Musculo-Skeletal Anatomy

Making the body move!

Goals

• Important muscle groups to know• Review muscle functions, types, and

general anatomy• In-depth look at skeletal muscle:

– Connective tissue covering– Skeletal muscle fibers– Neuromuscular junction

Three types of muscle

1. Skeletal2. Cardiac3. Smooth

The Anterior

(see handout)

Anterior = “Front”

The Posterior (See handout)

Posterior = “back”

Functions of Muscle

• Producing movement.• Maintaining posture.• Stabilizing joints.• Generating heat.

Characteristics of Muscles (some review, some *new*!)

• Muscle cells are elongated (*muscle cell = muscle fiber)

• *Contraction of muscles is due to the movement of microfilaments

• *All muscles share some terminology– Prefix myo refers to muscle– Prefix mys refers to muscle– Prefix sarco refers to flesh

Skeletal Muscle Characteristics

• *Most are attached by tendons to bones• Cells have many nuclei• Striated – have visible banding• Voluntary – subject to conscious control• *Cells are surrounded by and bundled by

connective tissue

Skeletal Muscle

• Striated, long, cylindrical, multi-nucleated.

• Attached to bones• Voluntarily controlled• * Range of contractile

speed

Cardiac Muscle• Striated, one nucleus,

branching chains of cells, intercalated discs (= dark bands)

• Found only in the heart.• Involuntary contraction.• *Slow speed of

contraction.• *Rhythmic contraction.

Smooth Muscle

• One nucleus, no striations.

• *Found along the walls of blood vessels and digestive canals.

• Involuntary contraction.

• *Very slow contraction.

Skeletal Muscle Attachments

• What structures do muscles attach to?– Bones– Cartilages– **extensions of connective tissue coverings

Connective tissue coverings• Layers of connective tissue enclose and

separate all parts of a skeletal muscle 1.Fascia2.Epimysium3.Perimysium4.Endomysium

FriendsEnjoyProtectingEach other

Fascia

• layers of connective tissue that separate individual skeletal muscles from each other– hold muscles in position– May extend beyond muscle to form:

• Tendon – cord-like structure• Aponeuroses – sheet-like structure

Connective Tissue Wrappings of Skeletal Muscle

• Fascia – on the outside of the epimysium

• Epimysium – covers the entire skeletal muscle

Figure 6.1

Connective Tissue Wrappings of Skeletal Muscle

• Perimysium – around a fascicle (bundle) of fibers

• Endomysium – around single muscle fiber

Figure 6.1

How does the structure of the coverings arrangement allow the muscles to function?

• Structure: layers of connective tissue enclose and separate all parts of a skeletal muscle

• Function: – allows parts to move somewhat independently– Blood vessels and nerves pass through the

layers allows for blood/nutrient supply and stimulation

Review

• Produce movement• Maintain posture• Stabilize joints• Generate heat

• Connective tissue coverings ?

Overall structure of muscle• Muscle

• Fascicles (bundles)

• Muscle fibers (cells)

• Myofibrils

• Thick and thin filaments

Muscle fibers• Definition: single cell that contracts in

response to stimulation, relaxes when stimulation ends

• Thin, elongated cylinder that could extend full length of muscle

Muscle fibers• Cells are multinucleate• Nuclei are just beneath the sarcolemma

Microscopic Anatomy of Skeletal Muscle

• Sarcolemma – specialized plasma membrane

• Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum

Figure 6.3a

Figure 6.3b

Microscopic Anatomy of Skeletal Muscle

• Myofibril– Bundles of myofilaments– Myofibrils are aligned to give distinct bands

• I band =light band

• A band = dark band

• Bands make muscle look STRIATED

Microscopic Anatomy of Skeletal Muscle

• Sarcomere– Contractile unit of a muscle fiber– From Z disc to Z disc

Figure 6.3b

Microscopic Anatomy of Skeletal Muscle• sarcomere organization (Section of

myofibrils)– Thick filaments = myosin filaments = dark

band• Composed of the protein myosin• Has ATPase enzymes (for contraction)

Figure 6.3c

Microscopic Anatomy of Skeletal Muscle

• Organization of the sarcomere– Thin filaments = actin filaments = light band

• Composed of the protein actin

Figure 6.3c

Microscopic Anatomy of Skeletal Muscle

• Myosin filaments have heads (extensions, or cross bridges)

• Myosin and actin overlap somewhat

Figure 6.3d

Microscopic Anatomy of Skeletal Muscle

• At rest, there is a bare zone that lacks actin filaments

• Sarcoplasmic reticulum (SR) – for storage of calcium

Figure 6.3d

Modeling activity• In pairs, using the available materials, create a

model of a myofibril segment between 2 M lines.• Include/indicate sarcomere, actin, myosin, 2 M

lines, I band, and A band