Download PULSE LECTURE_Sept 21_Neurons

Neuron Structure and Function
Lexy Adams and Zach Hutchinson
Second Year Medical Students
Penn State Hershey College of Medicine
Learning Objectives
1. 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.
2. Students will justify why the special
electrochemical properties of the neuronal
membrane are essential to neuron function.
MOVIE!!!!!!!!!!!!!!!!!!!!
https://www.youtube.com/watch?v=vyNkAuX29OU
• 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.
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 10-100 micrometers wide
(0.0001 meters).
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Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier
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Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier
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
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Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier
Dendrites
• The branching extensions of neurons that
RECEIVE the electrical signals and carry them
to the cell bodies.
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Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier
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?
Axon Terminal
Neurotransmitter
Dendrite
What other structures can neurotransmitters
stimulate or inhibit?
Axon Terminal
Neurotransmitter
Dendrite
What other structures can neurotransmitters
stimulate or inhibit?
Neurons can stimulate muscle cells, glands, or
other neurons.
Axon Terminal
Neurotransmitter
Dendrite
Each neuron can have thousands of dendrites
but only ONE axon.
The Synaptic Cleft
Step 2 (which got cut off): Vesicles fuse with the plasma membrane (exocytosis).
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.
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…)
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.
Cytoskeleton in green
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Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier
• Myelin: a fatty substance that coats long
nerve fibers to make the movement of nerve
impulses faster.
• Schwann cells make myelin.
• “Myelin”
https://www.youtube.com/watch?v=TFnwPJxV_VA
• “No Myelin”
https://www.youtube.com/watch?v=mMCKyhOzNU
4
“Schwann Cells”
https://www.youtube.com/watch?v=DEaUQ_Zg24c
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Cell body
Nucleus
Dendrites
Axon
Axon terminals
Schwann cell
Myelin sheath
Nodes of Ranvier
Nodes of Ranvier
• Gaps along the myelin sheath that speed up
the nerve impulses.
https://www.youtube.com/watch?v=lN4_CMj41
JQ
Can you label me?
Learning Objective #3
3. Students will list the different types of glial
cells and describe the functions of each.
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
Ependymal Cells (CNS)
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Line the spinal cord and ventricles of the brain
Create cerebrospinal fluid (CSF)
Beat cilia and keep CSF circulating
Make the blood-brain barrier
Astrocytes (CNS)
• Most abundant glial cell in CNS
• Anchors neurons to blood supply & regulates
blood flow
• Remove excess environmental ions and
neurotransmitters
Microglia (CNS)
• Macrophage protectors
• Direct the immune response to damage
Oligodendrocytes (CNS) &
Schwann Cells (PNS)
• Produce the myelin sheath
• Provide insulation for electrical signals
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
Putting it all Together
Quick Review!
What are the four functions of glial cells, and an
example cell for each function?
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
More Learning Objectives
4. Students will describe how the Nissl staining
technique is used to distinguish between
neural cells and glial cells.
5. Students will describe how the Golgi stain is
used to identify unique components of the
neuron, including the soma, the axon, and
dendrites.
Nissl Bodies
• Large granular bodies in the neuron
• Composed of rough endoplasmic reticulum
and ribosome rosettes
• Function: manufacture and release proteins
Nissl Stain
Aniline Stain for extranuclear RNA granules –
can see neuronal body and dendrites clearly!
Chromatolysis
• Degeneration of Nissl bodies
• Triggers: ischemia, toxicity, cell exhaustion,
viral infection
Why do we care?
• Chromatolysis shown in amyotrophic lateral
sclerosis (ALS), Alzheimer’s, and other disease
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
Structure and connectivity details are revealed!!
Final Question
• Which stain is used to reveal neuronal cells,
but not glial cells?
Final Question
• Which stain is used to reveal neuronal cells,
but not glial cells?
Nissl Stain!