Types of Skeletal Muscle Fibers

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All skeletal-muscle fibers do not have the same mechanical and metabolic characteristics. Different types of fibers can be identified on the basis of (1) their maximal velocities of shortening—fast and slow fibers— and (2) the major pathway used to form ATP—oxida-tive and glycolytic fibers.

Fast and slow fibers contain myosin isozymes that differ in the maximal rates at which they split ATP, which in turn determine the maximal rate of cross-bridge cycling and hence the fibers' maximal shortening velocity. Fibers containing myosin with high ATPase activity are classified as fast fibers, and those containing myosin with lower ATPase activity are slow fibers. Although the rate of cross-bridge cycling is about four times faster in fast fibers than in slow fibers, the force produced by both types of cross bridges is about the same.

The second means of classifying skeletal-muscle fibers is according to the type of enzymatic machinery available for synthesizing ATP. Some fibers contain

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

II. Biological Control Systems

11. Muscle

© The McGraw-Hill Companies, 2001

Muscle CHAPTER ELEVEN

Muscle CHAPTER ELEVEN

numerous mitochondria and thus have a high capacity for oxidative phosphorylation. These fibers are classified as oxidative fibers. Most of the ATP produced by such fibers is dependent upon blood flow to deliver oxygen and fuel molecules to the muscle, and these fibers are surrounded by numerous small blood vessels. They also contain large amounts of an oxygen-binding protein known as myoglobin, which increases the rate of oxygen diffusion within the fiber and provides a small store of oxygen. The large amounts of myoglobin present in oxidative fibers give the fibers a dark-red color, and thus oxidative fibers are often referred to as red muscle fibers.

In contrast, glycolytic fibers have few mitochondria but possess a high concentration of glycolytic enzymes and a large store of glycogen. Corresponding to their limited use of oxygen, these fibers are surrounded by relatively few blood vessels and contain little myoglobin. The lack of myoglobin is responsible for the pale color of glycolytic fibers and their designation as white muscle fibers.

On the basis of these two characteristics, three types of skeletal-muscle fibers can be distinguished:

1. Slow-oxidative fibers (type I) combine low myosin-ATPase activity with high oxidative capacity.

2. Fast-oxidative fibers (type Ila) combine high myosin-ATPase activity with high oxidative capacity.

3. Fast-glycolytic fibers (type lib) combine high myosin-ATPase activity with high glycolytic capacity.

Note that the fourth theoretical possibility—slow-glycolytic fibers—is not found.

In addition to these biochemical differences, there are also size differences, glycolytic fibers generally having much larger diameters than oxidative fibers (Figure 11-28). This fact has significance for tension development. The number of thick and thin filaments per unit of cross-sectional area is about the same in all types of skeletal-muscle fibers. Therefore, the larger the diameter of a muscle fiber, the greater the total number of thick and thin filaments acting in parallel to produce force, and the greater the maximum tension it can develop (greater strength). Accordingly, the average glycolytic fiber, with its larger diameter, develops more

Glycolytic fibers (large diameter)

Capillary blood vessels

Glycolytic fibers (large diameter)

Myoglobin Muscle Fibers

Oxidative fibers (small diameter)

FIGURE 11-28

Cross sections of skeletal muscle. (a) The capillaries surrounding the muscle fibers have been stained. Note the large number of capillaries surrounding the small-diameter oxidative fibers. (b) The mitochondria have been stained indicating the large numbers of mitochondria in the small-diameter oxidative fibers.

Courtesy of John A. Faulkner.

Oxidative fibers (small diameter)

FIGURE 11-28

Cross sections of skeletal muscle. (a) The capillaries surrounding the muscle fibers have been stained. Note the large number of capillaries surrounding the small-diameter oxidative fibers. (b) The mitochondria have been stained indicating the large numbers of mitochondria in the small-diameter oxidative fibers.

Courtesy of John A. Faulkner.

PART TWO Biological Control Systems

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

II. Biological Control Systems

11. Muscle

PART TWO Biological Control Systems

© The McGraw-Hill Companies, 2001

TABLE 11-3 Characteristics of the Three Types of Skeletal-Muscle Fibers

Slow-Oxidative Fibers

Fast-Oxidative Fibers

Fast-Glycolytic Fibers

Primary source of ATP

production Mitochondria Capillaries Myoglobin content Glycolytic enzyme activity Glycogen content Rate of fatigue

Oxidative phosphorylation

Many Many

High (red muscle) Low

Low Slow

Oxidative phosphorylation

Many Many

High (red muscle) Intermediate

Intermediate Intermediate

Glycolysis

Few Few

Low (white muscle) High

High Fast

Myosin-ATPase activity Contraction velocity

Low Slow

High Fast

High Fast

Fiber diameter Motor unit size Size of motor neuron innervating fiber

Small Small Small

Intermediate Intermediate Intermediate

Large Large Large

Slow-oxidative fibers

Slow-oxidative fibers ta JE c o

Time (min)

tension when it contracts than does an average oxidative fiber.

These three types of fibers also differ in their capacity to resist fatigue. Fast-glycolytic fibers fatigue rapidly, whereas slow-oxidative fibers are very resistant to fatigue, which allows them to maintain contractile activity for long periods with little loss of tension. Fast-oxidative fibers have an intermediate capacity to resist fatigue (Figure 11-29).

