Learning Objective: At the end of this session, the learner should be able to describe the origin, course, and distribution of sympathetic fibres to the head and neck, and correlate their function with clinical conditions such as Horner’s syndrome.
The sympathetic nervous system (SNS) is a division of the autonomic nervous system, responsible for the involuntary control of visceral functions. Its actions are classically described as part of the “fight or flight” response, increasing alertness, heart rate, and blood flow while inhibiting non-essential processes like digestion. In the head and neck, the sympathetic fibres primarily regulate smooth muscle of blood vessels, pupils, sweat glands, and glands of the face and eye.
Anatomical Course and Structure
- Sympathetic fibres supplying the head and neck originate from the thoracic spinal cord segments T1–T6.
- These preganglionic fibres ascend in the sympathetic chain (trunk) to synapse in the cervical ganglia.
Cervical Sympathetic Chain
The sympathetic chain runs from the base of the skull to the coccyx, consisting of interconnected ganglia.
In the neck, three main ganglia are usually identified:
- Superior cervical ganglion (C1–C4)
- Middle cervical ganglion (C6)
- Inferior cervical ganglion (C7, often fused with T1 to form the cervicothoracic or stellate ganglion)
Note: The middle ganglion may be absent, and the inferior ganglion often fuses with the first thoracic ganglion.
Superior Cervical Ganglion
Location: Posterior to the carotid artery, anterior to C1–C4 vertebrae.
Major branches:
- Internal carotid nerve: Forms the internal carotid plexus; supplies the eye and intracranial vessels.
- External carotid nerve: Forms plexuses along the external and common carotid arteries to supply facial arteries and glands.
- Nerve to pharyngeal plexus: Joins vagus and glossopharyngeal branches.
- Superior cardiac branch: Contributes to the cardiac plexus.
- Gray rami communicantes: Supply C1–C4 spinal nerves.
Targets:
Eyeball (dilator pupillae), superior tarsal muscle, lacrimal and salivary glands, sweat glands of the face.
Middle Cervical Ganglion
Location: Anterior to the C6 vertebra and inferior thyroid artery.
Major branches:
- Gray rami communicantes: To C5–C6 spinal nerves.
- Thyroid branches: Along the inferior thyroid artery to larynx, pharynx, trachea, and upper oesophagus.
- Middle cardiac branch: To the cardiac plexus.
Inferior Cervical (Cervicothoracic/Stellate) Ganglion
Location: Anterior to the C7 vertebra; often fused with T1 ganglion.
Major branches:
- Gray rami communicantes: To C7, C8, and T1 spinal nerves.
- Branches to subclavian and vertebral arteries: Regulate arterial tone.
- Inferior cardiac nerve: To the cardiac plexus.
Summary Table
| Ganglion | Vertebral Level | Arteries Involved | Target Organs / Functions |
|---|---|---|---|
| Superior cervical ganglion | C1–C4 | Internal, external, and common carotid arteries | Eye (dilator pupillae), superior tarsal muscle, facial sweat glands, nasal and palatine glands, lacrimal glands, salivary glands, pineal gland |
| Middle cervical ganglion | C6 | Inferior thyroid artery | Larynx, trachea, pharynx, upper oesophagus, heart |
| Inferior cervical ganglion | C7 (±T1) | Subclavian and vertebral arteries | Heart, smooth muscle of neck arteries |
Clinical Correlation
Horner’s Syndrome
Definition:
Horner’s syndrome results from interruption of sympathetic supply to the head and neck on one side.
Classic Triad:
- Ptosis – drooping of upper eyelid (paralysis of superior tarsal muscle)
- Miosis – constricted pupil (paralysis of dilator pupillae)
- Anhidrosis – absence of sweating on affected side (loss of sympathetic supply to sweat glands)
Common Causes:
- Spinal cord lesions (C8–T2)
- Neck trauma or surgery
- Pancoast tumour (apical lung cancer compressing sympathetic chain)
Clinical Note:
Pupil constriction and mild ptosis on one side are key signs for diagnosis.
