![]() ![]() Rest and digest(e.g., ↓ heart rate, ↑ GI motility, ↑ exocrine gland secretions).Fight or flight(↑ heart rate, ↓ GI motility, pupil and airway dilation).Overview of the sympathetic and parasympathetic nervous system Autonomic function can be affected by medications (e.g., selective serotonin reuptake inhibitors, anticholinergics) as well as diseases (e.g., diabetes mellitus, Parkinson disease, multiple system atrophy). The enteric nervous system controls gastrointestinal motility and secretion. In addition to the sympathetic and parasympathetic nervous systems, there is the enteric nervous system, which consists of enteric ganglia, the myenteric (Auerbach) and the submucosal (Meissner) plexuses, and the interstitial cells of Cajal. The effect of the parasympathetic nervous system on target organs include miosis, decreased heart rate, contractility, and conduction velocity increased intestinal motility and bronchoconstriction. The effects of the sympathetic nervous system on target organs include mydriasis, increased heart rate, contractility, and conduction velocity, bronchodilation, sweat secretion, decreased intestinal motility, and increased renin release. The sympathetic and parasympathetic nervous systems have antagonistic effects in some organ systems. The sympathetic preganglionic fibers stimulate the chromaffin cells of the adrenal medulla directly via acetylcholine on nicotinic receptors, which results in the release of norepinephrine and epinephrine mediating the fight or flight response. The adrenal medulla does not have a postsynaptic neuron. All postganglionic fibers of the sympathetic division are adrenergic fibers (release norepinephrine) that act on adrenergic alpha or beta receptors for neurotransmission, with the exception of the fibers innervating the sweat glands, which are cholinergic. The preganglionic fibers of both ANS divisions and the postganglionic fibers of the parasympathetic division are cholinergic fibers (release acetylcholine) that act on cholinergic receptors (nicotinic or muscarinic). ![]() The sympathetic and parasympathetic nervous systems consist of preganglionic and postganglionic neurons. The sympathetic nervous system has a thoracolumbar outflow and is activated during fight or flight response, while the parasympathetic nervous system has a craniosacral outflow and is activated during digestion and rest. It is divided into the sympathetic and parasympathetic nervous systems. In this article, we will discuss the anatomy of the auditory pathway – its components, anatomical course and relevant anatomical landmarks.The autonomic nervous system (ANS) is part of the peripheral nervous system and regulates involuntary, visceral body functions in different organ systems (e.g., the cardiovascular, gastrointestinal, genitourinary systems). In addition, unconscious processing of auditory information occurs in parallel. This pathway ultimately reaches the primary auditory cortex for conscious perception. Information travels from the receptors in the organ of Corti of the inner ear (cochlear hair cells) to the central nervous system, carried by the vestibulocochlear nerve (CN VIII). The auditory pathway conveys the special sense of hearing. Their cell bodies are found in the cerebral cortex or the brain stem, with their axons remaining within the CNS. Thus, all the neurones within the descending motor system are classed as upper motor neurones. At the termination of the descending tracts, the neurones synapse with a lower motor neurone. There are no synapses within the descending pathways. The lower motor neurones then directly innervate muscles to produce movement. The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurones. In this article, we shall look at the anatomy of the ascending tracts, and consider their clinical implications. Functionally, the ascending tracts can be divided into the type of information they transmit – conscious or unconscious. In some texts, ascending tracts are also known as somatosensory pathways or systems. The ascending tracts refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex. There are also articles on the visual pathways and auditory pathways to help you understand the intricacies of these important senses. The ascending and descending tracts are the first two articles, which cover the anatomy of the sensory and motor pathways of the central nervous system respectively. ![]() In this section on pathways, we will cover the important pathways that make up the central nervous system.
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