What are the properties of muscle tissue
The muscle cells are the basic building blocks of muscles. Here we explain to you which three types there are and how they are each structured.
Muscle cells simply explained
Humans have over 650 muscles. A muscle in your arm, for example, has a different structure than the muscles in the intestine, for example.
However, all muscle tissues have one thing in common: they are made up of Muscle cells, also Myocytes called. Depending on the muscle cell, different types of muscle are formed from it. According to their structure, you differentiate between heart, skeletal and smooth muscle cells.
Muscle cells can contract (contractility), allowing our muscles to contract. In this way the muscle tissues then control Movements of the body.
Muscle cell types
Your muscle tissue is made up of one of the following three types of muscle cells:
- Skeletal muscle cells are the muscle tissue of the skeletal muscles that are important for movement.
- Heart muscle cells form the muscle layer in the heart.
- smooth muscle cells ensure unconscious muscular movements, such as the contraction of the bowel.
The muscle cells of the heart and skeletal muscles can also be called muscle fibers because of their elongated shape.
The Skeletal muscles or striated muscles consists of muscle fibers. The skeletal muscles can move our skeleton, so to speak. For this purpose, they are attached to the bones at their ends by tendons.
Structure and properties of skeletal muscles
They differ significantly from other muscle cells in their structure and properties.
- The skeletal muscle cells are elongated, cylindrical cells that can reach a length of several centimeters.
- They contain several cell nuclei because some cells are fused together as they develop.
- Because of their high energy requirements, they need many mitochondria (energy-supplying cell organelles).
- You call your cell membrane sarcolemma and your cell plasma sarcoplasm.
- A muscle fiber consists of many muscle fibrils, which in turn are made up of the so-called Sarcomeres put together. The sarcomere contains the contractile proteins actin and myosin, which enable muscle contraction.
- Horizontal stripes can be seen under the microscope. They come from the light actin filaments and the darker myosin filaments.
Function of skeletal muscles
The skeletal muscles are for all of us Body movements responsible. To do this, they have to contract (pull together). Their contraction is triggered by electrical signals from the nerve cells. In order for this to work, muscle and nerve cells are in contact with one another via special connections - the motor end plate. In this way, nerve cells can control the muscle cells.
A nerve signal leads to the release of messenger substances. They trigger another electrical signal in the membrane of the muscle cell. It is quickly passed on to the inside of the muscle cell through membrane protuberances, the T-tubules. There it leads to many Calcium ions (Calcium ions, approx2+) are released from the sarcoplasmic reticulum. This is the special endoplasmic reticulum of the muscle cells. You can think of it as a network of thin tubes (L-tubules). Free approx2+-Ions from the sarcoplasmic reticulum activate the myocyte and release one Muscle contraction out.
Once the skeletal muscle cells are injured, they can heal themselves. Special stem cells help them with this. You can also use it as a Satellite cells describe.
The Heart muscle cells (Cardiomyocytes) are the second of the muscle fiber types and represent a special form of striated muscles. As the name suggests, they form the heart muscle (myocardium).
Structure and properties of the heart muscles
The structure of the heart muscle cells is more similar to the skeletal muscle cells, but they also have the properties of smooth muscle cells.
- There are muscle cells with mostly only a corelocated in the middle of the cell. This makes them similar to smooth muscle cells.
- They are rather short and narrow (0.1 mm long).
- They contain even more Mitochondria than the skeletal muscle cells for energy production. The sarcoplasm content of the cells is very high.
- They form a network in which the cells are connected to one another by shiny strips. Communication and signal transmission between the cells takes place via so-called gap junctions (cell-cell connection).
Two types of heart muscles can be distinguished:
- Working muscles: Heart muscle cells that are responsible for the contraction of the heart.
- Excitation conduction fibers: Heart muscle cells that are responsible for building up and transmitting impulses (Purkinje fibers).
Function of the heart muscles
The heart muscle cells ensure that our heart beats continuously in a regular rhythm. We don't have to consciously control them either, our heart beats without us thinking about it.
This means that they have to transmit the electrical excitation generated by the pacemaker cells in the heart quickly and in a coordinated manner. In order to pass the signals directly from cell to cell, their membranes are in direct contact. The membranes are glued together, so to speak, through the glossy strips. By contracting the heart muscle cells at the same time, the heart muscle generates enough force to pump blood around the body and supply the cells with sufficient oxygen.
The smooth muscle cells can be found mainly in the internal organs. In contrast to the other two muscle cell types, they do not show any transverse stripes under the microscope.
Structure and properties of smooth muscles
- The smooth muscle cell is one spindle-shaped Cell. With a maximum size of 600 µM, it is the smallest type of muscle cell.
- They only contain a nucleuslocated in the middle of the cell.
- Due to a different arrangement of their myofibrils, their structure does not appear streaked under the microscope, but rather smooth.
- They are arranged in layers on top of each other so that they can contract at the same time.
Smooth muscle function
The smooth muscles are also called involuntary Known muscles. This is because they move independently without our conscious control. Their contraction is regulated by the autonomic nervous system.
With us humans they are mainly in the Walls of hollow organs such as blood vessels, lungs, uterus, or bladder. But they also occur in our eyes. Without them, we would not be able to change our lens shape and thus not focus objects sharply. In the intestine, the smooth muscles use contractions to ensure that the food is moved in a targeted manner.
So that the cells all contract one after the other as a result of an electrical signal, they are also connected to one another via gap junctions like the heart muscle cells. As a result, the smooth muscles tense more slowly, but more strongly than the striated muscles.
Energy supply muscle
Because the muscle cells are constantly contracting, they need a lot of energy. But how does the muscle cell generate energy?
The muscles get the energy they need from the breakdown of adenosine triphosphate:
Adenosine triphosphate (ATP) → adenosine diphosphate (ADP) + phosphate (P)
In order to gain new, high-energy ATP, the cells use the molecule Creatine phosphate. This allows them to transfer a new phosphate group to adenosine diphosphate (ADP). Only a short time later, additional energy is obtained from the breakdown of grape sugar (glucose).
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