The Muscular System (rev 3-10)

1. The Muscular System (rev 3-10) Muscular tissue enables the body and its parts to move • Movement is caused by ability of muscle cells (called fibers) to shorten or contract • Function of muscle tissue is to contract (or shorten) • Muscle cells use energy to produce movement • We have 3 types of muscle tissue in our bodies Muscle Lecture-BIO 006 Handout

2. Skeletal muscle —also called striated or voluntary muscle • This type muscle has stripes or striations • Contractions can be voluntarily controlled Muscle Lecture-BIO 006 Handout

3. Cardiac muscle —composes bulk of heart • Striated muscle; involuntary (contractions not under voluntary control) • Characterized by unique dark bands called intercalated disks • Cells branch frequently • Interconnected nature of cardiac muscle cells allows heart to contract efficiently as a unit Muscle Lecture-BIO 006 Handout

4. Smooth or visceral muscle • Nonstriated, involuntary muscle • Lacks cross stripes or striations when seen under a microscope; appears smooth • Found in walls of hollow visceral structures such as digestive tract, blood vessels, and ureters • Contractions not under voluntary control; movement caused by contractions is involuntary Muscle Lecture-BIO 006 Handout

5. Structure of Skeletal Muscle • Each skeletal muscle is an organ composed of skeletal muscle cells and connective tissue • Most skeletal muscles extend from one bone across a joint to another bone • Parts of a skeletal muscle • Origin—attachment to the bone that remains relatively stationary or fixed when movement at the joint occurs • Insertion—point of attachment to the bone that moves when a muscle contracts • Body or Belly—main part of the muscle Muscle Lecture-BIO 006 Handout

6. Muscles attach to the bone by tendons which are made of strong fibrous connective tissue • Some tendons are enclosed in synovial-lined tubes, called tendon sheaths, and are lubricated by synovial fluid --Bursae—small synovial-lined sacs containing a small amount of synovial fluid; located between some tendons and underlying bones • Both tendon sheaths and bursae make it easier for a tendon to slide over bone Muscle Lecture-BIO 006 Handout

7. Microscopic structure • Specialized contractile cells called fibers aregrouped into bundles • Each skeletal muscle fiber contains thick myofilaments (formed from the protein myosin) and thin myofilaments (formed from the protein actin) • These myofilaments make the striations or stripes we can see in skeletal muscle fibers • The basic functional (contractile) unit of the muscle cell is called a sarcomere. Sarcomeres are separated from each other by dark bands called Z lines Muscle Lecture-BIO 006 Handout

8. Sliding filament model explains mechanism of contraction • Thick and thin myofilaments slide toward each other as a muscle contracts and shorten the muscle. This is called the sliding filament model. • Contraction requires calcium and ATP Functions of Skeletal Muscle: • Movement • Posture or muscle tone • Heat production Muscle Lecture-BIO 006 Handout

9. Movement • Muscles produce movement; as a muscle contracts, it pulls the insertion bone closer to the origin bone • Movement occurs at the joint between the origin and the insertion Muscle Lecture-BIO 006 Handout

10. Groups of muscles usually contract to produce a single movement • Prime mover —muscle whose contraction is mainly responsible for producing a movement • Synergist —muscle whose contractions help the prime mover produce a movement • Antagonist —muscle whose actions oppose the action of a prime mover in a movement Muscle Lecture-BIO 006 Handout

11. Types of Movements Produced by Skeletal Muscle Contractions • Flexion—movement that decreases the angle between two bones at their joint: bending • Extension—movement that increases the angle between two bones at their joint: straightening • Abduction--movement of a part away from the midline of the body • Adduction--movement of a part toward the midline of the body • Rotation—movement around a longitudinal axis Muscle Lecture-BIO 006 Handout

12. Supination--hand position with the palm turned to the anterior position • Pronation—hand position with the palm turned to the posterior position • Dorsiflexion--elevation of the dorsum or top of the foot and • Plantar flexion--the bottom of the foot is directed downward Muscle Lecture-BIO 006 Handout

13. Posture • A specialized type of muscle contraction, called tonic contraction, enables us to maintain body position • In a tonic contraction, only a few of a muscle’s fibers shorten at one time • Tonic contractions produce no movement of body parts but DO hold muscles in position • Tonic contractions maintain muscle tone called posture Muscle Lecture-BIO 006 Handout

