Anatomy: Bones of the Neck - EASY

Overview

• The neck serves as a vital pathway for numerous critical structures, acting as a conduit between the head and the trunk
• It houses several organs, including the larynx, trachea, pharynx, esophagus, thyroid gland, jugular veins, carotid arteries, nerves, lymphatics, and muscles

Clinical Note: Cervical Pain

• Cervical pain can arise from various causes
• These causes include inflamed lymph nodes, herniation of intervertebral discs, and bony abnormalities.
• Bone abnormalities are commonly chronic, often linked to arthritis.

Bones of the Neck

• The skeletal framework of the neck comprises several key bones
• These include the cervical vertebrae, hyoid bone, manubrium of the sternum, and clavicle
• The clavicle is associated with the upper limb

Cervical Vertebrae

• There are seven cervical vertebrae in the neck
• Common features of cervical vertebrae include a small body, a large vertebral foramen, and short, bifid spinous processes
• Transverse foramen (foramen transversarium) is present in the transverse processes, facilitating the passage of the vertebral artery

Typical Cervical Vertebrae

• The 3rd, 4th, 5th, and 6th cervical vertebrae share common characteristics

Atypical Cervical Vertebrae

• C1 (atlas), C2 (axis), and C7 (vertebra prominens) exhibit unique features
• The atlas lacks a spinous process and articulates superiorly with the occipital condyles
• The axis possesses an odontoid process (dens)
• Vertebra prominens has a long spinous process (not bifid) and a small transverse foramen that doesn't transmit the vertebral artery

Hyoid Bone

• The hyoid bone is positioned at the level of the C3 vertebra
• It lacks direct articulation with other bones, being suspended by muscles that serve as an attachment point for anterior neck muscles
• The hyoid bone firmly connects to the styloid process via the stylohyoid ligament
• Additionally, it attaches to the thyroid cartilage of the larynx through the thyrohyoid membrane
• Key components of the hyoid bone include the body, greater horn, and lesser horn, with the latter serving as an attachment site for the stylohyoid ligament

Superficial Muscles of the Neck

• The platysma, sternocleidomastoid, and trapezius are among the superficial muscles of the neck

Platysma Muscle

• The platysma is located within the subcutaneous tissue
• It functions as a muscle of facial expression
• The cervical branch of cranial nerve VII innervates it

Sternocleidomastoid Muscle (SCM)

• The SCM divides the neck into anterior and posterior triangles
• It originates with two heads from the manubrium of the sternum and the medial third of the clavicle
• The SCM inserts onto the mastoid process and the superior nuchal line
• Unilateral contraction of the SCM results in lateral bending of the head with the face turning to the opposite side
• Bilateral contraction can flex the neck
• The accessory nerve (CN XI) innervates the SCM

Clinical Note: Congenital Torticollis

• Congenital torticollis is often caused by a fibrous tissue tumor of the SCM that develops before birth
• It can also arise from injury to the SCM during birth
• Head typically bends to the affected side, with the face turned to the opposite side

Clinical Note: Spasmodic Torticollis

• Spasmodic torticollis generally involves the SCM and trapezius, along with other neck muscles

Trapezius Muscle

• The accessory nerve (CN XI) innervates the trapezius muscle,
• The trapezius is considered an upper limb muscle

Cervical Plexus

• The cervical plexus originates from the ventral rami of spinal nerves C1-C4
• It is positioned deep to the SCM and superficial to the carotid sheath
• Branches of the Cervical Plexus
  • Posterior branches supply the anterolateral neck and superior thorax through cutaneous (sensory) branches
  • Ansa cervicalis is a loop formed by superior and inferior branches that innervate the infrahyoid muscles, excluding the thyrohyoid muscle
  • Additional branches include the lesser occipital nerve (sensory), great auricular nerve (sensory), transverse cervical nerve (sensory), supraclavicular nerve (sensory), and phrenic nerve
  • The phrenic nerve primarily originates from C4, with contributions from C3 and C5, providing motor innervation to the diaphragm -Sensory fibers from the phrenic nerve give branches to the pleura and pericardium

Suprahyoid and Infrahyoid Muscles

• Both suprahyoid and infrahyoid muscles attach to the hyoid bone
• Suprahyoid muscles lie superior to hyoid bone
• Infrahyoid muscles lie inferior to hyoid bone
• These muscles are located within the anterior triangle of the neck
• They steady or move the hyoid bone and larynx superiorly and inferiorly

Suprahyoid Muscles

• The four suprahyoid muscles are the mylohyoid, geniohyoid, digastric, and stylohyoid muscles

