The Muscular System Although bones provide leverage and form the framework of the body, they cannot move the body by themselves. Motion results from alternating contraction and relaxation of skeletal muscles. Your strength reflects the prime function of muscle – changing chemical energy (in the form of ATP) into mechanical energy to generate force, perform work, and provide movement. Contents: 1. SKELETAL MUSCLE AND TENDONS (OVER 700 IN BODY) 2. SMOOTH MUSCLE 3. CARDIAC MUSCLE muscle = “LITTLE MOUSE” (LATIN) MYOLOGY – The study of muscles Functions: 1. Voluntary movements (skeletal muscle) 2. Involuntary movements (smooth muscle) 3. Pump blood (cardiac muscle) 4. Posture stabilization 5. Production of body heat (shivering) 1. Three Types of Muscle Tissue (skeletal, cardiac and smooth) - All specialized to CONTRACT or shorten - Muscles PULL, not push 1 a) Skeletal muscle tissue https://www.khanacademy.org/science/biology/human-biology/v/anatomy-of-a-muscle-cell - Striated and voluntary - About 40% total body weight 1 skeletal muscle cell = fiber Long and cylindrical shape Up to 1 foot long! Multinucleated Each fiber individually stimulated (innervated by a neuron to contract) 2 Building a skeletal muscle (EX: biceps brachii) i) Each fiber surrounded by an endomysium (areolar connective tissue) ii) When hundreds of fibers are bundled together it is called a fasciculus (fascicle) Each fasciculus is surrounded by a perimysium (dense irregular connective tissue) iii) When hundreds of fasciculi are bundled together = skeletal muscle each muscle is surrounded by an epimysium Tendon = attaches a muscle to a bone Extensions of the epimysium, perimysium and endomysium Collagen fibers align parallel with each otherdense regular connective tissue b) Smooth muscle tissue - Non-striated and involuntary Smooth muscle fibers are spindle-shaped Uninucleate Smooth muscle arranged in 3 ways: 1. Broad, flat sheet of cells a. Lining of digestive tract b. Lining hollow organs 2. Clump of cells a. Arrector pili in dermis 3. Individual fibers a. Glands 3 Smooth muscle contracts slowly and rhythmically Contractions controlled by 1. Hormones 2. Autonomic nervous system c) Cardiac muscle tissue - Striated and involuntary Cardiac muscle fibers are branched Uninucleate Found only in the heart Cardiac muscle has special cell-to-cell connection (intercalated disk) Function: allows a very rapid electric signal to spread from cell to cell Result: nearly simultaneous contraction of all cardiac cells Contractions are controlled by 1. Hormones 2. Autonomic nervous system 2. Three General Principles of SKELETAL Muscle a) A skeletal muscle extends from one bone to another, crossing at least one joint. EXCEPTIONS: muscles of facial expression and muscles that move eyeball 1. Origin = Fixed point of attachment. On the more stationary of the two bones. 2. Insertion = Attachment to the bone that is undergoing movement. 3. Belly (widest part) =The main contracting part of the muscle. The MEAT. 4 Intrinsic muscle = a muscle whose origin and insertion is on the same structure/region. Ex: tongue, hand, foot, eye Extrinsic muscle = a muscle whose origin and insertion is NOT on the same structure/region. Ex: biceps, quadriceps b) Contraction of a skeletal muscle occurs to maximize the motion of bones. * Get the most bang for your buck* Agonist (= prime mover) The muscle primarily responsible for producing a movement ex: biceps bracchii bends elbow Antagonist -the muscle that works opposite the agonist muscle. Ex: triceps Synergist one or more muscles that assist agonist muscle. Produce a movement Ex: brachioradialis Fixator One or more muscles that stabilize/fix the skeleton so agonist muscle can produce a clean movement. Ex: rotator cuff c) Most skeletal muscles are named in a logical or descriptive fashion. http://www.youtube.com/watch?v=dT879gG-X8A Location Tibiaalis anterior, temporalis, iliacus Size (with respect to muscles of the same grouping) ex: gluteus maxiumus (large!) Gluteus minims (small) Gluteus medius (medium size) longus (long) Brevis (short) Shape Ex: deltoid = triangle Trapezius= trapezoid Rhomboideus= rhombus 5 Origin and insertion RULE: origin is FIRST in name, insertion is second. Ex: sternohoid brachioradialis Number of origins In Greek, origin = “ceps” (head) Biceps – 2 origins Triceps -3 origins Quadriceps- Action produced Ex: extension digitorum - straightens a joint Flexor carpi ulnaris – bends a joint Adductor pollicis – adds back to body (pulls body back toward center) Quiz #1/Chicken Wing Lab 3. Innervation of Skeletal Muscles = Neuromuscular Junction A skeletal muscle fiber must receive a signal to contract from the nervous system. Signal = Action Potential Motor neuron = A specialized neuron that delivers an action potential to a skeletal muscle fiber. -Cell body (soma) in brain or spinal cord -Axon travels out to muscle *Axon pierces epimysium, perimysium and endomysium. It is common for branches of an axon (telodendria) to innervate several neighboring muscle fibers. Motor unit = One motor neuron and all of the skeletal muscle fibers it innervates. 