Muscle Diversity in Vertebrates and Invertebrates

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Muscle Diversity in Vertebrates and Invertebrates by Mind Map: Muscle Diversity in Vertebrates and Invertebrates

1. How animals achieve diversity in muscle structure and function within a single muscle over time (through remodeling), within an individual (through development), and between homologous muscles of different species (through evolution).

2. Physiological and Developmental Diversity in Vertebrate Striated Muscle

2.1. The diversity in muscle structure and contractile properties begins in embryogenesis

2.2. Diversity in muscle types requires both genetic variation and an ability to express individual genes in specific combinations.

3. Animals make muscles of different fiber types

3.1. The genetic controls that determine isoform ex- pression are used to produce muscles with distinct contractile properties, known as muscle fiber types

3.2. They may be called white and red muscle (based upon myoglobin content), fast twitch and slow twitch (based on the speed of con- traction), glycolytic and oxidative (based on meta- bolic specialization), or type II and type I (based on myosin heavy chain isoforms).

3.3. Slow muscle cells express specific types of pro- teins: “slow” isoforms of thick filament proteins (myosin, myosin light chains), thin filaments (tro- ponin, tropomyosin), and ion transport machinery.

4. Individuals alter fiber type in response to changing conditions

4.1. Thyroid hormones have long been known to influence the pattern of myosin isoform expression

4.2. By using a circulating en- docrine hormone like thyroid hormone to respond to physiological challenges, animals are able to co- ordinate the remodeling of many tissues and phys- iological functions

4.3. Mechanoreceptors in muscle cells can detect physical changes in muscle shape and trigger changes in signaling pathways

4.4. The IGF II binds to receptors on muscle plasma membranes to trigger signaling pathways that alter the expression of genes encoding muscle proteins.

5. Sonic muscles produce rapid contractions but generate less force

5.1. Typically, sonic muscles are built using fast skeletal isoforms of thick and thin filament proteins, resulting in cross-bridge cycling rates and ATPase rates that are similar to fast- twitch fibers

5.2. First, the muscles have a very fast Ca2+ transient. Sonic muscles have very abundant SR.

5.3. The second property necessary for rapid contraction rates is fast cross-bridge cycling.

5.4. Third, some muscles are able to shorten sarcomeres beyond the limit seen in most muscles.

6. Heater organs and electric organs are modified muscles

6.1. This first example of a trans-differentiated muscle is found in billfish, a group that includes marlin and swordfish

6.2. These fish possess a trans- differentiated eye muscle that functions as a heater organ.

6.3. All muscles produce some heat as a by-product of muscle metabolism, and all tissues produce heat in the reactions that lead to ATP production, as well as the reactions that lead to ATP hydrolysis.

6.4. A second type of trans-differentiated muscle is the electric organ, a tissue with modified muscle cells called electrocytes.

6.5. Electric organs have a polyphyletic origin, meaning they have arisen independently in many distant groups of fish

7. Invertebrate Muscles

7.1. All muscles share the features of myosin-based thick filaments and actin-based thin filaments, but the variation in the arrangement of filaments and regulation of contraction is much more pro- nounced in the invertebrates than the vertebrates.

7.2. Invertebrates possess smooth, cross- striated, or obliquely striate muscle

7.2.1. Obliquely striated muscle, found in many invertebrates, differs from cross-striated muscle in two respects