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Chapter 7 The Muscular System Specialized tissue that enable the body and its parts to move. Summary Functions of skeletal muscle Structure of skeletal muscle Contraction Muscles Head and neck Upper extremity Trunk Lower extremities Types of movements Functions of Skeletal Muscle Movement – muscle move bones by pulling not pushing. Synergists – any movement is generally accomplished by more than one muscle. All of the muscles responsible for a particular movement are synergists. The one that is most responsible for the movement is the Prime Mover. Antagonists - muscles and muscle groups usually work in pairs – example the biceps flex your arm and its partner, the triceps, extend your arm. The two muscles are antagonists, i.e. cause opposite actions. When one contracts the other relaxes. Levators – muscle that raise a body part. Functions of Skeletal Muscle Maintenance of posture or muscle tone We are able to maintain our body position because of tonic contractions in our skeletal muscles. These contractions don’t produce movement yet hold our muscles in position. Heat production – contraction of muscles produces most of the heat required to maintain body temperature. Structure of Skeletal Muscle Composed of striated muscle cells (=muscle fibers) and connective tissue. Tendons anchor muscle firmly to bones. Most muscles attach to 2 bones that have a moveable joint between them. Structure of Skeletal Muscle Bursae – small fluid filled sacs that lie between some tendons and the bones beneath them. They are made of connective tissue and are lined with synovial membrane that secretes synovial fluid. Figure Structure of Skeletal Muscle Contribution of the nervous system Electrochemical impulses travel from the frontal lobes of the cerebrum via motor nerves to the muscle fibers and cause them to contract. Sensation is a function of the brain – impulses are integrated in the parietal lobes of the cerebrum (conscious muscle sense) and in the cerebellum (unconscious). These activities promote coordination. Structure of Skeletal Muscle Microscopic anatomy Muscle cells (fibers) are grouped in a highly organized way in the muscle. The membrane that surrounds each muscle cell is called the sarcolemma. Muscle cells are filled with 2 types of fine threadlike proteins called myofilaments: The myofilaments are arranged in the cells in small units called sarcomeres. Structure of Skeletal Muscle Neuromuscular junction Spot where the axon of a motor nerve nears the muscle fiber. The axon terminal does not touch the muscle but comes close. The space between the axon and the muscle cell is called the synapse. Within the terminal end of the axon are small sacs filled with a neurotransmitter called acetylcholine. Muscle Contraction Sequence Electrical impulse travels down a motor neuron. When it reaches the end, acetylcholine (chemical) is released into the synapse. Acetylcholine binds to special receptors on the muscle cell and causes an electrical impulse to spread over the cell. The sarcomeres shorten and the muscle cell contracts. Excess acetylcholine is destroyed by acetylcholinesterase. *Myesthenia gravis Muscle Contraction Muscles contract only when the stimulus from the motor neuron is strong enough = Threshold stimulus is the minimum level of stimulation necessary to cause a contraction. Additional stimuli arriving rapidly cause an increase in the force of the muscle contraction. Botox Types of Skeletal Muscle Contraction Twitch – Tetanic – *Tetanus Isotonic contraction – Isometric contraction – Energy for Contraction Muscles require energy in the form of ATP to contract. ATP is produced by aerobic respiration. Secondary sources Creatine phosphate stored in the muscle is broken down to produce more ATP. Glycogen stored in the muscle and liver is broken down into glucose which is broken down to produce ATP. This process requires O2. Energy for Contraction O2 is transported to the muscle by the circulatory system (hemoglobin in RBCs). Some O2 is stored in the muscle by myoglobin. Strenuous exercise can cause the muscles to “run out” of O2 resulting in oxygen debt. Glucose is only partially broken down to lactic acid which causes muscle fatigue. Movements Produced by Muscle Contractions Flexion – movement reduces the angle between two bones at their joint. Extension – opposite of flexion – increases the angle at a joint. Abduction – moving a body part away from the midline of the body. Adduction – moving a body part toward the midline of the body. Rotation – movement of a body part around an axis. Movements Produced by Muscle Contractions Supination – refers to hand position – movement turns palm up to the anterior position (anatomical position). Pronation – palm of hand turned posteriorly. Dorsiflexion – top of foot is elevated with toes pointing upward. Plantar flexion – foot directed downward (standing on your toes). Muscles Head and Neck Frontal (frontalis) – over the frontal skull bone raise your eyebrows. Orbicularis oculi – closes the eye. Orbicularis oris – around the mouth; kissing muscle. Masseter – elevates mandible allowing use to close our mouth and chew food. Temporal (temporalis) – assists the masseter in closing the jaw. Muscles Head and neck Sternocleidomastoid – flexes the head toward the chest. Trapezius – helps elevate, lower, and adducts the shoulders (scapula) and extend the head backwards. Muscles Upper extremities Pectoralis major – upper anterior chest; flexor of the upper arm Latissimus dorsi – extensor of the upper arm. Deltoid – powerful abductor of the upper arm. Biceps Brachii – 2-headed muscle that serves as the primary flexor of the forearm. Triceps brachii – 3 headed muscle on the posterior surface of the upper arm; extensor of the elbow/forearm. Muscles Trunk Anterior abdomen – 3 layers of muscles whose fibers run in different directions – girdle effect. External oblique – outermost layer Internal oblique – middle layer Transversus abdominis – innermost layer Rectus abdominus runs down the midline of the abdomen from the thorax to the pubis. (6-pack) Respiratory muscles Intercostal muscles – between the ribs Diaphragm – separates the thoracic and abdominal cavities. Muscles Lower Extremities Gluteus maximus – forms the buttock; extensor of the thigh, supports the torso. Gluteus medius – abducts the femur; injection site. Hamstring muscles – flexors of the lower leg Semimembranosus Semitendinosus Biceps femoris Muscles Lower extremities Quadriceps femoris – covers the upper thigh, extends the leg. Rectus femoris Vastus lateralis – injection site Vastus medialis (Vastus intermedius) Tibialis anterior – dorsiflexes the foot Gastocnemius – primary calf muscle, plantar flexion of the foot. Intramusclular Injection Sites Deltoid Gluteus medius Vastus lateralis