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

Breakdown 2 Axon hillock Impulse direction Node of Ranvier Axon Schwann cell (one internode) Neurilemma (sheath of Schwann)

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 nucleus myelin sheath axon neurilemma Node of Ranvier

(secretory component) Breakdown 3 Impulse direction Axon terminals (secretory component) Terminal branches (Telodendria)

Remember this? Axon terminals Muscle fibers Axon (branches)

Breakdown 4 Axon Collateral

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

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

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

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)

(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 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

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

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)