Question

Describe the general anatomy and function of the somatic and autonomic efferent nervous systems. How are the functions of the two different from one another? What are the two subdivisions of the autonomic nervous system? Describe the specific anatomy of the sympathetic and parasympathetic nervous systems in term of the location of the preganglionic neuron, ganglia, and postganglionic neurons. What organ systems are stimulated by each; what organ systems are inhibited by each? What is the specific impact, if any, of each on the following organs: heart, lungs, small intestines, pancreas, liver, and kidneys?

Answer 1

ANATOMY and FUNCTION

SENSORY NERVOUS SYSTEM

In the head and neck, cranial nerves carry somatosensory data. There are twelve cranial nerves, ten of which originate from the brainstem, and mainly control the functions of the anatomic structures of the head with some exceptions. One unique cranial nerve is the vagus nerve, which receives sensory information from organs in the thorax and abdomen. The accessory nerve is responsible for innervating the sternocleidomastoid and trapezius muscles, neither of which being exclusively in the head.

For the rest of the body, spinal nerves are responsible for somatosensory information. These arise from the spinal cord. Usually these arise as a web ("plexus") of interconnected nerves roots that arrange to form single nerves. These nerves control the functions of the rest of the body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

Cervical spinal nerves (C1–C4)

Brachial plexus (C5–T1)

Lumbosacral plexus (L1–Co1)

(lumbar plexus

sacral plexus

pudendal plexus)

AUTONOMIC NERVOUS SYSTEM

The autonomic nervous system (ANS) controls involuntary responses to regulate physiological functions. The brain and spinal cord of the central nervous system are connected with organs that have smooth muscle, such as the heart, bladder, and other cardiac, exocrine, and endocrine related organs, by ganglionic neurons. The most notable physiological effects from autonomic activity are pupil constriction and dilation, and salivation of saliva. The autonomic nervous system is always activated, but is either in the sympathetic or parasympathetic state. Depending on the situation, one state can overshadow the other, resulting in a release of different kinds of neurotransmitters. There is a lesser known division of the autonomic nervous system known as the enteric nervous system. Located only around the digestive tract, this system allows for local control without input from the sympathetic or the parasympathetic branches, though it can still receive and respond to signals from the rest of the body. The enteric system is responsible for various functions related to gastrointestinal system.

Two divisions of autonomic nervous system are

Sympathetic nervous system

The sympathetic system is activated during a “fight or flight” situation in which mental stress or physical danger is encountered. Neurotransmitters such as norepinephrine, and epinephrine are released, which increases heart rate and blood flow in certain areas like muscle, while simultaneously decreasing activities of non-critical functions for survival, like digestion. The systems are independent to each other, which allows activation of certain parts of the body, while others remain rested.

Parasympathetic nervous system

Primarily using the neurotransmitter acetylcholine (ACh) as a mediator, the parasympathetic system allows the body to function in a “rest and digest” state. Consequently, when the parasympathetic system dominates the body, there are increases in salivation and activities in digestion, while heart rate and other sympathetic response decrease. Unlike the sympathetic system, humans have some voluntary controls in the parasympathetic system. The most prominent examples of this control are urination and defecation.

DIFFERENCES BETWEEN BOTH SOMATIC AND AUTONOMIC NERVOUS SYSTEM

Anatomy of the sympathetic and parasympathetic nervous systems in term of the location of the preganglionic neuron, ganglia, and postganglionic neurons

EFFECT OF AUTONOMIC NERVOUS SYSTEM ON DIFFERENT ORGANS