Autonomic and Somatic NS 
Connections to Effectors
Return to

Source: Dr. Donald DeWitt based on graphic 
in Structure and Function of the Body, 9th ed. by Gary Thibodeau

Neuron cell bodies are found only in grey matter of the CNS (brain or spinal cord) or in ganglia of the Autonomic Nervous System (ANS). The axons of these neurons exit the spinal cord via one of the 31 spinal nerves on either side of the spine or cranial nerves II, VII, IX or X.
R
R
R
R
R
R
R

Ganglia of the ANS

Ganglia are components of the Autonomic Nervous System (ANS) and are found either close to the spinal cord just outside the spine for Sympathetic ANS afferent pathways or close to the effectors innervated by the Parasympathetic ANS (SM = Smooth Muscle, CM = Cardiac Muscle or Glands).  Note that a majority of the effectors are dually innervated by both subdivisions of the Autonomic Nervous System. In general the SANS and PANS affects are opposite. At a ganglion, the presynaptic neuron ends at a synapse with the cell body of the postsynaptic neuron.

Motor neurons

In the Somatic Nervous System (SomNS) motor neurons extend from the spinal cord to the skeletal muscle effectors without ganglia.  The location where these motor neurons connect to multiple skeletal muscle cells is called a neuromuscular junction.  A single motor neuron axon and all of the muscle cells it connects to is called a motor unit.  All cells in a motor unit contract together.

Myelination

Presynaptic ANS axons and motor neurons of the SomNS are covered with Schwann cells with their myelin cytoplasmic inclusions.  These axons are called myelinated axons and they conduct neural information faster than unmyelinated fibers such as those found as ANS postganglionic neurons.

Neurotransmitters

The neurotransmitter at ANS ganglia and neuromuscular synapses is Acetylcholine (ACh).  The neurotransmitters released by ANS postganglionic axons are ACh for PANS neurons and Norepinephrine (NE) for SANS neurons.
 

To see a cross-section of the spinal cord at the level of one the spinal nerves, click HERE.
Return to the Top