Intrinsic and Extrinsic Back Muscles

Smooth Muscle

-found in walls of hollow organs

-contractions are involuntary movements trigged by impulses from autonomic nervous system

-ex. Peristalsis in digestive tract, expansion/contraction of bladder

Cardiac Muscle

-branched cells that allow connections to form network that facilitates coordinated contraction

-made up of cardiomyocytes

-have intercalated disc between cardiac muscle

-contraction of fibers is due to the heart pumping and induced by signaling of cardiac conduction system

Skeletal Muscle

-contracting and relaxing in response to voluntary messages from CNS/PNS

-organized into bundles (fascicles) which are supplied by blood vessels and innervated by motor neurons

Epimysium

Thin connective tissue that wraps around the whole muscle

Perimysium

Connective tissue that surrounds a fascicle of muscle

Endomysium

Connective tissue that surround one muscle fiber

Origin

Attachment site where bone reminds immobile during action

Insertion

Place on the bone that moves during an action

Agonist Muscle

Muscle that is performing an action

Antagonist Muscle

muscle that performs opposite action of the prime mover

Circular Muscle

-circular in shape

-ex. Muscles of mouth and eyes, sphincters of bowels and bladder

Convergent Muscle

-origin is wider than the point of insertion

-fiber arrangement allows for maximum force production

Ex. pectoralis major

Parallel Muscle

-fibers which run parallel to each other (sometimes called strap muscles)

-long muscles which require large movements

-have lower strength but higher endurance

-ex. sartorius and rectus abdominus

Fusiform Muscle

-muscle belly is wider than origin and insertion

-spindle-shaped

-ex. Biceps brachii

Pennate Muscle

-large number of muscle fibers, high strength

-divided into unipennate, bipennate, and multipennate

Unipennate Muscle

-fibers arranged to insert in diagonal direction onto the tendon

-ex. lumbarical, extensor digitorum longus

Bipennate Muscle

-two rows of muscle fibers facing in opposite diagonal directions

-central tendon, like a feather

-greater power, less range of motion

-ex. Rectus femoris (of quads)

Multipennate Muscle

-multiple rows of diagonal fibers

-central tendon that branches

-ex. Deltoid

Hypaxial Muscles

innervated by ventral rami; extrinsic back muscles

Epaxial Muscles

Innervated by dorsal rami; intrinsic back muscles

Superficial Back Muscles

-extrinsic back muscles (hypaxial, innervated by ventral rami)

-includes Trapezius, Latissimus dorsi, Levator scapulae, Rhomboideus major, Rhomboideus minor

Intermediate Back Muscles

-extrinsic back muscles (hypaxial, innervated by ventral rami)

-includes serratus posterior superior and serratus posterior inferior

Deep Back Muscles

-intrinsic back muscles (epaxial, innervated by dorsal rami)

-includes erector spinae group, transversospinalis group

Aponeurosis

-flat sheet of tendon that anchors a muscle

-takes place of tendon or bone in sheet-like muscles having wide area of attachment

Anterior Layer of Thoracolumbar Aponeurosis

-anterior to quadratics lumborum muscle

-ends medially in transverse process of lumbar vertebrae

-combines laterally with aponeurosis of trans versus abdominus

Middle Layer of Thoracolumbar Aponeurosis

-posterior to quadratus lumborum muscle, attaches to TP

-anterior to intrinsic muscles of the back

Posterior Layer of Thoracolumbar Aponeurosis

-covers the erector spinae group

-ends laterally in lumbar by blending with aponeurosis of transverse abdominus muscle

