Section 2 Notes - I Gross Organization of the Nervous...

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I. Gross Organization of the Nervous System The nervous system is the organ system responsible for producing, controlling and guiding our acts, thoughts and responses to the world around us. During embryological development it is derived from cells similar to those which go onto form our skin, but those precursor cells to the nervous system become incredibly specialized and diverse, working together more complexly and intricately than any other organ system in the body. The basic plan arises from the form of a simple hollow tube that expands and differentiates itself into something that looks and functions very different from the tube it once was. We will examine its major divisions (the central, CNS, and peripheral, PNS, nervous systems) and its subdivisions, both in architecture and in function. A. Peripheral The most "available" division of the nervous system to the early anatomists for examination is the peripheral nervous system (PNS). It consists of the nerves which directly connect to the skin, muscles, blood vessels and organs of the body. As a general simplification, if nerve tissue not encased in bone (skull, spinal column), it is part of the PNS. 1. Somatic(Voluntary) The somatic nervous system at one time was called the voluntary nervous system . This accurately describes the role and distribution of its connections. The somatic nervous system innervates the muscles, and connective tissues attached to the skeleton and our skin. It is responsible for our voluntary movements and the physical sensations (heat, cold, pressure, vibration, pain) we experience. The individual nerves are typically made up of both afferent and efferent nerve fibers. Such a nerve can be roughly thought of as a bidirectional cable that has wires, some of which send impulses out to the body from the nervous system and some of which carry impulses from the body to the nervous system. a. Afferent Nerves To describe a nerve fiberas afferent means simply that the direction of the impulses it transmits go toward the nervous system from the body's muscles and skin. Therefore, afferent nerves conduct sensory information towards the nervous system. b. Efferent Nerves An efferent nerve fiber sends impulses away from the nervous system in the direction of the body's muscles. The efferent fibers generate movements of the skeleton and hence are motor nerve fibers since their activation causes the locomotion of our limbs, torso and facial features. 2. Autonomic(Involuntary) The autonomic nervous system used to be called the involuntary nervous system . The autonomic system is responsible for sensory and motor functions outside of our voluntary control, such as internal organs and glands, smooth muscles in our gastrointestinal tract and blood vessels and the smooth muscles attached to our skin. Its subdivisions, the sympathetic and parasympathetic, have opposite and complementary actions on our bodies' organs and tissues.
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