Chapter 9 Muscular System

Functions of a Muscle Tissue Movement: Skeletal - locomotion , vision, facial expression. Cardiac – blood pumping Smooth – food digestion Posture - (skeletal) Joint Stability - (skeletal) Heat Generation - (skeletal)

Chapter 9 Muscular System Three Types of Muscle Tissues Skeletal Muscle usually attached to bones voluntary- under conscious control striated Cardiac Muscle wall of heart involuntary - not under conscious control striated Smooth Muscle walls of most viscera, blood vessels, skin involuntary - not under conscious control not striated 9-2

Structure of a Skeletal Muscle organs of the muscular system skeletal muscle tissue nervous tissue blood Connective tissues and muscle tissue: 1.fascia – covers the muscle 2.tendon – attaches the muscle 3.aponeuroses – muscle to muscle 9-3

Functional Characteristics of Muscle Excitability – receive and respond to stimuli Contractility – shorten forcibly and when stimulated Extensibility – stretched or extended Elasticity – bounce back to original length

Structure of a Skeletal Muscle Coverings of a muscle 1. Epimysium - outter 2. Perimysium - middle 3. Endomysium - inner Organization of Muscle muscle fascicles muscle fibers myofibrils thick and thin filaments 9-4

Structure of a Skeletal Muscle Coverings of a muscle 1. Epimysium – connective tissue surrounding the entire muscle 2. Perimysium – connective tissue surrounding a fascicle 3. Endomysium – thin connective tissue surrounding each muscle cell Organization of Muscle muscle fascicles – bundle of muscle cells muscle fibers – a muscle cell myofibrils – a long, filamentous organelle found within muscle cells that has a banded appearance thick and thin filaments (myofilament)- actin &myosin filaments sarcomere – contractile unit of muscle 9-4

Skeletal Muscle Fiber sarcolemma - sacroplasm sarcoplasmic reticulum transverse tubule triad cisterna of sarcoplasmic reticulum myofibril actin filaments myosin filaments sarcomere 9-5

Skeletal Muscle Fiber sarcolemma – Plasma membrane surrounding each muscle fiber sarcoplasm – specialized cytoplasm sarcoplasmic reticulum – network of tubes and sacs transverse tubule – tubular organelles that run across fibers, right angles triad cisternae of sarcoplasmic reticulum transverse tubule myofibril – consists of the many, bundled myofilaments actin filaments – thin filaments myosin filaments – thick filaments sarcomere – basic contractile unit of muscle

Acting and Myosin Filaments Actin and Myosin

Sarcomere I band A band H zone Z line M line 9-6

Sarcomere Structure A sarcomere is defined as the segment between two neighboring Z- lines .   Z-line- the disc in between the I bands. Appears as a series of dark lines.   I-band is the zone of thin filaments that is not superimposed by thick filaments. A-band contains the entire length of a single thick filament. H-band is the zone of the thick filaments that is not superimposed by the thin filaments. Finally, inside the H-zone is a thin M-line formed of cross-connecting elements of the cytoskeleton. 9-6

Sliding Filament Theory When sarcomeres shorten, actin and myosin filaments slide past one another VIDEO#1 VIDEO #2 9-12

Skeletal Muscle Contraction ? How does a muscle contract?

Sequence of a Muscle Contraction Neuromuscular Junction Brain Spinal Cord Nerve (Action potential) Motor Unit Neuromuscular Junction (Calcium is released) Acetylcholine (Neurotransmitter) Contraction

Motor Unit single motor neuron (a single nerve) one motor neuron and many skeletal muscle fibers 9-9

Neuromuscular Junction site where a motor nerve fiber and a skeletal muscle fiber meet 9-8

Muscle Contraction Action potential causes the release of Ca at the NMJ. a neurotransmitter releases a chemical substance from the motor end fiber, causing stimulation of the muscle fiber That substance is called acetylcholine (ACh) ACh causes the muscle fibers to become stimulated and contract (shorten). 9-10

Relaxation of a Muscle acetylcholinesterase – an enzyme that breaks down acetylcholine. NMJ muscle impulse stops calcium moves back into sarcoplasmic reticulum myosin and actin action prevented muscle fiber relaxes Cd 9-14

Sequence of a Muscle Contraction Neuromuscular Junction Brain Spinal Cord Nerve (Action potential) Motor Unit Neuromuscular Junction (Calcium is released) Acetylcholine (Neurotransmitter) Contraction

Recruitment of Motor Units Recruitment - increase in the number of motor units activated whole muscle composed of many motor units as intensity of stimulation or contraction increases, recruitment of motor units continues until all motor units are activated = all or none principle 9-22

Question ???? We now know how a muscle contracts and relaxes, so is energy needed for that to happen? NO or YES ?

