Sympathetic Nervous System Anatomy - Part 1

Understanding the Sympathetic Nervous System

Overview of the Autonomic Nervous System

• The autonomic nervous system is divided into two main parts: parasympathetic and sympathetic. The sympathetic nervous system is primarily responsible for the fight-or-flight response, reacting to physical stressors on the body.

Efferent Component Differences

• Unlike the somatic nervous system, which has a single neuron connecting the central nervous system (CNS) to peripheral targets, the autonomic nervous system employs a two-neuron sequence involving pre-ganglionic and post-ganglionic neurons.

Anatomical Aspects of Sympathetic Outflow

• Efferent sympathetic outflow originates from T1 to L2 segments in the lateral horn of the spinal cord. Pre-ganglionic neurons exit via the ventral horn, similar to motor neurons in somatic pathways.

Structure of Sympathetic Trunk

• The sympathetic trunk consists of a chain of ganglia extending from the base of the skull to the coccyx, known as paravertebral ganglia, which are collections of neuronal cell bodies outside CNS.

Pathways and Connections

• Sensory information enters through dorsal roots while efferent motor information exits via ventral roots. New structures include white and gray rami communicantes that connect with sympathetic ganglia; white ramus contains myelinated fibers while gray ramus contains unmyelinated fibers.

Neuronal Configurations in Sympathetic Pathways

• There are multiple configurations for how pre-ganglionic fibers can synapse:

• Some synapse at their entry level.

• Others ascend or descend before synapsing.

• Some travel within their own nerves (splanchnic nerves) without joining spinal nerves.

• A few bypass ganglia entirely and synapse near target organs instead.