The Muscular System rev 12-12 Muscle cells are involved in every movement that our bodies perform. They are found in every body organ and tissue Muscles can: Shorten or contract to produce movement (prime mover or agonist) Relax or be pulled back to their original length by gravity or by opposing muscle groups, called antagonistic muscles Work with other muscle groups, called synergistic muscles, to produce movement Resist movement to maintain our posture Generate heat to maintain our body temperature Shiver, sweat BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Muscle tissue is made up of tightly packed cells called muscle fibers. The muscle fiber cytoplasm contains proteins which allow the cell to contract BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT There are 3 types of muscles: Skeletal muscles Cardiac muscles Smooth muscles attach to the bones of our skeleton and provide strength and mobility (movement) for our body Cardiac muscle found in the heart; pumps blood throughout the body found in most internal organs; generally they work to push something (fluids or other body substances) through a body part BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Muscles may also be classified as voluntary (muscles over which we have conscious control and requires peripheral nervous stimulation to contract) involuntary (muscles over which we have no conscious control; require autonomic nervous stimulation to contract) The term sarcolemma refers to the cell membrane of a muscle cell BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Skeletal Muscles are multinucleated cells are arranged in a parallel fashion are responsible for all locomotion and manipulation enable us to respond quickly to changes in the external environment compared to other muscle types, their speed of contraction is fast BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Skeletal Muscle Is also called Striated or Voluntary muscle they have striations (or stripes) which are caused by alternating dark and light “bands” bands are composed of tightly packed contractile proteins called myofilaments which are made up of thicker myosin filaments and thinner actin filaments BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Cardiac Muscle Cells are striated, short, fat, branched and interconnected Have specialized areas called intercalated disks where the cells connect with each other Intercalated disks contain gap junctions that permit one cell to electrically stimulate the next one. because of these connections, cardiac muscle works as a single, coordinated unit usually contracts at a steady rate set by the heart’s pacemaker, but neural controls allow for a faster beat for brief periods (i.e. when you perform intense activities) compared to other muscle types, their speed of contraction is moderate BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Smooth Muscle Cells are shorter than skeletal and cardiac muscle cells Because the cells have fewer contractile proteins they do not have striations (thus their name, smooth muscle) Cells are spindle shaped (thicker in the middle and tapered at each end); each cell has a centrally located nucleus Are found in the walls of hollow visceral organs (i.e. stomach, intestines, bladder, blood vessels) role is to force fluids and other substances through body channels compared to other muscle types, their speed of contraction is slow and sustained BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Muscle Contraction Contractile proteins or myofilaments, called actin and myosin, slide past each other using energy from ATP molecules. These myofilaments produce alternating light and dark areas called striations Dark areas are called A-bands Lighter areas are called I-bands The Z-line is a thin, dark line where sets of actin myofilaments are woven together The space between 2 Z-lines is called a sarcomere A sarcomere is the smallest functional (contractile) unit of a muscle fiber BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Mechanism of Muscle Contraction: Nerve Activation of Individual Muscle Cells In order for a muscle to contract, its cells must be stimulated by a nerve The motor neuron secretes acetylcholine (ACh) at the neuromuscular junction (the space where the motor neuron and muscle cell meet). ACh is a neurotransmitter--a chemical which can either stimulate or inhibit another “excitable” cell (either a nerve cell or a muscle cell) The ACh diffuses across the space between the neuron and the muscle cell (called the synaptic cleft) and binds to receptor sites on the muscle cell membrane. BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT The ACh binding causes the muscle cell membrane to generate an electrical impulse which travels along the cell membrane and along the T-tubules (cylindrical extensions of the cell membrane [or sarcolemma] which travel into the interior parts of the cell and activate the sarcoplasmic reticulum); the function of the T-tubules is to allow the electrical impulse to quickly travel to all cell parts The electrical impulse triggers the release of calcium from the sarcoplasmic reticulum . Muscles require calcium in order to contract. Sliding Filament Mechanism: muscle contracts when the sarcomeres shorten. This occurs when the thick and thin filaments form cross bridges and slide past each other resulting in shortening of the sarcomere. BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Calcium binds to troponin, a protein molecule, and causes the Troponin–tropomyosin protein complex to shift position this exposes the actin-myosin binding sites and allow the myosin heads and actin filaments to make contact, forming cross-bridges. The actin filaments are pulled toward the center of the sarcomere and the muscle contracts. In order to stop the contraction, nerve cell stimulation stops calcium is no longer secreted and the troponin–tropomyosin protein complex shifts position so the myosin heads are no longer exposed. They can no longer make contact with the actin filaments and the muscle will be unable to contract BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html    http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/muscles/muscles.html http://www.dnatube.com/video/1310/Action-potential   GOOD ONE: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_cross-bridge_movement_during_muscle_contraction.html http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html  BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Muscle Relaxation Nerve activation ends, contraction ends Calcium pumped back into sarcoplasmic reticulum (requires ATP) Calcium removed from actin filaments Myosin-binding site covered No calcium = no cross-bridges BIO 102 Muscle Lecture HANDOUT

