General organization and localization
Sympathetic ganglia are located within the anatomical sympathetic trunk and also form major autonomic plexuses of the abdominal cavity (the most well-known being the celiac plexus).
Outside, each node is covered by a dense connective tissue capsule. From this outer sheath, connective tissue septa extend into the organ, forming the stroma. The most important histological feature of the sympathetic ganglion is the diffuse arrangement of neurons. Unlike spinal ganglia, where cells lie in distinct clusters, here the nerve cell bodies are scattered haphazardly among the elements of the connective tissue stroma.
The cellular composition of the ganglion is represented by two main populations: dominant effector neurons and an additional cell type—SIF cells.
Characteristics of effector neurons
The bulk of the cells in the ganglion consist of effector neurons. According to morphological classification, they belong to multipolar cells: numerous short branching dendrites and only one long axon extend from their cell body.
The cell body of each effector neuron is protected by three successive layers of sheaths:
- Satellite glial cells (mantle gliocytes) — they are located closest to the perikaryon and are easily identified by their small, rounded nuclei.
- Basal lamina.
- Thin connective tissue sheath — the outer layer, which is practically invisible in standard histological preparations.
Preganglionic myelinated fibers approach the ganglion from the spinal cord. They form cholinergic synapses on the bodies and dendrites of effector neurons. In turn, the axons of the effector cells leave the ganglion, head toward the target organ, and form adrenergic synapses there.
Neural connections: divergence and convergence
A sympathetic ganglion is not just a relay station, but a complex distribution center. It is characterized by two important neurophysiological phenomena:
- Divergence (impulse multiplication). A single preganglionic neuron, thanks to branching (collaterals) of its axon, is capable of simultaneously contacting numerous effector neurons. The number of such contacts can reach up to a hundred, ensuring widespread signal propagation.
- Convergence. The reverse process, in which branches from several completely different preganglionic fibers can converge and terminate in synapses on a single effector neuron.
SIF cells: built-in limiters
Of particular interest is the additional population—SIF cells. The name comes from the abbreviation for Small Intensely Fluorescent cells. They cannot be discerned on standard stained slide preparations; special visualization methods are required for this.
Functionally, SIF cells are interneurons with an inhibitory role. They are excited by incoming preganglionic fibers, but their main task is to inhibit the further transmission of the nerve impulse to effector neurons. Signal modulation is thus achieved: SIF cells limit the sympathetic response, preventing it from becoming excessive.
Briefly: answers to topical questions
What specific neurotransmitters are released by the axons of sympathetic ganglion effector neurons in target organs?
In target organs, axons of sympathetic ganglion effector neurons form adrenergic (sympathetic neuroeffector) synapses. Sources indicate norepinephrine as the neurotransmitter for such synapses. In adrenergic synapses, the mechanism of action of norepinephrine is metabotropic; the response of the organ depends on the prevailing receptor type: α1 and β1 are excitatory, while α2 and β2 are inhibitory.
From which embryonic source do the neurons of the sympathetic ganglion develop?
Sympathetic ganglion neurons develop from the neural crest; sources also refer to this source as the ganglionic plates. Neuroblasts (sympathoblasts) migrate from the common primordium of the sympathetic ganglia (the neural crest). Cells of the adrenal medulla develop from the neural crest and serve as analogues of effector sympathetic neurons.
Remember the rule of the three "D"s for the sympathetic ganglion: Diffuse cell arrangement, Long axons (and short dendrites), Divergence of the impulse.
Class and exam questions
What is the difference in cell arrangement between a sympathetic ganglion and a spinal ganglion?
In the sympathetic ganglion, neuronal cell bodies lie diffusely (scattered throughout the stroma), whereas in the spinal ganglion they form ordered groups at the periphery of the organ.
What synapses are formed on the dendrites of effector neurons?
On the bodies and dendrites of effector neurons, preganglionic myelinated fibers form cholinergic synapses.
Can SIF cells be visualized with hematoxylin and eosin staining?
No, these small intensely fluorescent cells are indistinguishable in standard histological preparations.
What is divergence in a sympathetic ganglion?
This is impulse multiplication, where a single preganglionic neuron transmits a signal to many (up to 100) effector neurons simultaneously via axon collaterals.
What else to study on this topic
- Morphology and ultrastructure of mantle gliocytes
- Specific methods for identifying SIF cells in tissue
- Mechanisms of adrenergic synapse formation
- Topography and structure of the celiac plexus
- Histochemistry of cholinergic synapses in the autonomic nervous system
Master the entire topic in the "Histology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the topic "Sympathetic ganglion" and 3,485 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 137 video lessons on the subject
Other topics in "Nervous system: nerves, ganglia, spinal cord"
Free video lessons: histologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.