Chapter 6 The Muscular System The Muscular System

Chapter 6 The Muscular System

The Muscular System o Muscles are responsible for all types of body movement o Three basic muscle types are found in the body o Skeletal muscle o Cardiac muscle o Smooth muscle

General Characteristics of Muscles o Contraction of muscles is due to the movement of microfilaments o All muscles share some terminology o Prefix myo refers to muscle o Prefix mys refers to muscle o Prefix sarco refers to flesh

Skeletal Muscle Characteristics o Most are attached by tendons to bones o Cells are multinucleate o Striated – have visible banding o Voluntary – subject to conscious control o Cells are surrounded and bundled by connective tissue o Muscle cells are elongated (muscle cell = muscle fiber)

Skeletal Muscle Characteristics l Rapid contraction - not very smooth l Powerful – reports of remarkable strength l Adaptable – different level of contraction strength (strong to delicate) l Tires easily - must rest after short periods of time

Smooth Muscle Characteristics o Has no striations o Spindle-shaped cells o Single nucleus o Involuntary – no conscious control o Found mainly in the walls of hollow organs o Slow smooth contractions

Cardiac Muscle Characteristics o Has striations o Usually has a single nucleus o Joined to another muscle cell at an intercalated disc o Involuntary o Found only in the heart

General Function of Muscles o Produce movement o Maintain posture o Stabilize joints o Generate heat- waste product of using ATP energy

Functional Characteristics l Excitability- ability to receive and respond to stimuli l Contractibility- the ability to shorten forcibly, when enough stimulus is received l Extensibility- ability to be stretched or extended, from a different force. contraction= shorten; relaxation= lengthen l Elasticity- ability to resume shape

Gross Anatomy of Skeletal Muscle l Cells- muscle fiber or myofiber; some muscles may have thousands of myofibers l Blood vessels and nerves- are present. Large amounts of energy is needed. Each muscle is served by at least one artery and vein. l Mitochondria- many present in each cell for extra energy.

Connective Tissue Wrappings of Skeletal Muscle l Endomysium – around single muscle fiber. l Perimysium – around a fascicle (bundle) of fibers.

Connective Tissue Wrappings of Skeletal Muscle l Epimysium – covers the entire skeletal muscle. l Fascia – on the outside of the epimysium. l Tendon- a collection and extension of all 3; used to attach muscle to bone.

Skeletal Muscle Attachments l Epimysium blends into a connective tissue attachment ¡Tendon – cord-like structure ¡Aponeuroses – sheet-like structure l Sites of muscle attachment ¡Bones ¡Cartilages ¡Connective tissue coverings

Arrangement of Fascicles l Fascicle- a muscle bundle made of muscle cells= different shape & function of muscles. ¡ 1. parallel- fascicles run along axis of muscles; greatest movement (bicep) ¡ 2. pennate- short fascicles at an angle to midline of muscle; more strength, less movement (rectus femoris) ¡ 3. convergent- broad origin, narrows to one tendon for connection (pectoralis major) ¡ 4. circular- arranged in a circle surrounding and external opening; opens and closes (orbicularis occuli)

Fascicle Arrangement ¡ 1. parallel ¡ 2. pennate ¡ 3. convergent ¡ 4. circular

Microscopic Anatomy of Skeletal Muscle o Cells are multinucleate o Nuclei are just beneath the sarcolemma

Microscopic Anatomy of Skeletal Muscle o Sarcomere o Contractile unit of a muscle fiber o Made of actin and myosin

Microscopic Anatomy of Skeletal Muscle o Sarcolemma – specialized plasma membrane o Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum

Microscopic Anatomy of Skeletal Muscle o Myofibril o Bundles of myofilaments that run the length of the muscle cell (where contraction occurs) o Myofibrils are aligned to give distinct bands o I band = light band o A band = dark band

Microscopic Anatomy of Skeletal Muscle o Organization of the sarcomere o Thick filaments = myosin filaments o Composed of the protein myosin o Has ATPase enzymes

Microscopic Anatomy of Skeletal Muscle o Organization of the sarcomere o Thin filaments = actin filaments o Composed of the protein actin

Microscopic Anatomy of Skeletal Muscle o Myosin filaments have heads (extensions, or cross bridges) o Myosin and actin overlap somewhat https: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 10 /animation__myofilament_contraction. html

Microscopic Anatomy of Skeletal Muscle o At rest, there is a bare zone that lacks actin filaments o Sarcoplasmic reticulum (SR) – for storage of calcium http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 10/anim ation__sarcomere_contraction. html

Properties of Skeletal Muscle Activity o Irritability – ability to receive and respond to a stimulus o Contractility – ability to shorten when an adequate stimulus is received

Nerve Stimulus to Muscles o Skeletal muscles must be stimulated by a nerve to contract o Motor unit o One neuron o Muscle cells stimulated by that neuron

Nerve Stimulus to Muscles o Neuromuscular junctions – association site of nerve and muscle

Nerve Stimulus to Muscles o Synaptic cleft – gap between nerve and muscle o Nerve and muscle do not make contact o Area between nerve and muscle is filled with interstitial fluid

Transmission of Nerve Impulse to Muscle o Neurotransmitter – chemical released by nerve upon arrival of nerve impulse o The neurotransmitter for skeletal muscle is acetylcholine o Neurotransmitter attaches to receptors on the sarcolemma o Sarcolemma becomes permeable to sodium (Na+)

Transmission of Nerve Impulse to Muscle o Sodium rushing into the cell generates an action potential o Once started, muscle contraction cannot be stopped

Action Potentials Animation: The Nerve Impulse

The Sliding Filament Theory of Muscle Contraction o Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament o Myosin heads then bind to the next site of the thin filament

The Sliding Filament Theory of Muscle Contraction o This continued action causes a sliding of the myosin along the actin o The result is that the muscle is shortened (contracted) o http: //www. cosmolearning. com/vid eos/muscular-system-slidingfilament-theory/