Myology
Muscles of the
Posterior Trunk
1
Latissimus Dorsi
• Fibers of the latissimus dorsi twist in such a way that the
superior fibers attach distally on the humerus and the inferior
fibers attach proximally.
• Sometimes the latissimus blends with the teres major
• The spinal and pelvic attachments are all via thoracolumbar
fascia.
• Since it has an attachment onto the inferior angle of the scapula,
it can move the scapula. When trunk is fixed, it can depress,
retract and downwardly rotate the scapula.
• If the arm is fixed, the lat can elevate the trunk at the shoulder
joint toward the humerus (as in a “pull up”).
• The latissimus dorsi and pectoralis major are both large
powerful muscles which attach trunk to the arm. The both
adduct and medially rotate the humerus.
2
Latissimus Dorsi
latissimus = wide
dorsi = back
O: Thoracolumbar aponeurosis, posterior
sacrum, posterior iliac crest, lower 3 or 4
ribs, and inferior angle of the scapula
I: Medial lip of the Bicipital Groove of the
humerus
A: Extends, medially rotates, adducts the arm
(handcuff position)
** Reversed muscle action bilaterally
causes anterior tilt of the pelvis.
Unilateral contraction causes elevation of
the pelvis, contralateral rotation of the
trunk, and lateral deviation of the trunk.
N: Thoracodorsal nerve
3
Palpation: Page 207
Rhomboids
• They are deep to the trapezius
• Rhomboid minor is superior to rhomboid major.
• Rhomboid minor attaches to the scapula, inferior to the levator
scapulae.
• Deep to the rhomboids are the splenius capitis, splenius cervicis,
serratus posterior superior and erector spinae
• They also cause downward rotation of the scapula.
• Are sometimes called Christmas Tree muscles due to their
shape.
• Rounded Shoulders is a common condition in which scapulae
are protracted (abducted) and depressed and the humeri are
medially rotated. When rhomboids are weak, the can contribute
to this condition. This is especially true if the protractors (pecs)
are tight.
4
Rhomboid Major and Minor
O: Rhomboid Major: Sp’s T2-T5
Rhomboid Minor: Sp’s C7-T1
I: Medial border of the scapula from the root
of the spine of the scapula to the inferior
angle of the scapula
A: Retracts, elevates, and downwardly
rotates the scapula.
**Reversed muscle action: Unilaterally
causes contralateral rotation of the trunk
N: Dorsal scapular nerve
Palpation: Page 212
5
Serratus Anterior
• Majority of this muscle lies deep to the scapula and lats
posteriorly and pecs anteriorly.
• Lowest 4-5 slips of costal attachments interdigitate with
external oblique.
• Lies next to (anterior to) the subscapularis.
• Serrated appearance comes from attaching onto separate
ribs, which creates the notched look of a serrated knife.
• Prime mover of protraction, upward rotation, & medial tilt
of scapula.
• Required during forceful protraction of scapula i.e.
reaching, pushing, punching, throwing.
6
Serratus Anterior
O: Outer borders of the 1st
through 9th ribs
I: Anterior surface of the
entire
medial border of the scapula
A: (PUSS) Protracts, upwardly
rotates, and stabilizes the
scapula
N. Long thoracic nerve (of
Bell)
Palpation: Page 215
7
Serratus Posterior Superior
• Thin, quadrilateral shaped muscle
• Important for respiration specifically inspiration since it
elevates ribs 2-5 increasing the size of the thoracic cage
(Boyle’s Law).
• Lies deep to the rhomboids
8
Serratus Posterior Superior
O: SP’s of C7-T3
I: Superior borders of Ribs 2-5
(deep to the rhomboids)
A: Elevation of ribs 2-5
N: intercostal nerves
Palpation: Page 219
9
Serratus Posterior Inferior
O: SP’s of T11-L2
I: Inferior borders of Ribs
9-12
A: Depression of ribs 9-12
N: subcostal & intercostal
nerves
Palpation: Page 221
10
The Erector Spinae Group
• Name tells us that these muscles make the spine erect.
• Lie deep in the back and neck
• In lumbar region, this group is deep to the lat and serratus
posterior inferior.
• In thoracic region, deep to trap, lats, rhomboids, serratus
posterior superior, splenius capitis & splenius cervicis.
• In cervical region, deep to trap, splenius cap/cerv, and SCM
• In trunk, erector spinae are superficial to transversospinalis
group, QL, and ribcage.
