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. Skeletal
2. Cardiac
3. 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, multinucleated.
• 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. Fascia
2. Epimysium
3. Perimysium
4. Endomysium
Friends
Enjoy
Protecting
Each 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

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
Figure 6.3b

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