The characteristics of the three types of skeletal-muscle fibers are summarized in Table 11-3.

Fast-oxidative fibers ta (m n o

Time (min)

Fast-glycolytic fibers g m

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Responses

  • Sebhat
    What is the fourth muscle fiber type?
    8 years ago
  • maria
    Why are white fibers larger in diameter?
    8 years ago
  • isengrin
    What are the two types of skeletal muscle fibers?
    8 years ago
  • Anja Savonheimo
    Why do muscle fibers with high glycolytic capacity fatigue easily?
    8 years ago
  • Adaldrida
    What part of the body slow oxidative fibres contain?
    8 years ago
  • Ulrike
    Why is it an advantage for muscle fibre to have large numbers of mitochondria?
    8 years ago
  • Esmeralda
    What is the function of muscle fibres in the body?
    8 years ago
  • myrtle took
    Which muscle type had highest glycolytic?
    8 years ago
  • Delores
    Why do oxidative fibres resist fatigue?
    8 years ago
  • Abdullah Paterson
    What is the cross sectional diameter of slow oxidative skeletal muscle fibers?
    8 years ago
  • abbondanzio
    What muscle activities are slow oxidative?
    8 years ago
  • pearl
    What muscles contain many fast glycolytic fibers?
    8 years ago
  • iida
    Why do most skeletal muscle fibers have numerous mitochondria?
    8 years ago
  • Helen
    What skeletal muscle fiber produce the most power?
    8 years ago
  • kiros yonas
    Why are fibers containing myosin with fast atpase activity considered fast fibers?
    8 years ago
  • Luce
    What are fast oxidative glycolytic skeletal muscle?
    8 years ago
  • Katariina Hursti
    Which skeletal muscle fibres type that produces the most powerful?
    8 years ago
  • anita
    Where is atp produced in skeletal muscle fiber?
    8 years ago
  • daniel
    Does fast myosin atpases have slow oxidative skeletal muscle fibers?
    8 years ago
  • roxy
    Why are there not any slow glycolytic fibers?
    8 years ago
  • chanelle
    Which muscles have high myosinatpase high oxidative capacity and intermediated glycolytic capacity?
    8 years ago
  • trahand
    Why are glycolytic fibers wider in diameter?
    8 years ago
  • natsnet
    What characteristics distinguish the three types of skeletal muscle fibers?
    8 years ago
  • ARNOLD
    Why do fast glycolytic fibres have a small diameter?
    8 years ago
  • Ciara
    Where are glycolytic fibers located and what are their function?
    8 years ago
  • RUFUS
    Why white muscle diameter larger?
    7 years ago
  • jessika duerr
    Why do type1 muscle fiber have a small diameter?
    7 years ago
  • Robel Robel
    Why do oxidative muscle fibers have smaller diameters then glycolytic muscle fibers?
    7 years ago
  • celendine
    Do fast fibres have a larger diameter?
    7 years ago
  • cassio
    Do glycolytic muscle fibers have mitochondria?
    7 years ago
  • peter
    What are the three primary fiber types in human skeletal muscle?
    7 years ago
  • carlos walter
    Why do oxidative muscle fibers have small diameters?
    5 years ago
  • Adam
    Why is it advantageous for oxidative muslce fibers to have smaller diameters?
    4 years ago
  • KRISTIAN HALONEN
    How atp produced in pale fibres?
    4 years ago
  • Lotho Greenhand
    Why are slow oxidative fibers have less mitochondria?
    3 years ago
  • Oliver
    What fibre has a bigger oxidative activity?
    3 years ago
  • WILLIAM
    Why white muscle fibers have high ATPase with less myoglobin?
    3 years ago
  • Joseph
    Which muscle fibre have maximum mitochondria?
    2 years ago
  • gorhendad hayward
    Is all skeletal muscles glycolytic?
    2 years ago
  • Rosario
    Does fast glycolytic muscle have less mitochondria and myoglobin?
    1 year ago
  • p
    What type of muscle fiber type has a small diameter and lots of mitochondria?
    11 months ago
  • Topias
    Which type of skeletal muscle contains abundant quantities of glycogen?
    10 months ago
  • ailie
    Which type of skeletal muscle fiber contains a high concentration of mitochondria?
    9 months ago
  • Lassi
    Why does fast glycolitic skeletal muscle fibers have little myoglobin?
    8 months ago
  • UTE
    Which muscle type contains a higher number of blood vessels?
    8 months ago
  • Quartilla
    Why fast glycotic skeletal muscle fibers has abundant glycogen stores?
    8 months ago
  • elen
    Which skeletal muscles in the human body have the most mitochondria?
    7 months ago
  • carla loggia
    Which type of skeletal muscle fiber is surrounded by the greatest number of capillaries?
    6 months ago
  • evelynn white
    Which skeletal muscle fiber type has slow myosin atpase activity?
    6 months ago
  • sara
    Which muscle type contains a high amount of small blood vessels?
    5 months ago
  • Tammi
    Which muscle type has highest number of small blood vessels?
    5 months ago

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