Sophie Bennett
The muscular system in chickens, as in other animals, provides the power for movement and physical activity. This includes the mobility of the skeleton and its appendages, as well as the movement of materials through organs and the pumping of blood through the circulatory system. There are three types of muscles in the chicken body: involuntary muscles found in the walls of tubular structures like the alimentary canal; cardiac muscle of the heart; and skeletal muscles that exhibit a striped effect due to bands across the myofibril. Two organs that are part of the chicken muscular system are the gizzard and the crop. The gizzard is a muscular stomach that grinds food with the help of small stones or grit, while the crop is a muscular bag at the bottom of the chicken's neck that stores food before it passes into the gizzard.
| Characteristics | Values |
|---|---|
| Purpose | Provides mechanical activity for the chicken in the form of mobility of the different parts of the skeleton or its appendages |
| Provides movement of materials along tubular organs such as the alimentary canal, air passages and blood vessels | |
| Provides the power for the chicken | |
| Types of muscle | Involuntary muscles found in the walls of the alimentary canal, blood vessels, air passages and other tubular structures |
| Cardiac muscle of the heart | |
| Muscle contraction | Occurs as a result of a stimulus usually originating from the nervous system either on a voluntary or involuntary basis |
| Occurs when myofibril segments shorten as a result of the actin filament caps sliding along the myosin filaments | |
| Muscle fibres | White fibres lack a compound called myoglobin, but store more glycogen and have a fast contraction of short duration |
| Red fibres | |
| Organs | Gizzard |
| Crop |
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What You'll Learn
- Skeletal muscle gives chickens their shape and enables voluntary movement
- Smooth muscle is found in the blood vessels, gizzard, intestines, and other organs
- Cardiac muscle is the muscle of the heart
- The muscular system powers the chicken's vocal cords
- Male chickens have internal reproductive organs, unlike mammals
Skeletal muscle gives chickens their shape and enables voluntary movement
The muscular system of a chicken is responsible for about three-quarters of its body weight. There are three types of muscles in a chicken: smooth, cardiac, and skeletal. Smooth muscles are controlled by the autonomic nervous system (ANS) and are found in the blood vessels, gizzard, intestines, and organs. Cardiac muscles, on the other hand, are specialized muscles of the heart.
Skeletal muscles, the focus of this discussion, are responsible for giving chickens their shape and enabling their voluntary movements. These muscles are attached to bones by tendons, which are tough, fibrous tissues. Interestingly, skeletal muscles only pull and never push, and they work in pairs. When a skeletal muscle contracts, it creates a pulling action, and its opposing muscle then relaxes. For example, when a chicken's wing moves down, the powerful pectoral or breast muscle contracts, providing the necessary pull. The supracoracoideus muscle then relaxes, allowing the wing to move back up. This is similar to the movement in a human arm, where the bicep contracts and the tricep relaxes during a bend.
The muscular system of chickens is essential for their overall motion and various systems, including the digestive system. Chickens use their leg muscles for sustained activities such as walking and running, resulting in darker meat in those areas due to increased oxygen demand and the presence of myoglobin. In contrast, the breast muscles of chickens are less frequently used, especially in commercial breeds that are too heavy to fly. This results in white meat, which is often preferred by consumers as it is considered healthier with higher protein and lower fat content.
Understanding the anatomy and physiology of chickens, including their muscular system, is crucial for recognizing and addressing any issues that may arise. It also helps in meeting their nutritional requirements and ensuring their overall health and well-being.
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Smooth muscle is found in the blood vessels, gizzard, intestines, and other organs
A chicken's muscle system is made up of three types of muscles: smooth muscles, cardiac muscles, and skeletal muscles. Smooth muscles are involuntary muscles and are found in the blood vessels, gizzard, intestines, and other organs.
Smooth Muscle in the Blood Vessels
Smooth muscle is found in the blood vessels of chickens. These muscles are involuntary, meaning they are beyond the control of the will. They are also found in the walls of the alimentary canal, air passages, and other tubular structures.
Smooth Muscle in the Gizzard
The gizzard is a part of the chicken's digestive system, and it contains smooth muscle. The gizzard has a novel type of cell at the interface of muscle and tendon, filled with intermediate filaments and some rough endoplasmic reticulum. It also contains a high concentration of myoglobin, a protein that gives muscle a red colour and provides continuous energy for contraction.
Smooth Muscle in the Intestines
Smooth muscle is also found in the intestines of chickens. The structure of the musculature of the chicken small intestine has been studied using immunofluorescence microscopy.
