Sympathetic Nervous System
Sympathetic nervous system
Summary..
Overview
- The sympathetic nervous system brings is active in states of action; it produces the so-called fight or flight response.
- It originates in the spinal cord from the intermediolateral cell column from T1 to L2.
- It relays in paravertebral and prevertebral ganglia.
- It innervates:
- Endocrine and exocrine glands.
- Nonglandular body organs.
- Blood vessels and skin.
the origins of the sympathetic nervous system
- The intermediolateral cell column lies from T1 to L2, which houses the origins of the sympathetic nervous system.
- The paravertebral chain (aka sympathetic chain) as a series of beads on a string.
Paravertebral Chain
24 Ganglia
- On average, it comprises 24 total ganglia:
- 3 cervical
- 10 thoracic
- 3 – 5 lumbar
- 3 – 5 sacral
- And the ganglion impar (which is the most caudal paravertebral ganglion); it neighbors the coccyx.
Cervical & Upper Thoracic Ganglia
- Superior cervical ganglion
- Middle cervical ganglion
- Inferior cervical ganglion
- First thoracic ganglion.
- Stellate ganglion refers to the combined inferior cervical and first thoracic ganglia.
Prevertebral Ganglia
They overlie the descending aorta from superior to inferior as the:
- Celiac
- Aorticorenal
- Superior mesenteric
- Inferior mesenteric
Clinical Correlation - Paraganglioma
Sympatheitc Innervation
Now, we're ready to walk through the sympathetic innervation of the body.
- Demarcate the ciliospinal center of Budge at C8 – T2.
- Show that it innervates the Head and Neck.
- Divide the intermediolateral cell column into:
- T1 to T5, which produce cardiopulmonary splanchnic nerves that innervate the thorax. These nerves originate from the paravertebral chain, which we'll illustrate in part 2 of the tutorial.
- T5 to L2, which produce abdominopelvic splanchnic nerves that innervate the abdomen and pelvis. These nerves bypass the paravertebral ganglia; they synapse in prevertebral ganglia (which we'll illustrate in part 2 of the tutorial).
- The ciliospinal center of Budge is innervated via the posterolateral hypothalamospinal tract. It innervates the superior cervical ganglion.
- Postganglionic superior cervical ganglion fibers ascend the carotid artery to innervate the head and neck.
Horner's Syndrome
See: Horner's syndrome*
- Exam findings of:
- Ptosis
- Miosis
- Anhidrosis
- Occurs from injury along the pathway, most commonly from:
- Medullary brainstem strokes,
- Paravertebral masses (such as Pancoast tumor (a form of apical lung tumor)
- Carotid dissection.
Postganglionic Fiber Projections
Thoracic projections
- Upper and lower postganglionic fibers project to the thorax.
- Lower respiratory tract:
- Trachea
- Lungs
- Heart
Divergence and convergence
Divergence
- To illustrate divergence, we draw a pair of preganglionic sympathetic fibers that originate from the same preganglionic neuron and synapse on separate postganglionic neurons.
Convergence
- To illustrate convergence, we draw a pair of preganglionic sympathetic fibers that originate separately and synapse together on a single postganglionic neuron.
Prevertebral ganglia
Celiac ganglion
- Preganglionic fibers pass the paravertebral chain and synapse on the celiac ganglion, which innervates the:
- Upper 1/3 of the GI tract: the esophagus to the duodenum (the foregut derivatives).
- Adominal organs, represented by the liver.
- Preganglionic fiber synapse on the aorticorenal ganglion, which innervates the:
- Kidneys
- Adrenal glands (aka suprarenal glands).
- Preganglionic fibers synapse on the superior mesenteric ganglion, which innervates the:
- Middle 1/3 of the GI tract: the small intestine to the proximal 2/3 of the transverse colon (the midgut derivatives).
- Preganglionic fiber synapse on the inferior mesenteric ganglion, which innervates the:
- Lower 1/3 of the GI tract: distal 1/3 transverse colon to anal canal (the hindgut derivatives).
- Lower urinary system – the bladder with lower portion of the ureters.
- Reproductive organs (represented by the uterus and fallopian tubes).
- Representative preganglionic sympathetic fiber bypass the paravertebral ganglia and synapse directly in the adrenal gland.
- The adrenal gland releases epinephrine (predominantly).
The abdominopelvic splanchnic nerves
From superior to inferior:
- The greater splanchnic nerve innervates the celiac ganglion.
- The lesser splanchnic nerve innervates the aorticorenal ganglion.
- The least splanchnic nerve innervates the superior mesenteric ganglion.
- The lumbar splanchnic nerve innervates the inferior mesenteric ganglion.
sympathetic innervation of the limbs
- One important clinical correlation is that the stellate ganglion innervates the upper extremity. Stellate sympathectomy is a treatment for upper extremity involvement in reflex sympathetic dystrophy (aka complex regional pain syndrome).