Cardiac Muscle Structure

If you are intrigued about the cardiac muscle structure, you are on the right page. Keep reading to know about cardiac muscle structure and functions.

Cardiac muscles are special muscles devoted to cardiac functioning. The human heart is a special organ and unique in its functioning. The heart functioning is largely made possible by the cardiac muscle structure and functioning. This article will talk about cardiac muscle structure, which will enable us to know how the heart is able to maintain its incessant beating throughout a person's life.

Muscle - A Special Tissue

Before we get into describing the cardiac muscle structure, let us see what do we mean by a 'muscle' and what makes them different from other tissues of the body. This will also clear up some basics which will help you in understanding the structure of cardiac muscles. Muscles are the only cell tissues that can contract and expand. This facility for elongation and contraction is enabled by filamentous nature of this tissue. By functionality, muscles are of three types: skeletal muscles, smooth muscles and cardiac muscles. Skeletal muscles are voluntary muscles. That is, their action is governed by your own conscious will. Whereas smooth muscles and cardiac muscles are involuntary muscles. They keep functioning without the force of will as they control all functioning of all the vital internal organs, including the heart.

Structure of Cardiac Muscle

Cardiac muscles are striated muscles which make the heart walls and they collectively constitute the myocardium. Though cardiac muscles are involuntary, they resemble skeletal muscles in a lot of respects. Both are similar with regards to appearance, striations and contraction properties.

One distinctive feature of the striated cardiac muscles is that they are branched, unlike skeletal muscles, which tend to be linear. They have alternate thick (Myosin) and thin (Actin) protein filaments. These are sliding filaments. Actin and Myosin are the two primary proteins that build the cardiac muscle fibers which are called myofibrils. The sub-units of myofibrils are called sarcomeres. Each sarcomere is made up of A bands and I bands. The A bands are subdivided by the M line and the H-zone, while I band is sub divided by the z-discs. The myofibril branches are connected by adherens junctions which help the heart in contracting forcefully.

The 'T-tubules' are another feature of the cardiac muscles which are comparatively more broader than those of skeletal muscles. These structures run along the Z-discs of cardiac muscles. The T-tubules play an important role in excitation contraction coupling which drives the heart.

Another feature that you see, when you observe a cardiac muscle, under an electron microscope are the intercalcated disks. They are dark thin lines that divide cardiac muscle cells and they are perpendicular to the direction of the individual muscle fibers. The intercalcated disks enable the transmission of muscle contraction signals. It is because of the intercalcated disks that action potentials spread fast and the myocardium contracts in harmony.

The cardiac muscles, unlike skeletal muscles, cannot rest even for a moment. They must work continuously. That is why, they have an abundant number of mitochondrias which are power generation centers of cells. The abundant number of mitochondrias enable constant aerobic respiration which supplies energy to these muscles continuously. That prevents these muscles from getting fatigued and ensure a lifetime of service!

The whole cardiac muscle structure is built in such a way that it can easily contract and expand with the action potential signal spreading through it periodically. The action potential signal is transmitted through every fiber of cardiac muscle structure through gap junctions. It takes a greater amount of time for the cardiac muscle structure to expand than it takes for it to contract.

The cardiac muscle structure has a very marginal store of glycogen which is the raw material for energy production in anaerobic conditions. So in case of a heart attack, when the heart muscles fall short of oxygen, they simply die.

Read More on 'Cardiac Muscle Function'.

The mechanism that triggers the contraction of your heart is an electric action potential that originates in the heart itself. The whole process is triggered by a neurotransmitter called acetylcholine. Hope this article has given you a rough idea of what the cardiac muscle structure is like.