Lecture 1 - Cells of the Nervous System Flashcards
How many neurons in our brain? How does this compare to that of a worm?
100 billion vs 302
How many non-neural cells in our brain?
1000 billion
What is the cell theory?
All tissues are composed of microscopic units called cells
Describe multipolar neurons. Where are they found?
They have 2 or more primary neuritic processes on the cell body
CNS
Describe pyramidal neurons. 2 types? What are there functions?
Triangular in shape and very favored.
Functions:
1. Spiny ones encode long-term info
2. Aspinous ones function as interneurons and modulate local information
Where are purkinje cell neurons found?
Cerebellum
Describe bipolar neurons. Where are they found?
Neurons with 2 opposing primary neurites.
Found in retina and inner ear
What are bipolar neurons in the inner ear called?
Hair cells
Describe unipolar neurons. What is their function?
Cell body is segregated from the single primary neurite.
Function as sensory/afferent neurons
What stains are used to stain neurons?
Vital dyes:
- Golgi stain
- Nissi stain
- Weigart stain
What lies below the 6 layers of the cerebral cortex?
Subcortical structures (eg corpus callosum) next to white matter
What are the 3 basic elements of the neuron? Describe their location.
- Perikaryon
- Dendrites at the receiving end
- Axon at the transmitting end
What are the neurites?
Structures that branch off the cell body: dendrites and axon
What are 2 another names for perikaryon?
Cell body = soma
What is another name for neurites?
Processes
What are the different types of dendrites?
- Primary: directly coming off of the soma
- Secondary: branch off primary dendrites
- Tertiary: branch off secondary dendrites
AND SO ON…
How do the dendrites’ diameter change as it gets further from the soma?
Decreases
How many axons do most neurons have?
1
Diameter of dendrite?
Thick/tapered
Length of dendrite: limited or not?
Limited
Branching of dendrites?
Many, acute
Spines on dendrites?
Yes
V-gated ion channels on dendrites?
Less
Diameter of axon?
1 micrometer, uniform
Length of axon: limited or not?
NOPE
Branching of axon?
Few, not acute
Spines on axons?
NOPE
V-gated ion channels on axons?
More
What are considered the antennae of neurons?
Dendrites
How does the diameter of axons and dendrites affect them?
Thicker neurite will allow an AP to propagate more quickly
What determines the length of the axon that goes from the bottom of one’s spinal cord to the end of a toe?
Length of the leg!
What is the function of dendritic spines?
To elaborate postsynaptic surfaces by increasing the surface area to volume ratio of neurons
What is the main component of dendritic spines?
Actin (microfilament)
Is the shape/diameter of dendritic spines critical? For what?
YUP
Critical for higher functioning
How do dendritic spines change with maturation?
They morph into the mature mushroom morphology
Where do we store a lot of info in our neurons?
Mature dendritic spines
3 neuron cytoskeletal elements?
- Microtubules
- Microfilaments
- Neurofilaments
What is another name for neurofilaments?
Intermediate filaments
Microtubules: size?
20 nm
Microfilaments: size?
5 nm
Neurofilaments: size?
10 nm
Microtubules: structure?
Globular tubulin protein which is hollow and longitudinal
Microfilaments: structure?
Actin protein
Neurofilaments: structure?
Long NF proteins
Microtubules: location?
Everywhere EXCEPT axon terminal or dendritic spine
Microfilaments: location?
Throughout
Neurofilaments: location?
Throughout
Do neurons have a cytoskeleton?
YUP
What is the role of Microtubule Associated Proteins (MAPs)?
They govern changes in neuron shape and size overtime
What are the 4 major MAPs?
- MAP-2
- Tau
- Kinesin
- Dynein
MAP-2: 2 locations?
- Dendrites
2. Soma
Tau: 1 location?
Axon
Kinesin: 2 locations?
- Axon
2. Dendrites
Dynein: 2 locations?
- Axon
2. Dendrites
MAP-2: function?
Stabilizes the shape of the mature neuron
Tau: function?
Stabilizes the shape of the mature neuron
Which MAP is defective in neurodegenerative disorders like Parkinsons and Alzheimers?
Tau
Dynein: function? What is this called?
Motor protein ATPase that transport proteins, nutrients, etc. intracellularly in vesicles from synaptic terminals to the cell body to be recycled = retrograde transport
Kinesin: function? What is this called?
Motor protein ATPase that transport proteins, nutrients, etc in vesicles intracellularly from cell body to synaptic terminal = anterograde transport
What is axoplasmic transport referred to as? Why?
Activity dependent transport because it uses ATP
Describe the flow on conduction.
Usually unidirectional but bidirectionality can have some functions as well
What do you call a neuron with dendritic spines?
Spinous = spiny
What do you call a neuron without dendritic spines?
Aspinous = non-spiny
What are the 4 components of the axon?
- Axon hillock
- Initial segment
- Axon proper
- Axon terminal
Describe the structure and location of the axon hillock.
Conical shape transition from soma to axon
Function of axon hillock?
Contains proteins that determine which information is propagated to post synaptic cells
What is the initial segment of the axon closely associated with?
The axon hillock
What is the function of the initial segment of the axon?
