Bio 100 Lecture Notes on the Muscular System PDF

Bio 100 - Lecture Notes for the Muscular System Muscle Cell = Muscle Fiber (they are the same) Muscle Tissue = A group of muscle cells working together - Key Characteristic: The cells contract (shorten) to cause movement Know the 3 types of muscle tissue (See homework and Chapters...

Bio 100 - Lecture Notes for the Muscular System Muscle Cell = Muscle Fiber (they are the same) Muscle Tissue = A group of muscle cells working together - Key Characteristic: The cells contract (shorten) to cause movement Know the 3 types of muscle tissue (See homework and Chapters 4 and 8 in the textbook) Key points: - Skeletal muscle is the only muscle tissue that is voluntary (i.e. you can contract it if you want to) - Smooth muscle is the only muscle tissue that does not have striations (little stripes on the muscle cells) - Skeletal muscle cells are the only muscle tissue cells that are multinucleated (having many nuclei) Locations: Skeletal muscle is attached to skeleton. Cardiac muscle is in heart. Smooth muscle is in all non-cardiac involuntary muscles Skeletal Muscle - Attaches to two different bones of the skeleton. - When the muscle contracts (shortens), it brings those two bones closer to each other - Defn: Tendon = connects a muscle to a bone Origin = where the muscle’s tendon attaches to the stationary bone Insertion = where the muscle’s tendon attaches to the moving bone Anatomy of a Skeletal Muscle: Defn: Fascicle = a bundle of muscle fibers (i.e. a bundle of muscle cells) Muscle Fiber = muscle cell Myofibril = an organelle within a muscle cell Sarcomere = The functional unit of skeletal muscle (from Z line to Z line) (i.e. if you understand how the sarcomere works, you understand how the skeletal muscle works) Anatomy of a Sarcomere (from Z line to Z line): Definitions: Note: filament = myofilament Protein = the functional chemical in the body Remember, just like a car has many different functional parts, the body has MANY different functional proteins. Thin filament – made mostly of the protein actin Thick filament - made of the protein myosin Sliding Filament Model for Contraction: First, the thick and thin filaments bind (i.e. form cross bridges). Then, the MANY myosin heads pull the thin filaments toward each other by acting as little levers. The filaments then unbind, cock their heads back, bind again, and pull again. This process repeats as the heads appear to “walk” on the thin filament. Thus, the Z lines move closer together  shortening the sarcomere (contraction). Two chemicals are required for Contraction: 1) Calcium - triggers the contraction by allowing the thick and thin filaments to bind 2) ATP – provides the energy for the myosin heads to move the thin filament What Causes Contraction? (i.e. Where does the Ca2+ come from to trigger the contraction?) Definitions: Smooth Endoplasmic Reticulum (Smooth ER) = organelle in muscle cell that stores & releases Ca2+ Neuron = a nerve cell Motor Neuron = a neuron that stimulates a muscle cell Nerve Impulse = an electrical signal that travels along the plasma membrane of a neuron or muscle cell Synaptic Knob = a part of a neuron that stores and releases neurotransmitters Neurotransmitter (NT) = a chemical used by neurons to communicate with muscles, glands, & other neurons Neuromuscular Junction (NMJ) = point of contact between a neuron and a muscle cell Note: The Neuromuscular Junction is a specific type of synapse (synapses will be described later) Ca 2+ ion pump = an ion pump on the smooth ER that is always pumping Ca2+ back into the smooth ER Steps for Contraction: 1) A nerve impulse travels on a motor neuron to the synaptic knob and causes the release of NTs. 2) The NTs stimulate the muscle cell which causes the Smooth ER to release Ca2+. 3) Ca2+ diffuses to the sarcomere and allows the thick and thin filaments to bind - causing contraction according to the sliding filament model (described on the bottom of the previous page). Steps for Relaxation: 1) The nerve impulses from the motor neuron stop. Thus, the synaptic knob stops releasing NTs. 2) Without NTs to stimulate the muscle cell, the Smooth ER stops releasing Ca2+. 