ppt on muscle

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Section 1, Chapter 9

Muscular System

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Muscle is derived from Musculus, for  “Mouse” 

Functions of Muscles:

1. Body movement

2. Maintain posture3. Produces heat

4. Propel substances

through body

5. Heartbeat

Types of muscles include:

1. Smooth muscle

2. Cardiac muscle3. Skeletal muscle

Imagine a mouse running beneath the skin.

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Characteristics of smooth muscles

• Involuntary control• Tapered cells with a single, central nucleus

• Lack striations

Smooth Muscle

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• Visceral (single-unit) Smooth Muscle

•

 Form sheets of muscle• Cells are connected by gap junctions

• Muscle fibers contract as a group

• Rhythmic contractions

• Within walls of most hollow organs

(viscera)

• Multi-unit Smooth Muscle

• unorganized cells that contract

as individual cells 

•

Located within the iris of eyeand the walls of blood vessels

There are two types of smooth muscles

Smooth Muscle

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Cardiac Muscle

•Located only in the heart

•Striated cells

•Intercalated discs

• Muscle fibers branch

•Muscle fibers contract

as a unit

• Self-exciting and rhythmic

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• Usually attached to bone

• Voluntary control

• Striated (light & dark bands)

• Muscle fibers form bundles

• Several peripheral nuclei

Skeletal Muscle

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Coverings of Skeletal Muscle

Fascia• Dense connective tissue surrounding skeletal muscles

Tendons

• Dense connective tissue that attaches muscle to bones• Continuation of muscle fascia and bone periosteum

Aponeurosis

• Broad sheet of connective tissue attaching muscles to

 bone, or to other muscles.

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Coverings of Skeletal Muscle

Epimysium

•  Connective tissue that covers the

entire muscle

•  Lies deep to fascia

Perimysium

• Surrounds organized bundles of

muscle fibers, called fascicles

Endomysium

• Connective tissue that covers

individual muscle fibers (cells)

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Figure 9.3 Scanning electron micrograph of a fascicle

surrounded by its perimysium. Muscle fibers within the

fascicle are surrounded by endomysium.

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Organization of Skeletal Muscle

Figure 9.2

Skeletal muscleorganization

Fascicle

Organized bundle of muscle fibers

Muscle Fiber

Single muscle cell

Collection of myofibrils

Myofibrils

Collection of myofilaments

Myofilaments

Actin filament

Myosin filament

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Sarcolemma

• Cell membrane of muscle fibers

Sarcoplasm

• Cytoplasm of muscle fibers

Sarcoplasmic Reticulum

• Modified Endoplasmic Reticulum• Stores large deposits of Calcium

Skeletal Muscle Fibers

sarcolemma

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Skeletal Muscle Fibers

Openings into t-tubules

(Transverse)T-tubules:

•  invaginations of sarcolemma,extending into the sarcoplasm.

Cisternae:

•  enlarged region of sarcoplasmic

reticulum, adjacent to the t-tubules

Triad 

• T-tubule + adjacent cisternae

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 Myofibrils

Figure 9.4 Organization of actin and myosin filaments

Myofibrils are bundles of

actin and myosin filaments.

• Actin –  thin filament

• Myosin –  thick filament

Striations appear from the

organization of actin andmyosin filaments

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SarcomereA sarcomere is the functional unit of

skeletal muscle

• A sarcomere is the area between

adjacent Z-lines.

•

During a muscle contraction the z-linesmove together and the sarcomere shortens.

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Sarcomere

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Figure 9.5 thin and thick filaments in asarcomere.

Z Line is the attachment site of actinfilaments (center of I bands)

Striations appear from alternate light and dark

 banding patterns.

I Bands (light band): consists of only

actin filaments

A Bands (dark band) : consists of

myosin filaments and the overlapping

portion of actin filaments

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 Thick filaments

composed of myosin proteins

During muscle contraction the

heads on myosin filamentsbind to actin filaments forming

a Cross-bridge

Thin filaments

composed of actin proteins

Thin filaments are

associated with troponin 

and tropomyosin proteins

filaments

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Cross-BridgesWhen a muscle is at rest, myosin heads are extended in the “cocked” position. 

During a contraction, myosin heads bind to actin, forming a cross-bridge and themyosin head pivot forward (Power Stroke) and back (Recovery stroke)

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 Tropomyosin

Blocks binding sites on

actin when a muscle is

at rest

Troponin

Ca2+  binds to troponin

during a muscle contraction.

Troponin moves repositions the

tropomyosin filaments, so the

myosin and actin filaments can

interact.

Troponin-Tropomyosin Complex

The troponin-tropomyosin complex prevents cross-bridge

formation when the muscle is at rest.