Autonomic Nervous System: Sympathetic and Parasympathetic Divisions

• The autonomic nervous system(ANS) is the part of the nervous system responsible for the control of the bodily functions not consciously directed, such as breathing, the heartbeat, and digestive processes.
• Sympathetic ganglia deliver information to the body about stress and impending danger and are responsible for the familiar fight-or-flight response.
  
• There are usually 22-23 pairs of sympathetic ganglia present in ANS: 3 in the cervical region (cervical ganglia), 11 in the thoracic region (note the presence of the stellate cervicothoracic ganglia), 4 in the lumbar region and 4-5 in the sacral region.
  
• So, the correct answer is '22'.

The autonomic nervous system is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of internal organs. 

• The autonomic nervous system has three branches: the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system.
  
• The autonomic nervous system is unique in that it requires a sequential two-neuron efferent pathway; the preganglionic neuron must first synapse onto a postganglionic neuron before innervating the target organ.
  
• So, the correct answer is 'Acts on skeletal muscles'.

• The hypothalamus is a small region of the brain. It's located at the base of the brain, near the pituitary gland. 
  
• The hypothalamus is the link between the endocrine and nervous systems. The hypothalamus produces releasing and inhibiting hormones, which stop and start the production of other hormones throughout the body.
• Hence Hypothalamus integrates Nervous and endocrine system.
• So, the correct answer is 'Hypothalamus'.

Vagus is $10^{th}$ cranial nerve. It originates from the sides of medulla oblongata. In vertebrates it consists of sensory and motor fibres.

The central nervous system includes brain and spinal cord. It integrates and stores the sensory information from external and internal sense organs and commands different organs to respond accordingly. This makes option A incorrect. Peripheral nervous system lies outside the central nervous system. It serves to carry the sensory information from external sensory receptors to CNS and motor signals from CNS to skeletal muscles via its somatic division (the voluntary actions). The autonomous division of peripheral nervous system controls the cardiac and smooth muscles and glands, thereby the functioning of internal organs, without our conscious control (the involuntary actions). This makes option B incorrect and option C correct. The 12 pairs of cranial nerves are part of peripheral nervous system and are mostly concerned with head, neck and facial region of the body (vagus nerve X being the part of autonomous division serves as an exception). Option D is incorrect.  Correct answer is C. 

• Myenteric plexus is also called as Auerbach's plexus, they are nerve cells and are controlled by the parasympathetic nervous system. It controls peristalsis (Swallowing of food).
  
• Argentaffin cells are present at the lining of the gastrointestinal tract and perform the function of secretion thus produces serotonin.
• Meissner's plexus is also called as submucosal plexus, it is located on the lining of the mucosa. It is responsible for the secretion of intestinal juice.
• The liver also called as 'Hepar' that contains hepatic cells. These hepatic cells are responsible for the secretion of heparin.
• So, the correct option is 'A - (ii), B - (i), C - (iv), D - (iii)'.

The sense of smell and sight of food are governed by olfactory and optic responses which work together to initiate the neural response during cephalic phase of digestion. Sight, smell and sense of food initiate the neural response in which central nervous system prepares the stomach to receive food. The responses include salivation and secretion of gastric juices. This makes options C and D incorrect and option B correct. The ingestion of food stimulates the hormonal responses to food which includes endocrine system to ensure releases of various digestive hormones at appropriate time. Correct answer is B.

The sympathetic system is the system which mainly controls the involuntary actins. There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter preganglionic neurons originate from the thoracolumbar region of the spinal cord (levels $T _1$-$L _2$). So, the correct answer is option C.

The parasympathetic nervous system is responsible for the rest and digest response, which includes slowing down the heart rate.

The sympathetic nervous system is responsible for the fight or flight response. It inhibits digestive processes, including the secretion of saliva, leading to a dry mouth.

The sympathetic nervous system deals with the response to stress and danger, releasing epinephrines (adrenaline), and in general, increasing activity and metabolic rate. So, due to sympathetic stimulation, heart rate increases, to provide body more and more oxygen and nutrients.