• In neck erector spinae group is superficial to suboccipitals.
• Spinalis, longissimus, and iliocostalis make up erector spinae
group.
• From medial to lateral the acronym SLI name the muscle of the
group
11
Erector Spinae Group
(Overview of entire group)
O: Pelvis
I: Spine, ribcage, head
A: Bilateral Contraction: causes
Extension of the trunk, neck, and
head; anterior pelvic tilting.
Unilateral contraction: causes
lateral flexion and Ipsilateral
rotation of the trunk, head, and
neck; elevation of the pelvis
N: Dorsal rami of the spinal nerves
12
Individual Erector Group Muscles
• Iliocostalis
– Subdivided into lumborum, thoracis, and cervicis
– Most lateral of the three
• Longissimus
– Subdivided into thoracis, cervicis, and capitis
– Longest & largest of the three with most superior
attachments.
• Spinalis
– Subdivided into thoracis, cervicis, and capitis
– Most medial of the three
13
Iliocostalis
O: Iliocostalis Lumborum: Medial iliac crest and
sacrum
Iliocostalis Thoracis: angles of ribs 7 – 12
Iliocostalis Cervicis: angles of ribs 3-6
I: Iliocostalis Lumborum: angles of ribs 7 – 12
Iliocostalis Thoracis: angles of ribs 1-7 and C7 TP
Iliocostalis Cervicis: TP’s of C4 – C6
A: Bilateral contraction: Extends the trunk and neck
and anteriorly tilts the pelvis.
Unilateral contraction: Lateral flexion and
ipsilateral rotation of the trunk and neck; elevation
of the pelvis at the lumbosacral joint.
N: Dorsal rami of the cervical, thoracic, and lumbar
spinal nerves
Palpation: Page 227
14
Longissimus
O: Longissimus Thoracis: Medial iliac crest, posterior
sacrum, and TP’s of L1 – L5
Longissimus Cervicis: TP’s of T1 – T5
Longissimus Capitis: TP’s of T1 – T5 and the
AP’s of C5 - Ct
I: Longissimus Thoracis: TP’s of all thoracic
vertebrae and the 9 lower ribs
Longissimus Cervicis: TP’s of C2 – C6
Longissimus Capitis: Mastoid process
A: Bilateral contraction: Extends the trunk and neck
and anteriorly tilts the pelvis.
Unilateral contraction: Lateral flexion and
ipsilateral rotation of the trunk, neck, and head;
elevation of the pelvis at the lumbosacral joint.
N: Dorsal rami of the cervical, thoracic, and lumbar
spinal nerves
Palpation: Page 230
15
Spinalis
O: Spinalis Thoracis: SP’s of T11 – T12
Spinalis Cervicis: Inferior nuchal ligament and SP of
C7
Spinalis Capitis: Usually considered to be part of
the semispinalis capitis
I:
Spinalis Thoracis: SP’s of T4 – T8
Spinalis Cervicis: SP of C2
Spinalis Capitis: Usually considered to be part of the
semispinalis capitis
A: Bilateral contraction: Extends the trunk and neck.
Unilateral contraction: Lateral flexion and ipsilateral
rotation of the trunk, neck, and head
N: Dorsal rami of the cervical, thoracic, and lumbar spinal
nerves
Palpation: Page 233
16
17
Transversospinalis Group
(Overview of entire group)
O: Pelvis
I: Spine & head
A: Bilateral contraction: Extension of the
head, neck, and trunk and Anterior tilting
of the pelvis
Unilateral contraction: Lateral flexion of
the head, neck, and trunk; Contralateral
rotation of the neck and trunk
N: Dorsal rami of the cervical, thoracic, and
lumbar spinal nerves
Transversospinalis Group
• Very deep in the back and lie in the laminar groove (over the
laminae between the SPs/TPs)
• In trunk, directly deep to the erector spinae group
• In neck, deep to trap, SCM, & splenius capitis.
• Name tells us that this group attaches from TP (transverso) to SP
(spinalis). The transverse process attachment is inferior with
the spinous process attachment superior.
• Subdivided, superficial to deep into: semispinalis, multifidus,
and rotatores.
– Semispinalis attaches superiorly to vertebrae 5 or more levels
above
– Multifidus attaches superiorly 2-4 levels
– Rotatores attach superiorly 1-2 levels.
• Only multifidus attaches onto pelvis.
• Only semispinalis attaches onto head.
