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Lesson Overview
SEC 32.2
The Muscular System
Lesson Overview
The Muscular System
THINK ABOUT IT
How much of your body do you think is
muscle?
As surprising at it might seem, about one third
of the mass of an average person’s body is
muscle.
Lesson Overview
The Muscular System
Muscle Tissue
Muscle tissue is found everywhere in the body.
There are three different types of muscle tissue,
each specialized for a specific function in the body:
skeletal, smooth, and cardiac.
Lesson Overview
The Muscular System
Skeletal Muscles
• usually attached to
bones.
• controlled by the central
nervous system
• under voluntary control
• appears to have
alternating light and dark
bands called striations
Lesson Overview
The Muscular System
Skeletal Muscles
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cells are large
have many nuclei
vary in length
smallest skeletal muscle (1 millimeter long) is found in
the middle ear
• longest skeletal muscle (up to 30 centimeters) runs
from the hip to the knee.
Because skeletal muscle cells are long and slender, they
are often called muscle fibers.
Lesson Overview
The Muscular System
Smooth Muscles
• do not have striations - look “smooth” under
the microscope
• spindle-shaped
• usually have a single nucleus
• found throughout body especially hollow
structures like stomach, blood vessels and
intestines
• usually under involuntary control
Lesson Overview
The Muscular System
Smooth Muscles
Smooth muscle movements
are usually involuntary
• moving food through the
digestive system
• control blood flow
through the circulatory
system
• decrease pupil size in
bright light
Lesson Overview
The Muscular System
Smooth Muscles
Most smooth muscle cells
can function without direct
stimulation by the nervous
system.
Smooth muscle cells are
connected to one another
by gap junctions that allow
electrical impulses to travel
directly from one muscle
cell to another muscle cell.
Lesson Overview
The Muscular System
Cardiac Muscle
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found in the heart
striated like skeletal muscle
smaller than skeletal muscle
usually have just one or two nuclei
Lesson Overview
The Muscular System
Cardiac Muscle
• not usually under the
direct control of the
central nervous system
• can contract on their own
• connected to their
neighbors by gap
junctions
Lesson Overview
The Muscular System
Muscle Contraction
How do muscles contract?
“Sliding Filament Model”
Lesson Overview
The Muscular System
Muscle Fiber Structure
Skeletal muscle cells, or
fibers, are arranged in
bundles called myofibrils.
Each myofibril contains thick
protein filaments called
myosin and thin protein
filaments called actin.
Lesson Overview
The Muscular System
Muscle Fiber Structure
The filaments overlap to produce the striations (stripes).
The actin filaments are connected in areas called Z lines.
Two Z lines and the filaments between them make up
the basic unit of a muscle called a sarcomere.
Lesson Overview
The Muscular System
The Sliding-Filament Model
During a muscle contraction, myosin filaments attach to the
actin filaments.
The myosin pulls the actin filaments toward the center of the
sarcomere.
This decreases the distance between the Z lines, and the
muscle fiber contracts (shortens).
Lesson Overview
The Muscular System
The Sliding-Filament Model
Then myosin detaches from actin, and repeats the cycle by
binding to another site on the actin filament.
As thick and thin filaments slide past each other, the length of
the fiber shortens. This is called the “sliding-filament model”
of muscle contraction.
Lesson Overview
The Muscular System
Control of Muscle Contraction
Skeletal muscles are useful only if they contract in a
controlled fashion.
Impulses from nerve cells (neuron)control the contraction of
muscle fibers. Nerve cells release a chemical that causes a
reaction between myosin and actin.
The point of contact between a neuron and a skeletal muscle
cell is called a neuromuscular junction.
Lesson Overview
The Muscular System
Control of Muscle Contraction
When you lift something light, such as a sheet of
paper, your brain stimulates only a few cells to
contract.
As you exert maximum effort, like this pole vaulter,
almost all the muscle cells in your arm are
stimulated to contract.
Lesson Overview
The Muscular System
Muscles and Movement
How do muscle contractions produce movement?
Skeletal muscles generate force and produce movement by
pulling on body parts as they contract.
Lesson Overview
The Muscular System
How Muscles and Bones Interact
Skeletal muscles are joined to bones by tough connective
tissues called tendons.
Tendons pull on the bones and make them move.
Lesson Overview
The Muscular System
How Muscles and Bones Interact
Most skeletal muscles work in opposing pairs—when one
muscle contracts, the other relaxes.
Lesson Overview
The Muscular System
How Muscles and Bones Interact
For example, when the biceps muscle contracts, it bends the
elbow joint.
Lesson Overview
The Muscular System
How Muscles and Bones Interact
When the triceps muscle contracts, it opens the elbow joint.
Lesson Overview
The Muscular System
Types of Muscle Fibers
Two principal types of skeletal muscle fibers—red and white.
Red muscle
•slow twitch muscle
•contains many mitochondria
•dark red color due to small blood vessels
•contains oxygen- storing protein called myoglobin
•derive their energy through aerobic respiration
•able to work for long periods of time
Lesson Overview
The Muscular System
Types of Muscle Fibers
White muscle
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fast-twitch muscle that contracts rapidly
generates more force than red muscle
cells contain few mitochondria
tire quickly.
useful for activities that require great strength or quick
bursts of energy