Peristalsis of the intestines is the example of the action of the autonomous nervous system. The organs of our body (viscera), such as the heart, intestines and stomach, are regulated by a branch of the nervous system known as the autonomic nervous system. It consists of autonomic neurons that conduct impulses from the central nervous system (brain and/or spinal cord) to glands, smooth muscle and cardiac muscle. ANS neurons are responsible for regulating the secretions of certain glands (i.e., salivary glands) and the regulation of heart rate and peristalsis (contraction of smooth muscle in the digestive tract), among other functions. So, the correct answer is option D.

In mammals, the purely sensory cranial nerves are the Olfactory (I), Optic (II), and Vestibulocochlear (VIII) nerves. There are three such pairs.

The parasympathetic nervous system promotes digestive activities, including gastrointestinal secretions and peristalsis, following the ingestion of food.

The sympathetic nervous system prepares the body for stress by increasing heart rate. It typically inhibits digestive secretions like saliva.

Preganglionic fibers in both the sympathetic and parasympathetic divisions of the autonomic nervous system are cholinergic, meaning they release acetylcholine.

The sympathetic nervous system is activated during stress, triggering the fight or flight response to help the body handle perceived threats.

Parasympathetic nerve endings release acetylcholine as their primary neurotransmitter to exert their effects on target organs.

The sympathetic nervous system mediates the fight or flight response, which causes physiological changes like increased heart rate and dry mouth during stressful situations like watching a horror movie.

The autonomic nervous system, consisting of the sympathetic and parasympathetic divisions, regulates the involuntary functions of visceral organs.

Stimulation of saliva secretion is a parasympathetic effect. The sympathetic nervous system typically inhibits salivary secretion, resulting in a dry mouth.

The sympathetic nervous system increases heart rate and relaxes bronchial smooth muscle to facilitate increased oxygen intake during the fight or flight response.

Humans typically have 22 pairs of sympathetic ganglia in the sympathetic chain.

Parasympathetic ganglia are generally located near or within the effector organs, and several are found in the head and neck region (e.g., ciliary, pterygopalatine, submandibular, and otic ganglia).

Dilation of the pupil is the function of the sympathetic nervous system. Parasympathetic stimulation causes: slowing down of the heartbeat; lowering of blood pressure; constriction of the pupils; decreased heart rate; salivation increase; peristalsis of the GI tract.

The pupil is a hole or opening in the middle of the iris. Iris is the coloured part of the eye that controls the amount of light entering the eye by adjusting the size of the pupil (contraction and dilation). Salivary glands are associated with digestion while intestinal peristalsis moves the food through the intestine. Tachycardia refers to the presence of faster heart beat. So, the correct answer is option B.

The sympathetic nervous system (SNS) is part of the autonomic nervous system (ANS), which also includes the parasympathetic nervous system (PNS).

Parasympathetic stimulation causes: slowing down of the heartbeat; lowering of blood pressure; constriction of the pupils; increased blood flow to the skin and viscera; salivation increase; peristalsis of the GI tract.

During the initial activation of the sympathetic system, norepinephrine gets released first as a preparatory hormone. This gets the body ready for the first stages of the emergency event. 

Parasympathetic nerve fibres arise from the central nervous system with the $S _2$, $S _3$, and $S _4$ spinal nerves and from the third, seventh, ninth, and tenth cranial nerves. 

The sympathetic nervous system is involved in the stimulation of activities that prepare the body for action, such as increasing the heart rate, increasing the release of sugar from the liver into the blood, and other generally considered as fight-or-flight responses (responses that serve to fight off or retreat from danger). 

The autonomic nervous system is made up of sympathetic nervous system and para-sympathetic nervous system. The sympathetic nervous system made up of sympathetic fibers is responsible for the body's flight or fight response The sympathetic nerves or fibers increases heart rate and helps enhancing the blood flow, while inhibiting digestion and peristalsis.

