Nervous System Histology Week 9 Expanded Studies

OBJECTIVES Identify the portions of a multipolar neuron using models & slides Differentiate between pseudounipolar, bipolar & multipolar neurons from slides Identify the components of the nerve cross section using diagrams & slides

What is a neuron? Neuron = Nerve cell Reflex Arc

Objective 1: Neuron Structure Parts of a Neuron animation – click here

Multipolar Neuron model Main parts of a neuron Dendrites (receive)  Cell Body (process)  Axon (send)  Axon Terminals (transfer) Cell Body Axon Terminals Multipolar Neuron model

Breakdown 1 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)

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 – End of axon Impulse direction Axon terminals (secretory component) Terminal branches (Telodendria)

Remember this? Axon terminals Muscle fibers Axon (branches)

Breakdown 4 Axon Collateral

Neuron Pathology Multiple Sclerosis MS is thought to be an autoimmune disease in which the myelin is lost in multiple areas, leaving scar tissue called sclerosis. These damaged areas are also known as plaques or lesions. Sometimes the nerve fiber itself is damaged or broken. Myelin not only protects nerve fibers, but makes their job possible. When myelin or the nerve fiber is destroyed or damaged, the ability of the nerves to conduct electrical impulses to and from the brain is disrupted, and this produces the various symptoms of MS.

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

Identify these structures: Telodendria Nissle Bodies Dendrite Node of Ranvier Axon Hillock

Identify these structures: Dendrites Nucleus (w/ nucleolus) Cell Body (Soma)

Objective 2: Neuron Classification

Multipolar (Interneuron) Pseudounipolar (Sensory) Multipolar (Motor) Bipolar

Pseudounipolar: - a short process (axon) emerges from the cell body and divides into proximal and distal branches - includes most sensory neurons In spinal nerves, the distal process is longer than the proximal process; The cell body (soma) is very close to the CNS in a structure called the dorsal root ganglion soma Receptive Endings Distal process (toward periphery) Proximal process (toward CNS)

Comparisons between Receptive Endings Pacinian Corpuscle

Pseudounipolar Cell Bodies in the Dorsal Root Ganglion of a Spinal Nerve

Pseudounipolar Cell Bodies High power Dorsal Root Ganglion Spinal Cord Pseudounipolar Cell Bodies Low power

Red arrows - Central Nuclei of Sensory Neurons “This is a low power slide of the Dorsal Root Ganglion. The key to knowing that you are looking at Neurons in the DRG is by looking for the CENTRALLY LOCATED NUCLEI, indicated by the Red arrows. These Large nuerons are Psuedouniplor, Sensory (Afferent) Neurons. They are responsible for conveying information to the Central Nervous System. You can tell that these Neurons have huge cell bodies. These are some of the largest cells in the body. The larger the cell body, the further away the information is coming from.” Red arrows - Central Nuclei of Sensory Neurons UMDNJ histsweb

- found in special sense organs (eye, ear, etc.) Bipolar neuron - has a single axon and a single dendrite attached to opposite sides of the cell body - found in special sense organs (eye, ear, etc.) dendrite axon (branched)

Human retina Bipolar neurons (nuclei visible)

Multipolar: - has multiple dendrites and a single axon includes: most neurons most CNS neurons (Interneurons) all motor neurons

Note: Multipolar neurons have diverse morphologies You do not need to memorize all these

Some Examples of Multipolar 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)

Identify the structural class of these neurons Bipolar

Identify the structural class of these neurons Multipolar

Identify the structural class of these neurons Pseudounipolar

Identify the structural class of these neurons Multipolar

Objective 3: Nerves 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

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

Epineurium Epineurium Perineurium Epineurium

Perineurium Endoneurium Axon (Nerve fiber)

Endoneurium Axon (Nerve fiber) Myelin Sheath

Identify the components of the nerve cross section ? ? ? ? ? ? ?

Try again: Label the structures Epineurium Perineurium Fascicle Endoneurium (nerve fibers)

Recap: Identify the portions of a multipolar neuron using models & slides Differentiate between pseudounipolar, bipolar & multipolar neurons from slides Identify the components of the nerve cross section using diagrams & slides