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Chapter 12b Muscles. Summation of Contractions Figure 12-17a.

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Presentation on theme: "Chapter 12b Muscles. Summation of Contractions Figure 12-17a."— Presentation transcript:

1 Chapter 12b Muscles

2 Summation of Contractions Figure 12-17a

3 Summation of Contractions Figure 12-17b

4 Summation of Contractions Figure 12-17c

5 Summation of Contractions Figure 12-17d

6 Motor Units Figure SPINAL CORD Neuron 1 Neuron 2 Neuron 3 Motor nerve Muscle fibers Motor unit 2 Motor unit 1 Motor unit 3 One muscle may have many motor units of different fiber types. KEY PLAY Interactive Physiology® Animation: Muscular System: Contraction of Motor Units

7 Mechanics of Body Movement Isotonic contractions create force and move load Concentric action is a shortening action climbing Eccentric action is a lengthening action Downhill skiing, going down stairs Isometric contractions create force without moving a load Series elastic elements; sarcomeres shorten while elastic elements stretch resulting in little change in overall length

8 Isotonic Contraction Figure 12-19a

9 Isometric Contraction Figure 12-19b

10 Series Elastic Elements in Muscle Figure Contractile components Elastic components Triceps muscle Biceps muscle Elastic element Sarcomeres Schematic of the series elastic elements Muscle at rest Isotonic contraction: Sarcomeres shorten more but, because elastic elements are already stretched, the entire muscle must shorten. Isometric contraction: Muscle has not shortened. Sarcomeres shorten, generating force, but elastic elements stretch, allowing muscle length to remain the same. Muscle length

11 The Arm is a Lever and Fulcrum System Figure 12-21a Lever Load Fulcrum Biceps muscle (a)

12 The Arm is a Lever and Fulcrum System Figure 12-21b F 2 = 2 kg F1F1 5 cm 15 cm (b)

13 The Arm is a Lever and Fulcrum System Figure 12-21c D1D1 D2D2 5 cm 25 cm A 7-kg load is added to the hand 25 cm from the elbow. (c)

14 The Arm Amplifies Speed of Movement of the Load Figure Lever Fulcrum 1 cm 5 cm

15 Load-Velocity Relationship in Skeletal Muscle Figure 12-23

16 Muscle Disorders Muscle cramp: sustained painful contraction Overuse Disuse/Atrophy Acquired disorders Inherited disorders Duchenne’s muscular dystrophy Dystrophin McArdle’s disease Myophosphorylase deficiency glycogenosis – glycogen not converted to glucose 6-phosphate

17 Duration of Muscle Contraction in the Three Types of Muscle Figure Skeletal Cardiac Smooth Time (sec) Tension

18 Smooth Muscle Contraction and relaxation slower Uses less energy Maintains force for long periods Low oxygen consumption

19 Smooth Muscle Smooth muscle is not studied as much as skeletal muscle because It has more variety Anatomy makes functional studies difficult It is controlled by hormones, paracrines, and neurotransmitters It has variable electrical properties Multiple pathways influence contraction and relaxation

20 Types of Smooth Muscle Figure 12-25a Small intestine Autonomic neuron varicosity Neuro- transmitter Receptor Gap junctions Smooth muscle cell (a) Single-unit smooth muscle cells

21 Smooth Muscle Much smaller than skeletal muscle fibers Has longer actin and myosin filaments Myosin ATPase activity much slower Myosin light chain plays regulatory role Not arranged in sarcomeres Has less sarcoplasmic reticulum IP3-receptor channel is the primary calcium channel Calcium also enters cell from extracellular fluid

22 Cardiac Muscle Shares features with both skeletal and smooth muscle Like skeletal: Striated; sarcomere structure Unlike skeletal: Muscle fibers shorter; may be branched; have single nucleus Like smooth: Electrically linked to one another; some exhibit pacemaker potentials; under sympathetic and parasympathetic control as well as hormone control

23 Muscle Summary Table 12-3

24 Muscle Summary Skeletal muscles Origin, insertion, flexors, extensors, and antagonistic muscles T-tubules, sarcoplasmic reticulum, myofibrils, thick filament, thin filament, actin, myosin, and crossbridges Sarcomere, Z disks, I bands, A band, H zone, and M line Muscle tension, load, sliding filament theory, tropomyosin, troponin, Ca 2+ -ATPase, myosin ATPase, power stroke, rigor state

25 Summary Skeletal muscle Excitation-contraction coupling, DHP receptors, and Ca 2+ release channels Twitch, latent period, phosphocreatine, and muscle fatigue Muscle fiber types, myoglobin, tetanus, and motor unit Mechanics of body movement Isotonic versus isometric contractions Series elastic elements, levers, and fulcrums

26 Summary Smooth muscle Types of smooth muscle, IP3-receptor channel, calmodulin, myosin light chain kinase, myosin light protein chains, and myosin phosphatase Myogenic contraction, slow wave or pacemaker potentials, and pharmacomechanical coupling Cardiac muscle Comparison to other muscle types


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