Difference Between Sympathetic and Parasympathetic Nervous System

Sympathetic vs Parasympathetic Nervous System

Autonomic nervous system is considered as a self-control system that comes under peripheral nervous system. It basically regulates the internal environment of the body, exchanging commands between peripheral nervous system and organs in order to maintain important body functions. There are two divisions in the autonomic nervous system; i.e. sympathetic nervous system and parasympathetic nervous system. Both systems usually act on the same organ and generate the same action potentials, yet their functions are different and oppose each other.

Sympathetic Nervous System

Sympathetic nervous system is the nerve network made up of short preganglionic axons that extend to ganglia situated near thoracic and lumbar regions of spinal cord, and of long postganglionic neurons extending from ganglia to target organs. Hence, the fibers of sympathetic efferent neurons are referred to as thoracolumbar outflow. The main function of the sympathetic nervous system is to prepare the body for emergency situation and to produce rapid mobilizations to avoid the danger.

Parasympathetic Nervous System

Parasympathetic nervous system is composed of preganglionic axons that are associated with organ-associated ganglions, located in the cranial and sacral regions of spinal cord, and of short postganglionic neurons extending from ganglia to target organs. Thus, the fibers of parasympathetic efferent neurons are referred to as craniosacral outflow. Acetylcholine is the neurotransmitter at the terminal synapses in this nervous system. This system is responsible to maintain the activities such as “rest- and – digest” or “feed- and- breed” that occur when body is at rest.

What is the difference between Sympathetic and Parasympathetic Nervous System?

• Sympathetic nervous system prepares the body for emergency situations while parasympathetic nervous system maintains conserving functions when the body is at rest.

• Sympathetic nervous system is responsible to produce rapid and total mobilization to avoid danger, whereas parasympathetic nervous system restores the organism to its normal position.

• Parasympathetic ganglia occur individually in the tissues and organs, whereas sympathetic ganglia occur on either side of spinal cord as two lateral chains.

• Preganglionic fibers of sympathetic nervous system arise from thoracic and lumbar segments of spinal cord, whereas that of parasympathetic nervous system arises from the midbrain and sacral segments of the spinal cord.

• Sympathetic nervous system forms the thoracolumbar outflow while parasympathetic nervous system forms the craniosacral outflow.

• In sympathetic nervous system, preganglionic fibers are shorter and postganglionic fibers are longer while, in parasympathetic nervous system, preganglionic fibers are longer and postganglionic fibers are shorter.

• Overall effect of sympathetic nervous system is excitatory while that of parasympathetic nervous system is inhibitory. For example, sympathetic nervous system increases the heart rate, whereas parasympathetic nervous system does the opposite.

• Postganglionic fibers of parasympathetic nervous system secrete acetylcholine, while that of sympathetic nervous system secrete adrenaline or noradrenaline at their synapse as neurotransmitters.

• Postganglionic sympathetic nerves are adrenergic, whereas postganglionic parasympathetic nerves are cholinergic.