Origin of Trapezius

-external occipital protuberance

-medial 1/3 of superior nuchal line

-ligamentum nuchae

-spinous processes of C7-T12

Insertion of Trapezius

-superior fibers: lateral 1/3 of clavicle

-middle fibers: spine and acromion of scapula

-inferior fibers: base of spine of scapula 1st

Innervation of Trapezius

-spinal accessory nerve (CN XI): motor

-ventral rami of 3rd and 4th cervical nerves: proprioception

-both make up the subtrapezial plexus on deep surface of muscle

Blood Supply of Trapezius

Superior: occipital artery

Middle:transverse cervical artery

Inferior: Dorsal scapular artery

Actions of Trapezius

-elevates, depresses, retracts and upwardly rotates the scapula

extends head/neck

-bilateral contraction of superior fibers extends the head

-unilateral contraction of upper fibers laterally flexes head and cervical vertebrae

Latissimus Dorsi

-covers the inferior 1/2 of the back

-large, wide fan-shaped

-lies superficial to inferior parts of intrinsic back muscles

-lies superficial to serratus posterior inferior, which may adhere to the deep surface

-passes from trunk to humerus, acts directly on shoulder joint and indirectly on pectoral girdle

Origin of Latissimus Dorsi

-spinous processes of T7-T12

-all lumbar and sacral vertebrae

-posterior part of iliac crest

Insertion of Latissimus Dorsi

crest of lesser tubercle, floor of bicipital groove of humerus

Innervation of Latissimus Dorsi

Thoracodorsal nerve (posterior cord of brachial plexus, C6-C8 fibers)

Blood Supply of Latissimus Dorsi

Thoracodorsal Artery (branch of subscapular artery)

Actions of Latissimus Dorsi

Extension, medial rotation, and adduction of arm

Levator Scapulae

-superior 1/3 lies deep to sternocleidomastoid muscle

-inferior 2/3 lies deep to trapezius

Origin of Levator Scapulae

transverse processes C1-C4

Insertion of Levator Scapulae

Medial border of scapula from superior angle to base of spine

Innervation of Levator Scapulae

-ventral rami of C3 and C4 from deep branches of cervical plexus

-twigs from dorsal scapular nerve (C5)

Blood Supply of Levator Scapulae

• Dorsal scapular artery

• Variant: Deep branch of transverse cervical artery

Actions of Levator Scapulae

-elevates and retracts scapula with trapezius

-laterally flexes cervical vertebral column when scapula is fixed

Rhomboideus Major and Minor

-always described as separate muscles, but often appear as a single fused muscular sheet

-lie deep to trapezius

-R. Minor is the more superior of the two; R. major is twice as wide as r. Minor

Origin of Rhomboideus Minor

-lower part of ligamentum nuchae

-spinous processes of C7 and T1

Insertion of Rhomboideus Minor

Medial border of scapula at base of spine

Innervation of Rhomboideus Minor

Dorsal scapular nerve (C4,C5)

Blood Supply of Rhomboideus Minor

• Dorsal scapular artery

• Variant : Deep branch of the transverse cervical artery

Action of Rhomboideus Minor

-elevate medial border of scapula

-retracts scapula

-rotation of scapula (downward)

Origin of Rhomboideus Major

Spinous processes of T2-T5

Insertion of Rhomboideus Major

Medial border of scapula between base of spine and inferior angle

Innervation of Rhomboideus Major

Dorsal scapular nerve (C4,C5)

Blood Supply of Rhomboideus Major

• Dorsal scapular artery

• Variant: Deep branch of transverse cervical artery

Actions of Rhomboideus Major

-elevates medial border of scapula

-retracts scapula

-rotation of scapula (downward)

Triangle of Auscultation

-formed by intersecting borders of Latissimus dorsi, trapezius, and vertebral border of scapula

-R. Major forms the floor

-allows for sounds of thorax to be heard

Origin of Serratus Posterior Superior

-lower end of ligamentum nuchae

-spinous processes of C7-T2/3

Insertion of Serratus Posterior Superior

Ribs 2-5 lateral to angle

Innervation of Serratus Posterior Superior

first four intercostal nerves (ventral rami of first four thoracic nerves)

