Neck

The neck is a cylindrical, flexible structure that connects the head to the torso. It serves as a passageway for vital structures such as the spinal cord, blood vessels, airways, esophagus, and muscles. The neck provides support and mobility for the head while protecting these essential components. Anatomically, it is divided into regions like the anterior, posterior, and lateral triangles.

Location

The neck is located between the head and the chest (thorax). It begins at the base of the skull and extends downward to the clavicles (collarbones) and the first rib. Posteriorly, it is bounded by the cervical vertebrae and extends to the upper back.

Anatomy

The neck is a complex and highly organized region of the body that serves as a connection between the head and the torso. It houses critical structures like the spinal cord, blood vessels, nerves, airways, esophagus, and muscles while maintaining flexibility and mobility. The neck is anatomically divided into compartments and regions that facilitate its organization and functions.

Below is a detailed description of the anatomy of the neck:

Boundaries and Regions of the Neck

The neck has distinct anatomical boundaries:

• Superior Boundary: The base of the skull, including the mandible and occipital bone.
• Inferior Boundary: The clavicles (collarbones), sternum, and C7 vertebra (seventh cervical vertebra).
• Posterior Boundary: The nuchal line of the skull and cervical spine.
• Anterior Boundary: The hyoid bone and anterior soft tissues.

The neck is divided into two major regions:

1. Anterior Triangle: Located in the front of the neck.
2. Posterior Triangle: Located at the back of the neck, lateral to the cervical spine.

Skeletal Framework of the Neck

The neck’s skeletal framework is primarily formed by the cervical spine and the hyoid bone:

Cervical Vertebrae

The neck contains seven cervical vertebrae (C1 to C7):

• C1 (Atlas): Supports the skull and allows for nodding movements.
• C2 (Axis): Contains the dens (odontoid process), which allows for rotational movements of the head.
• C3–C7: Provide structural support and flexibility.

The cervical vertebrae also protect the spinal cord and serve as attachment points for muscles and ligaments.

Hyoid Bone

• The hyoid bone is a U-shaped bone located at the level of C3 in the anterior neck.
• It does not articulate with any other bone but serves as an attachment site for muscles involved in swallowing and speech.

Muscles of the Neck

The muscles of the neck are organized into groups based on their location and function. They provide support, enable movement, and protect deeper structures.

 Superficial Muscles

• Platysma: A thin, broad muscle located just beneath the skin. It extends from the chest to the lower face and tenses the skin of the neck.
• Sternocleidomastoid (SCM): A prominent muscle running from the sternum and clavicle to the mastoid process of the temporal bone. It helps rotate and flex the neck.
• Trapezius: A large, triangular muscle that spans the back of the neck and upper back, extending from the skull to the shoulders.

 Anterior Neck Muscles

• Suprahyoid Muscles: Located above the hyoid bone, they include:
  • Digastric, Stylohyoid, Mylohyoid, and Geniohyoid.
  • These muscles assist in swallowing and raising the hyoid bone.
• Infrahyoid Muscles: Located below the hyoid bone, they include:
  • Sternohyoid, Omohyoid, Thyrohyoid, and Sternothyroid.
  • These muscles depress the hyoid bone and larynx during swallowing.

Lateral Neck Muscles

• Scalene Muscles:
  • Anterior, Middle, and Posterior Scalene muscles run from the cervical vertebrae to the first and second ribs.
  • They assist in neck flexion and aid in respiration.

Deep Neck Muscles

• Prevertebral Muscles:
  • Located deep to the cervical vertebrae, they stabilize and flex the neck.
  • Includes longus colli, longus capitis, and rectus capitis anterior/lateralis.

Fascia of the Neck

The neck is enveloped in layers of fascia that compartmentalize its structures:

Superficial Fascia:

Lies just beneath the skin and encloses the platysma muscle.^[1]

Deep Fascia:

Divided into three layers:

• Investing Layer: Surrounds the sternocleidomastoid and trapezius muscles.
• Pretracheal Fascia: Encloses the trachea, esophagus, thyroid gland, and infrahyoid muscles.
• Prevertebral Fascia: Surrounds the vertebral column and associated muscles.
• The carotid sheath, a specialized fascial compartment, encloses the common carotid artery, internal jugular vein, and vagus nerve.

