Skeletal Muscle Histology
Introduction
This page describes skeletal muscle histology which can identify cross-striational structure and /or properties related to contractile speed and fatigue.
Development of skeletal muscle, cardiac muscle and smooth muscle can be found in other notes.
Development of skeletal muscle from mesoderm occurs by mononucleated myoblasts fusing together to form mutinucleated myotubes that express contractile proteins forming sarcomeres within myofibers.
Some Recent Findings
Skeletal Muscle Stages
Myoblast - individual progenitor cells
Myotube - multinucleated, but undifferentiated contractile apparatus (sarcomere)
Myofibre (myofiber, muscle cell) - multinucleated and differentiated sarcomeres
- primary myofibres - first-formed myofibres, act as a structural framework upon which myoblasts proliferate, fuse in linear sequence
- secondary myofibers - second later population of myofibres that form surrounding the primary fibres.
Muscle Fibre Types
Muscle fiber types
- type IIB, IIA, IIX, and I fibres - based only on the myosin ATPase activity.
- Type I fibres appear red, due to the presence of myoglobin.
- Type II fibres appear white, due to the absence of myoglobin and their glycolytic nature.
- A group of individual myofibres within a muscle will be innervated by a single motor neuron (motor unit).
- The electrical properties of the motor neuron will regulate the contractile properties of all associated myofibres.
Fibre Type | Type I fibres | Type II a fibres | Type II x fibres | Type II b fibres |
---|---|---|---|---|
Contraction time | Slow | Moderately Fast | Fast | Very fast |
Size of motor neuron | Small | Medium | Large | Very large |
Resistance to fatigue | High | Fairly high | Intermediate | Low |
Activity Used for | Aerobic | Long-term anaerobic | Short-term anaerobic | Short-term anaerobic |
Maximum duration of use | Hours | <30 minutes | <5 minutes | <1 minute |
Power produced | Low | Medium | High | Very high |
Mitochondrial density | High | High | Medium | Low |
Capillary density | High | Intermediate | Low | Low |
Oxidative capacity | High | High | Intermediate | Low |
Glycolytic capacity | Low | High | High | High |
Major storage fuel | Triglycerides | Creatine phosphate, glycogen | Creatine phosphate, glycogen | Creatine phosphate, glycogen |
Myosin heavy chain, human genes |
MYH7 | MYH2 | MYH1 | MYH4 |
Myotome
In both development and the adult, the group of skeletal muscles supplied by a specific segmental spinal nerve is referred to as a myotome. The muscle arises from a specific somite and the spinal nerve arises from a specific level of the spinal cord (identified by veretebral column).
In humans this corresponds to the following spinal nerves (from top to bottom) and muscular functions:
- C3,4 and 5 supply the diaphragm for breathing.
- C5 supply shoulder muscles and muscles to bend our elbow.
- C6 for bending the wrist back.
- C7 for straightening the elbow.
- C8 bends the fingers.
- T1 spreads the fingers.
- T1 –T12 supplies the chest wall and abdominal muscles.
- L2 bends the hip.
- L3 straightens the knee.
- L4 pulls the foot up.
- L5 wiggles the toes.
- S1 pulls the foot down.
- S3,4 and 5 supply the bladder, bowel, sex organs, anal and other pelvic muscles.
Histology Images
References
- ↑ 1.0 1.1 <pubmed>18945372</pubmed>| PMC2596796 | BMC Syst Biol.
Search PubMed
June 2010 " Skeletal Muscle Development" All (19316) Review (2515) Free Full Text (5587) Manage Filters Search Pubmed: Skeletal Muscle Development
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Cite this page: Hill, M.A. (2024, June 19) Embryology Skeletal Muscle Histology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Skeletal_Muscle_Histology
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G