How is energy that is stored in carbohydrates released? Cellular Respiration Oxygen Glucose H2O + CO2 Useable Energy is Adenosine triphosphate (ATP)

Adenosine triphosphate (ATP) It serves as a source of energy for many metabolic processes. ATP releases energy when it is broken down into ADP by hydrolysis during cell metabolism.

ENERGY The energy used to power the interaction between actin and myosin filaments comes from ATP (useable chemical energy) produced by cellular respiration. ATP stored in skeletal muscle last only about six seconds. ATP must be regenerated continuously if contraction is to continue

Two Energy Sources for Contraction 1) Creatine phosphate (ADP) 2) Cellular respiration creatine phosphate – stores energy that quickly converts unusable energy (ADP) to usable energy (ATP) 6 Seconds!! 9-15

Cellular Respiration (CR) THREE SERIES OF REACTIONS in CR Glycolysis Citric acid cycle Electron transport chain Produces carbon dioxide water ATP (chemical energy) heat Two Types of Reactions Anaerobic Respiration (without O2) - produce little ATP Aerobic Respiration (requires O2) - produce most ATP 4-11

Anaerobic Reaction (Glycolysis) Recall that glycolysis results in pyruvate acid. If O2 is not present, pyruvate can be fermented into LACTIC ACID. Lactic Acid It is a waste product of pyruvate acid. Occurs in many muscle cells. Accumulation causes muscle soreness and fatigue.

Oxygen Supply and Cellular Respiration Anaerobic Phase Steps are called glycolysis. occur in the cytoplasm no oxygen produces pyruvic acid and produces lactic acid little ATP Aerobic Phase Steps are called citric acid cycle and electron transport chain. occur in the mitochondrion oxygen produces most ATP / CO2/ H2O 9-16

Summary of Cellular Respiration Total ATP Production 2 ATP – Glycolysis 2 ATP – Citrus Acid Cycle 34 ATP – Electron Transport Chain 38 ATP – Total energy released from one molecule of glucose.

Oxygen Debt Oxygen debt – amount of oxygen needed by liver to convert lactic acid to glucose oxygen not available glycolysis continues pyruvic acid converted to lactic acid 9-17

What happens to the lactic acid once it has accumulated? The liver filters the blood and rids the body of toxins. Lactic acid is a toxin. liver converts lactic acid to glucose

Muscle Fatigue Muscle fatigue- is a state of physiological inability to contract commonly caused from decreased blood flow ion imbalances accumulation of lactic acid Cramp – sustained, involuntary contraction 9-18

Muscle Cramp Muscle Cramp The exact cause of muscle cramps is still unknown, but the theories most commonly cited include: Altered neuromuscular control Dehydration Electrolyte depletion Poor conditioning Muscle fatigue Doing a new activity

Muscle Tone Muscle tone – continuous state of partial contraction Even when a muscle appears to be at rest, a certain amount of sustained contraction is occurring in its fibers. Atrophy – a wasting away or decrease in size of an organ or tissue. Hypertrophy – Enlargement of an organ or tissue. 9-23

Two Types of Isotonic Contractions Types of Contractions Two Types 1. Isometric – muscle contracts but does not change length 2. Isotonic – muscle contracts and changes length Two Types of Isotonic Contractions 1. Eccentric – (negative) lengthening contraction 2. Concentric – (positive) shortening contraction 9-24

Types of Contractions

Smooth and Cardiac Muscle

Smooth Muscle Fibers Compared to skeletal muscle fibers shorter single nucleus elongated with tapering ends myofilaments randomly organized no striations 9-26

Two Types of Smooth Muscle Multiunit Smooth Muscle irises of eye walls of blood vessels contractions are rapid and vigorous similar to skeletal muscle tissue Visceral Smooth Muscle Location - walls of most hollow organs (intestine) contractions are slow and sustained exhibit rhythmicity – pattern of repeated contractions exhibit peristalsis – wave-like motion that helps substances through passageways. 9-27

Smooth Muscle Contraction Resembles skeletal muscle contraction interaction between actin and myosin both use calcium and ATP both depend on impulses Different from skeletal muscle contraction hormones affect smooth muscle stretching can trigger smooth muscle contraction smooth muscle slower to contract and relax smooth muscle more resistant to fatigue 9-28

Cardiac Muscle Anatomy only in the heart striated uninuclear cells join end-to-end forming a network arrangement of actin and myosin are not as organized as skeletal muscle Physiology self-exciting tissue (Pacemaker) rhythmic contractions involuntary, all or nothing contractions Pumps blood to: 1. lungs for oxygenation 2. body for distribution of O2 and nutrients 9-29