Mike Gene
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Member # 149
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posted 24. May 2004 23:22
The manner in which human skeletal muscle and peripheral nerves are organized is strikingly similar.
1. In nerves, the individual axons are wrapped by a delicate connective tissue known as endoneurium. In muscles, individual muscle fibers are wrapped by a delicate connective tissue known as endomysium.
2. In nerves, the axons/endoneurium are bundled into fascicles by a connective tissue known as perineurium. In muscle, the muscle fibers/endomysium are bundled into fascicles by a connective tissue known as perimysium.
3. The entire nerve is surrounded by a connective tissue sheath called the epineurium. The nerve is thus a bundle of fascicles and blood vessels. The entire muscle is surrounded by a connective tissue sheath called the epimysium. The muscle is thus a bundle of fascicles and blood vessels.
4. With spinal nerves, the epineurium fuses with the dura mater of the spinal meninges. The dura mater is composed of dense irregular connective tissue. With skeletal muscle, the epimysium extends beyond the belly of the muscle to become the tendon (composed of dense regular connective tissue). The tendon connects to the periosteum of the bone, composed of dense irregular connective tissue.
Does anyone know if these structural similarities are explained by common descent, where some structure in a simple metazoan shared this basic organization and served as both nerve and muscle? Or might this be another example of convergence?
[ 24. May 2004, 23:24: Message edited by: Mike Gene ]
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