Ramus communicans is the branch which connects the spinal nerve and the sympathetic trunk.  There are two forms of ramus communicans. They are gray ramus communicans and white ramus communicans. They are responsible for conduction of signals in the sympathetic nervous system. The white rami communicans are the preganglionic sympathetic outflow from the spinal cord. The gray rami communicans contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons.

Parasympathetic nerve fibres arise from the central nervous system with the $S _2$, $S _3$, and $S _4$ spinal nerves and from the third, seventh, ninth, and tenth cranial nerves. Because of its location, the parasympathetic system is commonly referred to as having craniosacral outflow.

The autonomous nervous system control the heart beat rate via cardio regulatory centre in medulla oblongata. The emergency conditions activate the sympathetic motor nerve and make the adrenal medulla to release epinephrine and nor-epinephrine which in turn increase the heart beat rate.  Thus, the correct answer is C. The central nervous system (Central NS) includes brain and spinal cord. It integrates and stores the sensory information from external and internal sense organs and commands different organs to respond accordingly. Peripheral nervous system (PNS) lies outside the central nervous system and is further divided into somatic and autonomic nervous system. It serves to carry the sensory information from external sensory receptors to CNS and motor signals from CNS to skeletal muscles via its somatic division (the voluntary actions). The autonomic division of peripheral nervous system controls the cardiac and smooth muscles and glands, thereby the functioning of internal organs, without our conscious control (the involuntary actions). On the other hand, vagus nerve conducts the parasympathetic motor impulses which in turn slow down the hearth beat rate by effect of acetylcholine; a neurotransmitter released by parasympathetic nervous system. 

Esophageal peristalsis and sphincter function are controlled by the autonomic nervous system. Swallowing is a complex mechanism using both skeletal muscle (tongue) and smooth muscles of the pharynx and esophagus. The autonomic nervous system (ANS) coordinates this process in the pharyngeal and esophageal phases. Knee jerk is a sudden kicking of the lower leg after the tendon below knee cap has been tapped. The pupillary reflex is also controlled by autonomic nervous system.

The acetylcholine is the neurotransmitter that is released by the presynaptic nerve fibres into the synaptic cleft which is received by the receptors on the post-synaptic nerves. It allows the transfer of the information from the presynaptic neuron to the post-synaptic neurons. The preganglionic and the post-ganglionic parasympathetic nerves are cholinergic because they secrete the acetylcholine. The preganglionic nerve fibres of the sympathetic nervous system are also cholinergic.

Auerbach plexus is the interwoven network of the vagus nerve in the inner circular and outer longitudinal muscles of the muscularis layer of the visceral organs. 

The peripheral nervous system is that connects the body organs with brain and the spinal cord is divided into two parts:

Epinephrine and norepinephrine are released by the adrenal medulla and nervous system respectively. They are the flight/fight hormones that are released when the body is under extreme stress. They are also called as emergency hormone as it initiates quick reaction which makes the individual to think and respond quickly to the stress. The hormone increases metabolic rate. Dilation of blood vessels going to heart and the brain occurs. So, the correct answer is option A.

The autonomic nervous system is the part of the nervous system that supplies that internal organs, including the blood vessels, stomach, intestine, liver, kidneys, and digestive glands.

The parasympathetic nervous system is a division of the autonomic nervous system. The preganglionic nerve fibres of this system arise from the brain which includes cranial nerves III, VII, IX and X, that is, the oculomotor, facial, glossopharyngeal and vagus nerves, as well as from the sacral region of the spinal cord, that is, ramus communicans 2, 3 and 4. The sympathetic nervous system is called the thoracico-lumbar.

The autonomic nervous system is the part of the nervous system that supplies internal organs, including the blood vessels, stomach, intestine, liver, kidneys, and digestive glands.

There is a dual innervation of most organs of the body by the sympathetic and parasympathetic divisions of the ANS. The connection of both systems with the hypothalamus and higher brain areas have been omitted.