Question

12. Describe the sympathetic and parasympathetic nervous system. Include pre and postganglionic fibers with respect to target organs.

Answer 1

Question 12.

The nervous system in the human body is divided into central nervous system and peripheral nervous system. Central nervous system consists of brain and spinal cord. Peripheral nervous system consists of nerves which connects the organs and all the body parts to brain and spinal cord and helps in conducting the nerve signals from the body parts and organs to the central nervous system (brain and spinal cord) as well as from the central nervous system to organs and all the body parts.

Peripheral nervous system is further divided into somatic nervous system and autonomic nervous system. Somatic nervous system consists of nerves which control the movements of skeletal muscles of the body. Autonomic nervous system consists of nerves that control the functions of smooth muscles, glands and internal organs.

Autonomic nervous system is further divided into sympathetic nervous system and parasympathetic nervous system.

Sympathetic nervous system consists of nerves originating from the thoracic and lumbar region of the spinal cord hence called as thoraco-lumbar outflow. It helps in 'fight and flight' response of the body and functions of increased physiological states. Its ganglia are located on either side of the spinal cord but away from the effector organs hence its pre-ganglionic fibers are short and post-ganglionic fibers are long. Its post-ganglionic fibers release nor-adrenaline and adrenaline at their synapses hence it is also cslled as adrenergic system. It increases the heart rate, cardiac output, respiratory rate, causes bronchodilation, dilation of pupils (mydriasis), increases blood flow to the skeletal muscles, preparing the body an emergency situation.

Parasympathetic nervous system consists of nerves originating from the cranial and sacral region of the central nervous system hence called as cranio-sacral outflow. It controls the 'rest and digest' functions of the body. Its ganglia are located close to the effector organs hence its pre-ganglionic fibers are long and post-ganglionic fibers are short. Its post-ganglionic fibers release acetylcholine at their synapses hence it is also cslled as cholinergic system. It causes bronchoconstriction, pupils constriction (miosis), increases the blood flow to the gastrointestinal tract, increases the secretion of body fluids like saliva, digestive enzymes, tears, decreases the heart rate and respiratory rate, contracts the muscles of the urinary bladder but relaxes the sphincters.