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Chapter 12b - PowerPoint PPT Presentation


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Chapter 12b. Muscles. Summation of Contractions. Figure 12-17a. Summation of Contractions. Figure 12-17b. Summation of Contractions. Figure 12-17c. Summation of Contractions. Figure 12-17d. Motor Units. One muscle may have many motor units of different fiber types. SPINAL CORD.

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motor units
Motor Units

One muscle may havemany motor units ofdifferent fiber types.

SPINAL CORD

Neuron 1

Neuron 2

Neuron 3

Motornerve

KEY

Motor unit 1

Muscle fibers

Motor unit 2

Motor unit 3

Interactive Physiology® Animation: Muscular System:Contraction of Motor Units

PLAY

Figure 12-18

mechanics of body movement
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
series elastic elements in muscle
Series Elastic Elements in Muscle

Schematic of the series elastic elements

Elasticcomponents

Tricepsmuscle

1

2

3

Contractilecomponents

Elasticelement

Bicepsmuscle

Muscle length

Sarcomeres

Isotonic contraction:Sarcomeres shortenmore but, because elasticelements are alreadystretched, the entiremuscle must shorten.

Isometric contraction:Muscle has not shortened.Sarcomeres shorten, generatingforce, but elastic elementsstretch, allowing muscle lengthto remain the same.

1

Muscleat rest

2

3

Figure 12-20

the arm is a lever and fulcrum system
The Arm is a Lever and Fulcrum System

(a)

Biceps muscle

Lever

Load

Fulcrum

Figure 12-21a

the arm is a lever and fulcrum system1
The Arm is a Lever and Fulcrum System

(b)

F1

F2 = 2 kg

5 cm

15 cm

Figure 12-21b

the arm is a lever and fulcrum system2
The Arm is a Lever and Fulcrum System

(c)

A 7-kg load is addedto the hand 25 cmfrom the elbow.

D1

5 cm

D2

25 cm

Figure 12-21c

the arm amplifies speed of movement of the load
The Arm Amplifies Speed of Movement of the Load

Lever

5 cm

1 cm

Fulcrum

Figure 12-22

muscle disorders
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
duration of muscle contraction in the three types of muscle
Duration of Muscle Contraction in the Three Types of Muscle

Skeletal

Cardiac

Smooth

Tension

5

0

1

2

3

4

Time (sec)

Figure 12-24

smooth muscle
Smooth Muscle
  • Contraction and relaxation slower
  • Uses less energy
  • Maintains force for long periods
  • Low oxygen consumption
smooth muscle1
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
Types of Smooth Muscle

Autonomic neuronvaricosity

Smallintestine

Gapjunctions

Neuro-transmitter

Smooth musclecell

Receptor

(a) Single-unit smooth muscle cells

Figure 12-25a

smooth muscle2
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
cardiac 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
muscle summary
Muscle Summary

Table 12-3

muscle summary1
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, Ca2+-ATPase, myosin ATPase, power stroke, rigor state
summary
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
summary1
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