Human Body Explorer Week 9

Nervous System Histology Objective 1: Neuron Structure

Parts of a Neuron - animation Å Link Breakdown 1

Dendrites Cell body (Soma) Neuron (receptive (biosynthetic center cell regions) and receptive region) 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 Neurilemma (one internode) (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

neurilemma axon Node of Ranvier Breakdown 3

Impulse direction Axon terminals (secretory component)

Terminal branches (Telodendria) Remember this?

Axon Axon Muscle terminals (branches) fibers 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 A short process (axon) emerges from > the cell body and divides into proximal and distal branches

Receptive Distal process Proximal process Endings (toward periphery) (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 Multipolar neurons

Most sensory neurons Most neurons Most CNS neurons Cell body located in (interneurons) Dorsal Root Ganglion All motor neurons (spinal nerves)

Cell bodies located in Spinal cord & Brain Bipolar neurons

Found in special sense organs (eye, ear, nose, tongue)

Example: Retina HISTOLOGY

(Pseudo)uipolar Bipolar neurons 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: MultipolarMultipolar neuronsneurons have diverse morphologies

You do not need to memorize all these Some Examples of Motor Neurons

Neurons from the spinal cord Neuron from the (smear) 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 Purkinje cell Hippocampus & Cerebral cortex Cerebellum Pyramidal cell

(Low Power – Cerebrum) Purkinje cell

(Low Power - Cerebellum) Neuron Classifications

Recap: 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 Endoneurium Perineurium

Nerve fiber (axon) Fascicle

Epineurium

Electron micrograph image

QUICKQUICK REVIEWREVIEW OnOn thethe Practical:Practical:

Identify the portions of Identify the portions of the multipolar neuron the multipolar neuron from the models in lab 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)