Mylohyoid Muscle

• Paired mylohyoid muscles form the floor of the mouth, elevating the floor of the mouth, tongue, and hyoid bone
• These are innervated by the mandibular nerve

Geniohyoid Muscle

• The geniohyoid muscle elevates the hyoid bone anterosuperiorly and receives innervation from C1 via the hypoglossal nerve (CN XII)

Digastric Muscle

• The digastric muscle features two bellies (anterior and posterior) connected by an intermediate tendon
• Deep cervical fascia creates a fibrous band that encloses the tendon, as the band enables anterior and posterior movements of the muscle
• It depresses the mandible and raises hyoid bone
• The mandibular nerve innervates the anterior belly, while the facial nerve innervates the posterior belly

Stylohyoid Muscle

• The stylohyoid muscle runs parallel to the superior belly of the digastric, elevating the hyoid bone posterosuperiorly
• The facial nerve innervates this neck muscle

Infrahyoid Muscles

• The four infrahyoid muscles receive innervation from the cervical plexus via the ansa cervicalis
• These muscles are the sternohyoid, omohyoid, sternothyroid, and thyrohyoid

Sternohyoid Muscle

• This particular muscle depresses the hyoid bone

Omohyoid Muscle

• The omohyoid muscle depresses, retracts, and steadies the hyoid bone
• It features two bellies and an intermediate tendon attached to the clavicle by a fascial sling

Sternothyroid Muscle

• The sternothyroid muscle depresses both the hyoid bone and larynx

Thyrohyoid Muscle

• The thyrohyoid muscle depresses the hyoid bone while elevating the larynx

Deep Muscles of the Neck

• There are two groups of muscles at the root of the neck, collectively, prevertebral muscles
• Prevertebral muscles lie posterior to the prevertebral fascia

Anterior Vertebral Muscles

• Anterior vertebral muscles includes the longus capitis, longus colli, rectus capitis anterior, and rectus capitis lateralis

Lateral Vertebral Muscles

• Lateral vertebral muscles include the splenius capitis, levator scapulae, and anterior, middle and posterior scalene muscles

Longus Capitis Muscle

• This muscle is innervated by the ventral rami of C1-C3 spinal nerves.
• It flexes the head (anterior bending of the head relative to atlanto-occipital joints)

Longus Colli Muscle

• This muscle is innervated by the ventral rami of C2-C6 spinal nerves,
• It flexes the neck – anterior bending of the cervical vertebrae C2-C7
• Acting unilaterally, it rotates the head to the opposite side – rotation of the head occurs at the atlanto-axial joint

Rectus Capitis Anterior

• This muscle flexes the head

Rectus Capitis Lateralis

• This muscle flexes the head and helps stabilize the atlanto-occipital joint

Anterior Scalene Muscle

• The anterior scalene muscle elevates the first rib and flexes and laterally rotates the neck

Middle Scalene Muscle

• The middle scalene muscle elevates the first rib during forced inspiration, bending the neck laterally

Posterior Scalene Muscle

• The posterior scalene muscle elevates the second rib during forced inspiration , bending the neck laterally
• Scalene Muscles and Respiration
  • Scalene muscles contribute during inspiration by increasing thoracic volume through elevation the 1st and 2nd ribs.
  • Scalene muscles are classified under accessory muscles of respiration

Scalene Muscle Passageways

• Three significant structures pass between the anterior and middle scalene muscles
  • These structures include the subclavian artery, and the trunks of the brachial plexus
  • Also, the phrenic nerve also crosses between these muscles and can have the rare anatomical variant of piercing the anterior scalene

Fascia of the Neck

• Cervical fascia consists of two primary layers: superficial cervical fascia and deep cervical fascia
• Understanding the arrangement of the cervical fascia is crucial for determining how infections may spread in this region

Superficial Cervical Fascia

• This particular fascia is located between the skin and the investing layer of the deep cervical fascia
• It contains platysma muscle, superficial nerves, and vessels

Deep Cervical Fascia

• This consists of three layers: Investing (superficial) layer, pretracheal fascia, prevertebral fascia

Investing Layer

• Superiorly, it connects to the skull, including the superior nuchal line, mastoid process, zygomatic arch, and mandible, and the hyoid bone, and the spinous processes are cervical vertebrae
• Inferiorly, it connects to the spine, and acromion of scapula, clavicle, and the manibrium of sternum
• Also significant, it encloses the sternocleidomastoid and trapezius muscles

