Nervous System Histology Week 9 SB

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) Cell Body Axon Terminals Multipolar Neuron model

Dendrites and Cell Body (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)

Axon 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) Neurilemma - external layer containing bulk of cytoplasm with nucleus and organelles (cell membrane) Schwann cell nucleus myelin sheath axon neurilemma Node of Ranvier

Schwann cells myelinate axons Gaps between successive Schwann cells along the length of the axon are nodes of Ranvier

What you need to draw and label Axon Node of Ranvier Neurilemma

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.

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

Remember this? Axon (branches) Muscle fibers Axon terminals

Axon Collateral Axon Collateral

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

Objective 2: Neuron Classification

Pseudounipolar (unipolar) neurons include most sensory neurons have a short process which emerges from the cell body and divides into proximal and distal branches soma Distal process (toward periphery) Proximal process (toward CNS)

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

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 neurons are Pseudounipolar, 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

Bipolar neurons are found in special sense organs (eye, ear) Human retina are found in special sense organs (eye, ear) have a single axon & a single dendrite which are attached to opposite sides of the cell body bipolar neurons dendrite axon (branched)

Multipolar neurons: include most neurons including all motor neurons and most CNS neurons have multiple dendrites and a single axon Purkinje cell of the cerebellum Pyramidal cell of the hippocampus Neuron from the cerebral cortex

Silver Stained Neuron In Gray Matter

Spinal Cord - Anterior Horn Glial cell nuclei Multipolar neuron

Multipolar neurons you will be drawing Pyramidal cell Hippocampus & Cerebral cortex Purkinje cell Cerebellum

(Pseudo)unipolar neuron Multipolar neurons 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

Objective 3: Nerves Nerves are structures of the peripheral nervous system (PNS) that consist of axons and dendrites bundled together by connective tissue

Epineurium:. tough, fibrous connective. tissue sheath surrounding Epineurium: tough, fibrous connective tissue sheath surrounding a nerve Perineurium: loose areolar connective tissue sheath surrounding a fascicle (a bundle of axons or dendrites) Endoneurium: delicate connective tissue wrapping around each nerve fiber which electrically insulates each nerve fiber

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

a = epineurium b= perineurium                                                                            

perineurium endoneurium axon

EN = endoneurium Ax = axon NR = node of Ranvier My = myelin sheath