Vascular Structures of the Neck

The neck contains major blood vessels that supply the head and neck:

Arteries

• Common Carotid Artery:
  • Divides into the internal carotid artery (supplies the brain) and external carotid artery (supplies the face and neck).
• Subclavian Artery: Supplies blood to the upper limbs and part of the neck.

Veins

• Internal Jugular Vein: Drains blood from the brain and face into the subclavian vein.
• External Jugular Vein: Drains blood from superficial structures of the neck and face.

Nerves of the Neck

The neck contains both motor and sensory nerves:

• Cervical Plexus: A network of nerves (C1–C4) that innervate the skin, neck muscles, and diaphragm.^[2]
• Brachial Plexus: Nerve roots (C5–T1) supply the upper limbs and part of the neck.
• Cranial Nerves:
  • Vagus Nerve (CN X): Runs within the carotid sheath and innervates thoracic and abdominal organs.
  • Accessory Nerve (CN XI): Innervates the sternocleidomastoid and trapezius muscles.
  • Hypoglossal Nerve (CN XII): Controls tongue movement.
• Sympathetic Trunk: Part of the autonomic nervous system that runs along the cervical spine.

Lymphatic System

The neck contains numerous lymph nodes involved in immune function and drainage:

• Superficial Cervical Nodes: Located near the external jugular vein.
• Deep Cervical Nodes: Lie along the internal jugular vein and receive drainage from the head, neck, and face.

Visceral Structures of the Neck

The neck houses essential viscera, including:

• Pharynx: A muscular tube that connects the nasal cavity and mouth to the esophagus and larynx.
• Larynx: The voice box located anteriorly in the neck. It contains the vocal cords and regulates airflow to the lungs.
• Trachea: A cartilaginous tube that carries air to and from the lungs.
• Esophagus: A muscular tube located posterior to the trachea that transports food to the stomach.
• Thyroid Gland: A butterfly-shaped endocrine gland located in the anterior neck, responsible for hormone production.
• Parathyroid Glands: Small glands located on the posterior surface of the thyroid gland that regulate calcium levels.

Surface Landmarks of the Neck

Prominent surface landmarks include:

• Hyoid Bone: Located at the level of C3.
• Thyroid Cartilage: The “Adam’s apple,” located at C4–C5.
• Cricoid Cartilage: Located at C6, marking the junction of the larynx and trachea.
• Jugular Notch: Located at the superior border of the sternum.

Function

The neck serves as a critical connection between the head and the torso, housing and supporting vital structures necessary for life. Its unique anatomy, including bones, muscles, nerves, blood vessels, airways, and digestive structures, allows it to perform numerous essential functions. Below is a detailed explanation of the neck’s functions:

Structural Support and Head Mobility

The neck provides support for the head and enables its wide range of movements:

Cervical Spine

• The seven cervical vertebrae (C1–C7) form a flexible yet sturdy framework to support the skull and maintain its alignment with the body.
• The atlas (C1) and axis (C2) allow specialized movements:
  • • Flexion/Extension: Forward and backward movements of the head (nodding “yes”).
    • Rotation: Side-to-side turning of the head (shaking “no”).
    • Lateral Flexion: Tilting the head to either side.

Muscles

• Neck muscles, such as the sternocleidomastoid, trapezius, and scalenes, facilitate head movement and provide stability.
• The neck’s flexibility allows humans to orient the head for activities like seeing, hearing, and interacting with the environment.

Passage of Vital Structures

The neck acts as a conduit for essential structures that pass between the head and the torso:

• Respiratory System: The trachea carries air from the larynx (voice box) in the neck to the bronchi of the lungs.
• Digestive System: The esophagus transports food and liquids from the pharynx to the stomach.
• Vascular System:
  • Major blood vessels pass through the neck to supply the head and brain:
    • Common Carotid Arteries: Deliver oxygen-rich blood to the brain, face, and neck.
    • Jugular Veins: Drain deoxygenated blood from the head and neck back to the heart.^[3]
• Nervous System:
  • The spinal cord runs through the cervical spine, carrying motor and sensory information between the brain and the rest of the body.
  • Cranial Nerves and the brachial plexus pass through the neck to innervate the head, neck, and upper limbs.

The neck ensures the safe and organized passage of these critical structures, facilitating life-sustaining functions.

Respiration

The neck plays a vital role in breathing and maintaining the airway:

• The larynx (voice box), located in the anterior neck, ensures the passage of air to the trachea and lungs.
• The trachea carries air from the larynx to the bronchi during inhalation and exhalation.
• Neck Muscles:
  • The scalene muscles assist in breathing by elevating the first and second ribs during deep or forceful respiration.
  • The sternocleidomastoid helps expand the thoracic cavity during inspiration.

