Sympathetic nervous system

The sympathetic chain is a component of the autonomic nervous system and is composed of general visceral afferent and efferent axons that allow for involuntary control of bodily functions via the hypothalamus.

The sympathetic chain is external to the spinal column, adjacent to the vertebral bodies and within the peri-vertebral space. It is comprised of paired, longitudinally arranged, para-vertebral sympathetic ganglia linked together by myelinated axons forming the sympathetic trunk. It extends from the upper neck to the coccyx.

Branches from the pre-vertebralprevertebral sympathetic ganglia may communicate with para-vertebral sympathetic ganglia and/or form a plexus prior to innervating the target organ.

- The overarching function of the sympathetic system is to control 'fight or flight' (sympatho-adrenal) response. Several structures innervated by the sympathetic system include:

   - Periphery: vasoconstriction, activates sweat glands, and piloerection

   - Cardiac: increases heart rate and contractility

   - Respiratory: dilates bronchioles

   - GI tract: inhibits peristalsis and vasoconstrictor blood flow.

   - Kidney: increases renin secretion 

   - Eye: dilates pupils and retracts upper eyelid

Sympathetic chain and ganglia:

Structure:

• within the peri-vertebral space, lateral to the vertebral bodies and anterior to the intervertebral foramen at their respective spinal level
• extends from the upper neck to the coccyx
• 23 paired sympathetic ganglia and 1 unpaired coccygeal sympathetic ganglia

Origin

- ComprisedThe sympathetic chain and ganglia are comprised of discrete sympathetic ganglia (containing neuronal cell bodies) which communicate with each ganglia via the sympathetic trunk (containing myelinated axons).

General location:

- Within the peri-vertebral space, lateral to the vertebral bodies and anterior to the intervertebral foramen at their respective spinal level.

- Extends from the upper neck to the coccyx.

- 23 paired sympathetic ganglia and 1 unpaired coccygeal sympathetic ganglia.

Parts by region:

- Cervical

• cervical: 3 discrete ganglia - superior, middle and inferior cervical sympathetic ganglia.

       1. Superior

  • superior cervical ganglion - elongated cylindrical shape formed by embryologically fused C1 to C4 sympathetic ganglia.

         2. Middle

  • middle cervical ganglion

         3. 

  • Stellatestellate ganglion - Inferior: inferior cervical ganglia partially fuses with the T1 sympathetic ganglion - located within the cervicothoracic junction.

    - Thorax

• thorax: T2 to T12 thoracic sympathetic ganglia adjacent to their respective vertebral bodies, located within the posterior mediastinum.

  - Abdomen

• abdomen: L1 to L5 lumbar sympathetic ganglia. Located posteriorly to the thoracolumbar fascia within the peri-vertebral space and posteriomedial to psoas major.

  - Pelvis

• pelvis: S1 - S5-S5 sacral sympathetic ganglia. Located anterolateral to the anterior S1-S4 sacral foramina.

  - Unpaired

• unpaired coccygeal ganglion - also known as ganglion impar.

Course

Efferent pathway:

Intra-axial component:

- Sympathetic

• sympathetic nuclei are located within the hypothalamus.

  - White

• white matter tracts course to spinal cord segments between T1 and L2.

  - Axons

• axons synapse at cell bodies within the intermediolateral nucleus of the grey matermatter lateral horns between T1 and L2 spinal segments.

Thoracolumbar outflow:

- Pre

• pre-ganglionic myelinated fibres enter the sympathetic ganglia at that spinal level by coursing through the ventral roots, spinal nerve and then white ramus communicans.

  -  Above

• above T1 and below L2, there are only grey ramus communicans between the spinal nerve and the sympathetic ganglion.

Within the para-vertebralparavertebral sympathetic ganglion:

     1. Pre-ganglionic

• preganglionic axons may synapse at their respective ganglia, and then re-enter the spinal nerve as post-ganglionicpostganglionic axons (via grey ramus communicans).

            - Supplies

  • supplies dermatomes and myotomes

         2. Pre-ganglionic

• preganglionic axons travel superiorly or inferiorly along the sympathetic chain that connects each sympathetic ganglia, to innervate different body regions.

       3. Pre-ganglionic

• preganglionic axons can leave the sympathetic ganglion directly via sympathetic branches.

Afferent pathway:

1. Cell

• cell bodies are located within the dorsal root ganglion

  2. Axons

• axons travel from the target organ to the dorsal root ganglion via the same plexus and nerves that carry efferent fibres.

  3. Sympathetic

• sympathetic axons can synapse at the intermediolateral nucleus to form a sympathetic reflex arc, or ascend to the hypothalamus within the spinal cord.

