4.5 Neurology: Nerves of the Head, Face and Neck

4.5 Neurology: Nerves of the Head, Face and Neck

1. Neurology: Nervous System of the Head, Face, and Neck

Neurology is the scientific study of the structure, function, and pathology of the nervous system. The nervous system is the master regulatory network that coordinates every bodily function, sensory perception, and motor action.

Structural Divisions of the Nervous System

1. Central Nervous System (CNS): Comprises the brain and spinal cord. Controls consciousness, mental activities, voluntary motor commands, and processing of sensory data.
2. Peripheral Nervous System (PNS): A vast network of 12 pairs of cranial nerves and 31 pairs of spinal nerves that link the CNS to all sensory receptors, muscles, and glands.
3. Autonomic Nervous System (ANS): The involuntary branch regulating internal visceral organs, cardiac muscle, blood vessels, and cutaneous glands. Subdivided into:
   • Sympathetic Division: "Fight-or-flight" response; causes vasoconstriction, elevates heart rate, and stimulates sweat gland secretion.
   • Parasympathetic Division: "Rest-and-digest" state; promotes vasodilation, cellular repair, digestion, and systemic relaxation during esthetic treatments.

Functional Nerve Classifications

• Sensory (Afferent) Nerves: Carry electrochemical impulses from peripheral sensory receptors (pain, temperature, touch) toward the brain and spinal cord.
• Motor (Efferent) Nerves: Transmit motor impulses away from the brain and spinal cord to muscles (triggering contraction) or glands (triggering secretion).
• Mixed Nerves: Contain both sensory and motor fibers capable of bidirectional transmission.

The Three Critical Cranial Nerves in Esthetics

                     THREE CRITICAL CRANIAL NERVES
                                   │
       ┌───────────────────────────┼───────────────────────────┐
       ▼                           ▼                           ▼
FIFTH CRANIAL (V)          SEVENTH CRANIAL (VII)       ELEVENTH CRANIAL (XI)
  • Trigeminal / Trifacial   • Facial Nerve              • Accessory Nerve
  • CHIEF SENSORY of face    • CHIEF MOTOR of face       • MOTOR to neck muscles
  • Motor to mastication     • Controls muscles of         (SCM & Trapezius)
  • 3 Branches: Ophthalmic,    facial expression
    Maxillary, Mandibular

1. Fifth Cranial Nerve (Trigeminal / Trifacial Nerve - CN V)

• Nature: The largest cranial nerve; a mixed nerve serving as the chief sensory nerve of the entire face and the motor nerve for the muscles of mastication (masseter, temporalis).
• Three Primary Branches:
  • Ophthalmic Branch: Pure sensory branch supplying the forehead, upper eyelids, orbit, frontal sinuses, and bridge of the nose. Key divisions include the supraorbital nerve and supratrochlear nerve.
  • Maxillary Branch: Pure sensory branch supplying the upper jaw, teeth, gums, hard palate, lower eyelids, side of nose, upper lip, and cheekbones. Key divisions include the infraorbital nerve and zygomatic nerve.
  • Mandibular Branch: Mixed branch supplying sensory innervation to the lower jaw, lower teeth, chin, lower lip, and anterior tongue, while delivering motor fibers to the masseter and temporalis muscles. Key division is the mental nerve (exiting the mental foramen).

2. Seventh Cranial Nerve (Facial Nerve - CN VII)

• Nature: The chief motor nerve of the face. Emerges from the brainstem, passes through the parotid gland, and supplies motor innervation to all muscles of facial expression and the scalp.
• Key Branches:
  • Temporal Branch: Forehead, frontalis, orbicularis oculi, and corrugator.
  • Zygomatic Branch: Upper cheek muscles and orbicularis oculi.
  • Buccal Branch: Buccinator, risorius, and orbicularis oris.
  • Marginal Mandibular Branch: Lower lip and chin muscles (mentalis, depressor anguli oris).
  • Cervical Branch: Platysma muscle in the neck.

3. Eleventh Cranial Nerve (Accessory Nerve / Spinal Accessory - CN XI)

• Nature: A motor cranial nerve that controls the major skeletal muscles of the neck and upper shoulders—specifically the sternocleidomastoid (SCM) and trapezius.
• Esthetic Relevance: Vital during neck, shoulder, and upper back massage manipulations.

Cranial Nerve Summary Matrix

2. The Neuron and the Twelve Cranial Nerves

A neuron, or nerve cell, is the structural unit of the nervous system. Dendrites are short branched fibers that receive impulses, the cell body houses the nucleus, and the axon carries the impulse away toward the next cell across a junction called the synapse. Nerves are bundles of these fibers wrapped in connective tissue, and human nerve tissue repairs slowly — which is why nerve-adjacent injury is a serious complication rather than a cosmetic one.

Twelve pairs of cranial nerves leave the brain and are numbered front to back:

Only three of the twelve are examined in depth for esthetics, but knowing the numbering prevents the single most common error on this topic: pairing "seventh" with sensation instead of movement.

3. Named Branches You Work Over During a Facial

Sensory branches of the trigeminal nerve surface through named openings in the skull and can be tender if pressure is applied directly over them:

• Supraorbital and supratrochlear — forehead and upper eyelid, emerging along the superior orbital rim.
• Infratrochlear and nasal — the side and tip of the nose.
• Zygomatic and infraorbital — upper cheek, lower eyelid and upper lip, the infraorbital branch emerging roughly a finger's width below the lower orbital rim.
• Auriculotemporal — external ear and temple.
• Mental — chin and lower lip, emerging at the mental foramen.

The neck and shoulders are supplied by the cervical plexus, whose cutaneous branches are the lesser occipital, great auricular, transverse (cervical) cutaneous and supraclavicular nerves; the greater occipital nerve, a posterior branch of the second cervical nerve, serves the back of the scalp. When a facial includes a hand and arm massage you are working over the digital, radial, median and ulnar nerves.

Motor points and two conditions that change the plan

A motor point is the surface location at which a nerve enters its muscle, where stimulation produces the strongest contraction for the least current. Microcurrent and faradic pad placements are chosen from these points, and tapotement is directed over them rather than over unsupported soft tissue.

Two neurological conditions alter what is permissible. Bell's palsy is a one-sided paralysis of cranial nerve VII producing facial droop and incomplete eye closure; trigeminal neuralgia is severe stabbing pain along a branch of cranial nerve V, in which even light touch can trigger an attack. Both call for a physician release before stimulating current or firm massage is used, and both are conditions to recognize and refer — never to diagnose.