back of shoulder region

Back of the shoulder region

Back of the shoulder region
Muscle groups at the back Trapezius Latissimus dorsi Levator scapulaer & rhomboids Triangle of auscultation Dorsal scapular nerve

Muscles of the back

For descriptive purposes the muscles of the back are divided into three groups: superficial, intermediate, and deep

The deep group(intrinsic back muscles)

They are the true muscles of the back since they are concerned with maintenance of posture and movement of the vertebral column (spine); hence, they are also called erector spinae muscles.

The deep group(intrinsic back muscles)

They are supplied by branches of posterior primary rami of spinal nerves

The intermediate group

Consists of serratus posterior superior and inferior which are respiratory muscles

The superficial group

consists of muscles that connect the upper limb to the vertebral column and are thus concerned with movements of the upper limb
trapezius
Latissimus dorsi
Levator scapulae
rhomboids

Extrinsic back muscles

The intermediate and superficial groups constitute extrinsic back muscles which are supplied by anterior primary rami of spinal nerves

Extrinsic back muscles

They include trapezius

Extrinsic back muscles

They include trapezius latissimus dorsi



Extrinsic back muscles
They include trapezius latissimus dorsi levator scapulae

Extrinsic back muscles

They include trapezius latissimus dorsi levator scapulae and rhomboids

Trapezius

This is a flat triangular muscle that was given its name because the muscles of the two sides form a trapezion (G. = irregular 4-sided figure)

Origin of trapezius

The muscle arises from the occipital bone of the skull

Origin of trapezius

The muscle arises from the occipital bone of the skull (medial third of the superior nuchal line and external occipital protuberance)
External occipital protuberance
Superior nuchal line



Origin of trapezius
from the spines of the cervical and thoracic vertebrae, the latter directly but the former via the ligamentum nuchae because of the backward facing concavity of the cervical vertebrae

The ligamentum nuchae

is an intermuscular septum that represents the interspinous and supraspinous ligaments in the cervical spine.

The ligamentum nuchae

It is triangular in shape and is attached to the occipital bone, spinous processes of cervical vertebrae, and deep cervical fascia

Nerve supply of trapezius

The muscle is innervated by the spinal root of the accessory nerve

The accessory nerve

The 11th cranial nerve Has 2 roots, a cranial root arising from the medulla oblongata and a spinal root arising from the upper five cervical segments of the spinal cord
Cranial root
Medulla oblongata
Spinal root
trapezius
sternocleidomastoid
Cranial root Joins the vagus n.
Accessory n. containing spinal root fibers

Nerve supply of trapezius

The muscle also receives innervation from cervical spinal nerves (C3 and C4), these are proprioceptive (sensory).
Proprioceptives From C3 & C4

Proprioceptors

provide information about position of parts of the body and the range and direction of movement proprioceptors are present in tendons and joint capsules
Sensation (stretch)
motor (tone)

Proprioceptors

In general, motor nerves that supply muscles also carry proprioceptive fibers from them

Proprioceptors

however, there are few exceptions as in the case of trapezius muscle in which the motor and proprioceptive fibers are carried by two different nerves (accessory and cervical nerves respectively)
Cranial root
Medulla oblongata
Spinal root
trapezius
sternocleidomastoid
Cranial root Joins the vagus n.
Accessory n. containing spinal root fibers

Insertion of trapezius

The muscle is inserted into the lateral third of the clavicle, medial side of the acromion and the spine of the scapula above the origin of deltoid muscle
trapezius
deltoid

Insertion of trapezius

the two muscles, deltoid and trapezius may be regarded as being one large continuous sheet with the spine of the scapula, the acromion, and the lateral third of the clavicle exposed between them


Therefore, during abduction of the shoulder, trapezius will elevate the tip of the shoulder which carries with it the deltoid muscle and humerus, the latter being further elevated by deltoid
trapezius
deltoid

Action of trapezius

The upper fibers elevate the scapula as in shrugging the shoulder (in expressing dissatisfaction or uncertainty), squaring the shoulders as in standing in attention

Action of trapezius

This is the basis for the clinical test for the integrity of the accessory nerve
Elevating the shoulders against resistance

Action of trapezius

The tone of the muscle maintains the position of the shoulder and weakness of the muscle thus produces drooping of the shoulder (good tailors are aware of this and if the client has weak muscles they can give impression of health and virility by appropriate padding of the jacket)

Action of trapezius

Acting in opposite direction the upper fibers of the muscle can extend the head as in looking upwards