Pretracheal Layer

• The pretracheal layer stretches between the hyoid bone and thorax
• At the thorax, it fuses with the fibrous pericardium (membrane around the heart)
• It includes two layers:
  • Muscular layer which contains the infrahyoid muscles
  • Visceral layer that surround trachea thyroid gland and esophagus
• Continues with the buccopharyngeal fascia posterosuperiorly
• Laterally, it blends with the carotid sheath
• Forming an attachment for the digastric muscles middle tendons portion and the omohyoid
• Forms and attachment fro the digastric muscle to the intermediate tendon (portion) and omohyoid

Prevertebral Layer

The prevertebral layer forms a tube surrounding the vertebral column and accompanying muscles

• The top extends to the base of the skull, while the bottom reaches the T3 vertebra
• At the bottom, it blends in with the anterior longitudinal ligament
• It extends outward and forms the axillary sheath

Carotid Sheath

• The three layers of deep cervical fascia that forms the carotid sheath enclose the following -The carotid arteries ( both Common and Internal) and the nerve plexuses that surround them
  • The Internal jugular vein -The Vagus nerve -The carotid sinus nerve -Some nodes in the deep cervical lymph network
• The carotid sheath and the pretracheal fascia communicate with the cranial cavity superiorly and mediastinum (part of thoracic cavity) inferiorly

Retropharyngeal Space

• A potential space filled with loose connective tissue that's located between the alar and buccopharyngeal fascia
• It enables movement of the pharynx, larynx, and esophagus
• The superior end closes with the skull base, and is closed laterally by the carotid sheath
• At the inferior end, it connects with upper mediastium
• Alar Fascia
  • The alar fascia is a fascia layer that some describe as apart of the prevertebral fascia, some claim it is apart from it and in front of it
  • Infections to this space is a potential avenue into posterior mediastium

Danger Space

• The danger space comes after the alar fascia and runs along the vertebral column between the Crainial base and the diaphragm

Triangles of the Neck

• The neck is divided into two triangles using the SCM: Posterior triangle and Anterior triangle
• Anterior triangle location
  • Ant -- median line
  • Post - SCM
  • Sup - Mandible
  • Apex - jugular manubrium

Contents of the Anterior Triangle

• Contents of the anterior cervical triangle include the suprahyoid and infrahyoid muscles, common carotid artery, internal carotid artery, external carotid artery, branches of the internal juglar bein and trans cervical nerve, branches of the glossopharyngeal

Further Division of the Anterior Triangle

• A hyoid muscle seperates the Posterior into two -Supracalivicular -Occipatial

Subdivision of the Anterior Triangle into Further Smaller Triangles

• The anterior triangle is subdivided into even more small structures that allow you to locate specific structures in the neck
• The four subdivisions are the Submental Triangle, the Submandibular triangle, the Carotid Triangle and the Muscular Triangle

Further Notes on the Subdivisions

• The submental triangle is unpaired
• The remaining three triangles are of course, still triangles

Posterior Cervical Triangle

• Borders are of this triangle is;
  • Ant----- SCM
  • Post---- trapezius
  • Inf------ middle 1/3 of clavicle
  • Apex------- junction of trapezius and SCM
  • Roof----- investing layer of deep fascia -Floor ----- muscles covered by the prevertebral layer of the deep fascia

Contents of the posterior cervical triangle

• Structures
  • Splenius capitis, lavator scapula, middle scalene and posterior scalene muscles
• Veins
  • External jugular v, Subclavian v
• Branches of arteries*
  • Transverse cervical, Supurascapular, Occipital, Subclavian
• Nerves -Axillary cervical (axillary V1) - Roots of the brachial plexus - Pass between the anterior and middle scalene muscles -Cervial Plexus - formed by ventral amiof C2-C4
  • Lymph nodes - In two main groups Superficial ad Deep, superficially nodes drain the others

Anterior cervical triangle

• Borders of thistriangle are, – SCM – Median Line of the neck-Hyoid Bone
• Muscles include platysma, some that contribute to tongue, pharynx,, and some laynix control
• Vessels; carotid (both ) and branches of the jugulein network
• Nerves- transcer, Hypoglassl and glossophranges and and the brancehs that control that area
• Floor is muscular (pharynx, layngix adn thryoud
• Subdivsions of ant triangle include;

  • Sub mental unpaired, just below the chain. Super part of gyoud adn the ant belly. (mylohoid) – Contains only a few nodes from lymph

  • Submandibualr Triangle'

    • Lies inbetween the anduble and digastaric muscle on two end with glands/lymph in area -Caratid trangle – Btwn. Omo, post belly dygastric, s, cdm — Contains cartodi pulation in the Triangle — Common carotides devide at to and -. Muscular Triangle —- Btwn Oymiohiyf scdm and midline — Contains infra those and glands - (thryoud, parathyroif etc)