Human Physiology Chapter 6 DOERFLER THE MUSCULAR SYSTEM

Transcription

1 Human Physiology Chapter 6 DOERFLER THE MUSCULAR SYSTEM

2 Overview Movement would be impossible without muscle tissue Contractile cell allows muscles to do job Have specialized cell membrane and cytoskeleton that permit them to change their shape Can shorten along one or more planes Muscle cells are laid out as sheets of muscle tissue that produce coordinated contractions Over ½ of body s mass is composed of muscle tissue Over 90% of muscle tissue is involved in skeletal movement.

3 Overview, cont. Contractile cells have HIGH energy needs Associated with ample blood supply (lots) Blood provides glucose and oxygen while removing metabolic wastes Electrolytes transported by blood essential components of muscle cell contractions Along with nervous tissue, muscle consumes almost 70% of food energy

4 Body Mass Index BMI indirect measure of body density Muscle makes up large component of BMI People with a lean body have higher amounts of muscle mass compared with body fat composition Leanness is known to reduce heart disease and metabolic disorders

5 Muscle Categorization Categorized several ways 1 st - Evaluates microscopic appearance Nonstriated have random pattern of contractile proteins Provide weaker contractions than striated Contractile protein cytoskeleton proteins involved in contraction Striated striped appearance results from uniform arrangement of cytoskeleton Cardiac & skeletal

6 Muscle Categorization, cont. 2 nd Control Voluntary people have large degree of control Some function involuntary muscles needed for breathing, but you can control when needed Involuntary contract without conscious control Carry out jobs that must be done automatically 3 rd Location Cardiac - The muscle of the heart involuntary Skeletal - Muscle attached to bone; produces body movement Voluntary Smooth - Found in the linings of blood vessels and tubular organs Involuntary provide the body with weak contractions that can last for long periods of time

7 Types of Muscle Tissue End 6.1

8 6.2 Types of Muscle Tissue All muscle tissue develops from mesoderm in process called myogenesis Begins when stem cells in mesoderm form into myoblasts Myoblasts (stem cells) help develop the 3 muscle types

9 Cardiac Muscle Heart Involuntary, striated Provides strong contractions Cells have 2 nuclei Communicate at special junctions called intercalated disks Intrinsic beat a natural contraction cycle

10 Smooth Muscle Found in many organ systems Nonstriated Produce weak involuntary contractions Peristalsis weak, pulsating contractions that move food and wastes through the digestive system

11 Skeletal Muscle Focus of this chapter.. Provides movement of the bones and joints Voluntary, striated Powerful contractile capabilities Muscle fiber several myoblasts fused together, a muscle tissue cell Motor nerve cells contract skeletal muscle fibers

12 Muscle Cell Structure Skeletal muscles are long, cylindrical cells covered by excitable membrane filled with specialized cytoskeleton Respond to signals from others cells + environment Sarcolemma = membrane (covering) of muscle cells Cytoskeleton composed of band of proteins called myofilaments Thick composed of protein called myosin Thin 3 proteins actin, tropomyosis, and troponin Titin - elastic

13 Muscle Cell Structure, cont. Sarcomere contractile unit of muscle cell Many thousands run length of muscle cell Chains of sarcomeres form myofibrils Each muscle fiber is made of many bundled myofibrils Thick and thin myofilaments arrange to form overlapping pattern Overlapping is what carries out the muscle cell s contraction, and what gives it a striated pattern Z line marks the boundaries between each sarcomere Movement of Z line changes length of muscle Sarcoplasmic reticulum surrounds each sarcomere System of tubes that stores and transports calcium needed for muscle contraction

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15 Muscle Cell Structure

16 Its important to remember the heirarchy Actin Fasicles Muscles Myofilaments Myosin Myofibrils Muscle fibers muscles Composed of fasicles Composed of Muscle fibers Composed of Myofibrils bundles fibers Threads Light and Thin Actin myofilaments Individual types filaments Dark & thicker Myosin

