anatomy nervous tissue - Introduction *The nervous system...

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Introduction Organization of the Nervous System *The nervous system consists of two major divisions *Central nervous system (CNS) *Brain and spinal cord *Peripheral nervous system (PNS) *Cranial nerves that emerge from the brain, and spinal nerves that emerge from the spinal cord Components of the Nervous System and Anatomical Organization of the Nervous System Functional Organization of the Nervous System The Function of the Nervous System *Sensory function - sensory receptors *Integrative function - interneurons *Motor function - motor or efferent neurons Somatic Nervous System *The somatic nervous system (SNS) of the PNS consists of sensory and motor neurons *Somatic sensory neurons convey information from sensory receptors of the skin, skeletal muscles and joints to the CNS and receptors for special senses (results in the input of info to the CNS for processing) *The SNS also consists of motor neurons called somatic motor neurons convey information from the CNS to skeletal muscles only (results in output of info from the CNS resulting in voluntary muscle contraction) Autonomic Nervous System *Autonomic nervous system of the PNS also has sensory and motor components *Sensory neurons, called autonomic (visceral) sensory neurons , convey information mainly from visceral organs (smooth muscle organs in thorax, abdomen and pelvis) *Autonomic motor neurons convey information from the CNS to smooth muscle, cardiac muscle, and glands causing muscles to contract and glands to secrete. *Action of ANS is involuntary The Motor Branch of the ANS *The motor part of the ANS consists of two branches - the sympathetic division and the parasympathetic division *The sympathetic neurons increase heart rate *Fight-or-flight *The parasympathetic neurons slow it down *Rest-and-digest *Sympathetic division is the major regulator of smooth muscle of CV system, and has a wider distribution of blood vessels so these are located everywhere in the body *Parasympathetic division is a major regulator of smooth muscle of the digestive and respiratory systems Enteric Nervous System *The enteric nervous system (ENS) of the PNS is called the “brain of the gut” and consists of over 100 million neurons in the GI tract *The ENS also has both sensory and motor components that operate independently from the CNS *Sensory neurons of ENS monitor chemical changes within the GI tract and stretching of its walls *Motor neurons of ENS carry out contraction of GI tract smooth muscle to propel food through the GI tract; also regulate secretion of acid from stomach *ENS is involuntary
Histology *Nervous tissue is a vascular tissue comprised of two types of cells—neurons and neuroglia *Neurons are highly specialized cells *Neurons have lost the ability to undergo mitotic divisions *Neuroglia are smaller cells but they greatly outnumber neurons ( Neuroglia cells undergo mitosis but neurons don’t) *Support, nourish, and protect the neurons *Neuroglia cells continuously divide throughout one’s lifetime Neurons

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