Chapter 9, Section 1

Muscular System

Muscle is derived from Musculus, for “Mouse”

Imagine a mouse running beneath the skin.

Functions of Muscles:

1. Body movement

2. Maintain posture

3. Produces heat

4. Propel substances

through body

5. Heartbeat

Types of muscles:

1. Smooth muscle

2. Cardiac muscle

3. Skeletal muscle

Imagine a mouse running beneath the skin.

Smooth Muscle Fibers

Characteristics of smooth muscles

• Involuntary control

• Tapered cells with a single, central nucleus

• Lack striations

• Visceral Smooth Muscle

• Form sheets of muscle

• Cells are connected by gap junctions

• Multi-unit Smooth Muscle

• unorganized cells that

contract as individual cells • Cells are connected by gap junctions

• Muscle fibers contract as a group

• Rhythmic contractions

• Within walls of most hollow organs

(viscera)

contract as individual cells

•Located within the iris of eye

and the walls of blood vessels

Cardiac Muscle

•Located only in the heart•Located only in the heart

•Striated cells

•Intercalated discs

• Muscle fibers branch

•Muscle fibers contract

as a unit

• Self-exciting and rhythmic

Skeletal Muscle

• Usually attached to bone

• Voluntary control

• Striated (light & dark bands)

• Muscle fibers form bundles

• Several peripheral nuclei

Coverings of Skeletal Muscle

Fascia

• Dense connective tissue surrounding

skeletal muscles

Tendons

• Dense connective tissue that

attaches muscle to bones

• Continuation of muscle facia and • Continuation of muscle facia and

bone periosteum

Aponeurosis

• Broad sheet of connective tissue

attaching muscles to bone, or to

other muscles.

Coverings of Skeletal Muscle

Epimysium

• Connective tissue closely

surrounding a muscle

• Lies deep to fascia

PerimysiumPerimysium

• Surrounds organized bundles of

muscle fibers, called fascicles

Endomysium

• Connective tissue that surrounds

individual muscle fibers (cells)

Figure 9.3 Scanning electron micrograph of a

fascicle surrounded by its perimysium. Muscle

fibers within the fascicle are surrounded by

endomysium.

Organization of Skeletal Muscle

Fascicle

• Organized bundle of muscle fibers

Muscle Fiber

• Single muscle cell

• Collection of myofibrils

MyofibrilsMyofibrils

• Collection of myofilaments

Myofilaments

• Actin filament

• Myosin filament

Figure 9.2

Skeletal muscle

organization

Sarcolemma

• Cell membrane of muscle fibers

Sarcoplasm

• Cytoplasm of muscle fibers

Sarcoplasmic Reticulum

• Modified Endoplasmic Reticulum

Skeletal Muscle Fibers

• Modified Endoplasmic Reticulum

• Store large deposits of Calicium

sarcolemma

Figure 9.2 c. A single muscle fiber

composed of several myofibrils. A

sarcolemma (membrane) surrounds the

cell, and an extensive sarcoplasmic

reticulum runs along the cell.

Skeletal Muscle Fibers

(Transverse)T-tubules:

• invaginations of sarcolemma,

extending into the sarcoplasm.

Cisternae:

• Enlarged region of sarcoplasmic

reticulum, adjacent to t-tubules

Openings into t-tubules

reticulum, adjacent to t-tubules

Triad

• T-tubule + adjacent cisternae

Myofibrils

Myofibrils

• Actin – thin filaments

• Myosin – thick filaments

Striations

Figure 9.4 Organization of actin and myosin filaments

Striations

• appear from the

organization of actin and

myosin

Sarcomere

Sarcomere

• Functional unit of

skeletal muscle

•Area between

adjacent Z-lines

•During contraction

Z-lines approach together

and sarcomeres shorten

• I Bands (light): actin filaments

• Z Line = attaches to actin

filaments (center of I bands)

• A Band (dark) : Myosin

filaments and overlapping actin

filaments

Striation Pattern of Skeletal Muscle

Figure 9.5 thin and thick filaments in a

sarcomere.

• Thick myofilaments

• Myosin proteins

• Cross-bridges (heads) on myosin

• Cross-bridge attaches to actin

during contraction

• Thin myofilaments

• Actin proteins

• Associated with troponin

and tropomyosin proteins

MyofilamentsMyofilaments

Cross-BridgesCross-Bridges• Myosin cross-bridges are extended when muscles are at rest “cocked”

position.

•During a contraction, cross-bridges bind to actin and “spring” forward. (Power Stroke)

• Cross-bridges pull on actin as they spring forward.

• ATP is required to “recock” the cross-bridges. (Recovery stroke)

Myosin cross-bridge

In the “cocked” position

Myosin cross-bridge

In the “sprung” position

Actin binding site

Power stroke