• The term paraspinal musculature is used to describe erector
spinae and transversospinalis groups.
Semispinalis
O: Semispinalis Thoracis: TP’s T6-T10
Semispinalis Cervicis: TP’s T1 – T5
Semispinalis Capitis: TP’s of C7 – T6
and the AP’s of C4 – C6
I: Semispinalis Thoracis: SP’s of C6 – T4
Semispinalis Cervicis: SP’s of C2 – C5
Semispinalis Capitis: Occiput
A: Bilateral contraction: Extension of the head, neck,
and trunk
Unilateral contraction: Lateral flexion of the
head, neck, and trunk; Contralateral rotation of
the neck and trunk
N: Dorsal rami of the cervical, thoracic, and lumbar
spinal nerves
Palpation: page 240
Multifidus
O: Posterior sacrum, PSIS, L5-C4
I: SP’s 2-4 levels superior to inferior
attachment
A: Bilateral contraction: Extension of the neck
and trunk ; Anteriorly tilts the pelvis.
Unilateral contraction: Lateral flexion of the
neck, and trunk; Contralateral rotation of the
neck and trunk; Elevates the pelvis.
N: Dorsal rami of the cervical, thoracic, and
lumbar spinal nerves
Palpation: page 243
Rotatores
O: TP’s of the lumbar, thoracic, and cervical
vertebrae
I: Lamina of the vertebrae one to two levels
above
A: Bilateral contraction: Extension of the neck
and trunk;
Unilateral contraction: Contralateral
rotation of the neck and trunk
N: Dorsal rami of the cervical, thoracic, and
lumbar spinal nerves
Not palpable
Quadratus Lumborum
•
•
•
•
Refer to as QL
Very deep and forms part of posterior abdominal wall
Majority deep to erector spinae
Must be accessed with palpation from lateral to medial
(i.e. come in from the side).
• Can elevate the pelvis. Often the term “hiking the hip” is
used to describe the action.
Quadratus Lumborum
O: Rib 12, L1-4 TPs
I: Posterior Iliac Crest.
A: Bilateral contraction: Extension of
trunk; anterior tilting of the pelvis
Unilateral contraction: Lateral trunk
flexion; “hiking” up of the hip;
depression of the 12th rib
N: Lumbar plexus
Palpation: page 248
Interspinals
• Paired muscles that are located on either side of the
interspinous ligaments between the apices of the SPs of
adjacent vertebrae.
• Located deep to supraspinous ligament (nuchal ligament in
cervical region).
• Not located throughout entire spine. Primarily found in
cervical & lumbar regions.
• May be important at fixating the spine.
Interspinals
O: From a SP
I: SP directly superior (not well
developed or absent in the
thoracic spine)
A: Extension of neck and trunk
N: Dorsal rami of the cervical,
thoracic, and lumbar spinal nerves
Palpation: page 251
Intertransversarii
• Located between TPs and very deep.
• Attach onto anterior tubercles and posterior tubercles of TPs in
cervical spine.
• Do not exist in thoracic region since levator costarum and
intercostals take their place.
• Important as fixators of spine (stabilize)
Intertransversarii
O: From a TP of a vertebrae
I: TP directly superior (in the thoracic
region these muscles are found
between T10 and L1)
A: Lateral flexion of neck and trunk
N: Dorsal rami of the cervical,
thoracic, and lumbar spinal nerves
Not palpable
Levator Costarum
O: TP’s of C7-T11
I: Rib 1-12 (inferiorly)
A: Elevation of ribs (primary action). In addition
contributes to extension of the trunk when
contracting bilaterally and lateral flexion of
the trunk when contracting unilaterally
N: Dorsal rami of the thoracic spinal nerves
Not palpable
Which muscle of the deep
spinal group performs rotation?
1.
2.
3.
4.
interspinalis
intertansversari
rotatores
deep spinal
25%
1
25%
25%
2
3
25%
4
Levator Costarum
• Name tells us that the elevate the ribs
• Attach from vertebrae TP and run inferolaterally on to rib
directly inferior.
• Controversy as whether they are respiratory muscles that move
ribs or move/fixate spinal joints
Subcostales
• Usually well developed in lower thoracic region.
• Lie deep to the ribcage and superficial to the plural membrane.
• Thought to be respiratory muscles which depress the ribs for
forced expiration.
Subcostales
O: Ribs 10-12
I: Rib 8-10
A: Depression of ribs 8-10
N: Intercostal nerves 8 -11
Not palpable