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Muscular System
Objectives
• Describe the three types of muscle tissue
• Describe how muscles contract
• Describe how muscles and bones interact to
provide movement
Types of Muscle Tissue
• More than 40% of the
mass of the average
human body is muscle
• There are 3 types of
muscle tissue:
– Skeletal Muscles
– Smooth Muscles
– Cardiac Muscles
Skeletal Muscle
• Skeletal muscle is responsible for voluntary
movement
• Skeletal muscle is usually attached to bone
• Skeletal muscle is mostly controlled by the
central nervous system
Skeletal Muscle
• Complete skeletal
muscles consist of:
–
–
–
–
Muscle fibers
Connective tissues
Blood vessels
Nerves
Skeletal Muscle Structure
• Skeletal muscle tissue is
made of elongated cells
called muscle fibers
– Each muscle fiber
contains many nuclei
– Each muscle fiber is
crossed by light and dark
stripes called striations
• Dense bundles of
muscle fibers are called
fascicles
Skeletal Muscle Structure
• Muscle fibers consist of bundles of threadlike
structures called myofibrils
• Each myofibril is made up of two types of protein
filaments
– Thick filaments are made of the protein myosin
– Thin filaments are made of the protein actin
• Actin is anchored at its end points to a structure
called the Z line
• The region in between Z lines is called a
sarcomere
Skeletal Muscle Structure Overview
Muscle
Fascicles
Muscle
Fibers
Myofibrils
Filaments
Myosin
(Thick)
Actin
(Thin)
Smooth Muscles
• Smooth muscles are
usually not under
voluntary control
• A smooth muscle is
spindle-shaped, has one
nucleus, and is not
striated
• Smooth muscles are
found in the walls of
hollow structures such as
the stomach, blood
vessels, and intestines
Smooth Muscles
• Most smooth muscle
cells can function without
nervous stimulation
– They are connected by gap
junctions that allow
electrical impulses to
travel directly from one
muscle cell to the
neighboring muscle cell
Cardiac Muscles
• Cardiac Muscle is found only in
the heart and control heart
contractions
• Cardiac muscles shares
features of skeletal and smooth
muscle
• Like skeletal muscle:
– Has striations but is smaller
– Cells usually have one nucleus
but may have two
Cardiac Muscles
• Like smooth muscle:
– Not under direct control of
the central nervous system
– Cardiac cells are connected to
their neighbors by gap
junctions
Muscle Contraction
• The sarcomere is the
functional unit of muscle
contraction
• When a muscle contracts,
actin and myosin interact
to shorten the length of
the sarcomere
• A muscle contracts when
the thin filaments (actin)
slide over the thick
filaments (myosin)
• This process is powered
by ATP
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Muscle Contraction
Control of Muscle Contraction
• A skeletal muscle cell and a motor neuron connect at a point called the
neuromuscular junction
• Vesicles (pockets) in the axon terminals of the motor neuron release a
neurotransmitter called acetylcholine
– This causes a nerve impulse
• The nerve impulse causes a release of calcium ions within the muscle
fiber
– The calcium ions affect proteins that allow actin and myosin to
interact
• The muscle cell remains contracted until the release of acetylcholine
stops
Muscular Movement of Bones
• Skeletal muscles are
generally attached to one
end of a bone, stretch
across a joint, and are
attached to the end of
another bone
• Muscles are attached to
bone either directly or by a
tough connective tissue
called a tendon
Muscular Movement of Bones
• Origin – the point where
muscle attaches to
stationary bone
• Insertion – the point where
muscle attaches to the
moving bone
Muscular Movement of Bones
• Most skeletal muscles are
arranged in opposing pairs
– One muscle moves a limb in one
direction, and the other muscle
moves it in the opposite direction
– Muscles move bones by pulling them
• Flexor – a muscle that bends a
joint
– example: biceps
• Extensor – a muscle that
straightens a joint
– example: triceps
• To produce movement, one muscle
in a pair must relax while the
opposite muscle contracts
Notes Review Questions
• Describe the three types of muscle tissue.
– Skeletal
•
•
•
•
•
Responsible for voluntary movement
Controlled by the central nervous system
Usually attached to bone
Have striations
Cells have many nuclei
– Smooth
• Controls involuntary movement
• No striations
• Cells have one nucleus
– Cardiac
• Controls contractions of the heart
• Have striations
• Cells usually have one nucleus
Notes Review Questions
• Describe the structure of muscles from the
largest to the smallest structure.
– Muscles are made of groups of fascicles. Fascicles are
made of bundles of muscle fibers. Muscle fibers are
made of groups of myofibrils. Myofibrils are made of
thick protein filaments called myosin and thin
filaments called actin.
• Explain how muscles contract.
– Muscles contract when the thin filaments (actin) in
the muscle fiber slide over the thick filaments
(myosin).
Notes Review Questions
• Describe how muscles and bones interact to
provide movement.
– Skeletal muscles are attached to one end of a bone,
stretch across a joint, and are attached to the end of
another bone. Muscles are either attached directly to
the bone or by tendons. Most skeletal muscles are
arranged in opposing pairs, where one muscle in a
pair moves a limb in one direction and the other
muscle in the pair moves the limb in the opposite
direction. Muscles move bones by pulling them. To
produce movement, one muscle in a pair must relax
while the opposite muscle contracts. An example of
this is the biceps and triceps.