Energy Use by Muscle Cells Muscle contraction requires energy In the presence of calcium, myosin acts as an enzyme to split ATPADP + inorganic phosphate to release energy. So, ATP is the muscle’s energy source Typically muscle cells store enough ATP for approximately 10 seconds of heavy activity After this, ATP can be replenished by: Creatine phosphate which makes enough ATP for ~ 20-30 seconds After this short amount of time, energy must be obtained from stored glycogen BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT For long term energy, ATP can also be obtained via aerobic metabolism of glucose, fatty acids, and other high-energy molecules which are constantly supplied by the blood Glycogen is broken down by a process called glycolysis. (The end products of glycolysis begin the Krebs Cycle [Citric Acid Cycle] and the electron transport chain to generate energy for the organism.) BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Glucose molecules are removed from the glycogen and the cell uses the glucose to synthesize more ATP. Part of the glucose breakdown process can be done anaerobically (without oxygen). This is a fast process but only yields 2 ATP molecules per glucose molecule. Or glucose 2 ATP + lactic acid It also produces lactic acid as a waste product which can make muscles sore. BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT ---The most efficient, but much slower, process for energy production is aerobic metabolism. This yields 36 ATP molecules from 1 molecule of glucose. Carbon dioxide is produced as a waste product. or glucose + O2  36 ATP + CO2 + H2O When you perform strenuous activity, it usually takes a few minutes to start breathing heavily. The increase in respirations indicates that aerobic metabolism is now occuring. During strenuous exercise, typically the blood is unable to carry enough oxygen for complete oxidation of glucose in our muscles. So, the muscles will also contract anaerobically and produce lactic acid. BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT The lack of oxygen and subsequent production of lactic acid is called oxygen debt or oxygen deficit. So, oxygen debt occurs when the muscles have consumed oxygen at a faster rate than it can be replaced. The body must take in an extra amount of oxygen to replace the oxygen in the muscles and return the muscles to their resting state. Therefore, the reason we breathe heavily after exercise is to erase or pay back the oxygen debt. BIO 102 Muscle Lecture HANDOUT

