Peripheral Parasympathetic Ganglia and Cervical Sympathetic Chain

PARASYMPATHETIC GANGLIA OF HEAD AND NECK

– The head and neck contain four pairs of parasympathetic ganglia:

1. Submandibular ganglia.
2. Pterygopalatine ganglia.
3. Otic ganglia.
4. Ciliary ganglia.

General Features

• Each ganglion contains the cell bodies of postganglionic parasympathetic neurons.
• Preganglionic parasympathetic fibres synapse with these neurons within the ganglion.
• Sensory and postganglionic sympathetic fibres pass through or communicate with these ganglia without synapsing.
• The submandibular, pterygopalatine, and otic ganglia provide secretomotor innervation to glands.
• The ciliary ganglion supplies parasympathetic fibres to the sphincter pupillae and ciliary muscle.

Special Feature of Otic Ganglion

• Motor fibres from the nerve to medial pterygoid (a branch of the mandibular nerve) pass through the otic ganglion without synapsing.
• These fibres supply the tensor tympani and tensor veli palatini muscles.

CERVICAL SYMPATHETIC CHAIN

• The cervical sympathetic chains are paired structures situated on either side of the cervical vertebral column.
• They lie posterior to the carotid sheaths and anterior to the prevertebral fascia.
• They convey sympathetic fibres to the head, neck, upper limbs, and thoracic viscera.

Formation

Preganglionic Fibres

• The cervical spinal cord does not give rise to white rami communicantes.
• Preganglionic sympathetic fibres arise from the upper thoracic spinal cord, mainly T1–T5.
• They enter the thoracic sympathetic trunk and ascend to the cervical sympathetic ganglia.

Postganglionic Fibres

• Postganglionic fibres leave the cervical ganglia through grey rami communicantes and visceral or vascular branches.
• They reach cervical spinal nerves, blood vessels, glands, and other target structures.

Relations

Anteriorly

1. Internal carotid artery.
2. Common carotid artery.
3. Carotid sheath.

Posteriorly

1. Prevertebral fascia.
2. Longus capitis.
3. Longus colli.
4. Transverse processes of cervical vertebrae.

CERVICAL SYMPATHETIC GANGLIA

• The cervical sympathetic trunk usually contains three ganglia:
  1. Superior cervical ganglion.
  2. Middle cervical ganglion.
  3. Inferior cervical ganglion.
• These ganglia develop through fusion of embryonic cervical sympathetic ganglia.

Superior Cervical Ganglion

– It is the largest cervical sympathetic ganglion, formed by fusion of the upper four primitive cervical ganglia.

Morphology and Location

• Shape: Fusiform.
• Length: Approximately 2.5 cm.
• Position: It lies opposite C2 and C3 vertebrae, just below the skull base.
• Relations: It lies posterior to the internal carotid artery, on the longus capitis muscle, anterior to the prevertebral fascia.

Branches

1. Grey Rami Communicantes

– They connect the ganglion to the upper four cervical spinal nerves (C1–C4).

2. Pharyngeal Branches

• They contribute sympathetic fibres to the pharyngeal plexus.
• Small branches may reach the carotid sinus and carotid body.

3. Superior Cervical Cardiac Nerve

• It descends into the thorax and joins the cardiac plexus.
• Its fibres contribute to sympathetic regulation of cardiac activity.

4. External Carotid Branches

• They form a sympathetic plexus around the external carotid artery and its branches.
• Some fibres pass through the otic and submandibular ganglia without synapsing.
• They provide vasomotor and sudomotor innervation to structures supplied by the external carotid arterial system.

5. Internal Carotid Nerve

• It ascends along the internal carotid artery and forms the internal carotid sympathetic plexus.
• This plexus gives the following branches:

a. Caroticotympanic Nerves

– They enter the middle ear and contribute sympathetic fibres to the tympanic plexus.

b. Deep Petrosal Nerve

• It joins the greater petrosal nerve to form the nerve of the pterygoid canal.
• Its sympathetic fibres reach the pterygopalatine ganglion and pass through without synapsing.
• Other fibres from the internal carotid plexus reach the dilator pupillae and superior tarsal muscle through orbital pathways.

c. Nervus Conarii

– It is a small sympathetic pathway traditionally described as supplying the pineal gland.

d. Terminal Branches

– They accompany the intracranial branches of the internal carotid artery and provide sympathetic innervation to related structures.

Middle Cervical Ganglion

• It is the smallest cervical sympathetic ganglion and may occasionally be absent.
• It develops mainly from fusion of the fifth and sixth primitive cervical ganglia.

Location

• It lies near the C6 vertebral level, close to the inferior thyroid artery.
• It is situated anterior to the lower cervical transverse processes.

Communications

• The ganglion communicates with the inferior cervical ganglion through sympathetic connections.
• Ansa subclavia: It forms an anterior loop around the subclavian artery.
• Additional posterior connections may be closely related to the vertebral artery.

Branches

1. Grey rami communicantes: They connect with the C5 and C6 spinal nerves.
2. Thyroid branches: They accompany the inferior thyroid artery and provide sympathetic fibres to the thyroid and parathyroid glands.
3. Middle cervical cardiac nerve: It descends to the cardiac plexus and is usually the largest cervical sympathetic cardiac nerve.
4. Tracheal and oesophageal branches: They provide sympathetic innervation to the adjoining viscera.

Inferior Cervical Ganglion

• It develops mainly from fusion of the seventh and eighth primitive cervical sympathetic ganglia.
• It frequently unites with the first thoracic sympathetic ganglion to form the stellate (cervicothoracic) ganglion.

Location

• It lies near the junction of the transverse process of C7 and the neck of the first rib.
• It is closely related to the vertebral artery anteriorly and the C8 spinal nerve posteriorly.

Branches

1. Grey rami communicantes: They connect with the C7 and C8 spinal nerves.
2. Inferior cervical cardiac nerve: It descends to the cardiac plexus.
3. Vascular branches: They form sympathetic plexuses around the subclavian and vertebral arteries.

ANSA SUBCLAVIA

• The ansa subclavia is a sympathetic nerve loop connecting the middle and inferior cervical sympathetic ganglia.
• It curves around the subclavian artery near the root of the neck.
• It conveys sympathetic fibres between the two ganglia and contributes to the autonomic innervation of nearby vessels.

Clinical Integration

Referred Cardiac Pain

• Visceral pain fibres from the heart generally travel with sympathetic pathways towards the upper thoracic spinal cord.
• These sensory fibres mainly enter the spinal cord at T1–T5 segments.
• Pain may therefore be referred to corresponding somatic regions, including:
  1. Left anterior chest wall.
  2. Left shoulder.
  3. Medial aspect of the left upper limb.
  4. Medial forearm and hand.

– Anatomical basis: Convergence of cardiac visceral and somatic sensory inputs within the spinal cord causes referred pain.

HORNER SYNDROME

• Horner syndrome results from interruption of the sympathetic pathway supplying the eye and face.
• It may occur following injury to central, preganglionic, or postganglionic sympathetic fibres.