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9.1-9.4 Notes Nervous System Functions • Coordinate body functions • Maintain homeostasis • Respond to changing conditions internally and externally • Made of 2 parts – Neurons – Neuroglial cells Neurons (nerve cells) • Transmit information in the form of a nerve impulse • Different parts of a neuron – Cell body-round area/has nucleolus – Dendrites-branches that receive the signal – Axon-sends the single to the next neuron • Nerves-bundles of axons Neuroglial Cells • Provide physical support, insulation, and nutrients for the neurons • Protection devices Organs of nervous system are in 2 groups. • Central Nervous System (CNS) – Made of brain and spinal cord • Peripheral Nervous System (PNS) – Made of neurons that connect to CNS Have 3 general functions: Sensory Motor Integrative 3 general functions • Sensory-sensory receptors are at the end of peripheral neurons – Gather information about changes in and out of the body • Example: temperature, light, sound, oxygen levels • Integrative-bring all the information together to create perceptions from sensations 3 general functions (cont.) • Motor – Effectors-responsive structures that receive impulses • Are found outside the nervous system • Example: muscle, glands – 2 categories • Somatic-conscious control (skeletal muscles) • Autonomic-unconscious control (heart and smooth muscle) Neuroglial cells • Produce myelin (fat that surrounds the axon) • Fills space • Framework • There are different types of neuroglial cells. Types of neuroglial in CNS • Microglial-support neurons – Phagocytosis of bacteria and cell debris • Oligodendrocytes-found along nerve fibers – Provide myelin for myelin sheath (around axon within brain and spinal cord) • Astrocytes-between neurons and blood vessels – Support, join parts, help regulate ion and nutrient levels, form scar tissue when injury occurs to the CNS • Ependymal cells-cover special brain parts and close spaces between the brain and CNS Neuroglial in the PNS • Schwann cells-create myelin for neurons in the PNS • Too many neuroglial cells-cause brain tumors (fast growing gliomas) Neuron Structure • Cell body – Cytoplasm, organelles, cell membrane – Neurofibrils-fine threads – Chromatophilic substance (Nissl bodies)-like rough ER – Nucleolus • Dendrites – Short, highly branched, receptors Neuron structure (cont) • Axons – Axon hillock-elevated portion leading into the axon from the cell body – May have side branches – PNS axons-made of Schwann cells that make myelin – Neurilemma-covering that surrounds myelin sheath – Nodes of Ranvier-gaps in between myelin sheath of axon • Myelinated in CNS are called white matter • Unmyelinated in CNS are called gray matter – Axons can regenerate in PNS because of neurilemma – CNS are myelinated by oligodendrocytes-no neurilemma so can’t regenerate Label the picture on your notes. Groupings-Structural trigger point-sensitive region of axon;where nerve impulse begins to be sent down axon • Multipolar-one axon and many dendrites (brain and sc) • Bipolar-1 axon, 1 dendrite (eyes, nose, ears) Structural Differences (cont) • Unipolar neuron-one axon, no dendrites – Dendrite near peripheral body – Other part connected to brain or spinal cord – Cell bodies of these are bunched to form ganglia • Outside the brain or spinal cord Functional Groupings • Sensory (afferent)-carry impulse from peripheral into CNS – Specialized receptor ends on dendrite tips – Dendrites are closely associated with receptor cells in skin or in sensory organs – Unipolar, some bipolar • Interneurons-in brain and spinal cord – Transmit impulses from 1 to another by forming links with other neurons – multipolar Functional groupings (cont) • Motor neurons-efferent – Multipolar – Carry impulse out of CNS to the effectors – Stimulate muscle and glands to respond