lesson overview 32.2 the muscular system

Lesson Overview32.2 The Muscular System

Lesson Overview The Muscular System

Muscle Tissue• There are three different types of muscle

tissue, each specialized for a specific function in the body: skeletal, smooth, and cardiac.


Skeletal Muscles• Skeletal muscles are usually attached to bones.• Most skeletal muscle movements are voluntary

(you control them)• Skeletal muscle cells are large, have many

nuclei, vary in length, and are long and slender• When viewed under a microscope, skeletal

muscle appears to have alternating light and dark bands called “striations.” For this reason, it is said to be striated.


Smooth Muscles• Smooth muscle cells don’t have striations and

therefore look “smooth” under the microscope. • Smooth muscle cells are spindle-shaped and

have one nucleus. • Smooth muscles form part of the walls of

hollow structures such as the stomach, blood vessels, and intestines.


Smooth Muscles• Smooth muscle movements are

involuntary and perform functions such as moving food through the digestive tract, controlling the flow of blood through the circulatory system, and even decreasing pupil size in bright light.


Cardiac Muscle• Cardiac muscle is found in the heart. • It is striated like skeletal muscle but

has smaller cells and usually have just one or two nuclei.

• Involuntary muscle control and have their own “pace maker” cells that tell it when to contract


Muscle Fiber Structure • Skeletal muscle cells, or

fibers, are filled with tightly-packed filament bundles called myofibrils.

• Each myofibril contains thick filaments of a protein called myosin and thin filaments of a protein called actin.


Muscle Fiber Structure • The actin filaments are bound together in

areas called Z lines. • Two Z lines and the filaments between them

make up a unit called a sarcomere (the unit of muscle contraction)


The Sliding-Filament Theory• During a muscle contraction, myosin filaments form

cross-bridges with actin filaments.• The cross-bridges then change shape, pulling the actin

filaments toward the center of the sarcomere.• This action decreases the distance between the Z lines,

and the muscle fiber shortens.


The Sliding-Filament Theory• Then the cross-bridge 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, hence the name “sliding-filament theory” of muscle contraction.


Muscles and Movement• How do muscle contractions produce movement?• Skeletal muscles generate force and produce

movement by pulling on body parts as they contract. [muscles NEVER push, they only pull]


How Muscles and Bones Interact• Skeletal muscles are joined to bones by tough

connective tissues called tendons. • Tendons pull on the bones to produce movement

A = Deltoid

B= Biceps

C= Quadriceps

D= Pectoralis

E= Abdominals

F= Triceps

G = Hamstring

H= Gastrocnemius

I= Trapezius

J= Latissimus dorsi K= Gluteus maximus

lesson overview 32.2 the muscular system

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