Trunk musculature

typical motor innervation is via

ventral nerve root

typical sensory innervation is via

dorsal nerve root

a lot of back muscles are innervated

segmentally by dorsal n roots (abnormally)

ventral ramus innervation typically

forms a plexus - brachial, lumbar and sacral, to innervate extremities

ventral ramus innervation also forms

individual nerves like intercostal nerves and recurrent meningeal nerves

intercostal nerves

innervate abdominal segmentally (typically)

recurrent meningeal nerves

sensory nerve branching off ventral ramus to innervate areas of the back (atypical)

recurrent meningeal nerves innervate

dura mater, periosteum surrounding vertebral canal, PLL, and superficial parts of annulus fibrosis

dorsal ramus forms

highly segmental nerves that innervate essentially all intrinsic muscles of the deep posterior trunk (and skin, CT of posterior VB, joints, etc)

in the sagittal plane, longissimus thoracis acts to

extend the spine with a small IMA

in the sagittal plane, rectus abdominis acts to

flex the spine with a large IMA

AOR of the spine is

through the vertebral bodies

MA

IMA/EMA = EF/MF

short IMA

need high muscle force, but load will move a lot with a little shortening

long IMA

dont need as much muscle force to handle external force, but muscle needs to shorten a lot to move the load a little

in the sagittal plane, longissimus thoracis and rectus abdominis are

antagonists of motion

external oblique muscle has angular force vector that

allows horizontal forces for rotation and vertical forces for flexion and lateral flexion

if the scapula was fixed, middle trapezius could act as a

contralateral rotator by puling the spinous process towards the scapula (rhomboid, lower trap and lats could do this too)

if both scapulae were fixed, activation of bilateral lower trap could

take the trunk into extension

superficial and intermediate layers of the back are innervated by

ventral nerve roots (typically), and CN 11 for upper trap

deep layer of back muscles include

erector spinae group, transversospinal group, short segmental ground

erector spinae group includes

spinalis, longissimus, iliocostalis

attachments of SLI

spinous process, transverse process, angle of ribs

actions of SLI

extension, ipsi lateral flexion, ipsi rotation

global innervation of erector spinae muscles

dorsal rami of adjacent spinal nerve

spinalis OIA

common tendon to spinous processes, very vertically, primarily extends with a little ipsi lateral flexion and no rotation

longissimus OIA

common tendon to transverse processes, extends ipsi lateral flexion and ipsi rotation

iliocostalis OIA

common tendon to posterior angle of ribs, extension, ipsi lateral flexion and ipsi rotation

if erector spinal muscles were in spasm after injury

could pull into anterior tilt

features of all erector spinae

really large CSA, a lot of torque produced, pull into anterior tilt

longissimus capitis

from transverse process of lower cervical/upper thoracic spine to mastoid process

bilateral activation of erector spinase group

into extension

unilateral activation of erector spinae group

ipsilateral lateral flexion and rotation

erector spinae muscles fiber direction

Up and out

transversospinal group

semispinalis, multifidus, rotatores (superficial to deep)

all transversospinal muscles go from

transverse process to spinous processes

semispinalis attaches

across 4-8 spinal levels

multifidus attaches

across 2-4 levels

rotatores attaches

across 1-2 levels - activates with the tiniest movements to stabilize spine

semispinalis capitis

transverse process of C7-T7 to between superior and inferior nuchal lines of occiput

transversospinal group is oriented

deep to erector spinae

transversospinal muscles fiber direction

Down and in - actions are extension, ipsilateral lateral flexion, and contralateral rotation

rotation of transversospinal muscles pull the spinous processes

ipsilaterally causing VB to move contralaterally - contralateral rotation

most extension at the head comes from

semispinalis capitis

multifidi muscles have

preferential atrophy with injury - can atrophy 30% in a day, early postural responses, high muscle spindle density, large CSA (respond well to little motion and gentle motion)

multifidi is thickest in

lumbar region

rotatores are most dense in

thoracic region

rotatores brevis orientation

is horizontal because of SP orientation posterior inferiorly - just do rotation

erector and transversospinal muscles on same side are synergists in

extension and lateral flexion and antagonists in rotation (when comparing contralateral connection - synergists with extension and rotation, antagonists with lateral flexion)

diagonal line of pull

connects (L) erector spinae and (R) multifidi

short segmentals

intertransversarius, interspinalis

interspinalis muscles

spinous process to spinous process, in pairs at cervical, one at C1-C2, segmental dorsal rami innervation, extend and ipsi lateral flexion (no rotation)

short segmentals have

lots of spindles and have sensory function for proprioception

intertransversarius

transverse process to transverse process, ventral rami innervated, extension and ipsi lateral flexion (no rotation)

abdominal muscles

rectus abdominis, external oblique, internal oblique, transversus abdominis (superficial to deep)

innervation of abdominal muscles

segmentally innervated by intercostal nerves of ventral rami

posterior rectus sheath is formed by

transversus abdominis and internal oblique

anterior rectus sheath is formed by

internal and external oblique

anterior and posterior rectus sheath

meet to form linea alba (line of connective tissue)

rectus abdominis has unique

rows of tendinous insertion that increase strength

rectus abdominis OIA

crest of pubis to xiphoid process into cartilage of ribs 5-7, flex, ipsi flex and increase intrabd pressure

rectus abdominis nerve

intercostal nerve T7-T12

external oblique OIA

lateral side from ribs 4-12, inferior-medial to linea alba, iliac crest and contributes to rectus sheath contralaterally, flexion, ipsi lateral flexion, contra rotation

external oblique nerve

intercostals T8-T12

internal oblique OIA

iliac crest, inguinal ligament and thoracolumbar fascia to ribs 9-12 and contralateral rectus sheath, flexion, ipsi lateral flexion and ipsi rotation

internal oblique nerve

intercostal n T8-T12

transversus abdominis OIA

iliac crest, thoracolumbar fascia, inner surface of cartilage ribs 6-12 and inguinal ligament to linea alba and contralateral rectus sheath, activates anytime you activate abdominals

abdominal muscles could be considered

hip extensors because they can put pelvis into posterior tilt

deep back extensor muscles could be considered

hip flexors because they can put the pelvis into anterior tilt

to purely rotate

need flexors and extensors of the trunk

transversus abdominis acts as a

corset muscle and stabilizes the obliques

based on cross sectional area, torque is favored for the

trunk extensors (bigger CSA)

iliopsoas is made up of

iliacus and psoas major - fuse together at inguinal ligament to attach to the lesser trochanter

iliacus OI

iliac fossa and lateral sacrum to lesser trochanter

psoas major OI

TP T12-L5 and VB T12-L4 to lesser trochanter

iliopsoas innervation

femoral nerve

action of iliopsoas

hip flexion/anterior pelvic tilt

psoas major action

lower lumbar flexor, upper lumbar extensor, overall compressor

which spinal level is the psoas major IMA for flexion

L5

if iliopsoas is tight

spine is compressed and pulled into anterior tilt

quadratus lumborum OI

iliac crest and iliolumbar ligament to TP of L1-L4 and onto 12th rib

quadratus lumborum action

extends spine, posterior pelvic tilt and ipsilateral lateral flexion

quadratus lumborum nerve

ventral ramus T12-L3

hip hike

lateral flexion of spine to bring ASIS up, usually to lift toe with weak dorsiflexors

quadratus lumborum and iliopsoas are both

stabilizers of spine