Some muscle movement is voluntary, which means it is under conscious control. For example, a person decides to open a book and read a chapter on anatomy. Other movements are involuntary, meaning they are not under conscious control, such as the contraction of your pupil in bright light. Muscle tissue is classified into three types according to structure and function: skeletal, cardiac, and smooth Table 1. Skeletal muscle is attached to bones and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body.
Forty percent of your body mass is made up of skeletal muscle. Skeletal muscles generate heat as a byproduct of their contraction and thus participate in thermal homeostasis. Shivering is an involuntary contraction of skeletal muscles in response to perceived lower than normal body temperature.
The muscle cell, or myocyte , develops from myoblasts derived from the mesoderm. Myocytes and their numbers remain relatively constant throughout life. Cardiac muscle cells are organized in a parallel fashion and are connected via intercalated discs.
These intercalated discs or glossy stripes are organized in a Z-shaped or stair-step pattern. Interestingly, cardiac muscles have some elements similar to skeletal muscles, e. Being myogenic, cardiac muscles differ from skeletal and smooth muscles, and stimulus for contraction is generated within the cardiac muscles.
Electrical stimulation generates the action potential in the cardiac muscles for the contraction. As a result of the action potential generation, calcium ions are released into the sarcoplasm reticulum.
Elevated levels of calcium ion result in excitation and contraction of the cardiac muscles. Vagal and sympathetic nerves innervate the cardiac muscles and control them. Smooth muscles are the nonstriated involuntary muscles that line the viscera or the internal hollow organs like, urinary tract, blood vessels, and intestinal tract.
The ciliary muscle present in the eye is an example of smooth muscle. Ciliary muscles dilate and regulate the movement of the iris. Structurally, smooth muscles are fusiform in shape, i. Smooth muscles are made up of thick and thin filaments that are not arranged into sarcomeres resulting in a nonstriated pattern. Microscopically they appear to be homogenous and hence, named smooth muscles.
The cytoplasm of the smooth muscles contains actin and myosin in large amounts. Smooth muscles also have calcium-containing sarcoplasmic reticulum. This calcium-containing sarcoplasmic reticulum is responsible for prolonged contraction. Smooth muscles can be single-unit or multi-unit muscles. Single unit smooth muscles contract and relax as a single unit i. The contractions in the digestive tract are an example of the slow and steady involuntary contractions in the single-unit smooth muscles.
Vesicles of a nerve fiber or buttons surround the smooth muscle fibers and carry neurotransmitters. Smooth muscles have a greater elastic property in comparison to striated muscles. The elasticity of smooth muscles is a critical property as it helps to maintain contractile tone in organs like the urinary bladder. Due to the absence of the sarcomeres, the organization and stretchability of the smooth muscles are not limited.
Instead, smooth muscles exhibit a stress-relaxation response wherein the muscles of a hollow organ are stretched when the organ fills up. This mechanical stress due to the stretching of the organ triggers the contraction. However, muscle relaxation immediately after contraction ensures that the organ does not empty its content prematurely. This phenomenon is significant for the urinary bladder, wherein the smooth muscle tone ensures the efficient functioning of the excretory system.
Do you have a question on smooth muscle tissues? Ask our community. Skeletal muscles are under our conscious control, which is why they are also known as voluntary muscles. Another term is striated muscles, since the tissue looks striped when viewed under a microscope. Smooth muscle — located in various internal structures including the digestive tract, uterus and blood vessels such as arteries.
Smooth muscle is arranged in layered sheets that contract in waves along the length of the structure. Another common term is involuntary muscle, since the motion of smooth muscle happens without our conscious awareness. Cardiac muscle — the muscle specific to the heart.
The heart contracts and relaxes without our conscious awareness. Make-up of muscle Skeletal, smooth and cardiac muscle have very different functions, but they share the same basic composition.
A muscle is made up of thousands of elastic fibres bundled tightly together. Each bundle is wrapped in a thin transparent membrane called a perimysium.
An individual muscle fibre is made up of blocks of proteins called myofibrils, which contain a specialised protein myoglobin and molecules to provide the oxygen and energy required for muscle contraction. Each myofibril contains filaments that fold together when given the signal to contract. This shortens the length of the muscle fibre which, in turn, shortens the entire muscle if enough fibres are stimulated at the same time. The neuromuscular system The brain, nerves and skeletal muscles work together to cause movement.
This is collectively known as the neuromuscular system. A typical muscle is serviced by anywhere between 50 and or more branches of specialised nerve cells called motor neurones. These plug directly into the skeletal muscle. Organization at the Tissue Level.
Search for:. Muscular Tissue. Characteristics of Muscle Tissue The three types of muscle tissue are skeletal, smooth, and cardiac. Learning Objectives Describe the types of muscle tissue. Key Takeaways Key Points Muscle tissue can be divided functionally, is it under voluntary or involuntary control; and morphologically, striated or non-striated.
By applying these classifications three muscle types can be described; skeletal, cardiac and smooth. Skeletal muscle is voluntary and striated, cardiac muscle is involuntary and straited and smooth muscle is involuntary and non-striated.
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