Autonomic centers that control blood pressure, heart rate, and digestion are located in the … 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.
autonomic centers that control blood pressure, heart rate, and digestion are located in the
The autonomic nervous system is part of the peripheral nervous system and controls the function of many muscles, glands and organs within the body. We do not usually be very aware of the functioning of our autonomic nervous system, since it works reflexively and involuntarily. For example, we do not realize when our blood vessels change in size, and we are (usually) unconscious when our hearts accelerate or slow down their pulsations.
What is the Autonomic Nervous System?
The autonomic nervous system (ANS) is the involuntary division of the nervous system. It is composed of autonomic neurons that drive impulses from the central nervous system (brain and / or spinal cord) to the glands, smooth muscle and heart muscle. SNA neurons are responsible for regulating the secretions of certain glands (for example, the salivary glands) or the regulation of heart rate, as well as peristalsis (contraction of the smooth muscle in the digestive tract), among other functions.
Role of the SNA
The role of the SNA is to constantly adjust the functioning of organs and organ systems according to both internal and external stimuli.
The SNA helps maintain homeostasis (internal stability and balance) through the coordination of various activities such as hormonal secretion, circulation, respiration, digestion and excretion. The SNA is always “on” and works out of consciousness, carrying out very important tasks that are performed each vigil (and during sleep), every minute of every day.
The SNA is divided into two subsystems, the SNS (sympathetic nervous system) and the SNP (parasympathetic nervous system).
Sympathetic nervous system (SNS) – the activation reaction of the SNS is what is commonly known as the “fight or flight” reaction:
* Sympathetic neurons are generally considered to belong to the peripheral nervous system, although some of the sympathetic neurons are found in the CNS (central nervous system).
* The sympathetic neurons of the central nervous system (spinal cord) interact with peripheral sympathetic neurons through a series of sympathetic nerve cells or bodies known as ganglia.
* Through the chemical synapses within the ganglia, peripheral sympathetic neurons bind to sympathetic neurons (for this reason, the terms ‘presynaptic’ and ‘postsynaptic’ are used to refer to sympathetic neurons and spinal cord neurons) peripheral sympathetics, respectively)
* Presynaptic sympathetic neurons release acetylcholine at synapses in sympathetic ganglia. Acetylcholine (Ach) is a chemical messenger that binds nicotinic acetylcholine receptors in postsynaptic neurons.
* Postsynaptic neurons release norepinephrine (NE) in response to this stimulus.
* Prolonged activation of this stimulus response can trigger the release of adrenaline from the adrenal glands (specifically from the adrenal medulla).
* Once released, NE and adrenaline bind to adrenergic receptors in various tissues, giving rise to the characteristic effects of “fight or flight”.
The following effects are considered as a result of the activation of adrenergic receptors:
* Increased sweating
* Decreased peristalsis
* Heart rate (driving speed, decreased refractory period)
* Dilation of the pupil
* Blood pressure (increased contractility, increased ability of the heart to relax and refill)
System Parasympathetic nervous system (SNP) – the SNP is sometimes referred to as the “rest and digestion” system. In general, the SNP acts in a manner opposite to the SNS, reversing the effects of the fight or flight response. However, it is more correct to say that the SNS and the SNP have a relationship of complementarity, rather than opposition.
* The SNP uses Ach as its main neurotransmitter.
* When stimulated the presynaptic nerve releases acetylcholine (Ach) in the ganglion.
* Ach in turn acts on the nicotinic receptors of postsynaptic neurons.
* The postsynaptic nerves then release acetylcholine to stimulate the muscarinic receptors of the target organ.
The following effects are considered as a result of SNP activation:
* Decreased sweating
* Increased peristalsis
* Decreased heart rate (decreased driving speed, increased refractory period)
* Constriction of the pupil
* Decreased heart rate blood pressure (decreased contractility, decreased ability of the heart to relax and refill)
The Messengers of the SNS and the SNP
The autonomic nervous system releases chemical messengers to influence its target organs. The most common are norepinephrine (NE) and acetylcholine (Ach). All presynaptic neurons use Ach as a neurotransmitter. Ach is also released by some postsynaptic sympathetic neurons and all postsynaptic parasympathetic neurons. The SNS uses NE as its main postsynaptic chemical messenger. NE and Ach are the most known neurotransmitters of SNA. In addition to neurotransmitters, certain vasoactive substances are released by the automatic postsynaptic neurons, which bind to the receptors on the target cells and influence the target organ.
HOW DOES your SNS mediate your action?
In the sympathetic nervous system, the catecholamines (norepinephrine, epinephrine) act on specific receptors located on the cell surface of the target organs. These receptors are called adrenergic receptors.
* Alpha 1 receptors, which exert their effect on smooth muscle, mainly due to constriction. Effects may include constriction of the arteries and veins, decreased motility in the GI (gastrointestinal), and constriction of the pupil. The Alpa1 receptors are generally located postsynaptically.
