Muscular System

Facts about muscles…

• A skeleton cannot move by itself

• > 40% of the mass of the average human body is muscle

• Found everywhere in your body

• Power every movement from moving your lips to blinking your eyes

Types of Muscle Tissue:

• Skeletal• Smooth• Cardiac

3 Types of Muscle Tissue:

Type Voluntary/ Involuntary

Found Striations

(stripes)

Structure Nucleus

Skeletal

Smooth

Cardiac

Skeletal Muscles

• Voluntary

• Found attached to bones

• Yes, striations

• Cells are long and thin

• Many Nuclei

Smooth Muscles

• Usually involuntary• Found in hollow organs (i.e.

stomach, blood vessels, sm & lrg intestine)

• No striations• Spindle-shaped (draw a spindle)• One nucleus

Cardiac Muscle• Involuntary

• Cardio= –Greek word for Heart

• Found in the Heart

• Striations

• Intercalated Discs

• One to two nuclei

Type of muscle?

Type of muscle?

Type of muscle?

Type of muscle?

Type of muscle?

Type of muscle?

Skeletal Muscle Breakdown

• Muscle• Bundle• Fibers (cells)• Myofibril• Filaments

–Actin–Myosin

Closer look at the filaments:

• Actin:

• Myosin:

Closer look at the filaments:

• Actin: thin filaments on outside

• Myosin:

Closer look at the filaments:

• Actin: thin filaments on outside

• Myosin: thick filaments in the middle

Closer look at the filaments:

• Z lines:

Closer look at the filaments:

• Z lines: attach the actin together

ActinMyosinZ lines

Muscle contraction:

• Myosin heads grab and pull on actin

Muscle contraction

• Myosin heads grab and pull on actin

Muscle relaxed:

Muscle contracted:

Draw a picture of this in your notes

Muscles work in pairs

Superficial muscles of

the face

Anteriorsuperficial muscles

Posterior superficialmuscles

Superficial muscles of the thigh

Muscle Contraction

• Myofibrils are made of filaments• Striations are formed by a pattern of thick and thin

filaments made of protein• Thick filaments are made of the protein myosin• Thin filaments are made of the protein actin• Filaments are arranges in units called sarcomeres• Sarcomeres are separated by from eachother by regions

called Z discs

Actin and Myosin: Cause muscles to contract

• A muscle contracts when thin filaments slide over thick filaments

• Myosin forms a cross-bridge with actin• The cross bridge changes shape pulling

the actin filament toward the center of the sarcomere

• The distance between the Z discs decreases

• The cross-bridge then detaches

Control of Muscle Contraction• An enzyme produces an impulse causes the

release of Calcium ions (Ca+) allowing actin and myosin to interact

• The muscle remains contracted until the impulse ceases

• Calcium ions pumped back into storage and contraction ends

• Contraction of a single muscle fiber is an all-or-none process!

• Most skeletal muscles work in opposing pairs-when one contracts the other relaxes