Transcript axon
Nervous System Histology Week 9 Human Body Explorer Objective 1: Neuron Structure Parts of a Neuron - animation Link Breakdown 1 Dendrites (receptive regions) Cell body (Soma) (biosynthetic center and receptive region) Neuron cell body Nissl bodies (rough ER) Dendrite Neurofibrils Nucleus Nucleolus Axon (impulse generating and conducting region) Impulse direction Breakdown 2 Axon hillock Impulse direction Axon Neurilemma (sheath of Schwann) Schwann cell (one internode) Node of Ranvier Schwann cells - supporting cells of the PNS that myelinate axons. • Myelin sheath – whitish lipoprotein that surrounds and insulates the axon (nerve fiber) • Neurilamma - external layer containing bulk of cytoplasm with nucleus and organelles Schwann cell myelin sheath nucleus axon neurilemma Node of Ranvier Breakdown 3 Impulse direction Terminal branches (Telodendria) Axon terminals (secretory component) Remember this? Axon (branches) Muscle fibers Axon terminals Breakdown 4 Axon Collateral What you need to draw and label (Nuclei) Cell Body Spinal Cord Smear – Motor Neuron 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 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 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 Silver Stained Neuron in Gray Matter of spinal cord Spinal Cord - Anterior Horn Multipolar neuron Glial cell nuclei (supporting cells) 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 Fascicle: a bundle of axons or dendrites Epineurium: tough, fibrous connective tissue sheath surrounding a nerve Perineurium: loose, areolar connective tissue sheath surrounding fascicles Endoneurium: delicate connective tissue wrapping around each nerve fiber; the endoneurium electrically insulates each nerve fiber LAB ACTIVITY: Draw and label the components of the nerve cross section Perineurium Endoneurium Fascicle Epineurium Electron micrograph image Nerve fiber (axon) QUICK REVIEW On the Practical: Identify the portions of the multipolar neuron from the models in lab Identify the portions of the multipolar neuron from a prepared slide Identify the structural class of these neurons: pseudounipolar bipolar multipolar multipolar Identify the components of the nerve cross section Epineurium Perineurium Fascicle Endoneurium (nerve fibers)