PowerPoint Handout: Lab 1, Extrinsic Back Muscles

Slide Title Slide Number Osteology of Scapula Slide 2 Summary of Back, Posterior Neck, and Posterior Head Dermatomes Slide 3 Back Muscle Overview Slide4 Extrinsic Back Muscles: Layers Slide 5 Trapezius and Latissimus Dorsi Slide 6 Trapezius: Continued Slide 7 Rhomboid Major, Rhomboid Minor, and Levator Scapulae Muscles Slide 8 Thoracolumbar Fascia Slide 9 Osteology of Scapula

The osseous features of the scapula will be most relevant when we https://3d4medic.al/BwEkQyWz 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 muscle • Medial border: attachment site for rhomboid muscles • Lateral border: relevant now for palpation purposes

Features important for the upper extremity that will be studied later. • Coracoid process • Supraspinous fossa • Infraspinous fossa • Suprascapular notch • Spinoglenoid notch • Glenoid cavity (fossa). Summary of Back, Posterior Neck, and Posterior Head Dermatomes 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 head • C4, C5, C6, C7: Posterior neck • C7-L5: Stripe pattern from base of neck to sacrum Back Muscle Overview

Muscles of the back are organized into two major groups.

1. 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).

2. 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. Extrinsic Back Muscles: Layers

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

1. 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. • Trapezius • Latissimus dorsi • Levator scapula • Rhomboid major and minor

2. The 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 superior • Serratus posterior inferior Trapezius and Latissimus Dorsi https://3d4medic.al/212sIdvy

• 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.

MUSCLE ORIGIN INSERTION INNERVATION BLOOD SUPPLY ACTION External occipital • Superior fibers elevate scapula, upward rotation protuberance, superior Lateral 1/3 of clavicle, scapula (rotates glenoid cavity superiorly) Trapezius nuchal line, spinous acromion, spine of the Spinal accessory nerve Transverse cervical artery • Middle fibers retract scapula processes of cervical and scapula • Inferior fibers: depress scapula, upward rotation thoracic vertebrae scapula (rotates glenoid cavity superiorly) *Thoracodorsal artery, branch Spinous processes of lower Intertubercular groove on *Thoracodorsal nerve of subscapular a., which is a Latissimus dorsi thoracic and lumbar Extends, adducts and medially rotates arm (humerus) humerus branch of brachial plexus branch of 3rd part of axillary vertebrae, iliac crest, sacrum artery *These nerves and arteries will be viewed at a later time. Trapezius: Continued

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 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. Rhomboid Major, Rhomboid Minor, and Levator Scapulae Muscles Trapezius m. Transverse Cervical Superficial Branch • The rhomboid major, rhomboid minor, and https://3d4medic.al/212sIdvy Transverse Cervical Deep Branch levator scapula are all located deep to the Rhomboid m. trapezius muscle. Thyrocervical • The rhomboid muscles are named as two Trunk 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 Subclavian a scapular artery” can originate directly from Trapezius m. the subclavian artery, or be a deep branch of Transverse the transverse cervical artery. Thyrocervical Cervical a. Rhomboid m. Trunk

Subclavian a Dorsal Scapular: (Direct Branch Subclavian)

MUSCLE ORIGIN INSERTION INNERVATION BLOOD SUPPLY ACTION Dorsal scapular artery (Can be direct Spinous processes of lower Retracts and downwardly rotates Rhomboid major Dorsal scapular nerve (C5) branch of subclavian OR a deep cervical and upper thoracic Medial border of the scapula scapula (rotates glenoid cavity and minor from brachial plexus branch of transverse cervical a.) vertebrae inferiorly) ventral rami of 3-4 cervical Dorsal scapular artery (Can be direct Elevates and downwardly rotates Transverse processes of upper nerves and dorsal scapular Levator scapulae Superior angle of scapula branch of subclavian OR a deep scapula (rotates glenoid cavity cervical vertebrae nerve (C5) from brachial branch of transverse cervical a.) inferiorly) plexus Thoracolumbar Fascia 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). • The deep layer is located along the anterior surface of the quadratus lumborum https://3d4medic.al/212sIdvy 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.

Serratus Posterior Inferior

Latissimus Dorsi