Muscle

The muscular system along with the skeletal system forms the skeletomuscular system that is responsible for the movement and locomotion in vertebrates. The unit of the muscular system is called a muscle. Muscles are made up of proteins and fibres and form the major component of the body weight.

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General Structure of a Muscle

(Source: SEER Training)

Each muscle (mainly skeletal) has an outer covering called the perimysium. It covers and protects the muscle fibres. Around the entire structure lies the fibrous layer of the epimysium which protects the entire muscle. Each bundle of fibre is known as a ‘fascicle’. And each fibre is covered by the endomysium.

Browse more Topics under Locomotion And Movement

• Introduction to Locomotion and Movement
• Skeletal System
• Joints
• Disorders of Muscular and Skeletal System

Types of Muscles

Skeletal Muscles

These are found throughout the body where conscious movements are performed. They are attached to bones through a structure called as the tendon. We find them around joints so that they bring about movements in that part of the body. For this reason, skeletal muscles are also known as voluntary muscles.

The skeletal muscles are very specialized in their structure and function. Each is made up of many fibres. Each skeletal muscle fibre is made up myofibrils which are made up of smaller units called as the sarcomere. The cell membrane of these fibres is known as the sarcolemma. These muscles are also rich in mitochondria which are required to help each muscle fibre cell perform the activity of the muscle. From the sarcolemma, there are tubular extensions known as the T- tubules which conduct electrochemical impulses from the outer membranes to the centre of the muscles. Muscles are made up of proteins- actin, myosin, and troponin.

Skeletal muscles are named in different ways: Some are named depending on their location, some depending on their origin or insertion, some based on the number of origins of a single muscle and others on basis of their direction and function.

Smooth Muscles

These are also called as involuntary muscles as they are not under the control of our will. They are found in the visceral organs and so are also known as visceral muscles. They do not have striations when viewed under the microscope like the skeletal muscles and so they are called as smooth muscles. Smooth muscles are found in the digestive system, reproductive system, urinary system and are also found in the blood vessels.

Cardiac Muscles

These are striated involuntary muscles that are specialized to perform rhythmic contraction and relaxation and are found only in the heart. The cells of the cardiac muscles are branched and connected to adjacent cells via connections known as the intercalated disc. This branching along with the striations make these muscles strong and resilient to withstand demanding activity from the entire body. The branching also helps in quick transmission of signals to enable the heart to respond fast.

Solved Example for You

Q: What is the covering of the individual muscle fibrils called?

1. Endomysium
2. Epimysium
3. Fascia
4. Perimysium

Sol: The correct answer is (a) Endomysium

Endomysium covers the individual muscle fibres. Epimysium covers the entire muscle while the perimysium covers the muscle fibre bundles.