
The disease will eventually manifest itself within skeletal muscle system.
During the early years of life, our muscle mass increases as we develop and
grow. It reaches a plateua. From the age of 50, there is a natual decrease of
muscle mass between a half and 1% per year. (Sarcopenia)
Structure of skeletal muslce
660 skeletal muscles in humans
vary in shape and size
constitutes approx 45% of our body weight
lower in individuals with anorexia
higher in body builders
Skeletal muscle 1
, Functions of skeletal muscle
1. Converts chemical energy into force and mechanical work (Movement and
locomotion)
2. Maintains posture & body position
3. Support soft tissues (abdominal wall, floor of the pelvis cavity)
4. Encircle openings of the digestive and urinary tracts
5. Heat production (in humans, most important thermogenic organ)
6. Reservoir for protein storage - produce energy during starvation
Skeletal muscle naming and Shapes
Naming of skeletal muscle:
Direction - orientation of the muscle
fascicles relative to the body’s
midline eg rectus abdominus -
parallel to the midline of the body
Size - relative size of the muscle eg
gluteus maximus and gluteus
minimus
Shape - shape of the muscle eg
deloid and trapezium muscles
Action - principle action of the
muscle eg those muscles that
increase or decrease the angle of a
joint eg extensors or flexors in the
hand
Number of origins - number or
tendons at origin eg biceps or
triceps
Location - structure near which a
muscle is found
Origin and insertion - sites where
muscle originations and inserts
Skeletal muscle 2
, Musculotendinous Unit (MTU)
Most muscles cross atleast one joint and are attached at the articulating bones
via a tendon
When a muscle contracts, tension is placed on the tendon and bone, resulting in
movement
The musculotendinous unit (MTU) draws one articulating bone toward the other
Origin - the attachment to the stationary bone (or the bone that moves the least)
Insertion - the attachment to the moveable bone (or the bone that moves the
most
Skeletal Muscle Actions
When we use agonist and antagonist, we are describing the primary movement
of a skeletal portion. For eg, if we are describing the movement around the knee
and at particular, increasing the angle at the knee joint, then the quadraceps →
agonist and antagonist (muscle that opposes that movement) → hamstring.
However, if the primary skeletal movement that we want to describe is
decreasing the angle at the knee, then the hamstring would be the agonist and
the quadraceps would be the antagonist.
Muscle Architecture
1. Muscle
2. Muscle fascicle
Skeletal muscle 3
, 3. Muscle fibre
4. Myofibrils
5. Sarcomeres
6. Myofilaments
Skeletal muscle has a hierarchical structure.
Muscle fascicle (cylinders) - collection of individual muscle cells/fibres/myofibres
Myofibrils - long thin-like structures (strawlike) which runs from one end of the
muscle to the other end of the muscle cell. Cell is packed with myofibrils.
Each myofibril is made up of sarcameres (one sarcomere thick)
Sarcomeres are made up of filaments → myofilaments
Myofilaments = Thicker filaments → myosin;
thinner filaments → actin
Muscle Fibres Arrangement
Muscle fibres can be parallel to the force-generating axis of the muscle.
Skeletal muscle 4