Action of trapezius

The middle fibers retract the scapula

Action of trapezius

the lower fibers depress the scapula

Action of trapezius

The muscle as a whole acts as a fixator of the scapula when other muscles such as the deltoid are acting on the humerus



Action of trapezius
The upper and lower fibers rotate the scapula during abduction of the shoulder so that the glenoid fossa faces upwards. The upper fibers elevate the acromion while the lower fibers depress the medial end of the scapular spine acting as a couple
Upper fibers of trapezius
Lower fibers of trapezius

Action of trapezius

test: the shoulder is shrugged against resistance and the upper border of the muscle is seen and felt, if paralyzed, the combined actions of levator scapulae and serratus anterior may compensate

Latissimus dorsi

Is a wide flat muscle of the back. This is indicated by its name which in Latin means widest of the back
Latissimus dorsi

Latissimus dorsi

Its origin is overlapped by that of trapezius by six spine is i.e. it arises from the lower six thoracic spines
origin

Latissimus dorsi

its origin continues downward to the lumbar spines via the thoracolumbar fascia and then continues to the iliac crest
Thoracolumbar fascia
Iliac crest
origin

Latissimus dorsi

The upper border of the muscle loops (wraps) the inferior angle of the scapula from which it receives some fibers of origin
origin

Latissimus dorsi

some other fibers are also received from the lower 4 ribs
12
11
10
9
origin

Latissimus dorsi

The fibers of the muscle converge to form a strong ribbon-like tendon that wraps around the lower border of teres major muscle to be inserted into the floor of the intertubercular groove of the humerus
Teres major
tendon of latissimus dorsi
insertion

Latissimus dorsi

tendon of latissimus dorsi
Teres major
insertion

Latissimus dorsi

at the intertubercular groove pectoralis major is attached to the lateral lip, latissimus dorsi is attached to the floor, teres major to the medial lip and the mnemonic "Lady D lies in bed between two majors" may be useful
insertion
pectoralis major
latissimus dorsi
teres major

Latissimus dorsi

The muscle is innervated from the thoracodorsal nerve (nerve to latissimus dorsi) from the brachial plexus
Thoracodorsal n.
Nerve supply



Latissimus dorsi action
The muscle is an adductor, medial rotator and extensor of the humerus
Medial rotation

Action

The action of latissimus dorsi is similar to scratching the opposite scapula
Medial rotation


Acting from the opposite direction (if the arm is fixed) the muscle will pull the trunk and is thus important for climbers similar to pectoralis major, both acting as a sling from the trunk to the arm but latissimus dorsi is more powerful
Latissimus dorsi action

Levator scapulae & rhomboids

These muscles connect the scapula and the spine They extend from cervical and upper thoracic spine.

Arises from transverse processes of some cervical vertebrae

Levator scapulae
origin



Arise from spinous processes of cervical and upper thoracic vertebrae.
Rhomboids
origin


The 3 muscles are attached to the medial border of the scapula; levator scapulae to the superior part of the medial border, rhomboid minor at the root of the scapular spine, rhomboid major inferior to the scapular spine.
Levator scapulae & rhomboids
insertion
Levator scapulae
Rhomboids minor
Rhomboids major

All the three muscles are supplied by dorsal scapular nerve.

Levator scapulae & rhomboids
Dorsal Scapular n.
Nerve supply


All the three muscles elevate and retract the scapula and thus have a function similar to the upper and the middle fibers of trapezius. They also rotate the scapula so that the glenoid cavity faces downward and action opposite to that of trapezius and serratus anterior
Levator scapulae & rhomboids
Action
elevation
retraction

Triangle of auscultation

The boundaries of this triangle are trapezius, latissimus dorsi, and rhomboids major attached to the medial border of the scapula.

Triangle of auscultation

The triangle enlarges when the scapula is drawn forwards by folding the arms across the chest

Triangle of auscultation

The floor is formed of ribs 6 & 7 and the sixth intercostal space which thus becomes subcutaneous, therefore respiratory sounds maybe heard better with a stethoscope in the triangle of auscultation.

Triangle of auscultation

On the left side deep to the triangle is the cardiac orifice of the stomach where the splash of swallowed liquids was timed in cases of esophageal obstruction before the days of barium swallow.

Dorsal scapular nerve

This nerve is a branch of the brachial plexus

Dorsal scapular nerve

It can be seen in the back lying on serratus posterior superior deep to levator scapulae and rhomboids which it supplies it is accompanied by and lies medial to the descending branch of the transverse cervical artery