Blood Supply of Serratus Posterior Superior

Highest intercostal artery and posterior intercostal arteries

Actions of Serratus Posterior Superior

elevates upper ribs during inspiration

Origin of Serratus Posterior Inferior

Spinous process of T10-L2

Insertion of Serratus Posterior Inferior

Lower 3-4 ribs lateral to angles

Innervation of Serratus Posterior Inferior

Lowest 4 intercostal nerves (ventral rami of lower thoracic)

Blood Supply of Serratus Posterior Inferior

Posterior intercostal arteries

Actions of Serratus Posterior Inferior

Depresses lower ribs down and back during inspiration

Origin of Splenius Capitis

-caudal half of ligamentum nuchae

-spinous processes of C7-T3/T4

Insertion of Splenius Capitis

mastoid process and occipital bone inferior to lateral 1/3 of superior nuchal line

Innervation of Splenius Capitis

Upper cervical dorsal rami (c2,c3)

Blood Supply of Splenius Capitis

Muscular and deceiving branches of occipital artery, superficial branch of transverse cervical artery

Actions of Splenius Capitis

-unilaterally rotates head and neck (ipsilateral rotation)

-bilaterally extends head and neck

Origin of Splenius Cervicis

Narrow, tendinitis band from SP of T3-T6

Insertion of Splenius Cervicis

Posterior tubercles of TP of upper 2-3 cervical vertebrae

Innervation of Splenius Cervicis

Dorsal rami of lower cervical nerves (C6, C7, and C8)

Blood Supply of Splenius Cervicis

-muscular and descending branches of occipital artery

-superficial branch of transverse cervical artery

Actions of Splenius Cervicis

-unilaterally draws head to one side and slightly rotates

-bilaterally extends head

Erector Spinae Group

Divided into the iliocostalis, longissimus, and spinalis

Origin of Iliocostalis Lumborum

Thoracolumbar fascia

Insertion of Iliocostalis Lumborum

Lower borders of lower 9 ribs near angles

Innervation of Iliocostalis Lumborum

Dorsal rami of lumbar and spinal nerves (L1-L5)

Blood Supply of Iliocostalis Lumborum

Posterior intercostal arteries and lumbar arteries

Actions of Iliocostalis Lumborum

Extension and lateral flexion of vertebral column

Origin of Iliocostalis Thoracis

Upper borders of lower six ribs medial to insertion of iliocostalis lumborum (does not attach to vertebral column)

Insertion of Iliocostalis Thoracis

Upper six ribs and sometimes TP of C7

Innervation of Iliocostalis Thoracis

Dorsal rami of thoracic spinal nerves (T1-T12)

Blood Supply of Iliocostalis Thoracis

Posterior intercostal artery

Actions of Iliocostalis Thoracis

Extension of vertebral column

Origin of Iliocostalis Cervicis

Upper six ribs medial to the insertion of iliocostalis Thoracis

Insertion of Iliocostalis Cervicis

TPs of C4-C6

Innervation of Iliocostalis Cervicis

Dorsal rami of spinal nerves C4-C6

Blood Supply of Iliocostalis Cervicis

Posterior intercostal arteries

Actions of Iliocostalis Cervicis

Extension and lateral flexion of vertebral column

Origin of Longissimus Thoracis

Thoracolumbar fascia, and accessory processes of lumbar vertebrae

Insertion of Longissimus Thoracis

TP of the lower nine thoracic vertebrae and lower nine ribs

Innervation of Longissimus Thoracis

Dorsal rami of spinal nerves T1-T12

Blood Supply of Longissimus Thoracis

Posterior intercostal arteries and lumbar arteries

Actions of Longissimus Thoracis

Extension and lateral flexion of vertebral column

Origin of Longissimus Cervicis

TP of upper 4 to 6 thoracic vertebrae medial to insertion of longissimus thoracis

Insertion of Longissimus cervicus

TP of C2-C6

Innervation of Longissimus Cervicis

Dorsal rami of spinal nerves C4-C8