6 Diagram of neuromuscular junction = synapse 7 a) Presynaptic terminal (=synaptic end bulb) Distal – most expansion of a telodendria Contains vesicles of a chemical called neurotransmitter ex: acetylcholine (ACH) b) Synaptic cleft A small gap or space in between axon and muscle fiber The neurotransmitter diffuses (highlow) from presynaptic terminal to postsynaptic terminal c) Postsynaptic terminal = motor end plate A specialized region of the sarcolemma of a muscle fiber. Contains protein receptors that neurotransmitter binds to. Result: once ACH binds to receptor, initiates contraction of muscle fiber. 8 4. Contraction of Skeletal Muscle = Sliding Filament Model a) Sarcoplasmic reticulum (SR) A highly modified endoplasmic reticulum Function: temporary storage of calcium ions Can empty very quickly a flood of calcium Can refill very quickly using ATP b) Myofibrils and myofilaments Inside of each muscle fiber are thousands of long, thread-like proteins called myofibrils. Each myofibril consists of two subunits called myofilaments. a. Actin = thin myofilament b. Myosin = thick myofilament The interaction of actin and myosin results in contraction. c) Sarcomere = the functional unit of muscle contraction - Repeating units within a myofibril 9 Sliding Filament Model: contraction 1. Postsynaptic terminal stimulated - action potential sent along entire sarcolemma 2. Sarcoplasmic reticulum stimulated to quickly empty, thereby flooding sarcomere with calcium 3. Calcium initiates interactions between actin and myosin - Using ATP energy, actin and myosin ratchet together 4. Two Z discs of a sarcomere slide closer together = CONTRACTION - When thousands of sarcomeres shorten –> muscle contraction Sliding Filament Model: relaxation 5. ATP pumps quickly returns calcium back into sarcoplasmic reticulum 6. Absence of calcium ends interactions between actin and myosin - Actin and myosin release grip on one another 7. Two Z discs of a sarcomere slide apart = RELAXATION - When thousands of sarcomeres lengthen –> muscle relaxation http://www.youtube.com/watch?v=f0mDFP7qn1Y http://www.youtube.com/watch?v=pWP1u7rRJS8 10 5. Muscle physiology a) All-or-none principle ** A muscle fiber contracts fully (100%) or not at all. There is no partial contraction of a muscle fiber b) Recruitment Increasing the number of motor units participating in a given contraction • The more motor units that contract, the more strength is provided. Ex: 1. Lifting a pencil – few motor units needed to contract (10%) 2. Lifting a book – because it is heavier, ore motor units are recruited to contract (40%) 3. Lifting many books – now most all-motor units are recruited to lift this heavy object. (90%) c) Chemical environment Certain chemicals are required for optimal muscle contraction to occur. 1) O2 – used in cellular respiration to make ATP 2) Calcium – needed to hook actin and myosin 3) Glucose –used in cellular respiration to make ATP d) Rigor mortis The stiffening of skeletal muscles several hours after death -Upon death, calcium begins to leak out of SR -Calcium causes actin and myosin to hook together thus leading to a contraction -Because person is dead, no ATP is there to pump calcium back into SR. Result: muscle is “locked” in permanent contraction. After about 24 hours, muscle tissue decays and muscles loosen 11 6. Disorders of the Muscular System a) Atrophy A very general term that describes a decrease in muscle size and strength. Caused by: inactivity, certain disorders, damage to motor neurons, old age b) Muscular dystrophy A group of inherited muscle disorders *Degeneration of individual muscle fibers Muscles wither and weaken with atrophy. Affects both sides of body equally Treatment: certain drugs to slow degeneration, massage therapy c) Myasthenia gravis A disorder of the neuromuscular junction The ACH receptors on postsynaptic terminal are blocked. No ACH can bind thus no contraction Symptoms: progressive paralysis Treatment: drugs to unblock receptors d) Shin splints An informal name for pain associated with the tibialus anterior muscle When exercising, all skeletal muscles expand slightly due to increased blood flow The tibia anterior is tightly wrapped in epimysium and resting against the tibia. When it expands, it has no room, so it cuts off its own blood supply Symptoms: pain, aching in leg Treatment: rest, massage 12 .