NSC - Peripheral Nervous System Lesson
Peripheral Nervous System
The main function of the peripheral nervous system is to create common pathways for electrochemical signals between the central nervous system and peripheral muscles and organs. The PNS consists of nerves and ganglia (nerve cell clusters) that extend outside of the brain and spinal cord. Nerves are cable-like bundles of axons and connective tissue in the peripheral nervous system (these bundles are known as tracts in the CNS). The PNS is more vulnerable than the CNS since it is not protected by bone or the blood-brain barrier, which leaves it exposed to toxins and mechanical injuries.
The peripheral nervous system can be further subdivided into the somatic nervous system and the autonomic nervous system.
Somatic Nervous System
The somatic nervous system (SoNS) is a division of the PNS associated with the voluntary control of skeletal muscles. The nerves of the SoNS are divided into two categories, depending on whether the information is flowing to or from the CNS: afferent (sensory) nerves and efferent (motor) nerves. Afferent (sensory) nerves are responsible for relaying sensation from the body to the central nervous system (CNS); efferent (motor) nerves are responsible for sending out commands from the CNS to effectors in the body, such as muscles and glands.
Autonomic Nervous System
The autonomic nervous system (ANS) is a division of the PNS that is regulated by the hypothalamus and associated with involuntary functions in the body. The ANS acts to control bodily functions such as heart rate, digestion, respiratory rate, pupillary response, urination, and certain reflex actions such as coughing, sneezing, swallowing, and vomiting. The autonomic nervous system can be further divided into two parts: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system is often considered the "fight or flight" system, while the parasympathetic nervous system is often considered the "rest and digest" system. In many cases, both of these systems have "opposite" actions where one system activates a physiological response and the other inhibits it. As with the SoNS, the autonomic nervous system also has afferent and efferent divisions in the nerves depending upon whether the information is flowing to or from the CNS.
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