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Physiology 2
Physiology 2, Comparison of Muscle Types
| Characteristic | Skeletal Muscle | Multiunit Smooth Muscle | Single unit Smooth Muscle | Cardiac Muscle |
|---|---|---|---|---|
| Location | attached to skeleton | large blood vessels, eys & hair follicles | walls of hollow organs in digestive, reproductive, & urinary tracts & in small blood vessels | heart ONLY |
| Function | movement of body in relatin to external environment | varies with structure involved | movement of contents within hollow organs | pumps blood out of heart |
| Mechanism of Contraction | sliding filament mechanism | sliding filament mechanism | sliding filament mechanism | sliding filament mechanism |
| Innervation | somatic nervous systemt (alpha motor nuerons) | autonomic nervous system | autonomic nervous system | autonomic nervous system |
| Level of Control | under voluntary control, also subject to subconscious regulation | under involuntary control | under involuntary control | under involuntary control |
| Initiation of Contraction | Neurogenic | Neurogenic | Myogenic (pacemaker potentials & slow-wave potentials) | myogenic (pacemaker potentials |
| Role of Nervous Stimulation | initiates contractions accomplishes gradation | initiaties contraction; contributes to gradation | modifies contraction; can excite or inhibit; contributes to gradation | modifies contraction; can excite or inhibit; contributes to gradation |
| Modifying effect on hormones | no | yes | yes | yes |
| Presence of thick myosin & thin actin filaments | yes | yes | yes | yes |
| striated by orderly arrangement of filaments | yes | no | no | yes |
| Presence of troponin & tropomyosin | yes | tropomyosin ONLY | tropomyosin ONLY | yes |
| Presence of T tubules | yes | no | no | yes |
| Level of development of Sarcoplasmic Reticulum | well developed | poorly developed | poorly developed | moderately developed |
| Cross Bridges Turned on by Ca2+ | yes | yes | yes | yes |
| Source of increased cytosolic Ca2+ | Sarcoplasmic reticulum | extracellular fluid & sarcoplasmic reticulum | extracellular fluid & sarcoplasmic reticulum | extracellular fluid & sarcoplasmic reticulum |
| Site of Ca2+ Regulation | troponin in thin filaments | myosin in thick filaments | myosin in thick filaments | troponin in thin filaments |
| Mechanism of Ca2+ Action | physically repositions troponin-tropomyosin complex to uncover actin cross-bridge binding sites | chemically brings about phosphorylation of myosin cross bridges so they can bind with actin | chemically brings about phosphorylation of myosin cross bridges so they can bind with actin | physically repositions troponin-tropomyosin complex |
| Presence of Gap junctions | no | yes (very few) | yes | yes |
| ATP used directly by Contractile apparatus | yes | yes | yes | yes |
| Myosin ATPase Activity; Speed of Contraction | fast or slow, depending on type of fiber | very slow | very slow | slow |
| Means by which gradation accomplished | Varying number of motor units contracting (motor unit recruitment) & frequency at which they're stimulated (twitch summation) | Varying number of muscle fibers contracting & varying cytosolic Ca2+ concentration in each fiber by autonomic & hormonal influences | Varying cytosolic Ca2+ concentration through myogenic activity & influences of the autonomic nervous system, hormones, mechanical stretch, & local metabolites | Varying length of fiber (depending on extent of filling of the heart chambers) & varying cytosolic Ca2+ concentration through autonon hormonal, & local metabolite influence |
| Presence of tone in absense of external stimulation | no | no | yes | no |
| Clear-cut length-tension relationship | yes | no | no | yes |
Created by:
JYarger
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