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Generalities of the muscular system
- evolution in terms of muscles
As you go up the evolutionary tree, there is a decrease in huge muscle mass and an increase in smaller muscles with more defined functions; trend is to reduce large masses and make more smaller individual muscles that with more defined functions; the trend is to reduce large masses and make more smaller individual muscles that have more specialized function
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Generalities of the muscular system
- evolution in terms of skeletal elements
decrease in the number of joints but an increase in the number of complexity; these two events accompany a decrease in the muscle masses and an increase in smaller, more differentiated muscles
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Structural Classification
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Characteristics of skeletal muscle
- 1) striated due to arrangement of contractile proteins, which are actin and myosin across the muscle fibers
- 2) banding pattern of light and dark alterations
- 3) voluntary--under our control and governed by the somatic NS
- 4) Instead of being called cells, they are called fibers because, during embryogenesis, different myoblasts fuse together to form long, multinucleated fibers
- 5) Because they are long fibers, they are very fast at contracting--fastest contracting muscles
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Characteristics of smooth muscle
- 1) non-striated
- 2) does not have banding pattern: even though it has actin and myosin, it's just that they are not regularly arranged
- 3) involuntary--autonomic NS
- 4) Slowest contracting muscle because, when you look at it, it is made up of sheets of spindle-shaped cells; individual cells; tapered ends and fat bellies
- 5) In order to get contraction, every single muscle cell in the sheet must be individually stimulated. There is no transmission from among cells
- 6) It is the muscle of the viscera except the heart
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Characteristics of Cardiac muscle
- 1) striated
- 2) involuntary-- autonomic NS
- 3) when yo look at it, there are individual cells whose end membranes are modified to form intercalated discs
- 4) The muscles interdigitate, which allow for increased transmission from cell to cell. It is not as fast as skeletal muscle because it gets impeded by stimulation. It is faster than smooth. Still, intercalated disks speed up transmission
- 5) Cells form a network int he heart, which branch
- 6) Only located in the myocardium (middle layer of the heart-- muscle layer)
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Embryology of muscle
- When the embryo develops, there is __ on both sides of the __; and, there are tissues organized on either side of the __.
The tissue that is more dorsal is the __. The tissue that is organized lateral to the gut is the __.
- organized tissue
- notochord
- gut
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Embryology of muscle cont.
As development proceeds, the __ becomes organized into blocks, called __. The __ does not.
The __, with further development, differentiate into three regions-- __, __, __.
hypomere
somites
dermatome, myotome, and sclerotome
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Dermatome becomes
dermis of skin
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Myotome becomes
skeletal muscle
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Schlerotome becomes
the vertebrae and the caudal portion of the chondrocranium
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The myotome further divides as development proceeds into two regions of muscle-- one that is __ and the other that is __.
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Epaxial becomes
dorsal musculature of the trunk
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Hypaxial becomes?
ventral musculature of the trunk (small contribution to limb musculature)
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Hypomere-->
- main contribution of limb musculature and also a small portion of ventral musculature
- smooth muscle of the gut and to serous membranes and cavities
- cardiac muscle of the heart
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The myotome behind the head and pharynx
The musculature in front of the pharynx in the head region is the __.
form the axial musculature; musculature of the body wall
epaxial portion of it.
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Epaxial muscles in the head region
give rise to the somitomores (somitomeres); form the extrinic muscles of the eye
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The somatimeres also divide into __
epibranchial and hypobranchial muscles
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Cardiac muscle also comes from the __.
hypomere
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