Download Muscular System

Muscular System

Muscle is the most abundant tissue in most animals.

Your body is equipped with more than 600 skeletal muscles.

A skeletal muscle contains hundreds to thousands of muscle cells, which look like
long, striped fibers and the fibers cells are arranged in bundles.

Connective tissue surrounds the bundles and extends beyond them to form tendons,
which attach both ends of the muscle to bone.

It allows for the movement of body parts by exerting force upon tendons, and they
also lend support to the body and provide protection to the organs that lie beneath
them

There are 3 types of muscle tissue in animals:
1. Skeletal or striated muscle (voluntary)
2. Cardiac muscle (involuntary)
3. Smooth or visceral muscle (involuntary)

Muscle tissues are distinguished from other tissues by its ability to contract and
perform mechanical work
1. Skeletal muscle:
A. this muscle is also called striated because it overlapping filaments give it a striped
appearance under the microscope
B. this muscle makes the voluntary movement of body parts possible
C. they are attached to bones by tendons, which are fibrous connective tissues
D. Skeletal muscles are composed of sarcomere, myofibrils, and nuclei
2. Cardiac muscle:
A. this muscle is what makes up the walls of the heart, which contracts involuntarily
B. one thing that differentiates cardiac muscle cells from other muscle cells is the
presence of intercalated disc
 Intercalated discs are found at the ends of cardiac muscle cells and, in effect,
join them.
 They relay the nerve impulses that cause contraction from cell to cell
C. cardiac muscle is striated, like skeletal muscle
3. Smooth or Visceral muscle:
A. this muscle lacks striations, and is found in the walls of the internal organs,
namely the digestive tract, bladder, and arteries.
B. these cells contract more slowly than do skeletal muscle cells, but they can
contract for longer periods of time
C. smooth muscle movements are involuntary, meaning that you cannot consciously
control them, as you can control skeletal muscle.
Muscle Contraction

The movement of the body depends on the activity of the skeletal muscle, and they do
so in response to commands from the nervous system.

The skeletal muscle is also the most abundant type of muscle, which is also called
striated muscle because it has visible light and dark bands
1. with very few exceptions, all skeletal muscle is connected to some part of the
skeleton, and tendons, which are composed of fibrous proteins, connect muscle to
bone
2. each muscle is a set of hundreds of fused cells called muscle fibers—a muscle
fiber is a muscle cell
3. muscle cells are very long and have nuclei that contain their genetic material
4. muscle fiber (cell) is enclosed by a plasma membrane known as sarcolemma, and
the cytoplasm of a muscle cell is called the sarcoplasm
 each muscle cell contains up to 20 myofibrils in its sarcoplasm

a single myofibril is composed of smaller units called sarcomere—this muscle
is responsible for contraction

sarcomere is composed of 2 types of filaments
1. thin actin filaments—ball-shaped molecules
2. thick myosin filaments—a protein with a head and long tail

the filaments run parallel to one another and are composed of the proteins
actin and myosin, respectively

where the adjacent sarcomeres interweave, there is a dense black line called
the Z line

a central one called the H zone exists between myosin filaments; there are no
actin filaments in this zone

the thin actin filaments are anchored to the Z line, but the myosin filaments
are not

During muscle contraction, nerve impulses enter the muscle cell, stimulating
actin filaments to slide toward one another along the myosin filaments

Contracting muscle pulls a bone, which creates movement
RESEARCH
The action of sliding filaments was further clarified by recent
discoveries that explain how actin and myosin filaments operate

The actin filament consists of chains of globular proteins, which are indicated by the
circular globules

Located alongside these chains of proteins is a protein called tropomyosin

At rest, tropomysoin prevents myosin from binding to actin by masking the action
binding site on the globular actin molecules

Another protein called torponin lies near the action filament and help stabilize the
tropomyosin molecule

Calcium ions are released in the muscle fiber as a result of an action potential and the
muscle contracts

Calcium ions unite with the troponin molecules, and this union causes the troponin
molecules to shift position

The movement reveals the actin binding sites, and they unite with the myosin heads

The myosin head then curves and pulls the actin filament

This is the power stroke that moves the actin filament across the stationary myosin
filament

When nerve impulses cease, the bound calcium ions are released and the binding sites
are once again covered; the muscle in now at rest
DETAIL ON CONTROL OF CONTRACTION
A. The nervous system communicates with muscles by way of motor neurons, which
deliver signals that can stimulate or inhibit contraction of muscle cells.
B. Action potential is a sudden reversal in charge resulting from a flow of charged
ions across the membrane caused by motor neurons.
1. As is true in all cells, they show a difference in electric charge across their
plasma membrane.
2. The cytoplasm is more negative than the fluid outside the membrane.
3. In “excitable” cells (neurons, muscle cells, etc.), the difference in charge
reverses suddenly and briefly in response to adequate stimulation.
4. Action potentials spread from the point of stimulation and rapidly reach small,
tubular extensions of the plasma membrane.
5. When the signals reach the sarcoplasmic reticulum, they trigger the outward
flow of calcium ions from it.
 Sarcoplasmic reticulum—is the system the takes up, stores, and releases
calcium ions in controlled ways.
6. The released calcium ions diffuse into the myofibrils and reach actin filaments
7. Contraction occurs
8. Afterward, calcium ions are actively transported back into the membrane
storage system.
Muscular System

Muscle is the most abundant tissue in most animals.

