1. Nervous System Histology
Week 9
Expanded Studies

2. 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

3. What is a neuron?
Neuron = Nerve cell
Reflex Arc

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

5. 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

6. 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)

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

8. 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

9. (secretory component)
Breakdown 3 – End of axon
Impulse
direction
Axon terminals
(secretory component)
Terminal branches
(Telodendria)

10. Remember this?
Axon terminals
Muscle fibers
Axon
(branches)

11. Breakdown 4
Axon Collateral

12. 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.

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

14. 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

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

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

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

18. Objective 2: Neuron Classification

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

20. 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)

21. Comparisons between Receptive Endings
Pacinian Corpuscle

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

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

24. 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

25. - 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)

26. Human retina
Bipolar neurons
(nuclei visible)

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

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

29. Some Examples of Multipolar Neurons
Neurons from the spinal cord (smear)
Neuron from the cerebral cortex

30. Silver Stained Neuron in Gray Matter of spinal cord
Spinal Cord - Anterior Horn
Multipolar neuron
Glial cell nuclei
(supporting cells)

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

32. Pyramidal cell
(Low Power – Cerebrum)

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

34. Identify the structural class of these neurons
Bipolar

35. Identify the structural class of these neurons
Multipolar

36. Identify the structural class of these neurons
Pseudounipolar

37. Identify the structural class of these neurons
Multipolar

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

39. 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

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

41. Epineurium
Epineurium
Perineurium
Epineurium

42. Perineurium
Endoneurium
Axon
(Nerve fiber)

43. Endoneurium
Axon
(Nerve fiber)
Myelin Sheath

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

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

47. 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