Back Muscles
1. Splenius Capitis
Action:
Bilateral contraction: Extends the head and neck.
Unilateral contraction: Rotates and laterally flexes the head to the same side.
Origin:
Nuchal ligament and spinous processes of C7-T3 (or T4).
Insertion:
Mastoid process of the temporal bone and the lateral third of the superior nuchal line of the occipital bone.
Notes:
Involved in head and neck movements, particularly for extension and rotation.
Works synergistically with other muscles for neck movements.
2. Splenius Cervicis
Action:
Bilateral contraction: Extends the cervical spine.
Unilateral contraction: Laterally flexes and rotates the neck to the same side.
Origin:
Spinous processes of T3-T6.
Insertion:
Transverse processes of C1-C3 (C4).
Notes:
Located beneath the splenius capitis.
Plays a role in neck rotation and extension, but is more focused on the cervical portion of the spine.
3. Semispinalis Capitis
Action:
Bilateral contraction: Extends the head and neck.
Unilateral contraction: Rotates the head to the opposite side.
Origin:
Transverse processes of C7-T6 (sometimes T7-T12).
Insertion:
Between the superior and inferior nuchal lines of the occipital bone.
Notes:
Part of the deeper layer of back muscles, contributing to fine control of head movements.
It’s a part of the "transversospinalis" group, along with semispinalis cervicis and semispinalis thoracis.
4. Semispinalis Cervicis
Action:
Bilateral contraction: Extends the cervical spine.
Unilateral contraction: Rotates the cervical spine to the opposite side.
Origin:
Transverse processes of T1-T5 (or T6).
Insertion:
Spinous processes of C2-C5.
Notes:
It lies deeper than the splenius muscles and works together with them for spinal extension and rotation.
Helps stabilize the cervical spine and assists in postural control.
5. Deltoid
Action:
Anterior part: Flexes and medially rotates the arm.
Middle part: Abducts the arm.
Posterior part: Extends and laterally rotates the arm.
Origin:
Lateral third of the clavicle (anterior part), acromion (middle part), and spine of the scapula (posterior part).
Insertion:
Deltoid tuberosity of the humerus.
Notes:
Major muscle for shoulder abduction, especially after the first 15 degrees, which is done by the supraspinatus.
It has three distinct parts (anterior, middle, and posterior) that are involved in different movements of the shoulder.
Commonly involved in overhead movements and lifting.
The deltoid muscle also stabilizes the shoulder joint during dynamic activities, ensuring proper alignment and function.
6. Trapezius
Action:
Elevates, retracts, and rotates the scapula.
Superior fibers elevate the scapula (shoulder shrug).
Middle fibers retract the scapula.
Inferior fibers depress the scapula.
Origin:
Occipital bone, nuchal ligament, and spinous processes of C7-T12.
Insertion:
Lateral third of the clavicle, acromion, and spine of the scapula.
Notes:
The trapezius is a large, superficial muscle of the upper back and neck.
It plays a key role in stabilizing and moving the scapula, contributing to various upper limb movements.
Often involved in posture and tension-related issues, like neck stiffness.
7. Teres Major
Action:
Adducts, extends, and medially rotates the arm at the shoulder joint.
Origin:
Dorsal surface of the inferior angle of the scapula.
Insertion:
Medial lip of the intertubercular groove of the humerus.
Notes:
Sometimes referred to as the "little latissimus dorsi" because of its similar function.
Important in shoulder movements, particularly in actions like pulling or reaching backward.
8. Teres Minor
Action:
Laterally (externally) rotates the arm at the shoulder joint.
Helps stabilize the shoulder joint.
Origin:
Lateral border of the scapula.
Insertion:
Greater tubercle of the humerus (below the infraspinatus insertion).
Notes:
Part of the rotator cuff group, which helps stabilize the shoulder joint.
Often works in synergy with other rotator cuff muscles (like infraspinatus) for shoulder stability and movement.
9. Rhomboid Major
Action:
Retracts (adducts) and elevates the scapula.
Helps rotate the scapula downward.
Origin:
Spinous processes of T2-T5.
Insertion:
Medial (vertebral) border of the scapula, below the spine of the scapula.
Notes:
The rhomboid major is responsible for pulling the scapula toward the vertebral column and stabilizing it during shoulder movements.
Often works in tandem with the rhomboid minor.
10. Rhomboid Minor
Action:
Retracts (adducts) and elevates the scapula.
Helps rotate the scapula downward.
Origin:
Nuchal ligament and spinous processes of C7 and T1.
Insertion:
Medial border of the scapula, at the level of the spine of the scapula.
Notes:
Smaller than the rhomboid major but serves a similar function in scapular movement and stabilization.
Works together with rhomboid major to perform scapular retraction and rotation.
11. Levator Scapulae
Action:
Elevates the scapula.