17 Muscle Cell Function Contraction is achieved by simultaneous shortenings of all sarcomeres in a cell Process of contraction *Each on individual slide Neural stimulation (1 st ) Muscle cell contraction (2 nd ) Muscle cell relaxation (3 rd )

18 Neural Stimulation (1 st ) Takes place at neuromuscular junction Where nerve cells communicate with muscles Contraction initiated when end of nerve cell releases neurotransmitter Chemicals used for cell-to-cell communication Acetylcholine neurotransmitter that communicates with muscle cells Binds to acetylcholine receptors, located on sarcolemma Sodium-potassium pump controls the ionic distribution of Na and K inside and outside of cell In resting cell, Na+ is higher outside cell, K+ higher inside Pumps maintains this unequal ion concentrations When stimulated, it loses its ability to maintain the imbalance Imbalance opens ions channel s causing free flow of ions, initiating the muscle contraction phase.

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21 Muscle Cell Contraction (2 nd ) Begins when calcium released by sarcoplasmic reticulum binds to troponin on thin myofibrils Results in temporary rigid tension that keeps filaments in place ATP provides energy Swivel motion brings the two Z-lines together, shortening sarcomere Takes another neural stimulation to continue another cycle 1 muscle contraction requires several cycles of neural stimulation

22 Sliding Filament Model

23 Muscle Cell Relaxation (3 rd ) When no more neural stimulations are exciting the sarcolemma Calcium leakage out of the sarcoplasmic reticulum into the sarcomere is common after death Rigor mortis muscle stiffness Eventually, this stops Creatine phosphate stores energy in cells Collects ATP from cells, can store for long periods of time Glycogen stored form of glucose Myoglobin stores oxygen for muscle cells

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25 6.3 Musculature Muscle morphology shape of muscle Determined by arrangement of muscle fibers Most muscles attach to two or more bones Origin stable, immovable attachment point Insertion connects a muscle to the body part it moves

26 Muscle Terminology Muscle PATTERNS Parallel Sheets of muscle cells that run in the same direction Provide contractions for moving light loads over a long distance Latissimus dorsi (back) Pinnate feather-patterned Provide great strengths for moving heavy loads over a short distance Laid out in various directions to provide greater strength Arms and legs

27 Muscle Terminology, cont. Pinnate and parallel form different gross muscle SHAPES Deltoid (triangular) broad origin, narrow insertion Deltoid, latissimus dorsi Provide pulling power Trapezius (trapezoid) broad origin, narrow insertion Rhomboideus diamond-shaped Provide holding power (levator scapulae) Serratus saw-toothed Involved in short movements of arm, rib cage, and shoulders Deep, not visible under skin Serratus anterior

28 Muscle Terminology, cont. ORIGINS Biceps muscle with 2 origins Biceps brachii 2 points on the scapula Triceps muscle with 3 origins Triceps brachii 2 points on humerus, 1 on scapula Quadriceps muscle with 4 origins Quads of upper leg includes rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis 1 origin on the ilium, 3 on the femur

29 Muscle Terminology, cont. SIZE Maximus largest of muscle group Provides great pulling power Minimus smaller muscle of group Gluteus maximus v gluteus minimus Longus longest muscle of group Brevis shorted muscle of group Extensors of forearms and legs have longus and brevis groups

30 6.4 Skeletal Muscle Structure Skeletal muscle = complex organ composed of striated muscle tissue and connective tissues Nerve cells and blood vessels are integral parts of muscle structure

31 Skeletal Muscle Structure, cont. Basic structure = muscle fiber, or cell Endomysium = CT, covers muscle fiber Maintains chemical environment of contracting cells Fascicles = bundles of muscle tissue Perimysium = CT, surrounds each fascicle Epimysium = CT, covers gross muscle Holds fascicles in place, provides lubricating surfaces for muscles Covers tendons that attach muscle to bone and skin