Smooth Muscle in Other Organs
While it is not clear which other specific organs contain smooth muscle, it is known that the muscular system comprises approximately three-quarters of a chicken's body weight. The skeletal muscles, which form the shape of the chicken, are the muscles that are eaten, and the breast meat of a chicken is referred to as white meat because the breast muscles are used less frequently.
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Cardiac muscle is the muscle of the heart
The chicken muscular system consists of skeletal muscle, smooth muscle, and cardiac muscle. Cardiac muscle, also called the myocardium, is one of the three major categories of muscles found within the body, with the other two being smooth muscle and skeletal muscle.
Cardiac muscle is the specialised muscle of the heart. It is an involuntary, striated muscle that constitutes the main tissue of the heart wall. The heart is made up of three layers—the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells that form the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium.
The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium), with blood supplied via the coronary circulation. It is composed of individual cardiac muscle cells or cardiomyocytes joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. The intercalated discs consist of three different types of cell-to-cell junctions: the actin filament anchoring fascia adherens junctions, the intermediate filament anchoring desmosomes, and gap junctions. These junctions allow action potentials to spread between cardiac cells by permitting the passage of ions between cells, producing depolarization of the heart muscle.
Cardiac muscle cells are striated, branched, and contain many mitochondria. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma contains voltage-gated calcium channels, specialized ion channels that skeletal muscle does not possess. Cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
The primary function of cardiomyocytes is to contract, which generates the pressure needed to pump blood through the circulatory system. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
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The muscular system powers the chicken's vocal cords
The muscular system of a chicken is comprised of about 175 different muscles, which make up about 75% of the bird's weight. These muscles are responsible for all of the chicken's movements, from the flapping of its wings to the internal contractions of its intestines. The chicken's musculature is also what powers its vocal cords, allowing it to make sounds such as clucks and crows.
Unlike mammals, birds produce sound through a structure called the syrinx, which is located at the base of the trachea where it forks into the lungs. The syrinx produces sound through the vibration of its membranes and the bronchial openings, which is caused by airflow passing through it. This sets up a self-oscillating system that modulates the airflow to create sound. The syrinx enables some bird species, such as parrots, crows, and mynas, to mimic human speech.
The syrinx is a unique feature of bird anatomy, having evolved from the larynx-based sound source of their dinosaur ancestors. While birds do still have a larynx, it does not produce sound. The syrinx's position, structure, and musculature vary widely across different bird groups, with some species lacking a syrinx altogether and communicating through throaty hisses.
In chickens, the syrinx is powered by the muscles of the respiratory system, which contract and relax to allow for respiration and sound production. These muscles work in pairs, with one muscle contracting and the other relaxing to create movement. For example, when a chicken flaps its wing, the pectoral or breast muscle contracts to pull the wing down, while the supracoracoideus muscle relaxes, and then contracts to raise the wing back up.
Thus, the muscular system of the chicken is essential not only for its physical movements but also for its vocalizations. The interaction of the syrinx and the respiratory muscles allows chickens to communicate with each other and with other species, showcasing the fascinating evolution of bird anatomy.
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Male chickens have internal reproductive organs, unlike mammals
The muscular system in chickens consists of smooth muscle, cardiac muscle, and skeletal muscle. Smooth muscle is controlled by the autonomic nervous system and is found in the blood vessels, gizzard, intestines, and organs. Cardiac muscle is the specialised muscle of the heart, while skeletal muscle is responsible for the shape of the chicken and its voluntary movement.
Male chickens, or roosters, have internal reproductive organs, which is unlike mammals. All male birds' reproductive organs are located inside the body cavity, whereas male mammals have external reproductive organs. The male chicken's reproductive system consists of two testes, each with a deferent duct that leads to the cloaca. The testes are bean-shaped and located against the backbone, in front of the kidney. They can change size, becoming larger when the bird is actively mating, and the left testis is often larger than the right. Inside each testis is a small, flattened area believed to correspond to the epididymis in mammals, where the deferent duct begins. The deferent duct transports sperm from the testes to the cloaca, from which they enter the female's oviduct during mating. This duct enters a small pimple-like structure in the cloaca, equivalent to the penis in mammals.
The female chicken's reproductive system, on the other hand, consists of the ovary and the oviduct. Unlike most female animals, the chicken usually has only one functioning ovary, the left one, while the right ovary stops developing after hatching. The ovary is attached to the abdominal cavity wall and contains thousands of tiny ova or yolks. As the chicken matures, these yolks develop and are released from the ovary, entering the infundibulum, the entrance of the oviduct. The rest of the egg is formed around the yolk as it passes through the oviduct, and the complete cycle takes a little over 24 hours.
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