14. Heat production • Survival depends on the body’s ability to maintain a constant body temperature • Fever—an elevated body temperature; often a sign of illness • Hypothermia—a reduced body temperature • Contraction of muscle fibers produces most of the heat required to maintain normal body temperature • Energy for muscle contraction is obtained from ATP. Some of the energy is lost as heat and this is what maintains our body temperature Muscle Lecture-BIO 006 Handout

15. Fatigue • Causes reduced strength of muscle contraction due to lack of sufficient rest • Caused by repeated muscle stimulation • Repeated muscular contraction uses up the cellular ATP store and exceeds the ability of the blood supply to replenish oxygen and nutrients Muscle Lecture-BIO 006 Handout

16. Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness • Oxygen debt —term used to describe the metabolic effort to remove the excess lactic acid that may accumulate during prolonged periods of exercise; the body is attempting to return the cells’ energy and oxygen reserves to pre-exercise levels • Heavy breathing after exercises helps to return level of oxygen in blood to normal levels Muscle Lecture-BIO 006 Handout

17. Motor Unit • Stimulation of a muscle by a nerve impulse is required before a muscle can produce movement • A motor neuron is the nerve that transmits an impulse to a muscle, causing contraction • A neuromuscular junction is the specialized point of contact between a nerve ending and the muscle fiber it innervates • A motor unit is the combination of a motor neuron with the muscle cell or cells it innervates Muscle Lecture-BIO 006 Handout

18. Muscle Stimulus • A muscle will contract only if the stimulus reaches a certain level of intensity • A threshold stimulus is the minimal level of stimulation required to cause a muscle fiber to contract • Once stimulated by a threshold stimulus, a muscle fiber will contract completely; this is called an all or none response Muscle Lecture-BIO 006 Handout

19. Different muscle fibers in a muscle are controlled by different motor units having different threshold-stimulus levels • Although individual muscle fibers always respond all or none to a threshold stimulus, the muscle as a whole does not • Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force Muscle Lecture-BIO 006 Handout

20. Types of Skeletal Muscle Contraction • Isotonic contractions • Contraction of a muscle that produces movement at a joint • During isotonic contractions, the muscle changes length, causing the insertion end of the muscle to move relative to the point of origin • Most types of body movements such as walking and running are caused by isotonic contractions Muscle Lecture-BIO 006 Handout

21. Types of Skeletal Muscle Contraction • Isometric contractions • Isometric contractions are muscle contractions that do not produce movement • Although no movement occurs, tension within the muscle increases Muscle Lecture-BIO 006 Handout

22. Selected Skeletal Muscle Groups • Muscles of the head and neck • Muscles of the head and neck • Facial muscles • Orbicularis oculi—closes your eye • Orbicularis oris—puckers your lips (kissing muscle) • Zygomaticus—raises the corners of the mouth (smiling muscle) • Temporalis—chewing muscle; closes jaw • Masseter—chewing muscle; closes jaw • Neck and Shoulder muscles • Sternocleidomastoid—flexes head • Trapezius—elevates shoulders and extends head Muscle Lecture-BIO 006 Handout

23. Muscles that move the upper extremities • Pectoralis major—flexes upper arm; hugging muscle • Latissimus dorsi—extends upper arm • Deltoid—abducts upper arm • Biceps brachii—flexes forearm • Triceps brachii—extends forearm Muscle Lecture-BIO 006 Handout

24. Muscles of the trunk • Abdominal muscles • Rectus abdominis—flexes trunk • Respiratory muscles • Intercostal muscles • Diaphragm Muscle Lecture-BIO 006 Handout

25. Muscles that move the lower extremities • Iliopsoas—flexes thigh • Gluteus maximus—extends thigh • Hamstring muscles—flex lower leg • Semimembranosus • Semitendinosus • Biceps femoris Muscle Lecture-BIO 006 Handout

26. Muscles that move the lower extremities • Quadriceps femoris group—extend lower leg • Rectus femoris • 3 Vastus muscles • Tibialis anterior—dorsiflexes foot • Gastrocnemius—plantar flexes foot Muscle Lecture-BIO 006 Handout