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

Multipolar Neuron model 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 Impulse direction Nucleus Nucleolus Axon (impulse generating and conducting region)

Axon hillock Impulse direction Node of Ranvier Axon Schwann cell (one internode) Neurilemma (sheath of Schwann)

(secretory component) Impulse direction Axon terminals (secretory component) Terminal branches (Telodendria)

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 nucleus myelin sheath axon neurilemma Node of Ranvier

Gaps between successive Schwann cells along the length of the axon 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

Spinal Cord Smear – Motor Neuron What you need to draw and label Cell Body Spinal Cord Smear – Motor Neuron

Objective 2: Neuron Classification

A short process (axon) emerges from the cell body and divides into proximal and distal branches > Receptive Endings Distal process (toward periphery) Proximal process (toward CNS) Has a single axon and a single dendrite attached to opposite sides of the cell body < dendrite axon (branched) > Has multiple dendrites and a single axon dendrites 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 Example: Retina special sense organs (eye, ear, nose, tongue) Example: Retina

(Pseudo)uipolar neurons HISTOLOGY (Pseudo)uipolar neurons Bipolar neurons Multipolar neurons

Pseudounipolar cell bodies in the dorsal root ganglion of a spinal nerve

Pseudounipolar cell bodies Centrally located nuclei Dorsal Root Ganglion Spinal Cord Pseudounipolar cell bodies

Bipolar neurons in the human retina

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)

(Low Power - Cerebellum) Purkinje cell (Low Power - Cerebellum)

Recap: Neuron Classifications Be able to identify each type of neuron by classification

Objective 3: Nerve Structures Nerves are structures of the PNS that consist of axons and dendrites bundled together by connective tissues

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

Electron micrograph image Endoneurium Perineurium Nerve fiber (axon) Fascicle Epineurium Electron micrograph image

LAB ACTIVITY: Draw and label the components of the nerve cross section