The neck ensures uninterrupted airflow while protecting the airway through structures like the epiglottis, which prevents food or liquid from entering the trachea during swallowing.

Swallowing (Deglutition)

The neck facilitates the movement of food and liquids from the mouth to the stomach:

• The pharynx and esophagus are essential components of the digestive pathway:
  • The pharynx connects the oral cavity to the esophagus.
  • The esophagus, a muscular tube, passes through the neck to transport food to the stomach using peristalsis (rhythmic muscular contractions).^[4]
• Hyoid Bone and Muscles: The suprahyoid and infrahyoid muscles move the hyoid bone and larynx during swallowing, enabling the epiglottis to close and prevent aspiration.

This coordinated process ensures efficient and safe swallowing.

Protection of Vital Structures

The neck protects critical structures that are essential for survival:

• Cervical Vertebrae: The cervical spine encloses and protects the spinal cord, which transmits signals between the brain and the rest of the body.
• Muscles and Fascia: Neck muscles and layers of fascia provide additional protection to the trachea, esophagus, blood vessels, and nerves.
• Thyroid Cartilage: Part of the larynx, it shields the vocal cords and airway from trauma.

The neck’s anatomical structures safeguard critical pathways while ensuring their functionality.

Vocalization and Speech

The neck houses the larynx, which is essential for vocalization:

• The vocal cords within the larynx vibrate as air passes through them, producing sound.
• The neck muscles adjust the position and tension of the vocal cords to modify pitch and tone.
• The larynx works with the oral cavity, tongue, and lips to articulate speech.

This function is critical for communication and vocal expression.^[5]

Lymphatic Drainage

The neck plays a major role in immune function through its extensive lymphatic system:

• Superficial and Deep Cervical Lymph Nodes filter lymphatic fluid and trap pathogens, playing a role in the body’s immune defense.
• Lymph nodes in the neck drain lymph from the head, face, oral cavity, and neck structures.

Blood Circulation

The neck is vital for maintaining blood flow to and from the brain:

Arteries:

The common carotid arteries branch into the internal carotid arteries (supply the brain) and the external carotid arteries (supply the face and neck).

Veins:

• The internal jugular veins drain blood from the brain.
• The external jugular veins drain superficial structures of the face and neck.

This circulation ensures a continuous supply of oxygen and nutrients to the brain and other structures.

Sensory and Motor Innervation

The neck serves as a hub for nerves that transmit sensory and motor signals:

• The spinal cord passes through the cervical spine, transmitting nerve signals between the brain and body.
• The cervical plexus innervates the skin, muscles, and diaphragm.^[6]
• The brachial plexus provides innervation to the upper limbs.
• Cranial nerves such as the vagus nerve (CN X) regulate functions like swallowing, speech, and heart rate.

Head and Facial Positioning

The neck enables precise positioning of the head for various tasks:

• Orienting the eyes for vision.
• Aligning the ears to optimize hearing.
• Allowing adjustments for activities like eating, speaking, and social interaction.

Clinical Significance

The neck is a vital anatomical region housing essential structures, making it clinically significant for various conditions:

Trauma and Injury

The neck is prone to blunt or penetrating trauma, which can damage the spinal cord, trachea, carotid arteries, jugular veins, or esophagus, leading to life-threatening complications.^[7]

Cervical Spine Disorders

Conditions such as cervical spondylosis (degeneration of cervical vertebrae), herniated discs, and whiplash injuries can cause neck pain, stiffness, and neurological symptoms.

Thyroid and Parathyroid Disorders

The thyroid gland is susceptible to disorders like hypothyroidism, hyperthyroidism, goiter, and thyroid cancer, requiring medical evaluation and treatment.

Infections and Swellings

• Lymphadenopathy (enlarged lymph nodes) may indicate infections, malignancies, or systemic diseases.
• Infections like abscesses or pharyngitis often present with neck swelling and pain.

Vascular Conditions

• The carotid arteries can develop atherosclerosis, increasing the risk of stroke.
• Carotid artery dissection or aneurysm can cause severe neurological deficits.

Airway Obstruction

Conditions like tracheal compression, foreign bodies, or swelling in the neck can obstruct the airway, requiring urgent intervention.^[8]