* Alpha 2 receptors, which bind to both epinephrine and norepinephrine, thereby reducing the effect of alpha 1 receptors to some extent. However, alpha 2 receptors have several specific effects of their own, including vasoconstriction. The effects may include constriction of the coronary arteries, constriction of the smooth muscle, constriction of the veins, decrease in intestinal motility and inhibition of insulin release.
* Beta 1 receptors, which exert their effect mainly on the heart, causing an increase in cardiac output, increased contractility and increased cardiac conduction, which leads to an increase in heart rate. It also produces the stimulation of the salivary glands.
* The beta 2 receptors, which exert their effect mainly on the skeletal and cardiac muscles. Increase in the speed of contraction of the muscles and their mass, as well as the dilation of the blood vessels. The receptors are stimulated through the circulation of neurotransmitters (catecholamines).
HOW DOES your SNP action mediate?
As mentioned, acetylcholine is the main neurotransmitter of the SNP. Acetylcholine acts on the cholinergic receptors known as muscarinic and nicotinic receptors. Muscarinic receptors exert their effect on the heart. There are two main muscarinic receptors:
M2 receptors activated by acetylcholine, M2 receptors are found in the heart, stimulation of these receptors causes the heart to decrease heart rate and contractility and increase refractoriness.
M3 receivers located throughout the body; its activation causes an increase in the synthesis of nitric oxide, which causes the relaxation of cardiac smooth muscle cells.
HOW is the autonomic nervous system organized?
As previously discussed, the autonomic nervous system is subdivided into two separate divisions: the sympathetic nervous system and the parasympathetic nervous system. It is important to understand how these two systems work in order to determine how each affects the body, taking into account that both systems work in synergy to maintain homeostasis in the body.
Both sympathetic nerves and parasympathetic nerves release neurotransmitters, mainly norepinephrine and adrenaline for the sympathetic nervous system and acetylcholine in the parasympathetic nervous system. These neurotransmitters (also called catecholamines) transmit nerve signals through the gaps (synapses) created when the nerve connects to other nerves, cells or organs.
The neurotransmitters then adhere to sympathetic or parasympathetic receptor sites in the target organ to exert their effect. This is a simplified version of how the autonomic nervous system works.
HOW is the autonomic nervous system controlled?
The SNA is not under conscious control. There are several centers that play a role in controlling their functioning:
* The cerebral cortex-areas of the cerebral cortex control homeostasis by regulating the SNS, the SNP and the hypothalamus.
* The limbic system-the limbic system is formed by the hypothalamus, the amygdala, the hippocampus and other nearby areas. These structures are found on both sides of the thalamus, just below the brain.
* Hypothalamus-the cells that lead to SNA are found in the lateral medulla. The hypothalamus is projected into this area, which includes the parasympathetic vagal nuclei, and also to a group of cells that lead to the sympathetic system in the spinal cord. By interacting with these systems, the hypothalamus controls digestion, heart rate, sweating and other functions.
* Brain stem: the brain acts as a link between the spinal cord and the brain. Sensory and motor neurons travel through the brain stem, transporting messages between the brain and the spinal cord. The brainstem controls many autonomous functions of the SNP, including heart rate, respiration, and blood pressure.
* The spinal cord and two ganglia chains are located on each side of the spinal cord. The external chains form the parasympathetic nervous system, while the chains near the spinal cord form the sympathetic element.
What Are Some Receptors of the Autonomic Nervous System?
Dendrites of sensory neurons are sensory receptors that are highly specialized, receive certain types of stimuli. We are not aware of the impulses of these receptors (except perhaps the pain). There are numerous sensory receptors:
* Photoreceptors, which respond to light.
* The thermoreceptors, which respond to changes in temperature.
* The mechanoreceptors, which respond to stretch and pressure (blood pressure or touch).
* Chemoreceptors, which respond to changes in the body’s internal chemistry (ie, O2, CO2) and dissolved chemicals in relation to taste and smell sensations.
* Nociceptors, which respond to various stimuli associated with tissue damage (the brain interprets pain).
Autonomic (visceral) motor neurons synapse in neurons located in the lymph nodes of the sympathetic and parasympathetic nervous system, which in turn directly innervate the muscles and some glands. In this way, visceral motor neurons can be said to innervate the smooth muscles indirectly from the arteries and the heart muscle. Autonomic motor neurons work by increasing (in the SNS) or decreasing (in the SNP) activities of their target tissues. In addition, autonomic motor neurons can continue to function even if their nerve source is damaged, although to a lesser extent.
Where are the Neurons of the Autonomic Nervous System Located?
The SNA is essentially composed of two types of neurons connected in series. The nucleus of the first neuron is found in the central nervous system. (The SNS neurons begin in the thoracic and lumbar areas of the spinal cord, the SNP neurons begin in the cranial nerves and the sacral spinal cord). The axons of the neuron are first found in the autonomic ganglia.
In relation to the second neuron, its nucleus is found in the autonomic ganglia, while the axons of the second neuron are found in the target tissue. The two giant types of neurons communicate using acetylcholine. However, the second neuron communicates with the target tissue using acetylcholine (SNP) or norepinephrine (SNS). Both the SNP and the SNS are connected to the hypothalamus.