The preganglionic neurons of the parasympathetic nervous system come from brainstem nuclei and the sacral spinal cord, specifically S2-S4. Neurons that begin in the brainstem exit the CNS through cranial nerves, while those from the sacral cord join to form the pelvic splanchnic nerves.

Preganglionic parasympathetic neurons are located within the nuclei of the four cranial nerves (CN III, VII, IX, X) as well as the sacral spinal segments (S2-S4); therefore, parasympathetic outflow is both cranial and sacral. Parasympathetic cardiac innervation originates from the medulla oblongata in the brainstem.

The parasympathetic nervous system is also called the craniosacral division of the autonomic nervous system, as its central nervous system components are located within the brain and the sacral portion of the spinal cord. The presynaptic neurons that innervate the head and neck are found in the medulla oblongata; the presynaptic neurons that innervate the thorax, abdomen and pelvis lie within the gray horn of the sacral segments (S2-S4) of the spinal cord.

The pre-ganglionic neurones originate in the brainstem and sacral segments (S2-S4) of the spinal cord. For this reason, the parasympathetic nervous system is also referred to as the craniosacral division of the autonomic nervous system.

Parasympathetic fibers exit the CNS via cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus), **as well as through the S2 to S4 spinal nerve roots**. The term “parasympathetic” historically refers to the **craniosacral autonomic outflow** that complements the thoracolumbar sympathetic system, with its name originating from the Greek para, meaning “beside.”

The parasympathetic nervous system is defined by the **craniosacral origin of its nerve fibres**, which come out of the **brainstem and the S2–S4** sacral nerve roots. For the cranial nerves, the cell bodies of the preganglionic neurons sit in the cranial nerve nuclei of the brainstem, and for the sacral nerves they rest in the intermediolateral laminae (V–VII) of the second, third and fourth sacral spinal cord segments.

The sacral outflow, or the sacral part has their preganglionic neurons originate in the lateral gray matter of the second, third, and fourth sacral segments of the spinal cord. Myelinated axons leave the spinal cord in the anterior nerve roots of the corresponding spinal nerves, then leave the S2 to S4 spinal nerves and form the pelvic splanchnic nerves. Because of these levels of origin and departure from the CNS, we call the parasympathetic division craniosacral outflow.

The **sacral portion of the parasympathetic nervous system arises from the grey matter of the sacral segments of the spinal cord at the level of S2–S4**. These preganglionic fibers form the pelvic splanchnic nerves which synapse in the inferior hypogastric plexus.

The parasympathetic division has craniosacral outflow, meaning that the neurons begin at the cranial nerves (CN3, CN7, CN9, CN10) and the sacral spinal cord (S2–S4). The parasympathetic system is referred to as having craniosacral outflow because of the location of PSNS fiber origins.

The allocation of the sacral autonomic outflow to the parasympathetic division of the visceral nervous system—as the second tier of a “cranio-sacral outflow”—has an ancient origin, yet a simple history: It is rooted in the work of Gaskell, was formalized by Langley, and has been universally accepted ever since. Thus, the parasympathetic nervous system receives input from cranial nerves exclusively and the sympathetic nervous system from spinal nerves, thoracic to sacral inclusively.

The parasympathetic part of the autonomic division of the PNS leaves **cranial and sacral regions of the CNS** in association with: cranial nerves III, VII, IX, and X … and **spinal nerves S2 to S4**. Sacral parasympathetic fibers innervate inferior abdominal viscera, pelvic viscera, and the arteries associated with erectile tissues of the perineum.

In humans, the spinal preganglionic outflow has classically been confined to the segments T1-L2 and S2-S4 based on the absence of white rami communicantes caudal to segment L2, and on the perceived discontinuity of the spinal autonomic outflow cell column. As the autonomic outflow is concentrated around the T1-L2 and S2-S4 levels, a parallel is therefore often drawn between the parasympathetic and sympathetic divisions, assigning the sacral S2-S4 outflow to the parasympathetic system.

The nerves that make up the parasympathetic nervous system originate in the brainstem and the sacral spinal cord. The preganglionic neurons that originate in the brainstem arise from the cranial nerve nuclei for the oculomotor, facial, glossopharyngeal, and vagus nerves. The preganglionic neurons that originate in the sacral spinal cord come together to form the pelvic nerves.

The parasympathetic (or craniosacral) subdivision is associated with the 3rd, 7th, 9th and the 10th cranial nerves as well as with the 2nd, 3rd, and 4th sacral nerves. Thus, parasympathetic outflow arises from specific cranial nerve nuclei and from sacral spinal cord segments S2–S4.

The parasympathetic division is anatomically defined by a craniosacral outflow: preganglionic neurons originate in brainstem nuclei associated with cranial nerves III, VII, IX, and X, and in the sacral spinal cord (S2-S4).

It originates from the brainstem and sacral spinal cord, which is why it is often called the craniosacral division. Origin: Cranial nerves III, VII, IX, X and sacral spinal cord segments S2–S4 provide parasympathetic fibers.

Because of its location, the parasympathetic system is commonly referred to as having **craniosacral outflow**. Parasympathetic ganglia of the head: The parasympathetic division has craniosacral outflow, meaning that the neurons begin at the **cranial nerves (CN3, CN7, CN9, CN10) and the sacral spinal cord (S2–S4)**.

Nerve fibres of the parasympathetic nervous system arise from the central nervous system. Specific nerves include several cranial nerves, specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve. Three spinal nerves in the sacrum (S2-4), commonly referred to as the pelvic splanchnic nerves, also act as parasympathetic nerves.

The cranial parasympathetic and sacral sympathetic ganglia differ from each other and from sympathetic ganglia. This work argues that pelvic organs receive no parasympathetic innervation and that sacral outflow is sympathetic, challenging the traditional view of a craniosacral parasympathetic division.

The parasympathetic nervous system has their preganglionic fibers coming from the brainstem, which travels towards a peripherally located ganglion. As well as from the sacral region, going towards a parasympathetic ganglion that lies either near the organ, or within the organs they innervate.