PowerPoint Handout: Lab 1, Extrinsic Back Muscles - PowerPoint Presentation

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PowerPoint Handout: Lab 1, Extrinsic Back Muscles

Slide Title

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Osteology of Scapula

Slide 2

Summary of Back, Posterior Neck, and Posterior Head Dermatomes

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Back Muscle Overview

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Extrinsic Back Muscles: Layers

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Trapezius and Latissimus

Dorsi

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Trapezius: Continued

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Rhomboid Major, Rhomboid Minor, and Levator Scapulae Muscles

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Thoracolumbar Fascia

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Osteology of Scapula

The osseous features of the scapula will be most relevant when we study the upper limb, but some features of the scapula are important to identify because extrinsic back muscles attach to the scapula. The learning objective for this lab includes all osseous features of the scapula, but I organize the list below by the most relevant for the extrinsic back lab.

Features relevant to extrinsic back muscle

Scapular spine

: attachment site for trapezius muscle (and deltoid, which will be studied later)Acromion: attachment site for trapezius (and deltoid, which will be studied later)Inferior angle: attachment site for latissiumus dorsi and most inferior fibers of rhomboid major m.Superior angle: attachment site for levator scapula muscleMedial border: attachment site for rhomboid musclesLateral border: relevant now for palpation purposesFeatures important for the upper extremity that will be studied later.Coracoid processSupraspinous fossaInfraspinous fossaSuprascapular notchSpinoglenoid notchGlenoid cavity (fossa).  

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A dermatome is a region of skin on one side of the body that is innervated by sensory neurons located in one specific

spinal nerve root/spinal nerve level

.

Note that dermatome maps always show clearly defined lines, but the reality is that there is much overlap between adjacent dermatomes. (More information on dermatomes will be presented in future sessions.)

C2, C3: posterior headC4, C5, C6, C7: Posterior neckC7-L5: Stripe pattern from base of neck to sacrum Summary of Back, Posterior Neck, and Posterior Head Dermatomes

Muscles of the back are organized into two major groups.

Extrinsic back muscles

Movement: Contraction of extrinsic back muscles results in movement of the

upper limb

(superficial layer) or elevation/depression of the ribs during ventilation of the lung (intermediate/deep layer). They DO NOT move the back. Innervation: The extrinsic back muscles are innervated by branches of the ventral primary rami. The exception to this ”rule” is the trapezius muscle, which is innervated by cranial nerve XI (accessory nerve). Intrinsic back muscles Movement: Intrinsic back muscles are responsible for maintaining posture and movement of the head and vertebral column. Innervation: The intrinsic back muscles are innervated by dorsal rami. Back Muscle Overview

The extrinsic back muscles are can be divided into two groups.

The

superficial layer

consists of muscles that connect the axial skeleton to the upper extremity. Because of their attachment to the upper extremity, these muscles are involved with moving the upper limb, and NOT the back. The following muscles are superficial extrinsic back muscles.

TrapeziusLatissimus dorsiLevator scapulaRhomboid major and minorThe intermediate (deep) layer of muscle attaches the vertebrae to the ribs. Due to the attachment on the ribs, these muscles play a minor role in ventilation of the lungs. Because of the minor role they play in ventilation, we place little emphasis on these muscles. These two insignificant muscles are listed below. Serratus posterior superiorSerratus posterior inferiorExtrinsic Back Muscles: Layers

MUSCLE

ORIGIN

INSERTION

INNERVATION

BLOOD SUPPLYACTIONTrapeziusExternal occipital protuberance, superior nuchal line, spinous processes of cervical and thoracic vertebraeLateral 1/3 of clavicle, acromion, spine of the scapulaSpinal accessory nerveTransverse cervical artery

Superior fibers

elevate scapula, upward rotation scapula (rotates glenoid cavity superiorly)

Middle fibers retract scapula

Inferior fibers:

depress scapula, upward rotation scapula (rotates glenoid cavity superiorly)

Latissimus

dorsi

Spinous processes of lower thoracic and lumbar vertebrae, iliac crest, sacrum

Intertubercular groove on humerus

*

Thoracodorsal nerve

branch

of brachial plexus*Thoracodorsal artery, branch of subscapular a., which is a branch of 3rd part of axillary arteryExtends, adducts, and medially rotates arm (humerus)

Trapezius and Latissimus Dorsi

The trapezius and latissimus dorsi are large, flat muscles that both have their proximal attachments on the central axis of the body, while their distal attachments extend laterally to attach to bones of the upper extremity. The axial skeleton (mainly vertebral column) becomes the anchoring point for these muscles to move the upper extremity. Note that the trapezius is divided into 3 parts, each with its own action. See the table below.

