Chapter 12 b Muscles Summation of Contractions Figure

Chapter 12 b Muscles

Summation of Contractions Figure 12 -17 a

Summation of Contractions Figure 12 -17 b

Summation of Contractions Figure 12 -17 c

Summation of Contractions Figure 12 -17 d

Motor Units One muscle may have many motor units of different fiber types. SPINAL CORD Neuron 1 Neuron 2 Neuron 3 Motor nerve KEY Muscle fibers Motor unit 1 Motor unit 2 Motor unit 3 PLAY Interactive Physiology® Animation: Muscular System: Contraction of Motor Units Figure 12 -18

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

Isotonic Contraction Figure 12 -19 a

Isometric Contraction Figure 12 -19 b

Series Elastic Elements in Muscle Schematic of the series elastic elements Elastic components Biceps muscle 1 Muscle at rest Contractile components 1 Muscle length Triceps muscle 2 3 Elastic element Sarcomeres 2 Isometric contraction: 3 Isotonic contraction: Sarcomeres shorten Muscle has not shortened. more but, because elastic Sarcomeres shorten, generating elements are already force, but elastic elements stretched, the entire stretch, allowing muscle length muscle must shorten. to remain the same. Figure 12 -20

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

The Arm is a Lever and Fulcrum System (b) F 1 5 cm 15 cm F 2 = 2 kg Figure 12 -21 b

The Arm is a Lever and Fulcrum System (c) A 7 -kg load is added to the hand 25 cm from the elbow. D 1 D 2 5 cm 25 cm Figure 12 -21 c

The Arm Amplifies Speed of Movement of the Load Lever 5 cm Fulcrum 1 cm Figure 12 -22

Load-Velocity Relationship in Skeletal Muscle Figure 12 -23

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

Duration of Muscle Contraction in the Three Types of Muscle Skeletal Smooth Tension Cardiac 0 1 2 3 Time (sec) 4 5 Figure 12 -24

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

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

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

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 • IP 3 -receptor channel is the primary calcium channel • Calcium also enters cell from extracellular fluid

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

Muscle Summary Table 12 -3

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

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

Summary • Smooth muscle • Types of smooth muscle, IP 3 -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