Your body is equipped with more than 600 skeletal muscles.

A skeletal muscle contains hundreds to thousands of muscle cells, which look like
long, striped fibers and the fibers cells are arranged in bundles.

Connective tissue surrounds the bundles and extends beyond them to form tendons,
which attach both ends of the muscle to bone.

It allows for the movement of body parts by exerting force upon tendons, and they
also lend support to the body and provide protection to the organs that lie beneath
them

There are 3 types of muscle tissue in animals:
4. Skeletal or striated muscle (voluntary)
5. Cardiac muscle (involuntary)
6. Smooth or visceral muscle (involuntary)

Muscle tissues are distinguished from other tissues by its ability to contract and
perform mechanical work
4. Skeletal muscle:
E. this muscle is also called striated because it overlapping filaments give it a striped
appearance under the microscope
F. this muscle makes the voluntary movement of body parts possible
G. they are attached to bones by tendons, which are fibrous connective tissues
H. Skeletal muscles are composed of sarcomere, myofibrils, and nuclei
5. Cardiac muscle:
D. this muscle is what makes up the walls of the heart, which contracts involuntarily
E. one thing that differentiates cardiac muscle cells from other muscle cells is the
presence of intercalated disc
 Intercalated discs are found at the ends of cardiac muscle cells and, in effect,
join them.
 They relay the nerve impulses that cause contraction from cell to cell
F. cardiac muscle is striated, like skeletal muscle
6. Smooth or Visceral muscle:
D. this muscle lacks striations, and is found in the walls of the internal organs,
namely the digestive tract, bladder, and arteries.
E. these cells contract more slowly than do skeletal muscle cells, but they can
contract for longer periods of time
F. smooth muscle movements are involuntary, meaning that you cannot consciously
control them, as you can control skeletal muscle.
Muscle Contraction

The movement of the body depends on the activity of the skeletal muscle, and they do
so in response to commands from the nervous system.

The skeletal muscle is also the most abundant type of muscle, which is also called
striated muscle because it has visible light and dark bands
5. with very few exceptions, all skeletal muscle is connected to some part of the
skeleton, and tendons, which are composed of fibrous proteins, connect muscle to
bone
6. each muscle is a set of hundreds of fused cells called muscle fibers—a muscle
fiber is a muscle cell
7. muscle cells are very long and have nuclei that contain their genetic material
8. muscle fiber (cell) is enclosed by a plasma membrane known as sarcolemma, and
the cytoplasm of a muscle cell is called the sarcoplasm
 each muscle cell contains up to 20 myofibrils in its sarcoplasm

a single myofibril is composed of smaller units called sarcomere—this muscle
is responsible for contraction

sarcomere is composed of 2 types of filaments
3. thin actin filaments—ball-shaped molecules
4. thick myosin filaments—a protein with a head and long tail

the filaments run parallel to one another and are composed of the proteins
actin and myosin, respectively

where the adjacent sarcomeres interweave, there is a dense black line called
the Z line

a central one called the H zone exists between myosin filaments; there are no
actin filaments in this zone

the thin actin filaments are anchored to the Z line, but the myosin filaments
are not

During muscle contraction, nerve impulses enter the muscle cell, stimulating
actin filaments to slide toward one another along the myosin filaments

Contracting muscle pulls a bone, which creates movement
RESEARCH
The action of sliding filaments was further clarified by recent
discoveries that explain how actin and myosin filaments operate

The actin filament consists of chains of globular proteins, which are indicated by the
circular globules

Located alongside these chains of proteins is a protein called tropomyosin

At rest, tropomysoin prevents myosin from binding to actin by masking the action
binding site on the globular actin molecules

Another protein called torponin lies near the action filament and help stabilize the
tropomyosin molecule

Calcium ions are released in the muscle fiber as a result of an action potential and the
muscle contracts

Calcium ions unite with the troponin molecules, and this union causes the troponin
molecules to shift position

The movement reveals the actin binding sites, and they unite with the myosin heads

The myosin head then curves and pulls the actin filament

This is the power stroke that moves the actin filament across the stationary myosin
filament

When nerve impulses cease, the bound calcium ions are released and the binding sites
are once again covered; the muscle in now at rest
DETAIL ON CONTROL OF CONTRACTION
C. The nervous system communicates with muscles by way of motor neurons, which
deliver signals that can stimulate or inhibit contraction of muscle cells.
D. Action potential is a sudden reversal in charge resulting from a flow of charged
ions across the membrane caused by motor neurons.
9. As is true in all cells, they show a difference in electric charge across their
plasma membrane.
10. The cytoplasm is more negative than the fluid outside the membrane.
11. In “excitable” cells (neurons, muscle cells, etc.), the difference in charge
reverses suddenly and briefly in response to adequate stimulation.
12. Action potentials spread from the point of stimulation and rapidly reach small,
tubular extensions of the plasma membrane.
13. When the signals reach the sarcoplasmic reticulum, they trigger the outward
flow of calcium ions from it.
 Sarcoplasmic reticulum—is the system the takes up, stores, and releases
calcium ions in controlled ways.
14. The released calcium ions diffuse into the myofibrils and reach actin filaments
15. Contraction occurs
16. Afterward, calcium ions are actively transported back into the membrane
storage system.