Learning Objective: By the end of this session, the learner will be able to describe muscles using a six-part framework covering site, shape, attachments, action, nerve supply, and blood supply.
A 6-Part Framework for Learning Muscle Anatomy
The study of muscle anatomy is essential for understanding movement, posture, and common musculoskeletal disorders. Because the human body contains a large number of muscles, a consistent method for analysing their features supports accurate and efficient learning.
This six-part framework can be applied to any skeletal muscle.
1. Site
The site refers to the anatomical location of the muscle. This creates context for the region influenced by the muscle and the joints it acts upon.
Examples:
- The pectoralis major lies in the anterior chest.
- The flexor carpi radialis lies in the anterior forearm.
- The gastrocnemius lies in the posterior leg.
2. Shape
Muscles present a range of shapes reflecting fibre arrangement and functional demand.
Examples
- Fusiform: thick mid-portion, tapered ends (biceps brachii).
- Strap: long parallel fibres (sternocleidomastoid, rectus abdominis).
- Triangular: broad origin, narrow insertion (pectoralis major).
- Circular: ring-shaped around an opening (orbicularis oculi).
- Unipennate: fibres insert obliquely on one side of a tendon (flexor pollicis longus).
- Bipennate: fibres insert on both sides of a tendon (rectus femoris).
- Multipennate: several feather-like fascicles (deltoid).
3. Attachments
Each muscle has a proximal and distal attachment. Understanding these allows prediction of the resulting movement across a joint. Attachment sites are routinely used in surgical, clinical, and radiological interpretation.
Examples:
- Pectoralis major: clavicle, sternum, upper costal cartilages → lateral lip of intertubercular sulcus.
- Biceps brachii: supraglenoid tubercle, coracoid process → radial tuberosity.
- Sternocleidomastoid: sternum, medial clavicle → mastoid process.
4. Action
Muscle action is determined by fibre orientation and attachment points. The direction of pull dictates the resulting motion.
Examples:
- Iliopsoas: flexes the hip joint.
- Quadriceps femoris: extends the knee joint.
- Deltoid: abducts the shoulder joint.
5. Nerve Supply
Skeletal muscles are supplied by specific motor nerves that enable voluntary contraction.
Examples:
- The median nerve supplies many anterior forearm muscles.
- Axillary nerve supplies the deltoid.
- The femoral nerve supplies the quadriceps.
6. Blood Supply
Arterial supply maintains muscle function through oxygenated blood.
Examples:
- The brachial artery supplies the biceps brachii.
- The profunda femoris artery supplies the adductor magnus.
- The posterior tibial artery supplies the gastrocnemius.
