![]() ![]() This cookie is set by GDPR Cookie Consent plugin. The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The cookie is used to store the user consent for the cookies in the category "Analytics". These cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly. Fig 1 - Diagram showing the components that make up the somatic nervous system Sympathetic and Parasympathetic Nervous Systems In this article, we will discuss the peripheral nervous system, its divisions, and its functions. The central nervous system (CNS)consists of the brain and spinal cord, leaving everything else in the peripheral nervous system (PNS). The nervous system is classified into the central and peripheral nervous systems. Noradrenaline (NA, adrenergic) in most cases The table below shows a comparison of these 2 systems. The sympathetic and parasympathetic pathways have very similar structures but with a few key differences. Both preganglionic and postganglionic neurones use the neurotransmitter acetylcholine. This system consists of long preganglionic neurones and short postganglionic neurones. It originates from craniosacral segments of the spinal cord. The PSNS is responsible for the rest and digest actions of the body. It is designed to mobilise energy stores, allowing us to cope with the stress and increase our chances of survival. The actions mediated by SNS are most apparent when the body is faced with stressful situations. Hence, the activation of chromaffin cells via preganglionic cells leads to the release of two neurotransmitters: adrenaline and to lesser extent noradrenaline, directly into the bloodstream. They act as a modified sympathetic ganglion without the postganglionic neurones. The exception to this rule is the innervation of the sweat glands and chromaffin cells of the adrenal medulla, which are cholinergic as they use acetylcholine as a neurotransmitter.Īnother exception is the chromaffin cells of the adrenal medulla. The preganglionic neurones use acetylcholine as a neurotransmitter while the postganglionic neurones use noradrenaline. It incorporates short preganglionic neurones and long postganglionic neurones. The SNS is responsible for the fight or flight response of the body and originates from the thoracolumbar segments of the spinal cord. A ganglion then gives rise to a postganglionic neurone which innervates the target organ. Hence, the preganglionic neurone must first travel to and synapse upon a ganglion, a collection of neuronal cell bodies in the PNS. The autonomic nervous system has a unique structure as it employs a sequential two-neurone efferent pathway. The SNS and PSNS are sub-divisions of the autonomic nervous system. ![]() Sympathetic and Parasympathetic Nervous Systems The enteric nervous system is classified as a separate component of the autonomic nervous system and is sometimes even considered a third independent branch of the PNS. The afferent (sensory) arm of this system includes receptors that monitor the arterial pressure, levels of carbon dioxide and oxygen in the blood or the chemical composition of the content of the gastrointestinal tract. The efferent arm of this system can be further subdivided into the parasympathetic (PSNS) and sympathetic (SNS) components, which control numerous smooth muscles and glands. These visceral functions include the regulation of heart rate, digestion, salivation, urination, digestion, and many more. The autonomic (visceral) nervous system control the visceral functions of the body and acts largely unconsciously. Its afferent arm links sensory receptors on the body surface or deeper within it with relevant processing circuits, whereas the efferent arm directly controls skeletal muscles using motor nerves. The somatic nervous system of the PNS is responsible for voluntary, conscious control of skeletal muscles (effector organ). Effector organs can either be muscles or glands. The efferent arm consists of motor (or effector) neurones running from the CNS to the effector organ.Afferent nerves exist in both the somatic and autonomic nervous systems as both can use sensory signals to alter their activity. Afferent nerves detect the external environment via receptors for external stimuli such as pressure or temperature etc. The afferent arm consists of sensory (or afferent) neurones running from receptors to the CNS.The peripheral nervous system is itself classified into two systems: the somatic nervous system and the autonomic nervous system. ![]()
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