How to Learn Anatomy: Muscles

Written by Oliver Jones

Last updated June 14, 2025
18 Revisions

The study of muscle anatomy is essential for understanding movement, posture, and common musculoskeletal disorders. Given the large number of muscles in the human body, using a consistent method to learn their features is beneficial.

In this article, we shall look at a six-part framework for describing muscles – site, shape, attachments, action, nerve supply, and blood supply. This structure can be applied to any skeletal muscle and forms the basis for effective anatomical learning.

A 6-part framework for learning the anatomy of muscles

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Site

The site refers to the anatomical location of the muscle. This provides context for which region it influences and which joints it may act upon.

Examples:

  • The pectoralis major is a muscle of the anterior chest.
  • The flexor carpi radialis lies in the anterior forearm.
  • The gastrocnemius is located in the posterior leg.

Shape

Muscles exhibit a variety of shapes, which often reflect their function and fibre arrangement.

Common muscle shapes include:

  • Fusiform – thick in the middle and tapered at both ends (e.g. biceps brachii)
  • Strap – long and thin with parallel fibres (e.g. sternocleidomastoid, rectus abdominis)
  • Triangular – broad origin with fibres converging on a narrow insertion (e.g. pectoralis major)
  • Circular – fibres arranged in a ring, usually around an opening (e.g. orbicularis oculi)
  • Unipennate – fibres insert obliquely on one side of a central tendon (e.g. flexor pollicis longus)
  • Bipennate – fibres insert obliquely into both sides of a central tendon (e.g. rectus femoris)
  • Multipennate – multiple feather-like fascicles converging obliquely on a central tendon (e.g. deltoid)

Fig 2
Muscle classification by shape

Attachments

Each muscle has a proximal attachment (closer to the midline of the body) and a distal attachment (further away). Identifying these bony attachments allows the resulting movements at a joint to be predicted.

Sites of attachment are often used as landmarks in surgical and radiological procedures.

Examples:

  • The pectoralis major originates from the clavicle, sternum, and upper costal cartilages. It inserts into the lateral lip of the intertubercular sulcus of the humerus.
  • The biceps brachii  originates from the supraglenoid tubercle and coracoid process of the scapula. It inserts into the radial tuberosity.
  • The sternocleidomastoid originates from the sternum and medial clavicle. It inserts into the mastoid process of the temporal bone.

Action

A muscle produces movement by acting across one or more joints.  The action can usually be deduced by considering its attachments and the orientation of its fibres – as these determine the direction and type of pull exerted on the joint.

Examples:

  • The iliopsoas causes flexion at the hip joint.
  • The quadriceps femoris extends the knee joint.
  • The deltoid abducts at the shoulder joint.

Nerve Supply

Skeletal muscles are innervated by motor branches of peripheral nerves. Each muscle has a specific nerve supply, which facilitates voluntary contraction and coordination.

Example:

  • The median nerve supplies many muscles of the anterior forearm.
  • The axillary nerve supplies the deltoid.
  • The femoral nerve supplies the quadriceps femoris.

Blood Supply

Muscles receive oxygenated blood via one or more arteries, supporting metabolism and function.

Example:

  • The brachial artery supplies the biceps brachii.
  • The profunda femoris artery supplies the adductor magnus.
  • The posterior tibial artery supplies the gastrocnemius.