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Cells of the Nervous System Layout of the Nervous System Central Nervous System (CNS) Brain (in the skull) Spinal Cord (in the spine) Interprets sensory input, initiates movement, and mediates complex cognitive processes Peripheral Nervous System (PNS) Located outside of the skull and spine Serves to bring sensory information into the CNS and carry motor signals out of the CNS Functional Unit of the Nervous System The functional unit of the nervous system is the neuron. Neurons are specialized cells for the reception, conduction, and transmission of electrochemical signals Many sizes and shapes ~100 billion neurons ~100 trillion connections Major External Features of a Neuron A typical neuron has a cell body, dendrites and an axon. Flow of information: • dendrites receive inputs from other neurons • the cell body (or soma) integrates (processes) information • the axon transmits the output of processing to other neurons Major Internal Features of a Neuron Similarities with other cells: • Contains a nucleus that holds genetic information • Contains organelles that support the life of the cell, including mitochondria and ribosomes • Surrounded by a membrane that protects the cell Differences with other cells: • Stop dividing (reproducing) after birth • Have dendrites and axons, specialized structures designed to receive and transmit information The Cell Membrane Lipid bilayer with embedded proteins • separates inside and outside of cell • selective permeability controls flow of substances into and out of the cell The particular composition of embedded proteins in the cell membrane is critical for proper neuron function Visualizing Neurons 1 The major problem in visualizing neurons is not their minuteness. Rather, the major problem is neurons are so tightly packed and their dendrites and axons intricately intertwined. Golgi stain: for as-yet unknown reasons, silver stains some neurons black in their entirety but stains others not at all. Allows for visualization of individual neurons Visualizing Neurons 2 Nissl stain: selectively stains cell bodies. Used to indicate the number of neurons in an area Visualizing Neurons 3 Electron microscopy: provides information about the details of neuronal structure Visualizing Neurons 4 Tract tracing techniques: used to trace the paths of axons Anterograde: to trace axons projecting away from cell bodies www.seriousmadscience.com Retrograde: to trace axons projecting into an area of cell bodies cmbn-approd01.uio.no Neuroanatomical Structures Two kinds of gross neural structures; those composed primarily of cell bodies and those composed primarily of axons. CNS PNS Clusters of cell Nuclei bodies (singular nucleus) Grey matter Ganglia (singular ganglion) Bundles of axons Nerves Tracts White matter Anatomical Classes of Neurons Neurons do not all look alike. One way to classify them is based on the number of processes emanating from their cell bodies. Functional Classes of Neurons information from tissue/organs integrate intermediate information to effector cells www.studyblue.com CNS Neurons Are Usually Multipolar PNS Neurons are Unipolar or Multipolar Connections Between Neurons Direction: afferent (approaching) efferent (exiting) Type: axon-dendrite but also axon-soma, axon-axon, dendrite-dendrite Neuroscience: Exploring the Brain, 3rd ed Glia: The Forgotten Cells of the NS • Helper cells (glia = “glue”) • Outnumber neurons 5:1 • Provide structural/metabolic support to neurons • Recent evidence for glial communication and modulatory effects of glia on neuronal communication www.jaynejubb.com Classes of Glial Cells • Oligodendrocytes: extensions rich in myelin; create myelin sheaths in CNS • Schwann cells: similar to function of oligodendrocytes, but in PNS; can guide axonal regeneration • Microglia: involved in response to injury or disease • Astrocytes: largest glia; starshaped; many functions blogs.scientificamerican.com Myelination of neurons Microglia respond to injury or disease ramified motile ucsf.edu Astrocytes perform a variety of duties Control and communicate widely with many neurons: • form a barrier to unwanted substances entering the brain • control blood flow to neurons (activity allows functional imaging) • maintain the proper chemical state outside of neurons/remove waste • surround synapses and can modify neuronal signals • send nutrients (glucose) to neurons • digest old neuronal parts • secrete neurotransmitters and glialtransmitters www.nature.com