Muscular system: Overview

Muscular system: OverviewClassification of the muscles. Types of muscle tissue. Form and shape of the muscles. Functions of the muscles
~ 2 min

Myology is the study of the muscular system.

Muscles perform many functions. They provide mobility, produce heat, and are partly involved in digestion and respiration. They also form the walls of the cavities of the human body.

Depending on structural and functional features, there are three types of muscle tissue.

  • Smooth muscle tissue is a component of the walls of internal organs and blood vessels

    Smooth muscle tissue
    Smooth muscle tissue
  • Skeletal striated muscle tissue is a component of the skeletal muscles that provides their motion

Skeletal striated muscle tissue
Skeletal striated muscle tissue
  • Cardiac striated muscle tissue forms a muscle layer of the heart called the myocardium

    Cardiac striated muscle tissue
    Cardiac striated muscle tissue

    The muscle cells called myocytes are structural and functional components of muscles

    Each muscle fiber is surrounded by a loose connective tissue membrane called the endomysium.


    Numerous muscle fibers are grouped into muscle bundles, which are surrounded by the proper connective tissue membrane, called the perimysium.


    Ultimately, a group of muscle bundles forms an entire muscular belly, which is surrounded on the outside by another layer of connective tissue called the epimysium.


    This structure gives muscle tissue four basic physiological properties:

  • Excitability – ability to detect the neural

  • Contractility – ability to contract in response to a neural stimulus

  • Extensibility – ability of a muscle to be stretched without tearing

  • Elasticity – ability of a muscle to return to its normal shape after being extended.

    The general outline of the structure of the skeletal muscle (musculus) includes the following parts:

  • Head (caput), which usually corresponds to the place of the beginning of the muscle

  • Belly (venter)

  • Tendon (tendo), which usually corresponds to the place of insertion of the muscle (sometimes called the tail (cauda))

Some muscles have an intermediate tendon located between the two bellies, such as the digastric muscle (musculus digastricus).

Digastric muscle (musculus digastricus) – anterior venter
Digastric muscle (musculus digastricus) - anterior venter
Digastric muscle (musculus digastricus) – posterior venter
Digastric muscle (musculus digastricus) - posterior venter

In some muscles, for example, in the rectus abdominis (musculus rectus abdominis), the course of the muscle bundles is interrupted by several short intermediate tendons, the so-called tendinous intersections (intersectiones tendineae).

Rectus abdominis (musculus rectus abdominis)
Rectus abdominis (musculus rectus abdominis)
Tendinous intersections (intersectiones tendineae)
Tendinous intersections (intersectiones tendineae)

Muscles may have different shapes:

  • Fusiform muscles, which are wide and short

  • Unipennate, bipennate, and multipennate muscles

  • Two-headed, three-headed, and four-headed muscles

  • Ribbon-shaped and orbicular muscles

When a muscle contracts, one end of it remains immobile. This place is called a fixed end. And the other end changes its location and is called a mobile end.

Muscles perform their functions together with various anatomical structures, which are commonly referred to as “additional structures of the muscle”.

They include the following structures:

Fascia (fascia)
Fascia (fascia)

Fascia (fascia), which is a connective tissue covering of a muscle. Forming sheaths for muscles, fasciae delimit them from each other.

Superficial (subcutaneous) fascia (fascia superficialis)
Superficial (subcutaneous) fascia (fascia superficialis)

Superficial (subcutaneous) fascia (fascia superficialis) is located under the skin. Such fasciae are wide and surround all the muscles in a certain area.

Deep fascia (fascia profunda)
Deep fascia (fascia profunda)

Deep fascia (fascia profunda) is a muscular membrane formed by the synergistic muscles, or the muscles performing the same functions. The deep fascia covering an

Loose fatty tissue
Loose fatty tissue

individual muscle is called a proper fascia (fascia propria).

A thin layer of loose fatty tissue is located between the surface of the muscle, its connective tissue membrane,

Extensor retinaculum
Extensor retinaculum
Flexor retinaculum
and the fascia.

and the fascia.

Inserting into the bony protrusions, the fascia forms the so-called retinacula (retinaculum). They prevent the tendons from shifting to the sides and give them the correct direction when the muscles contract.

In places where the tendon adheres to the bone protrusion, there are synovial bursae (bursa synovialis), which

Flexor muscles
Flexor muscles

contain synovial fluid and smoothen friction.

Extensor muscles
Extensor muscles

Depending on the function performed, the following muscle groups are distinguished:

Adductor muscles
Adductor muscles
  • Flexor muscles. These muscles carry out flexion (flexio)

    Abductor muscles
    Abductor muscles
  • Extensor muscles. These muscles carry out extension (extensio)

    Pronator muscle
    Pronator muscle
  • Adductor muscles. These muscles carry out adduction

Supinator muscle
Supinator muscle

Muscular system: Overview

flexor muscle
musculus flexor
extensor muscle
musculus extensor
adductor muscle
musculus abductor
abductor muscle
musculus abductor
rotator muscle
musculus rotator
superficial fascia
fascia superficialis
deep fascia
fascia profunda
proper fascia
fascia propria
rectus abdominis muscle
musculus rectus abdominis
tendinous intersections
intersectiones tendinae
synovial bursa
bursa synovialis
fixed end
punctum fixum
mobile end
punctum mobile
fusiform muscle
musculus fusiformis
two-headed muscle
musculus biceps
three-headed muscle
musculus triceps
four-headed muscle
musculus quadriceps
unipennate muscle
musculus unipennatus
pennate muscle
musculus pennatus
bipennate muscle
musculus bipennatus
multipennate muscle
musculus multipennatus
orbicular muscle
musculus orbicularis
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