a. Neurocytology 1
Terms
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- 2 main features of neuron:
-
1. Dynamic polarization
2. Connectional specificity - 2 parts to neuron soma:
-
-Nucleus/cytoplasmic organelles
-Axon hillock - What is in the cytoplasm/nucleus??
-
-Euchromatin
-Nissl substance
-Neurofilament - What type of nucleus do glial cells have?
- Heterochromatin
- What is nissl substance?
- Stacked RER that stains with nissl stain - indicates active protein synthesis.
- What is not in the axon hillock?
- Nissl substance
- What type of neurons have basal dendrites?
- Pyramidal
- 2 Types of dendrites:
-
-Apical - extends away from axon
-Basal - off the sides of soma - Characteristics of the Axon cytoplasm:
-
-No Ribosomes
-No RER - What occurs at the initial segment of the Axon
- Initiation of APs
- What are varicosities?
- Presynaptic swellings at the terminals of axons that pass impulse to OTHER NEURONS - not the target.
- Unipolar or pseudounipolar neurons are usually:
-
Sensory ganglion neurons
-invertebrates - Bipolar neurons are usually:
- Retina or olfactory
-
Multipolar neurons are:
(3 examples) -
The most common ones...
-Pyramidal neurons in cerebral cortex
-Purkinje cells in cerebellum
-Motor neurons in SC -
Type of axons in:
-Golgi type I neurons
-Golgi type II neurons -
I: long/project
II: short/connect -
How many can a neuron have?
-dendrites
-axons -
one or many dendrites
only one axon - Organelles that dendrites can have:
- All except golgi
- Organelles that axons can have
-
No Golgi, RER, or RIBOSOMES
-NO PROTEIN PRODUCTION HAPPENS IN THE AXON - Shape of Dendrites
- taper w/ spines
- Shape of axons
- cylinder with branches
- What is myelinated?
- Axons not dendrites
- What type of neurons don't have dendrites?
- Unipolar
- What uses the most energy; axons or dendrites?
- Dendrites
- Energy use in axons:
- LOW energy consumption
- 3 Main features of Neuron cell membranes:
-
-Maintains resting Em
-Electrically excitable
-Has ion pumps/channels - What color is nissl substance and where is it found?
- Basophilic - anywhere EXCEPT axon hillock or axon.
- Is nissl substance seen in dendrites?
- yes
- 3 constituents of the Neuron cytoskeleton:
-
1. Actin microfilaments
2. Neurofilaments (intermediate)
3. Microtubules -
Microfilament features
-size
made of what
-Where in neurons -
5-8 nm diameter - made of 2 Actin strands braided together (G->F)
-associated w/ membrane -
Neurofilament features
-what are they
-size
-where in neuron -
Neuron-specific intermediate filaments
10 nm in diameter
-in soma, dendrites, & axons. - What important disease is associated with intermediate neurofilaments?
- Alzheimer's disease - neurofibrillary tangles
- What are Neurofibrils?
- Aggregates of neurofilaments seen at light microscope level
-
Microtubules
-diameter
-components
-function -
25 nm diameter
-Tubulin chains
-Function in axonal/dendritic transport of stuff - Function of microtubules
- GTPase for transport
- What are MAPs
- Microtubule associated proteins
- 3 High MW MAPs:
-
-Kinesin
-Dynein
-MAP2 - Low MW MAP:
- Tau
- What is Kinesin?
- Motor/ATPase that propels organelles along microtubules.
- What stabilizes microtubules?
- Taxol
- What depolymerizes Microtubules?
- Colchicine
- What is the function of lysosomes in neurons?
- Membrane turnover
- What is lipofuscin?
- Indigestible lysosome material - pigented inclusions associated with aging and dementia
- Why do neurons need special transport mechanisms?
- B/c no protein transport in axons, and junk needs to be returned from axons too.
- 3 types of neuron transport:
-
1. Slow axonal - only antero
2/3. Fast axonal - antero/retro - Stuff transported by SLOW axonal transport:
-
-Microtubules, neurofilaments, soluble proteins (slower)
-Proteins, metabolic enzymes, Calmodulin (faster) - Major difference between slow and fast anterograde transport:
- Fast needs ENERGY
- Main protein needed for fast anterotransport:
- KINESIN -> a MAP that is an ATPase to motor junk along
- What inhibits kinesin?
- Colchicine
- What gets transported by fast anterotransport?
-
-Subcellular organelles
-Mitochondria
-Synaptic vesicle precursors
-Smooth ER vesicles/contents - Major protein for fast RETROgrade transport:
- Dynein
- Stuff that gets transported by Dynein/retrotransport:
-
-Stuff that's dying
-Stuff for being reused
-Stuff endocytosed at nerve terminal - What's a bad thing about retrograde transport?
- Viruses and toxins take advantage of it
- What is HRP
- Horseradish peroxidase - a retrograde tracer to see where the cell body is of a long axon
- Towards which end of the MT and neuron does dynein go?
- Towards the neg end of MT at the neuron's cell body.
- Towards which end of the MT and neuron does kinesin go?
- Towards the pos end of MT at the neuron's axon terminal.