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Nervous System Histology In Lab Today: • Draw & identify the portions of a multipolar neuron from slides • Draw & differentiate between pseudounipolar, bipolar & multipolar neurons from slides • Identify the components of the nerve cross section using diagrams & slides • Identify the portions of a multipolar neuron from the models What is a neuron? Neuron = Nerve cell Reflex Arc Objective 1: Neuron Structure Main parts of a neuron Dendrites (receive) Cell Body (process) Axon (send) Axon Terminals (transfer) Multipolar Neuron model Cell Body Axon Terminals Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Neuron cell body Nissl bodies (rough ER) Dendrite Neurofibrils Nucleus Nucleolus Axon (impulse generating and conducting region) Impulse direction Axon hillock Impulse direction Axon Neurilemma (sheath of Schwann) Schwann cell (one internode) Node of Ranvier Impulse direction Terminal branches (Telodendria) Axon terminals (secretory component) Schwann cells - supporting cells of the PNS that myelinate axons. • Myelin sheath – whitish lipoprotein that surrounds and insulates the axon (nerve fiber) • Neurilemma - external layer containing bulk of cytoplasm with nucleus and organelles Schwann cell myelin sheath nucleus axon neurilemma Node of Ranvier Nodes of Ranvier Gaps between successive Schwann cells along the length of the axon Microscopic Views What you need to draw and label Axon Node of Ranvier Neurilemma What you need to draw and label Cell Body Spinal Cord Smear – Motor Neuron Objective 2: Neuron Classification > Receptive Endings Distal process (toward periphery) A short process (axon) emerges from the cell body and divides into proximal and distal branches Proximal process (toward CNS) Has a single axon and a single dendrite attached to opposite sides of the cell body < dendrite > dendrites axon axon (branched) Has multiple dendrites and a single axon (Pseudo)unipolar neuron Most sensory neurons Cell body located in Dorsal Root Ganglion (spinal nerves) Multipolar neurons Most neurons Most CNS neurons (interneurons) All motor neurons Cell bodies located in Spinal cord & Brain Bipolar neurons Found in special sense organs (eye, ear, nose, tongue) Example: Retina HISTOLOGY (Pseudo)uipolar neurons Bipolar neurons Multipolar neurons Pseudounipolar cell bodies in the dorsal root ganglion of a spinal nerve Centrally located nuclei Dorsal Root Ganglion Spinal Cord Pseudounipolar cell bodies Bipolar neurons in the human retina Bipolar neurons Bipolar neuron nuclei axons Note: Multipolar neurons have diverse morphologies You do not need to memorize all these Some Examples of Motor Neurons Neurons from the spinal cord (smear) Neuron from the cerebral cortex Multipolar neurons you will be drawing Pyramidal cell Hippocampus & Cerebral cortex Purkinje cell Cerebellum Pyramidal cell (Low Power – Cerebrum) Purkinje cell (Low Power - Cerebellum) Recap: Neuron Classifications Be able to identify each type of neuron by classification Objective 3: Nerves are structures of the PNS that consist of axons and dendrites bundled together by connective tissues Nerve Structures NERVE Epineurium: tough, fibrous connective tissue sheath surrounding a nerve Perineurium: loose, areolar connective tissue sheath surrounding fascicles Fascicle: a bundle of axons or dendrites Endoneurium: delicate connective tissue wrapping around each nerve fiber; the endoneurium electrically insulates each nerve fiber Perineurium Endoneurium Fascicle Epineurium Electron micrograph image Nerve fiber (axon) LAB ACTIVITY: Draw and label the components of the nerve cross section