The key difference between endomysium and sarcolemma is that endomysium is a layer of connective tissue that surrounds a muscle cell while sarcolemma is the plasma membrane of a muscle cell.
Muscle tissue is one of the four main types of tissues present in our body. The muscle cell is the structural unit of muscle tissue. The cytoplasm of the muscle cell is known as the sarcoplasm, and the plasma membrane is known as the sarcolemma. A thin layer of connective tissue called endomysium surrounds a muscle cell. Therefore, endomysium lies adjacent to the sarcolemma.
CONTENTS
1. Overview and Key Difference
2. What is Endomysium
3. What is Sarcolemma
4. Similarities Between Endomysium and Sarcolemma
5. Side by Side Comparison – Endomysium vs Sarcolemma in Tabular Form
6. Summary
What is Endomysium?
Endomysium is a layer of connective tissue which surrounds individual muscle cells. Thus, endomysium is adjacent to the sarcolemma of the muscle cell. We can see endomysium in between each individual muscle cell. Endomysium contains capillaries and nerves. Collagen is the main protein in endomysium.
Figure 01: Endomysium
Functionally, endomysium aids in providing an appropriate chemical environment for the exchange of calcium, sodium, and potassium, which are essential for the excitation and subsequent contraction of a muscle fibre. Furthermore, endomysium interacts with epimysium and perimysium and creates the collagen fibres of tendons, which provide the tissue connection between muscles and bones.
What is Sarcolemma?
Sarcolemma is the plasma membrane of the muscle cell. It is composed of a phospholipid bilayer comprising of hydrophilic heads and hydrophobic tails. The sarcolemma also contains an outer polysaccharide layer known as the glycocalyx. The sarcolemma forms the dynamic outer membrane and is the boundary to the muscle cell contents. The muscle cell contents are embedded in the sarcoplasm.
The muscle cell plasma membrane (sarcolemma) has specialized structures known as transverse tubules. Transverse tubules are invaginations of the sarcolemma. These membranous invaginations extend longitudinally into the cytoplasm of the muscle cell. The transverse tubules are also referred to as T tubules. The terminal cisternae are formed on either side of the t tubules. When the t tubule is surrounded by two cisterns, it is referred to as a triad.
Figure 02: Sarcolemma
The main function of the sarcolemma, in terms of muscle contraction, is to facilitate the permeability of Calcium ions required for the contraction process. Calcium ions are transported across the sarcolemma via ion channels and are transported into the cytoplasm of the muscle cell (sarcoplasm) via the transverse tubules. And, this will initiate the muscle action potential to bring about muscle contraction. Sarcolemma also contains various signal receiving receptors, which are required in controlling the muscle cell activities.
What are the Similarities Between Endomysium and Sarcolemma?
- Endomysium and sarcolemma are found in muscle tissue.
- Both sarcolemma and endomysium surround individual muscle cells.
- They lay next to each other. In fact, endomysium surrounds sarcolemma.
What is the Difference Between Endomysium and Sarcolemma?
Endomysium is a thin layer of connective tissue that surrounds individual muscle cells, while sarcolemma is a plasma membrane of each muscle cell. So, this is the key difference between endomysium and sarcolemma. Moreover, sarcolemma is a phospholipid bilayer, while endomysium is a connective tissue.
Below infographic tabulates the difference between endomysium and sarcolemma.
Summary – Endomysium vs Sarcolemma
Muscle cells are the structural and functional units of muscle cells. Each muscle cell is surrounded by a thin layer of connective tissue called endomysium. The plasma membrane of each muscle cell is called sarcolemma. Endomysium surrounds the sarcolemma of each muscle cell. Thus, this is the difference between endomysium and sarcolemma.
Reference:
1. “Endomysium.” Wikipedia, Wikimedia Foundation, 18 Aug. 2019, Available here.
2. “Sarcolemma.” Sarcolemma – an Overview | ScienceDirect Topics, Available here.
Image Courtesy:
1. “Illu muscle structure” (Public Domain) via Commons Wikimedia
2. “Blausen 0801 SkeletalMuscle” By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia