Question

Name the type of muscle fibres that has automatic rhythmicity.

Answer 1

Hint:-Muscle is a specialised tissue originated from the germ layer, mesoderm. The muscular tissue is made up of specialised cells called myocytes. It brings about different types of movements in internal and external body parts. A human body is made up of 639 muscles which have unique properties like contractibility, excitability, elasticity and extensibility.

Complete answer:Muscles can be classified on various criteria namely location appearance, nature of regulation of their activities Based upon location, the muscles can be of following types:
Skeletal muscle or striped or striated or voluntary muscles: These muscles are attached to the skeleton component of the body and are primarily involved in the locomotory actions and changes of the body posture.
When they are seen under a microscope, alternate light and dark bands are observed on the muscle fibres. Due to the striated appearance of the muscle fibres, these muscles are called striated or striped muscles as the name given
These muscles are voluntary as they can be controlled by the will of animals, that is when we want to move them we can move. For example, muscles of hind limbs, forelimbs, body wall, tongue, pharynx and beginning of oesophagus etc.

Skeletal (striated) muscle tissue
Smooth or non-striated or non-striated or involuntary muscles: The cells of these muscles are elongated, spindle-shaped, broad from the middle and have tapering ends.
These muscles do not have alternate light or dark bands that do not have striations on their muscle fibre and hence give a smooth appearance when observed under a microscope. Their fibres are not organised into parallel arrays, These muscles line the hollow organs and are involuntary. e.g., posterior region of oesophagus, stomach, intestine, lungs, urinary bladder, urogenital tract.
The transfer of food with the help of the digestive tract and gametes through the genital tract occurs due to the contraction of smooth muscles.
Cardiac muscle: Cardiac means heart, hence muscles of the heart are called cardiac muscle. The cells of cardiac muscle assemble in a branching pattern.
These are striated in nature i.e., alternate light and dark bands could be observed on the muscle fibre when kept under the microscope. These are involuntary in nature as they generate their own impulse or excitation and hence allow the heart to continue its pumping activity of rhythmic contraction and relaxation.
These are meant for increasing and decreasing the rate of muscular activity.

so cardiac muscles are auto excitable in nature

Note:- The myocytes have an ability to contract. They can shorten by $\dfrac{1}{3}$ to $\dfrac{1}{2}$ of their length due to contraction and then return to its original length, so the property of shortening and then returning to relaxed state of the muscle fibre is called contractility. A stimulus such as nerve impulse, hormone, mechanical, thermal or chemical stimulus is required for excitation of the muscles which then causes muscles to contract.