32 Skeletal Muscle responds Regular disuse of muscles will call muscle atrophy When not in regular use, cells lose sarcomere proteins, will cause muscle shrinkage Also trophy when there is lack of neural stimulation Regular use will produce muscle hypertrophy Increased blood flow during regular use enlarges muscle cells Produces more muscle strength

33 Skeletal Muscle Action Tendon fixes the muscle origin to a firm foundation of bone Origin point of attachment that remains fixed during contraction Muscles insert onto surface of moveable component Shortening brings origin closer to insertion Threshold level of stimulation needed to induce muscle cell to contract Anatagonistic one muscle opposes or resists the action of another muscle Weakens muscle strength Gravity also can have antagonist effect on muscle Essential for pulling relaxed muscles back to their original length

34 Categories of Muscle Action Abductor move a bone away from body s midline Adductor move a bone closer to the body s midline Depressor produce a downward movement Extensor increase the angle of a joint Flexor decrease the angle of a joint Levator produce an upward movement

35 Categories of Muscle Action, cont. Pronator turn the palm downward Rotator move a bone around its longitudinal axis in a circular direction Sphincter decrease the size of an opening Supinator turn the palms upward Tensor make a body part more rigid or tense

36 Isotonic vs. Isometric Isotonic occurs when a muscle is actively shortening or lengthening Lifting a weight with the arm, shortens the muscle involved, and returning the weight to its original position Isometric does NOT lengthen muscle Muscle remains at steady length Has indistinguishable pulses of shortening and lengthening Pushing against something that is too heavy to move

37 6.5 Pathology of Musculature Many disorders of the musculature are due to interactions with the skeletal and nervous system Strains overworking the muscle s force on the joints Most common muscle ailment Sprains resulting from sudden stress on a joint or muscle Injury More severe than strains Require time for muscle tissue to repair muscle cell proteins

38 Muscle pathology, cont. Contusions caused by direct hit or battering of muscle Common in falls and impacts Spasms involuntary, abnormal muscle contraction Not always painful Cramps painful contraction of a muscle Caused by extreme muscle exertion & working in cold conditions Muscle sensitivity continuous muscle pain due to muscle tissue damage or inflammatory disease

39 Muscle pathology, cont. Paralysis complete failure of muscle function Rigid paralysis - caused by muscle stiffness Flaccid paralysis lack of muscle contraction Tetanus caused by soil bacteria that produce toxic secretions from a food-poisoning bacterium Can cause death

40 Neuromuscular disorders Myopathy, or neuromuscular disorders are characterized by the nervous system s inability to communicate with the muscular system

41 Neuromuscular disorders, cont. Dermatomyositis inflammation of muscle and skin Familial periodic paralysis periodic weakness in the arms and legs; genetic Glycogen storage diseases cause muscle weakness due to a diminished ability to use glucose Mitochondrial myopathies genetic mitochondrial abnormalities that prevent muscle for producing energy Muscular dystrophy progressive weakness of voluntary muscles

42 Neuromuscular disorders, cont. Myoglobinurias affect how my0globin provides oxygen to muscles Myositis ossificans bone growing within muscle tissue Myotonia slow relaxation of muscles after contraction Neuromyotonia nerve disorder; bouts of muscle twitching and stiffness Stiff-man syndrome rigidity, and spasms of the spine and lower-extremity muscles Tetany periods of arm and leg muscle spasms caused by calcium imbalances

43 Muscle System Aging Cachexia muscle loss Associated with diseases such as AIDS and Cancer Common consequence of anorexia and bulimia Protein turnover rate at which a cell replaces damaged proteins Worsens with malnutrition and undernutrition Insulin-Like Growth Factor-1 or IGF-1 Chemical needed for muscle cell growth, maintenance and repair Levels lower with maturity Aromatase enzyme that reduces the level of sex hormones needed for muscle mass and strength BMI increases as you age, stimulates production or aromatase