Voluntary Muscles vs. Involuntary Muscles

The difference between voluntary and involuntary muscles is that voluntary muscles are under the conscious control of one’s own will while involuntary muscles are not under the control of one’s own will.

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Voluntary Muscles vs. Involuntary Muscles

In the human body, there are three types of muscles. Skeletal muscles, smooth muscles and cardiac muscles. Skeletal muscles can be controlled according to the desire of the person so they are called voluntary muscles while smooth muscles and cardiac muscles cannot be controlled by one’s desire, so they are called involuntary muscles. Skeletal muscles are found in the form of bundles of muscle fibers, and they are long, unbranched and cylindrical muscles while smooth muscles are tapered at the end, so they are spindle-shaped and small. Voluntary muscles have multinucleate cells, and the nucleus is present at the rim. While involuntary muscles have cells which have a single nucleus which is located in the center.

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Sarcolemma (outer membrane) of voluntary muscles is thick while that of involuntary muscles is thin. Contractions of skeletal muscles are strong and rapid while those of involuntary muscles are rhythmic and slow. Since contractions of skeletal muscles are strong, so they need high energy. Contractions of smooth muscles are slow, so their energy demand is low.

Voluntary muscles are tired early and easily because of their higher metabolic rate while smooth muscles are not fatigued so easily even after a longer duration of work. Voluntary muscles need rest after some intervals while involuntary muscles do not demand rest even our heart which is composed of cardiac muscles, work throughout the life 24 hours a day without the rest of even a few seconds. Voluntary muscles make the bulk of the body flash of any animal or human being. They contain 40% of the body mass while smooth muscles are present in the hollow organs like the gastrointestinal tract and urinary tract etc.

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Skeletal muscles (skeletal muscles) are attached to the bones and skin by specialized structures called tendons. Thus they contract and relax against the movement of bones while smooth muscles (Involuntary muscles) are not attached to bones or skin and have nothing to do with the movement of bones. Skeletal muscles have one origin and one insertion, i.e. two points of attachments while smooth muscles have no origin and insertion.

Voluntary muscles are under the control of the somatosensory nervous system while involuntary muscles are under the control of the autonomic nervous system.

Voluntary muscles join at a Z disk while involuntary muscles join by an intercalated disc. Troponin is present in all voluntary muscles while present in some of the involuntary muscles, I.e. heart muscles.

Comparison Chart

BasisVoluntary MusclesInvoluntary Muscles
Other namesAlso known as striated muscles, striated muscles or skeletal muscles.Also known as visceral muscles, plain muscles, unstriped muscles or non-striated muscles.
Part in bodyThey form the bulk of body flash.They are present only in the hollow organs.
Ends of muscles They have one origin and one insertion.They do not have origins and insertions.
Attachment with bonesThey are attached with bones via tendons. They are not attached to bones.
Attachment with other muscles They are attached by Z disk.They are attached by intercalated disk.
Structure They are unbranched, long and cylindrical muscles.They are small and tapered at the ends.
NucleusThey have many nuclei.They have a single nucleus.
Location of nucleusTheir nuclei are present at the periphery.Their nucleus is present in the centre.
ContractionsTheir contractions are strong and rapid.Their contractions are rhythmical and slow.
Energy requirementThey need a high amount of energy.They need less energy.
Tiredness They are tired early.They are not tired early.
Controlled byThey are controlled by the somatosensory nervous system.They are controlled by the autonomic nervous system.

What are Voluntary Muscles?

Voluntary muscles are those muscles which are under the control of our will. They contract and relax under a conscious level.  Somatosensory nervous system control t them. Skeletal muscles are the voluntary muscles in our body. They are attached with bones via specialized connective tissues called tendons and contract and relax against the movements of the skeleton. The contractile unit of voluntary or skeletal muscles is called a sarcomere. When a muscle is required to contract, its contractile unit, i.e. sarcomere shortens and contractions occur. When sarcomere lengthens, relaxation of the muscle occurs. The sarcomere is composed of three types of proteins. Actin, tropomyosin and troponin. These proteins are arranged in a special way and form the sarcomere. Sliding movements of filaments of these proteins result in the contraction of the skeletal muscles. It is known as the sliding filament theory of skeletal muscle contraction. One sarcomere is attached with the other sarcomere via Z disc. Skeletal muscles work in pair forms mostly. This paired action is antagonistic which occurs at

  • Extensors and flexors. Extensor muscles extend the limb while flexor muscles flex the limb.
  • Abductors and adductors. Abductor’s muscles move the limb away from the body, and adductor muscles move the limb towards the body.
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Structure of the Voluntary Muscles

Voluntary muscles are a thread like long and cylindrical muscles. Their size range from 1mm to 30cm. Their cells are covered by sarcolemma which is a transparent membrane consisting of two layers, plasma membrane and basement membrane. Their sarcoplasm resembles cytoplasm. Their nuclei are oval shaped and present below sarcolemma.

Examples of voluntary muscles.

Biceps and triceps in the upper limb, quadriceps and hamstrings in the lower limbs and pectoralis muscles are examples of voluntary muscles.

What are Involuntary Muscles?

The muscles which are not under the control of our will are called involuntary muscles. The autonomic nervous system controls them. The muscles contract and relax even we do not know about their contraction. Types of involuntary muscles are smooth muscles and cardiac muscles.  Smooth muscles are found in the hollow organs, and cardiac muscles are found in the heart. Cardiac muscles are branched and join at intercalated discs. The myofibrils of smooth muscles are not arranged in a symmetrical way rather they are dispersed. They also have actin and myosin, but these proteins are not arranged in sarcomeres. Smooth muscles contract slowly and fatigue slowly. While cardiac muscles contract strongly throughout life without relaxing for a few seconds. Cardiac muscles do not need nerve stimulus for their function.

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Sarcolemma of smooth muscles is thin. Their cells have a single round nucleus which is present centrally. Smooth muscles do not have striations.

Examples of Involuntary Muscles.

Examples of involuntary muscles include the cardiac muscles of the heart and smooth muscles found in hollow viscera like smooth muscles of stomach, oesophagus, urinary bladder, pharynx, ureter, uterus and blood vessels. In the gastrointestinal tract, they push the food by peristalsis, in the uterus, they cause the contraction of uterus to expel the fetus during labor and in the walls of blood vessels and ureter, they maintain the lumen of the vessels and ureter.

Key Differences between Voluntary Muscles and Involuntary Muscles

  1. Voluntary muscles are the type of muscles which are under conscious control. They are controlled by the will of the person while involuntary muscles cannot be controlled by conscious level. They cannot be controlled willingly.
  2. Voluntary muscles have one origin and one insertion while involuntary muscles do not have origin and insertion.
  3. Voluntary muscles are controlled by the somatosensory system while involuntary muscles are controlled by the autonomic nervous system.
  4. Voluntary muscles have many peripheral nuclei while involuntary muscles have one central nucleus.
  5. Voluntary muscles have strong contractions and thus have a high energy requirement while involuntary muscles have slow contractions and have low energy demand.

Conclusion

Voluntary and involuntary muscles are the types of muscles found in the bodies of humans and animals. The internal and external functions of the body, i.e. locomotion, movement of limbs, eating and digestion of food, respiration, urination, circulation and childbirth are due to the functions of these muscles, so the difference between them must be known.

Video Explanation

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