Branches

Branches of the para-vertebralparavertebral ganglia, pre-vertebralprevertebral ganglia and plexus (from superior to inferior):

Head:

1. Superior

• superior cervical ganglia send branches to the head via sympathetic branches that accompany the internal and external carotid arteries.

       - Sympathetics

  • sympathetics course with the ophthalmic artery to innervate the dilator pupillae and levator palpabrae superioris.

         - Forms

  • forms the deep petrosal nerve, which combines with the greater petrosal nerve to form the nerve of the pterygoid canal

         - May

  • may course with branches of the external carotid artery to supply sublingual gland, submandibular gland and parotid gland.

Neck/Thorax:

2. Superior

• superior, middle and inferior cardiac nerves (T1-T4) - arise from superior cervical ganglion, middle cervical ganglion, inferior cervical ganglion respectively.

       - Form

  • form the superficial/deep cardiac plexus and pulmonary plexus - supplies the heart and bronchi.

    3. Thoracic

• thoracic cardiac branches - arising from T1-T4 sympathetic ganglia - innervate cardiac plexus.

       - Contribute

  • contribute to oesophageal plexus and thoracic aortic plexus - supplies the oesophagus and thoracic aorta.

Abdomen:

4. Greater

• greater (T5-10) and Lesserlesser (T10-11) splanchnic nerves - arise from the respective thoracic sympathetic ganglia within the posterior mediastinum.

       - Pierce

  • pierce the crura of the diaphragm to enter the abdominal cavity, join the coeliac and superior mesenteric ganglia - communicates with the inferior mesenteric ganglia via the inter-mesenteric plexus.

             - Coeliac

  • coeliac plexus - supplies the liver (via hepatic plexus), gallbladder, bile duct, spleen (via splenic plexus), pancreas, adrenal glands (via suprarenal plexus), and foregut.

             - Superior

  • superior mesenteric plexus - supplies the midgut (via mesenteric branches) by following the superior mesenteric artery.

             - Aorticorenal

  • aorticorenal ganglion - supplies the kidneys via branches from lesser splanchnic (T10-11) - sympathetics course with the renal arteries to innervate the kidneys.

              - Fibres

  • fibres course with the gonadal arteries to innervate the ovaries/testes.

    5. Least

• least (T12) splanchnic nerve and lumbar splanchnic nerves (L1 and L2)

       - Communicate

  • communicate with inferior mesenteric ganglia and course with the inferior mesenteric artery to supply the hindgut.

    6. Superior

• superior hypogastric plexus -: formed by descending fibres from the inferior mesenteric ganglion

Pelvis:

7. Right

• right and left inferior hypogastric plexus - formed as the inferior continuation of superior hypogastric plexus - each courses anterolateral to the sacral promontory.

  8. Sacral

• sacral splanchnic nerves arising from the S1 - S5 sacral sympathetic ganglia provide branches to the inferior hypogastric plexus.

       - Supplies

  • supplies bladder (via vesical plexus), rectum (via rectal plexus), uterus/prostate (via uterovaginal/prostatic plexus).

Relations:

-

Neck

     - Anterior - scalenus anterior

     - Anterolateral -

     - Lateral -

     - Posterior -

- Root of the neck

• posterior:

     - Posterior - T1 spinal nerve

     - Lateral - suprapleural

     - Anterior - Carotid

- Thorax

• posterior:

     - Posterior - intercostal nerves, ribs, intercostal vessels

     - Anterior -

     - Lateral -

- Abdomen

• anterior:

     - Anterior - IVC, abdominal aorta

     - Posterior -

     - Lateral -

- Pelvis

• medial:

     - Medial - sacral foramina, spinal nerves

     - Posterior - sacrum

Blood supply:

- Neck -

• neck: ascending cervical artery and inferior thyroid artery

  - Thorax -

• thorax: posterior intercostal arteries

  - Abdomen -

• abdomen: lumbar arteries

  - Pelvis -

• pelvis: lateral and median sacral arteries

Lymphatic drainage:

- Neck -

• neck: deep cervical chain lymph nodes

  - Thorax -

• thorax: posterior mediastinal lymph nodes

  - Abdomen -

• abdomen: para-aortic lymph nodes, cisterna chyli

  - Pelvis -

• pelvis: internal iliac lymph nodes

Variants:Variant anatomy

- Unfused

• unfused T1 and inferior cervical ganglia (absent stellate ganglion)

  - Doubled

• doubled superior cervical ganglion

  - Absent

• absent superior cardiac branch (usually on the right)

  - Accessory

• accessory L3 white ramus communicans

Interventional procedures:

- Coeliac

• coeliac plexus block

  - Percutaneous

• percutaneous splanchnic nerve radiofrequency ablation

  - Renal

• renal sympathetic denervation