THE MUSCULAR SYSTEM CHAPTER 8

Objectives To explain the structure of muscle To list various outcomes of muscular actions Describe how connective tissue is part of a skeletal muscle Name the major parts of a skeletal muscle fiber, and describe the function of each

Introduction Muscles are responsible for all types of body movement Use chemical energy stored in nutrients to contract muscle tone, propel body fluids and food, generate heartbeat, and distribute heat Types: Skeletal Smooth Cardiac

Skeletal Muscle Attaches to bones Tendon: muscle to bone Ligament: bone to bone Conscious control Come in antagonistic pairs: flexor (bends a joint) and extensor (straightens a joint) Contract and shorten

Skeletal Muscle (cont.) Composed of: Skeletal muscle tissue Nervous tissue Blood Connective tissue

Connective Tissue Coverings Fascia: layers of fibrous connective tissue that separates an individual skeletal muscle from adjacent muscles Epimysium: layer of connective tissue that closely surrounds a skeletal muscle Perimysium: extend inward from epimysium, separates muscle tissue into small compartments Fascicles: bundles of skeletal fibers Endomysium: thin covering of each fiber within a fascicle

Skeletal Muscle Fibers Single cell that contracts in response to stimulation, relaxes when stimulation ends. myofibrils divided into sections called sarcomeres Sarcomere functional unit of muscle contraction contain myofilaments (alternating bands of thin (actin) and thick (myosin) protein filaments)

Thin Filaments (Actin) Complex of proteins Helix of actin molecules and tropomyosin fibers Tropomyosin fibers secured with troponin molecules which block the spot where the myosin fiber will attach (must be moved for muscle contraction)

Thick Filaments (Myosin) Each thick filament consists of many myosin molecules consist of head, neck and tail head binds to actin molecules

*Organization of filaments produces striations*

Neuromuscular Junction Motor Neuron stimulates muscle contraction Neuromuscular junction: connection between motor neuron and muscle fiber Nerve impulse reaches end of motor neuron axon, vesicles release neurotransmitter (acetylcholine) Neurotransmitter received by receptors on muscle cell, contraction is then stimulated Animation

Skeletal Muscle Contraction Sliding Filament Theory Sarcomeres shorten because cross-bridges pull on thin filaments Thin filaments slide toward M line Width of the A band remains the same Z lines move closer together

Steps of Contraction Step 1: Action Potential Nerve action potential releases acetylcholine into synaptic cleft, opening Na+ channels Action potential spreads across sarcolemma, releases Ca2+ into sarcoplasm

Steps of Contraction (cont) Step 2: Myosin-actin binding a. Upon stimulation, Ca2+ binds to receptor on troponin molecule b. Troponin-tropomyosin complex changes, exposing active site of actin 2. Myosin head attaches to actin using energy from ATP, forming a cross-bridge

Steps of Contraction (cont.) Step 3: Power Stroke Side arm pivots towards M line so actin and myosin slide by each other, shortening the sarcomere ADP and P are released

Steps of Contraction (cont.) Step 4: ATP Binding, Actin-myosin release Myosin head binds another ATP molecule Cross-bridges detach, releasing actin

Steps of Contraction (cont.) Step 5: ATP Cleavage ATPase splits ATP and captures released energy, detached myosin head is reactivated Cycle will repeat if Ca2+ is still available

Hmmmmm….. If a muscle is contracted, what happens if a new molecule of ATP is not available? Why does rigor mortis occur? Place your fingers along the angle of your jaw just in front of your ear. Grit your teeth and feel what happens. What muscle is contracting?

Do Now: Complete #’s 1-6 on the upper leg. Fill out the diagram and the function.

Steps of Contraction (all together now!) https://www.youtube.com/watch?v=YAJ-9nPSqwA

Rigor Mortis Occurs 2-4 hours after death due to lack of ATP Muscles remain contracted until the muscle tissue itself starts to deteriorate.

TENSION PRODUCTION The all-or-none principle As a whole, a muscle fiber either contracts completely or does not contract at all

NUMBER OF MUSCLE FIBERS ACTIVATED Recruitment (multiple motor unit summation) In a whole muscle or group of muscles, increasing tension is produced by slowly increasing the size or number of motor units stimulated

MOTOR UNITS Figure 7-8

NUMBER OF MUSCLE FIBERS ACTIVATED Muscle tone The normal tension and firmness of a muscle at rest Muscle units actively maintain body position, without motion Increasing muscle tone increases metabolic energy used, even at rest

MUSCLE CONTRACTION A muscle fiber will contract after threshold stimulus has been reached. Once stimulated, the entire fiber completely contracts which is called the all-or-none response. *the extent of shortening depends on resistance.

MYOGRAM Twitch: single muscle contraction Latent period: time between stimulation and response Period of contraction: muscle is contracted Relaxation: fiber returns to former length

TYPES OF GRAPHS Twitch- full contraction Twitch summation (treppe)- stimulating the muscle before it completely relaxes Incomplete tetanus- minimal amt. of relaxation after each stimulus Complete tetanus- no relaxation, continuous calcium ion deposit

Objectives (P. 3 2/17) To identify the stages of contraction on a myogram To discuss the role of ATP and cellular respiration in muscle fatigue To compare and contrast hypertrophy and atrophy To create dance/workout routines using anatomical terms of movement

ATP AND MUSCLE CONTRACTION Sustained muscle contraction uses a lot of ATP energy Muscles store enough energy to start contraction Muscle fibers must manufacture more ATP as needed

Finish the muscles of the leg (functions and diagram) Do Now Finish the muscles of the leg (functions and diagram)

MUSCLE FATIGUE Cells undergo both aerobic and anaerobic respiration to supply ample atp (lactic acid fermentation) Lactic acid creates an oxygen debt because the liver cells must now use oxygen to break down the lactic acid (can take several hours) Lactic acid lowers the ph, which diminishes the muscle fibers response to stimulation More exercise = more glycolytic enzymes = increased capacity for glycolysis= increased capacity for aerobic respiration!! … start working out ☺

HYPERTROPHY VS. ATROPHY Hypertrophy- muscles respond to exercise and enlarge Slow twitch fibers activated by low intensity exercise such as swimming or running, develop more mitochondria and capillaries, prolonging fatigue Fast twitch fibers activated by weight lifting can produce new myofilaments & enlarge the muscle (they are still fatigable) Atrophy- when regular exercise stops, capillary networks shrink, mitochondria decrease, actin & myosin decrease, and muscle shrinks.

TETANUS Caused by Clostridium tetani bacteria present in soil Bacteria produces a neurotoxin which blocks the release of inhibitory neurotransmitters.

Muscle Workout/Dance Activity Your group must come up with instructions for a workout/dance routine that can be done in the classroom. You must include at least 3 muscles from each section that we covered. Write out the instructions for the next group. They will have to do your “dance” and try to guess which muscles you focused on!

Happy Heart Day!!!