1. Neuron Structure and Function Lexy Adams and Zach Hutchinson Second Year Medical Students Penn State Hershey College of Medicine

2. Learning Objectives
Students will explain the structures and functions of the cellular features of a neuron including: the neuronal membrane, the cytoskeleton (especially microtubules), the axon, the axon terminal (including the synaptic vesicles), and dendrites.
Students will justify why the special electrochemical properties of the neuronal membrane are essential to neuron function.

3. MOVIE!!!!!!!!!!!!!!!!!!!!

4. The human brain is an incredibly complicated calculating machine
The human brain is an incredibly complicated calculating machine. It receives, processes, and sends millions of messages every minute to help you sense things, make decisions, and control your body.
Nerves transmit information to and from the brain and spinal cord.

5. Our goal is that by the end of this lecture, you will all be experts on the neuron. We’ll be going through the structure and function of each of the main components of neurons. Keep this picture in the back of your head, because we’re going to go through and label it at the end of the lecture.

6. Fun Facts about Neurons
There are approximately 100 BILLION neurons in the human brain (That’s 100,000,000,000)!
If you were to line up all the neurons in the brain in a row, they would extend ~600 miles.
Neurons range in length from less than 1 mm up to 3 feet in length.
Neurons are about micrometers wide ( meters).
Question: Where are the longest neurons in the body?
Make a period on your piece of paper. How many neurons could fit into a period? 50 of the small width neurons and 5 of the large width neurons.

7. Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier

8. Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier

9. Cell Body
The metabolic center of the neuron that produces the energy to keep the cell alive.
Contains the nucleus, the site of DNA storage, as well as:
endoplasmic
reticulum,
ribosomes,
and Golgi
apparatus
What organelle produces energy? mitochondria

10. Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier

11. Dendrites
The branching extensions of neurons that RECEIVE the electrical signals and carry them to the cell bodies.
Think of these like octopus tentacles, which sense the environment and carry that information back to the cell body.

12. Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier

13. Axons
Extension of the neuron that carries electrical impulses AWAY from the cell body (“the tail”).
The axon terminal is the end of the axon, where neurotransmitters are released to send the signal along to the next neuron.
What part of the neuron senses the neurotransmitters that are released from the preceding neuron?
Dendrites sense electrical signals.

14. What other structures can neurotransmitters stimulate or inhibit?
Axon Terminal
Neurotransmitter
Dendrite
Muscle cells and glands

15. What other structures can neurotransmitters stimulate or inhibit
What other structures can neurotransmitters stimulate or inhibit? Neurons can stimulate muscle cells, glands, or other neurons.
Axon Terminal
Neurotransmitter
Dendrite
Muscle cells and glands

16. Each neuron can have thousands of dendrites but only ONE axon.
Axon Terminal
Neurotransmitter
Dendrite
Muscle cells and glands

17. The Synaptic Cleft
Step 2 (which got cut off): Vesicles fuse with the plasma membrane (exocytosis).
Now we’ll take a closer look at this important step in neurotransmission. After the electrical signal makes its way down the axon, vesicles with neurotransmitters inside fuse with the PM. NT’s are like the messengers of the nervous system.
The binding of the neurotransmitter to the receptor on the postsynaptic neuron (dendrite)
opens various ion channels. This changes the permeability of the cell membrane and the
membrane potential. This can either be an inhibitory or stimulatory effect.

18. Neuronal Membrane
Serves as a barrier to enclose the cytoplasm inside the neuron, and keep unwanted substance out.
Contains receptors on the outer surface that bind neurotransmitters (lock and key mechanism). This allows for great specificity.
Contains ion channels that allow some ions to enter the cell while blocking others.
This establishes an electrical potential along the cell membrane (a difference between positive and negative charges inside the cell vs outside the cell).
This serves as the basis for ion flow along the cell membrane = action potentials
(More to come on this
next week…)

19. Cytoskeleton
Network of tiny fibers within cells. These tiny fibers are called microtubules, microfilaments, and intermediate fibers.
Gives cells shape and stability.
Provides a scaffold for intracellular transport of vesicles (such as neurotransmitter containing vesicles in neurons).
Also involved in endocytosis, cell division, cell movement (flagella), and others.

20. Cytoskeleton in green

21. Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier

22. Myelin: a fatty substance that coats long nerve fibers to make the movement of nerve impulses faster.
Schwann cells make myelin.

23. “Myelin”
“No Myelin”
“Schwann Cells”

24. Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier

25. Nodes of Ranvier
Gaps along the myelin sheath that speed up the nerve impulses.

26. Can you label me?

27. Learning Objective #3
Students will list the different types of glial cells and describe the functions of each.

28. Glial cells (“Neuroglia”)
GLIA = GLUE …plus some other stuff
Neurons’ “partners” with important functions:
1. Support – hold neurons in place
2. Homeostasis – food & O2
3. Insulation – myelin formation
4. Protection – destroy pathogens

29. Ependymal Cells (CNS) Line the spinal cord and ventricles of the brain
Create cerebrospinal fluid (CSF)
Beat cilia and keep CSF circulating
Make the blood-brain barrier

30. Astrocytes (CNS) Most abundant glial cell in CNS
Anchors neurons to blood supply & regulates blood flow
Remove excess environmental ions and neurotransmitters

31. Microglia (CNS) Macrophage protectors
Direct the immune response to damage

32. Oligodendrocytes (CNS) & Schwann Cells (PNS)
Produce the myelin sheath
Provide insulation for electrical signals

33. Satellite Cells (PNS) External surroundings sensors
Regulate ion concentrations in response to chemical environment
Highly sensitive to injury and inflammation -play a role in chronic pain

34. Putting it all Together

35. Quick Review!
What are the four functions of glial cells, and an example cell for each function?

36. Quick Review!
What are the four functions of glial cells, and an example cell for each function? 1. Support – astrocytes, ependymal cells 2. Homeostasis – satellite cells, astrocytes 3. Insulation – Schwann cells, oligodendrocytes 4. Protection – microglia, ependymal cells

37. More Learning Objectives
Students will describe how the Nissl staining technique is used to distinguish between neural cells and glial cells.
Students will describe how the Golgi stain is used to identify unique components of the neuron, including the soma, the axon, and dendrites.

38. Nissl Bodies Large granular bodies in the neuron
Composed of rough endoplasmic reticulum and ribosome rosettes
Function: manufacture and release proteins

39. Nissl Stain Aniline Stain for extranuclear RNA granules –
can see neuronal body and dendrites clearly!

40. Chromatolysis Degeneration of Nissl bodies
Triggers: ischemia, toxicity, cell exhaustion, viral infection

41. Why do we care?
Chromatolysis shown in amyotrophic lateral sclerosis (ALS), Alzheimer’s, and other disease

42. Golgi Stain
Silver stain used to visualize tiny details of neuron and glia, including axons and dendrites
Four day process – fix with potassium dichromate and then immerse in silver nitrate, allowing crystallization of silver chromate

43. Structure and connectivity details are revealed!!

44. Final Question
Which stain is used to reveal neuronal cells, but not glial cells?

45. Final Question
Which stain is used to reveal neuronal cells, but not glial cells?
Nissl Stain!