Downwardly rotates the scapula.
Unilateral contraction also laterally flexes the neck.
Origin:
Transverse processes of C1-C4.
Insertion:
Superior (medial) border of the scapula.
Notes:
The levator scapulae primarily functions in elevating the scapula but is also important for neck movement, especially in lateral flexion.
Commonly involved in neck tension, especially with poor posture.
12. Latissimus Dorsi
Action:
Extends, adducts, and medially (internally) rotates the arm at the shoulder joint.
Helps in actions like pulling, swimming, and lifting.
Origin:
Spinous processes of T7-T12, lumbar vertebrae, sacrum, iliac crest, and lower three or four ribs.
Insertion:
Intertubercular groove of the humerus (anterior surface).
Notes:
The latissimus dorsi is a large, flat muscle on the back and is often referred to as the "lats."
It plays a crucial role in upper limb movements like reaching overhead or pulling actions.
It works with other muscles like the teres major for movements such as pulling or lifting.
13. Serratus Posterior Superior
Action:
Elevates the upper ribs (helps with inspiration during breathing).
Origin:
Spinous processes of C7-T3 and nuchal ligament.
Insertion:
Superior borders of ribs 2-5.
Notes:
Located in the upper back, beneath the rhomboids and the trapezius.
It assists in respiration by lifting the upper ribs, helping expand the thoracic cavity during inhalation.
14. Serratus Posterior Inferior
Action:
Depresses the lower ribs (helps with forced expiration during breathing).
Origin:
Spinous processes of T11-L2.
Insertion:
Inferior borders of ribs 9-12.
Notes:
Located in the lower back, deep to the latissimus dorsi.
Works in breathing by aiding in forced exhalation, helping to lower the ribs during expiration.
15. Supraspinatus
Action:
Abducts the arm at the shoulder joint (first 15 degrees).
Helps stabilize the shoulder joint as part of the rotator cuff.
Origin:
Supraspinous fossa of the scapula.
Insertion:
Greater tubercle of the humerus (superior facet).
Notes:
The supraspinatus is one of the four rotator cuff muscles, which are crucial for stabilizing the shoulder joint.
It is particularly involved in the initial phase of arm abduction and also helps keep the humeral head centered in the glenoid fossa.
16. Infraspinatus
Action:
Laterally (externally) rotates the arm at the shoulder joint.
Stabilizes the shoulder joint.
Origin:
Infraspinous fossa of the scapula.
Insertion:
Greater tubercle of the humerus (middle facet).
Notes:
The infraspinatus is another important rotator cuff muscle, responsible for lateral rotation and stability of the shoulder.
17. Subscapularis
Action:
Medially (internally) rotates the arm at the shoulder joint.
Adducts the arm and helps stabilize the shoulder joint.
Origin:
Subscapular fossa of the scapula.
Insertion:
Lesser tubercle of the humerus.
Notes:
The subscapularis is one of the four rotator cuff muscles, which are critical for shoulder stability.
It is the primary internal rotator of the shoulder and is involved in motions like reaching behind your back.
18. Spinalis
Action:
Bilateral contraction: Extends the vertebral column (spine).
Unilateral contraction: Laterally flexes the vertebral column to the same side.
Origin:
Spinous processes of the upper lumbar and lower thoracic vertebrae.
Insertion:
Spinous processes of the upper thoracic vertebrae and cervical vertebrae (C2, C3).
Notes:
Spinalis is the most medial of the three muscles that make up the erector spinae group (along with longissimus and iliocostalis).
It primarily functions in extending and stabilizing the spine, especially in postural control.
19. Longissimus
Action:
Bilateral contraction: Extends the vertebral column (spine).
Unilateral contraction: Laterally flexes the vertebral column to the same side.
It also helps extend and rotate the head when acting on the cervical spine.
Origin:
Transverse processes of the lumbar, thoracic, and cervical vertebrae.
Insertion:
Ribs between the tubercles and angles, transverse processes of thoracic and cervical vertebrae, and mastoid process of the temporal bone (for the longissimus capitis).
Notes:
Longissimus is the intermediate muscle of the erector spinae group, located between the spinalis and iliocostalis.
It plays a major role in trunk extension and lateral flexion, contributing to overall posture and spinal stability.
20. Iliocostalis
Action:
Bilateral contraction: Extends the vertebral column (spine).
Unilateral contraction: Laterally flexes the vertebral column to the same side.
Origin:
Iliac crest, sacrum, and the spinous processes of the lumbar vertebrae.
Insertion:
Angles of the ribs and the transverse processes of cervical vertebrae (C4-C6).
Notes:
Iliocostalis is the most lateral of the three muscles in the erector spinae group.
It is crucial for maintaining posture and assisting in the movement and stabilization of the trunk, especially in lateral flexion and extension.