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Difference between Voluntary and Involuntary muscles, Practice Problems and FAQs

We perform lots of movements everyday in our life. These movements are broadly classified into two categories such as movements that are under our control and the movements that are not under our control. The movements that are under our control occur with our will and are called voluntary actions. Examples include walking, running, sitting and many more. On the other hand, the movements that are not under our control are called involuntary movements. Examples include breathing, blinking of eyes, beating of heart, peristalsis and many more.

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GIF: Voluntary and involuntary movements

Do you know why these movements are different? Yes, this is because the movements that are under our control are initiated by voluntary muscles and the movements that are not under our control are initiated by involuntary muscles. The voluntary and involuntary muscles are present in different parts of our body. So, let’s understand the difference between these two types of muscles in this article.

Table of contents

Muscles

Muscle is described as a specialised tissue that is formed from the mesoderm. The muscles contribute about 40 - 50% of the adult human weight. They have special properties like excitability, contractibility, extensibility and elasticity. Myocytes are the cells that make up muscles. These are highly specialised thin and elongated cells. With the help of these cells, the muscles can contract. It has the ability to go shorter and then go back to the normal length. Myocytes shrink upto 1/3 to 1/2 of their original length during contractions. The contraction stimulation is transmitted to nearby cells. There are 320 pairs of muscles in an adult human.

Fig: Muscle contraction

Types of muscles

The muscles are divided into two types based on the method of control. They are as follows:

  • Voluntary muscles
  • Involuntary muscles

Voluntary muscles

The muscles we can control with our will are referred to as voluntary muscles. The common example of voluntary muscle is skeletal muscle. Skeletal muscle is described as a striated muscle that is seen attached to the bone. Each muscle fibre is elongated and multinucleated. It is unbranched and cylindrical. Its membrane is called sarcolemma and the cytoplasm is called sarcoplasm. The somatic nervous system is responsible for controlling these voluntary muscles.

Fig: Skeletal muscle tissue

Involuntary muscles

Involuntary muscles are those types of muscles that cannot be controlled by our will. The common examples of involuntary muscles are smooth muscles and cardiac muscles.

Smooth muscles

These are non-striated muscles because they do not have striations. Smooth muscles are made up of long, narrow and spindle shaped fibres that are generally shorter than the striated muscle fibres. These are uninucleate and sarcolemma is absent. These types of muscles are present in hollow organs such as the stomach, intestines, blood vessels, urinary bladder and uterus.

Fig: Smooth muscle tissue

Cardiac muscles

Cardiac muscle is another type of involuntary muscle that is striated. This type of muscle is present in the wall of the heart and enclosed in collagen fibres. It consists of short, cylindrical, fibres which are joined end to end and are interconnected by oblique bridges. At the end of the fibres are specialised regions of cell membrane forming dense zigzag junctions called intercalated discs. Cardiac muscle continuously contracts without getting tired.

Fig: Cardiac muscle tissues

Difference between voluntary and involuntary muscles

The following are the major differences between the voluntary and involuntary muscles:

Voluntary muscles

Involuntary muscles

These muscles possess cylindrical, long and unbranched muscle fibres

Fig: Skeletal muscle tissue

These muscles possess small spindle-shaped muscle fibres

Fig: Smooth muscle tissue

The muscle fibres are multinucleated

Fig: Multinucleated

The muscle fibres are uni-nucleated

Fig: Smooth muscle tissue

These muscles are attached to bones

GIF: Muscles attached to bone

These muscles are present in the walls of the internal organs like heart, blood vessels, intestines etc

Fig: Muscles on organs

They require high energy to work

They require comparatively low energy to work

The nucleus of voluntary muscles is present at the periphery

Fig: Nucleus at periphery

The nucleus of involuntary muscles is present at the centre

Fig: Smooth muscle tissue

These muscles are regulated by the somatic nervous system

These muscles are regulated by the autonomic nervous system

Their contractions are rapid and powerful

GIF: Powerful contractions

Their contractions are slow and rhythmic

GIF: Contractions

The voluntary muscles are involved in the movement of body parts and locomotion of the body

GIF: Movement of the body

The involuntary muscles are involved in the internal movements of the organs and they also help in the movement of fluids and food in the digestive system

GIF: Movement of food

The examples of voluntary muscles include diaphragm, abdominal wall, pharynx, muscles of middle ear and the muscles present under the skin

Fig: Location

The examples of involuntary muscles include blood vessels, alimentary tract, urogenital tract, respiratory tract and many more

Fig: Location

Practice Problems

  1. Identify the location of voluntary muscles.
  1. Alimentary canal
  2. Iris of the eye
  3. Kidneys
  4. Limbs

Solution: The muscles we can control with our will are referred to as voluntary muscles. The common example of voluntary muscle is skeletal muscle. These muscles are present in our limbs because the movement can be done as per our will. Hence, the correct option is d.

Fig: Skeletal muscles on limbs

2. Which of the following voluntary muscles are striated?

  1. Skeletal
  2. Smooth
  3. Cardiac
  4. Skeletal and Cardiac

Solution: Skeletal muscles are voluntary as well as striated. These muscles appear striated due to the presence of the alternate light and dark bands when viewed under the microscope. The muscles we can control with our will are referred to as voluntary muscles. The common example of voluntary muscle is skeletal muscle. Skeletal muscle is seen attached to the bone. Each muscle fibre is elongated and multinucleated here. It is unbranched and cylindrical. Its membrane is called sarcolemma and the cytoplasm is called sarcoplasm. The somatic nervous system is responsible for controlling these voluntary muscles. Hence, the correct option is a.

3. Involuntary muscles that have characteristic striations ____________________.

  1. are present in the wall of the alimentary canal
  2. are present in the muscles of the heart
  3. help in locomotion
  4. are present in limbs

Solution: The heart's muscles are comprised of involuntary muscles with distinctive striations. They are referred to as cardiac muscles. It consists of short, cylindrical, fibres which are joined end to end and are interconnected by oblique bridges. At the end of the fibres are specialised regions of cell membrane forming dense zigzag junctions called intercalated discs. On the other hand, muscles present in the wall of the alimentary canal are smooth muscles. These are non-striated and involuntary muscles. Moreover, the muscles that help in locomotion are skeletal muscles and these are striated and voluntary and found in limbs. Hence, the correct option is b.

Fig: Cardiac muscle tissues

4. Why are involuntary muscles called smooth muscles?

Answer: Any muscle that moves involuntarily that means the movements cannot by our will is referred to as involuntary muscles. As these lack striations when viewed under a microscope, these are also known as smooth muscles or non-striated muscles. Internal organs, blood arteries, and organs like those in the digestive and reproductive systems are lined by these muscles.

FAQs

  1. Which part of the brain controls muscles?

Answer: The cerebellum located at the back of the brain controls muscles. This is because it regulates balance, movement and coordination.

Fig: Cerebellum

  1. Is the tongue a muscle?

Answer: The tongue is described as an extremely movable set of muscles. It includes hyoglossus muscle, genioglossus muscle, styloglossus muscle and palatoglossus muscle. It is supplied with blood and nerves. The tongue muscles are oblong-shaped and are supplied with dense connective tissue.

Fig: Tongue

  1. Name the smallest skeletal muscle present in the human body?

Answer: Stapedius muscle is the smallest skeletal muscle present in the human body. It is one of the intratympanic muscles that help in the regulation of sound.

  1. Which muscles help in closing the eyes?

Answer: The orbicularis oculi muscles help in closing the eyes. It is present under the skin and aids in opening and closing the eyelids. It is one of the important muscles in facial expression.

Fig: Orbicularis oculi muscles

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