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
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
Interactive Physiology® Animation: Muscular System: Contraction of Motor Units
PLAY
Figure 12-18

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

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

12. The Arm is a Lever and Fulcrum System
(b) F1
F2 = 2 kg
5 cm
15 cm
Figure 12-21b

13. The Arm is a Lever and Fulcrum System
A 7-kg load is added to the hand 25 cm from the elbow. D1
5 cm D2
25 cm
Figure 12-21c

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

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

16. Muscle cramp: sustained painful contraction Overuse Disuse/Atrophy
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
Skeletal
Cardiac
Smooth
Tension 1 2 3 4 5
Time (sec)
Figure 12-24

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

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

21. Much smaller than skeletal muscle fibers
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. Shares features with both skeletal and smooth muscle
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. Skeletal muscles Muscle Summary
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, Ca2+-ATPase, myosin ATPase, power stroke, rigor state

25. Mechanics of body movement
Summary
Skeletal muscle
Excitation-contraction coupling, DHP receptors, and Ca2+ 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. Smooth muscle Cardiac muscle Summary
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