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The Parasympathetic Nervous System (PSNS) helps the body “rest-and-digest”, conserving energy and maintaining functions under ordinary conditions. Stress often leads to overactivation of the hypothalamic-pituitary-adrenal axis, the system that controls hormonal contribution to the fight or flight response. This system is not only active for life-threatening situations a project deadline or an urgent email might be stressful enough to trigger it. As is often written in neuroscience and psychology textbooks - it controls the four F’s - fleeing, feeding, fighting and mating. The sympathetic system quickens the heart rate and breathing to increase oxygen, dilates pupils for better vision, reduces digestion to conserve energy, and prepares the muscles of the body to either defend or escape. When a potentially threatening experience occurs, the body reacts with what has been called the “fight-or-flight” phenomenon. The Sympathetic Nervous System (SNS) prepares the body to react and expend energy in times of stress. The constant shifting of control between these two occurs in response to demands such as the fight or flight response. The autonomic motor division is divided into two complementary subsystems: the sympathetic system, which works to shift the body into more prepared states and the parasympathetic system, which facilitates more relaxed states. Although the word autonomic (from autonomy) means involuntary or unconscious, some of these activities are perceived and can be controlled consciously. The autonomic sensory receptors receive information from these systems and send it to the CNS while the autonomic motor division sends information from the CNS to these systems. The autonomic nervous system primarily regulates involuntary or unconscious activity such as heart rate, breathing, pupil dilation, regulating glands and internal organs, blood pressure, digestion, and many other chemical processes that keep our body working. The somatic sensory receptors receive information from the senses and send it to the CNS while the somatic motor division sends information from the CNS to control the actions of the skeletal muscles. The somatic system relays information about most of the body’s conscious activity to and from the CNS. Sōma means ‘body’ in Greek so somatic means relating to the body. Consequently, the properties of the PNS have been studied in regenerative research 1.
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In contrast with CNS neurons, PNS neurons are able to regenerate. The PNS contains neurons that junction with the CNS and have long axons that extend to all parts of the body. Unlike the CNS, the PNS is not protected by the vertebral column and skull, or by the blood–brain barrier, which leaves it more exposed to toxins and mechanical injuries. The PNS acts as a relay, transmitting information between the CNS and the rest of the body. The reason why patients are not simply given dopamine is that dopamine itself is not able to cross the blood brain barrier. A related example would be the manufacture of L-Dopa, a man-made version of the neurotransmitter dopamine which is used as treatment for Alzheimer’s disease. It does however allow the transfer of beneficial molecules such as amino acids and glucose into the CNS. As its name suggests, the blood brain brain barrier prevents the transfer of non-lipid soluble molecules, which may include toxic molecules. The Blood Brain Barrierīetween the brain and its blood supply is the blood brain barrier. The CNS acts as the control centre, using neurons to send and receive information to and from muscles, glands, organs and others systems in the body primarily through the Peripheral Nervous System. Both are made of soft delicate tissue protected by the skull and spinal vertebrae. The CNS consists of the brain and the spinal cord. The nervous system is separated in two classes: the central and peripheral nervous systems.ĭivisions of the Nervous System Credit: Cenveo CC BY 3.0 US Central Nervous System (CNS) Electrochemical signals connect the circuitry of the body and the brain, allowing for bidirectional signaling.
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Much of the executive activity occurs in the brain, while the spinal cord mostly acts as an information highway to connect the brain to many cells throughout the body. The human nervous system is an extensive network of specialized cells that allow us to perceive, understand and act on the world around us.