Gross Anatomy of Skeletal Muscle Individual muscle fibers are wrapped and held together by several different layers of connective tissue The individual muscle fibers are surrounded by a fine sheath of connective tissue called the endomysium. The fibers within the muscle are grouped into fascicles, bundles of muscle fibers with a connective tissue covering and look like a bunch of sticks with an outer wrapping The perimysium layer is fibrous connective tissue that surrounds the fascicles. The outermost connective tissue layer is called the epimysium and surrounds the whole muscle. Portions of the epimysium project inward and divide the muscle into compartments BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Skeletal muscles can be made up of hundreds or thousands of muscle fibers bundled together Myofibrils are contractile units made up of long protein molecules called myofilaments BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Fascia, connective tissue outside the epimysium, surrounds the entire muscle At the ends of the muscle, all of the connective tissues come together and form the tendon that attaches the muscle to bone. BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Movememt If the muscle spans a joint, one bone moves while the other one remains stationary the muscle’s origin is on the bone which does not move the muscle’s origin is generally closer to the midline of the body than its insertion the insertion is on the bone which moves All muscle cells in a muscle have the same origin and insertion BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Muscle Contractions Isotonic contractions: occur when the muscle shortens and movement occurs Isometric contractions occur when muscle tension develops but the muscle doesn’t shorten and no bony movement occurs. These contractions help stabilize the skeleton. Degree of nerve activation influences force generated by the muscle A single muscle consists of many individual muscle cells typically organized into groups of cells that work together cooperatively. Each group of cells is controlled by a single nerve cell called a motor neuron. BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Terms to know: Motor unit: the motor neuron and all the muscle fibers it supplies. Is the smallest functional unit of muscle contraction. Muscle tension: force generated by a contracting muscle upon an object How much tension is generated by a muscle depends on The number of muscle cells in each motor unit The number of motor units active at the time The frequency of stimulation of individual motor units All-or-none principle: muscle cells are completely under the control of their motor neuron. Muscle fibers always respond with a complete cycle of contraction and relaxation every time they are stimulated. Muscle tone: low level of contractile activity in a relaxed muscle. BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Muscle Activity Muscle twitch: a complete cycle of contraction and relaxation Humans have 2 types of skeletal muscle fibers: slow-twitch and fast-twitch fibers. The difference is based on how quickly the fibers can produce a contraction and whether the muscle contracts aerobically or anaerobically. Most muscles contain a mixture of both types of fibers Ratio of fibers depends on the function of the muscle Abnormal muscle twitches occur when almost all muscle spindles are excited simultaneously BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Slow twitch fibers: break down ATP slowly and contract slowly Tend to make ATP aerobically, as they need it endurance, long duration contraction, contain myoglobin to store oxygen Jogging, swimming, biking Fast twitch: break down ATP quickly, contract more quickly Store large amounts of glycogen and tend to rely on anaerobic metabolism for quick bursts of high energy Rapid, powerful contractions but can’t be sustained strength, short duration contraction: Sprinting, weight lifting, tennis BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Exercise Training Strength training: Resistance training: Short, intense Builds more fast-twitch myofibrils Aerobic training: Builds endurance Increases blood supply to muscle cells Target heart rate at least 20 minutes, three times a week BIO 102 Muscle Lecture HANDOUT

Muscle Contraction: Myogram Latent period-the time between stimulation and the start of a contraction Contraction-time when the muscle actually shortens Relaxation-muscle returns to its original length Summation vs. tetanus Summation: an increase in the frequency with which a muscle is stimulated so that the muscle doesn’t relax completely. This causes a “summation” of the contractile force so total force produced is greater than the force produced by one twitch. Tetanus: If muscle stimulation is so rapid that the muscle can’t relax at all, it will remain in a state of maximal contraction. BIO 102 Muscle Lecture HANDOUT Figure 6.10

Diseases and Disorders of the Muscular System Muscular dystrophy –group of inherited muscle diseases in which muscle fibers are unusually susceptible to damage. Muscles, primarily voluntary muscles, become progressively weaker. In the late stages of muscular dystrophy, fat and connective tissue often replace muscle fibers OR loss of muscle fibers due to muscle’s inability to create some proteins it needs to function normally OR Leak of calcium into the muscle cell which damages muscle proteins and may kill the cell results in muscle wasting and paralysis; death usually from heart failure or respiratory failure BIO 102 Muscle Lecture HANDOUT

BIO 102 Muscle Lecture HANDOUT Tetanus or “lock jaw” –bacterial infection resulting in overstimulation of nerves and therefore muscles resulting in tetanic contractions; death from exhaustion or respiratory failure Muscle cramps – painful, uncontrollable muscle contractions; caused by dehydration and ion imbalances caused by heavy exercise Pulled muscles –caused by stretching a muscle too far causing some fibers to tear apart Fasciitis –inflammation of the connective tissue fascia that surrounds a muscle BIO 102 Muscle Lecture HANDOUT