Site of signal integration and generation of AP through Na+ and K+ VG channels
Describe the structure of the axon proper.
Uniform width
Function of axon proper?
Signal propagation through Na+ and K+ VG channels
What are axon collaterals? Function?
Axon branches off primary axon which influence neighboring neurons
What does it mean when an axon collateral is able to inhibit a neighboring neuron?
It is firing faster and more easily than the neighboring neuron
Describe the structure of the axon terminal.
Enlargement of the axon where microtubules terminate
What is another name for the axon terminal?
Presynaptic bouton
What does the synapse contain?
Axon terminal + synaptic cleft + postsynaptic dendrite
How big is the synaptic cleft?
20 nm
What is the function of the axon terminal?
Convert the electrical signal into a chemical one by using calcium VG channels and many membrane proteins to release synaptic vesicles containing NTs into the cleft
What does the absence of microtubules at the axon terminal mean?
Less plasticity
What is the site of neurotransmission?
Axon terminal
What % of our brain cells are neurons?
10%
What are nonelectrically stimulated brain cells called?
Glial cells
What are the 6 types of glial cells? Are they in CNS or PNS?
CNS: 1. Astrocytes 2. Ependymal cells 3. Microglia 4. Oligodendrocytes PNS: 5. Satellite cells 6. Schwann cells
Which glial cells are most prevalent in the CNS?
Astrocytes
Where are astrocytes found?
Wrapped around capillaries on cortex or cerebellum, or ventral Tegmental Area or other brain structures
Astrocytes: main/overall function?
Supporting structure connecting the circulatory and nervous systems so that nutrients can be propagated to neurons
Ependymal cells: function?
Produce and circulate cerebrospinal fluid which contains waste and essential molecules by rapidly beating their apical cilia in a circular motion through the brain ventricles/central canal of spinal cord
Which glial cell most resembles a neuron morphologically? How do they differ?
Microglial cell
But they do not have VG channels so are electrically silent
Describe the structure of ependymal cells.
Squamous with apical cilia
What is the function of microglial cells?
Immune cells of CNS
What is the RMP of microglial cells? How does this compare to other NS cells? What is it mainly due to?
- 90 mV (more negative than normal)
Leakage K+ channels
What are we discovering more and more about neurological disorders?
They have an immune component
Oligodendrocytes: function?
Produce concentric layers of myelin sheath in CNS to insulate axons and reduce the current leakage to increase conduction velocity
Schwann cells: function?
Produce concentric layers of myelin sheath in PNS to insulate axons and reduce the current leakage to increase conduction velocity
Oligodendrocytes: location?
Wrapped multiple times around naked axons in CNS
Schwann cells: location?
Wrapped multiple times around naked axons in PNS
How many oligodendrocytes per neuron axon?
Many
How many neuron axons per oligodendrocytes?
Many
What are satellite cells compared to? What does this mean for their function?
Astrocytes + microglial cells of PNS = structural and immune functions of PNS
Where are satellite cells found?
Form a ring around somas of neurons of the PNS
What are 3 diseases that have issues with neuron myelination?
- ALS
- Guillain-Barre
- Multiple Sclerosis
How many Schwann cells per neuron axon?
Many
How many neuron axons per Schwann cell?
One
What are the Schwann cells separated by on an axon?
Nodes of Ranvier
Are all neurons myelinated?
NOPE
Where are the mitochondria located in the neuron axon?
In the axoplasm of myelinated portions
What protein do astrocytes express? What is it?
GFAP = Glia fibrillary acidic protein: intermediate filament found ONLY in astrocytes
What is another name for astrocytes?
Astroglia
What is special about astrocytes?
They are very dynamic and can change shape and size in response to many stimuli
What are the 9 functions of astrocytes?
- Regulate the BBB by effecting endothelial cells and angiogenic factors that regulate the passage or not of molecules to the brain
- Brain glycogen reserves
- Regulate extracellular ions (K+, Na+, H+, water)
- Uptake and regulate NTs (eg: GABA, serotonin)
- Regulate glutamate by converting it to glutamine (glutamate sponges from synapse)
- Express neurotrophic factors to contribute to learning, memory, and development to promote neuronal survival and myelanation
- Synaptogenesis and neurogenesis by secreting and modifying the extracellular matrix
- Immune modulation (w/ microglia)
- Remove cellular debris from dead or dying neurons
How do astrocytes contribute to the maturation of dendritic spines?
By secreting and modifying the extracellular matrix
What does the BBB consist of?
Endothelial cells entirely wrapped around lumen forming tight junctions with themselves
What are pericytes?
Cells that interact closely with endothelial cells of the BBB to regulate the opening/closing of the blood vessels aka the capillary lumen diameter
What covers the lumen, endothelial cell, and pericytes of the BBB?
Basal lamina
What are astrocytic foot processes?
Parts of astrocytes found around the capillaries of the BBB containing specialized membrane transporters to allow the passage of some LIPID SOLUBLE molecules to the brain tissue
What is rapid anesthesia provided by? Why?
Gases because lipid-soluble (uncharged) so can pass the BBB
Can local anesthetics pass the BBB? Why?
NOPE because not lipid soluble
Where are Golgi apparati found in neurons?
Soma and axons