3) Ca2+ is pumped back into the smooth ER by the Ca2+ ion pump. Without Ca2+ at the sarcomere, the thick & thin filaments cannot bind. If the thick & thin filaments can’t bind, there is no contraction. Where does the ATP come from to energize the contraction? Two Ways to Make ATP: 1) Aerobically - uses O 2 - uses mitochondria - provides long-term energy, but not at maximum muscle strength 2) Anaerobically - does not use O 2 , thus does not use mitochondria - results in the production of lactic acid (which causes a muscle “burn” sensation) - can provide maximum muscle strength, but not for a long time Aerobic Exercise: Exercise that relies on oxygen and the mitochondria to make the needed ATP to energize the muscle contractions. The muscle contractions during aerobic exercise must be slow enough for the mitochondria to keep up. Anaerobic Exercise: Exercise that uses muscle contractions that are so strong or so fast that the mitochondria can’t keep up. Additional ATP is made anaerobically by a process that produces lactic acid as a byproduct. This lactic acid produces the muscle pain (the “burn” that we are all familiar with). Note: During anaerobic exercise, you are still making ATP aerobically. You are just supplying additional ATP by the anaerobic process. Muscle Fatigue: Weak contractions due to low ATP, high lactic acid, or other factors Definitions: Motor Unit - one motor neuron AND all the muscle cells it stimulates Twitch - contraction due to one nerve impulse in one motor unit (all muscle fibers in motor unit will contract together one time) - causes a quick, jerky contraction (this is not a useful nor a functional contraction) Tetanic contraction - due to many nerve impulses in rapid succession (a high frequency of nerve impulses) - causes a smooth, steady contraction (which is a useful and functional contraction) Isotonic contraction - same muscle tension during a contraction, while the muscle length changes - the length can change in two ways, thus two types of isotonic contractions: “Iso-” means “same” - Two Types: 1) Concentric contraction - muscle shortens during contraction 2) Eccentric contraction - muscle lengthens during contraction Isometric contraction - same muscle length during a contraction, while the tension increases - no movement (the length is not changing) Training - 2 Main Types 1) Strength Training - to increase muscle strength - How? By increasing muscle tension during anaerobic exercise - Result: Hypertrophy = Bigger muscle cells (not more cells) - What changed? There becomes more thick and thin filaments within the muscle cells Thus, there are now more myosin heads pulling on the thin filaments - resulting in more strength - What color is the trained muscle? Whitish because actin and myosin are whitish 2) Endurance Training - to increase muscle endurance - How? By increasing the amount of aerobic exercise (with low muscle tension) - Result: The muscle cells become more equipped for aerobic ATP production - What changed? 1) More mitochondria in the muscle cells to produce ATP aerobically 2) More blood vessels in the muscle tissue to supply more O 2 & nutrients to the mitochondria 3) More myoglobin in the muscle cells to store more O 2 for the mitochondria - What color is trained muscle? Dark red because blood vessels & myoglobin are dark red - Note: The muscle doesn’t get bigger because there is low muscle tension (thus, no hypertrophy) Be able to define the following movements: (see Table 7-7 as well as Figures 8-7 thru 8-9) flexion vs. extension, abduction vs. adduction, rotation, supination vs. pronation, dorsiflexion vs. plantar flexion. - Know names & functions of the muscles as indicated in the review sheet. Movement Note: Several muscles work together to cause a certain movement, however there is usually only one muscle that is primarily responsible for the movement. Definitions: - Prime mover - The muscle that is mainly responsible for a certain movement. - Ex: the biceps brachii is the prime mover for flexing the elbow - Synergist - A muscle that helps the prime mover with a certain movement. - Ex: the brachialis is a synergist for flexing the elbow - Antagonist - A muscle that has the opposite action as the prime mover. Therefore, it relaxes as the prime mover contracts. - Ex: the triceps brachii is the antagonist for flexing the elbow