NOTE: Origins and insertions are not testable. This information is provided to help you gain a better understanding of the muscles anatomical location and to better understand a muscle’s action.

*These nerves and arteries will be viewed at a later time.

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FUNCTIONAL ANATOMY:

Trapezius Muscle Innervation

The trapezius is the only muscle of the upper limb not innervated by a branch of the brachial plexus (the plexus formed by the ventral primary rami of the C5-T1 spinal nerves). The accessory nerve is considered a cranial nerve because it exits the cranial cavity through a foramen, in this case the jugular foramen.

CLINICAL ANATOMY:

Testing Spinal Accessory Nerve (CN XI)The accessory nerve passes through the lateral and posterior neck to reach the deep surface of the trapezius muscle. This course takes it in close vicinity to the internal jugular vein, the common carotid artery, and the numerous lymph nodes (deep cervical chain of lymph nodes) associated with these structures.  The accessory nerve is susceptible to injury in surgical procedures involving these structures. The function of the trapezius muscle and its nerves supply is tested clinically by asking the patient to shrug his/her shoulders against resistance.Common Carotid a.Internal Jugular v.Trapezius: ContinuedCN XI Testing

MUSCLE

ORIGIN

INSERTION

INNERVATION

BLOOD SUPPLYACTIONRhomboid major and minorSpinous processes of lower cervical and upper thoracic vertebraeMedial border of the scapulaDorsal scapular nerve (C5) from brachial plexusDorsal scapular artery (Can be direct branch of subclavian OR a deep branch of transverse cervical a.)

Retracts and downwardly rotates scapula (

rotates glenoid cavity inferiorly)

Levator

scapulae

Transverse processes of upper cervical vertebrae

Superior angle of scapula

ventral rami of 3-4 cervical nerves and dorsal scapular nerve (C5) from brachial plexus

Dorsal scapular artery

(Can be direct branch of subclavian OR a deep branch of transverse cervical a.)

Elevates and downwardly rotates scapula (

rotates glenoid cavity inferiorly)

The

rhomboid major

, rhomboid minor, and levator scapula are all located deep to the trapezius muscle.

The rhomboid muscles are named as two separate muscles, but form one continuous sheet of muscle.

The blood supply to the rhomboids and levator scapula is supplied by the dorsal scapular artery, but note that the “dorsal scapular artery” can originate directly from the subclavian artery, or be a deep branch of the transverse cervical artery. Rhomboid Major, Rhomboid Minor, and Levator Scapulae Muscles

Dorsal Scapular:

(Direct Branch Subclavian)

Subclavian a

Subclavian a

Thyrocervical

Trunk

Thyrocervical

Trunk

Transverse Cervical Superficial Branch

Transverse Cervical Deep Branch

Trapezius m.

Trapezius m.

Rhomboid m.

Rhomboid

m.

Transverse Cervical a.

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The thoracolumbar fascia

is a fascial complex that covers the deep muscles of the back and trunk. It is attached to the iliac crest, sacrum, rib 12, vertebrae (spinous and transverse processes), and associated intervertebral ligaments. It is thick and opaque in the lumbar region, but is thin and transparent in the thoracic region.

It forms 3 layers that surround muscles.

Posterior: When the skin is removed, only the posterior layer is visible as a thick connective tissue sheet that covers the erector spinae muscle group (an intrinsic back muscle group). Since the erector spinae muscle group is completely surrounded by thoracolumbar fascia, the posterior layer must be incised to reveal the muscle.

The middle layer separates the erector spinae group from the quadratus lumborum muscle (an abdominal muscle that forms a portion of the the posterior abdominal wall by spanning from the 12th rib to the iliac crest). Thoracolumbar Fasciahttps://3d4medic.al/212sIdvyLatissimus DorsiSerratus Posterior InferiorThe deep layer is located along the anterior surface of the quadratus lumborum muscle. The latissimus dorsi and serratus posterior inferior have their proximal attachment on the posterior layer of the thoracolumbar fascia.The thoracolumbar fascia is much thicker and opaque in the lumbar region as compared to the thoracic region where it is thin and transparent.