3.7 The Nervous System in Cosmetology
Key Takeaways
- The nervous system has three divisions: the central nervous system (brain and spinal cord), the peripheral nervous system (sensory and motor nerves), and the autonomic nervous system (involuntary control, split into sympathetic and parasympathetic).
- The fifth cranial nerve, the trigeminal, is the chief sensory nerve of the face and controls chewing; its three branches are the ophthalmic, maxillary, and mandibular.
- The seventh cranial nerve, the facial nerve, is the chief motor nerve of the face and controls facial expression.
- The eleventh cranial nerve, the accessory nerve, supplies the muscles of the neck and back, and the cervical nerves supply the scalp, neck, and back of the head.
- Sensory nerves carry impulses toward the brain and produce touch, heat, cold, pressure, and pain; motor nerves carry impulses from the brain to muscles and are what massage and electrotherapy stimulate.
Why Nerves Matter at the Chair
Massage feels good because it stimulates motor nerve points — the places where a motor nerve enters the muscle. Electrotherapy works because current follows nerve pathways. And the single most-tested nerve fact in cosmetology, the difference between the trigeminal (fifth cranial) and facial (seventh cranial) nerves, is the difference between sensation and movement.
Neurology is the study of the nervous system.
The Three Divisions
| Division | Components | Function |
|---|---|---|
| Central nervous system (CNS) | Brain and spinal cord | Controls consciousness, mental activity, voluntary function of the five senses, and voluntary muscle action |
| Peripheral nervous system (PNS) | Sensory and motor nerves extending from the brain and spinal cord to the rest of the body | Carries messages to and from the CNS |
| Autonomic nervous system (ANS) | Sympathetic and parasympathetic divisions | Regulates involuntary muscles, glands, breathing, digestion, and circulation |
The sympathetic division drives the fight-or-flight response; the parasympathetic division restores calm and normal function. A relaxing facial or scalp massage is, physiologically, a parasympathetic shift — which is why clients often fall asleep.
The brain is the largest mass of nerve tissue in the body, weighing roughly 44 to 48 ounces (about 3 pounds), and 12 pairs of cranial nerves emerge from it. The spinal cord originates in the brain, extends down the length of the trunk, and gives rise to 31 pairs of spinal nerves.
The Neuron
A neuron — a nerve cell — is the primary structural unit of the nervous system:
DENDRITES CELL BODY / NUCLEUS AXON --> AXON TERMINAL
(receive impulses) --> (processes) --> (sends impulse away from cell)
- Dendrites are tree-like branches that receive impulses from other neurons.
- The axon and axon terminal send impulses away from the cell body to other neurons, glands, or muscles.
Nerve Types
| Type | Also Called | Direction | Produces |
|---|---|---|---|
| Sensory nerves | Afferent nerves | Toward the brain and spinal cord | Touch, heat, cold, sight, hearing, taste, smell, pain, pressure |
| Motor nerves | Efferent nerves | Away from the brain, to muscles and glands | Movement and secretion |
| Mixed nerves | — | Both directions | Both sensation and movement |
Sensory nerve endings called receptors are located near the surface of the skin, in the papillary layer of the dermis. A reflex is an automatic nerve reaction to a stimulus — pulling the hand away from a hot curling iron before the brain consciously registers heat.
Cranial Nerves of the Face and Head
Of the 12 cranial pairs, three dominate cosmetology examinations:
Fifth Cranial Nerve — Trigeminal (Trifacial)
The chief sensory nerve of the face, and the nerve that controls chewing. It has three branches:
| Branch | Area Supplied |
|---|---|
| Ophthalmic | Skin of the forehead, upper eyelids, and interior of the nose; includes the supraorbital, supratrochlear, infratrochlear, and nasal nerves |
| Maxillary | Upper part of the face; includes the zygomatic, infraorbital, and zygomaticofacial nerves |
| Mandibular | Lower part of the face; includes the auriculotemporal, mental, and mandibular nerves |
Seventh Cranial Nerve — Facial
The chief motor nerve of the face. It emerges near the lower part of the ear and extends to the muscles of the neck. Its branches — posterior auricular, temporal, zygomatic, buccal, mandibular, and cervical — control the muscles of facial expression.
Eleventh Cranial Nerve — Accessory
A motor nerve that supplies the muscles of the neck and back, controlling head and shoulder movement.
The exam discriminator. Fifth = sensation (and chewing). Seventh = expression. If the question describes what the client feels, it is trigeminal. If it describes what the client's face does, it is facial.
Cervical Nerves
Cervical nerves originate at the spinal cord and supply the scalp, neck, and back of the head:
- Greater occipital nerve — back of the head, up to the crown.
- Lesser occipital nerve — the scalp and muscles behind the ear.
- Greater auricular nerve — the side of the neck, the external ear, and the areas in front of and behind the ear.
- Cervical cutaneous nerve — the front and side of the neck to the breastbone.
These are the nerves stimulated in a scalp massage during a shampoo service, which is why a properly performed shampoo massage relieves tension well beyond the scalp itself.
Nerves of the Arm, Hand, and Lower Leg
| Nerve | Supplies |
|---|---|
| Ulnar | Little-finger side of the arm and palm |
| Radial | Thumb side of the arm and back of the hand |
| Median | Smaller nerve than ulnar and radial, running the mid-forearm into the hand; supplies both arm and hand |
| Digital | Fingers and toes |
| Tibial | Subdivides in the knee, supplying the ankle and the underside of the foot and toes |
| Common peroneal | Divides into the deep and superficial peroneal nerves supplying the top of the foot |
| Sural | Outer side and back of the foot and leg |
| Saphenous | Inner side of the leg and foot |
The median nerve is the one compressed in carpal tunnel syndrome — an occupational risk for cosmetologists themselves, described in Section 2.3, and a reason to keep pressure off the center of the wrist during a hand massage.
Practical Consequences
- Massage over motor nerve points produces the strongest response with the least force; grinding pressure is unnecessary.
- Any loss of sensation reported by a client is a stop signal. Numbness in the fingers or toes may indicate compression or neuropathy, and it removes the client's ability to warn you about heat or pressure.
- Electrotherapy contraindications track nerve pathways. Clients with pacemakers or metal implants, open lesions, or impaired sensation are excluded from galvanic and high-frequency treatments — covered in Section 7.4.
Which cranial nerve is the chief sensory nerve of the face and also controls the muscles of chewing?
Which statement correctly distinguishes sensory nerves from motor nerves?
Which nerve supplies the little-finger side of the arm and palm?