Neurons

The Autonomic Nervous System

Since the word "autonomic" literally means "self-governing," the autonomic nervous system (ANS) typically runs without the user being aware of what it is doing. The smooth and cardiac muscle and glands are innervated by a system of motor neurons. The smooth and cardiac muscles are stimulated by ANS to contract, and glands are stimulated to secrete. The visceral organs constantly send signals into the central nervous system (CNS), and the ANS constantly modifies to provide the best possible support for bodily functions. Examples of autonomic reactions include changes in the size of the pupils, heart rate increase and decrease, and blood vessel dilation and constriction. The ANS is split into two components, each of which affects the same visceral organs but in a different way. The other division counteracts an action that the first division stimulates, such as a smooth muscle contracting or a gland secreting. The two divisions balance each other's activities through this process of dual innervations to keep the body system functioning properly. They consist of:

• The sympathetic division
• The parasympathetic division

Sympathetic Division (Thoraco-lumbar Division)

The thoracic, lumbar, and thoracolumbar areas of the spinal cord contain the cell bodies that make up the sympathetic pathways (T1 through L2). The sympathetic division is sometimes known as the thoracolumbar division for this reason. Because it supplies more organs, the sympathetic division is more complex than the parasympathetic division.

From the level of the first thoracic nerve all the way down to the level of the second lumbar spinal nerve, the sympathetic fibers emerge from the spinal cord. The nerve fibers that originate from this region of the cord travel to the ganglia, where they connect with a second group of neurons whose fibers travel to the glands and involuntary muscle tissues.

Numerous sympathetic ganglia combine to produce the sympathetic chains, two cord-like strands of ganglia that run from the lower neck to the upper abdomen on either side of the spinal column. Three solitary ganglia located further from the spinal cord are where the nerves that supply the organs of the abdominal and pelvic cavities synapse. The neurotransmitter epinephrine is released by the second sympathetic nervous system neurons, which then affect the effectors (adrenaline).

Parasympathetic Division (Cranio-sacral Division)

The craniosacral regions are where the parasympathetic routes start. These fibers are produced by the medulla, midbrain, and lower (sacral) spinal cord cell bodies. The parasympathetic division is sometimes known as the craniosacral division for this reason. According to the parasympathetic, it surrounds the sympathetic division.

The first group of fibers from these centers travel to the autonomic ganglia, which are often found next to or inside the walls of the effector organs. The pathways then go on to stimulate the involuntary tissues along a second set of neurons. Acetylcholine, a neurotransmitter, is released by these neurons.

Functions of the Autonomic Nervous System

Both sympathetic and parasympathetic nerves, which have opposing roles, supply the majority of bodily organs.

The Sympathetic Responses:

• The sympathetic nervous system and the adrenal chemicals noradrenaline and adrenalin help the body get ready to handle stressful conditions. It gets the body ready for a fight-or-flight reaction.
• Enlargement of the pupil and diminished capacity to focus (for near objects)
• Heartbeats beat more quickly and forcefully.
• An increase in blood pressure brought on by a combination of a heartbeat that is more efficient and the narrowing of tiny arteries in the skin and internal organs.
• Vascular dilation in the skeletal muscles increases blood flow to these tissues.
• The expansion of the bronchial passages to increase oxygenation.
• Elevated metabolism

Parasympathetic Responses

The biological processes that preserve and repair bodily energy during times of rest are supported by the parasympathetic responses. Once a crisis has passed, it typically serves as a balance for the sympathetic system. Its principal answers are:

• Decrease in heart rate.
• Enlargement of the pupils.
• Bronchial tube constriction.
• Additionally, it promotes the production and excretion of urine.
• Additionally, it promotes digestion and absorption.
• There is an increase in lacrimation.

Table: Effects of the Sympathetic and Parasympathetic Systems on Selected Organs