What are the muscles of the neck, their functions, and the cosmetic effects of neuromodulators like Botox (Botulinum Toxin)

Muscles of the Neck and Cosmetic Effects of Botulinum Toxin

Botulinum toxin injections to the neck muscles are highly effective for cosmetic improvement by temporarily paralyzing specific muscles through inhibition of acetylcholine release at neuromuscular junctions, with optimal results achieved using 135 units of OnabotulinumtoxinA (Botox) administered every 84 days. 1

Neck Muscles and Their Functions

The neck muscles can be categorized into several functional groups:

Anterior Neck Muscles

• Sternocleidomastoid (SCM)

  • Function: Rotation and flexion of the head; when both sides contract, they flex the neck
  • Cosmetic concerns: Prominent bands that can create a "corded" appearance

• Platysma

  • Function: Depresses the lower jaw and lip
  • Cosmetic concerns: Creates vertical bands and contributes to neck sagging with age

Posterior Neck Muscles

• Trapezius

  • Function: Elevation, retraction, and rotation of the scapula; extension of the neck
  • Cosmetic concerns: Bulky appearance at the base of the neck

• Splenius muscles (splenius capitis and splenius cervicis)

  • Function: Extension and rotation of the head and neck
  • Cosmetic concerns: Contribute to thick neck appearance

Deep Neck Muscles

• Scalene muscles (anterior, middle, posterior)

  • Function: Elevation of first and second ribs; lateral flexion of the neck
  • Cosmetic concerns: Less visible but contribute to neck contour

• Suboccipital muscles

  • Function: Extension and rotation of the head
  • Cosmetic concerns: Affect upper neck contour and head position

Mechanism of Action of Neuromodulators

Botulinum toxin works through a specific biochemical pathway:

1. Binding: The toxin binds to receptors on cholinergic nerve terminals 2
2. Internalization: After binding, the toxin is internalized into the nerve terminal
3. Enzymatic action: The light chain of the toxin acts as a zinc proteinase that cleaves proteins essential for acetylcholine release 3
4. Blockade of neurotransmission: This prevents the release of acetylcholine at the neuromuscular junction, causing temporary muscle paralysis 2, 3

Cosmetic Applications of Botulinum Toxin in the Neck

Treatment Targets and Effects

• Platysmal bands: Injection into the platysma muscle reduces vertical banding and creates a smoother neck contour
• Horizontal neck lines: Treatment softens transverse neck wrinkles
• Neckline definition: Strategic injections can improve the jawline and neck contour
• "Turkey neck": Can reduce the appearance of sagging neck skin by relaxing the platysma

Dosing and Administration

• Recommended dose: 135 units of OnabotulinumtoxinA (Botox), not exceeding 400 units 1
• Frequency: Every 84 days for optimal results 1
• Alternative formulations with similar efficacy include:
  • AbobotulinumtoxinA (Dysport)
  • IncobotulinumtoxinA (Xeomin)
  • RimabotulinumtoxinB (Myobloc) 1

Technique Considerations

• Precision targeting: EMG guidance may be used for precise muscle identification 1
• Injection pattern: Multiple small injections are typically used to create a natural effect
• Depth of injection: Superficial injections for platysmal bands, deeper for other muscles

Potential Side Effects and Complications

• Dysphagia (difficulty swallowing): Can occur if toxin spreads to pharyngeal muscles 4, 1
• Airway concerns: Risk of airway obstruction in rare cases 4, 1
• Voice changes: Breathy voice may result from spread to laryngeal muscles 1
• Neck weakness: Excessive dosing can cause functional limitations
• Asymmetry: Uneven injection technique can lead to asymmetric results

Management of Complications

• Adjust dose and injection sites for future treatments
• Use precise targeting with EMG guidance
• Apply local cooling and analgesics if needed 1

Clinical Pearls

• Patient selection: Best results are seen in patients with good skin elasticity and dynamic wrinkles
• Combined approach: Often paired with other cosmetic procedures for comprehensive rejuvenation
• Treatment failures: May require switching to another botulinum toxin serotype 1
• Contraindications: Include allergy to botulinum toxin and caution in pregnancy and with anticoagulant use 1
• Follow-up: Patients should be reassessed within 1 month after initial treatment to evaluate results and side effects 1

Special Considerations

• Effects are temporary, lasting approximately 3-4 months
• Repeated treatments may lead to longer-lasting effects due to muscle atrophy
• Treatment should be tailored based on individual neck anatomy and aesthetic goals
• Combination with other modalities (fillers, skin tightening procedures) may enhance results

Botulinum toxin has transformed from being known as a potent toxin 5 to a valuable therapeutic and cosmetic agent with applications extending far beyond its original use 6.