Cellular Neuroanatomy (1) Flashcards
Structural and functional unit of the NS
Neuron
2 principal cell types in nervous system
Neurons and glia
3 functions of glia
- Physical support ( protection)
- Electrical insulation
- Metabolic exchange b/n vascular system and NS
Function of neuronal cell body. Other name?
Produces proteins and provides metabolic function. Also called soma
Which neuronal structures receive input from other neurons.
Dendrites
What kind of inputs are are preferentially on to dendrites and dendritic spines?
Excitatory synaptic inputs
What three functions do dendritic spines serve as the anatomical substrate for?
- Synaptic transmission
- Synaptic plasticity
- Memory storage
How many axons does each neuron have? Function?
One and ONLY ONE axon. Axons conduct electrical output from one neuron to another.
How many dendritic spines may be on a dendrite?
Hundreds to thousands. Remember they are the small membranous protrusions from the dendrites themselves, sort of like microvilli.
Soma of neurons is esp. rich in what organelle?
Rough ER
What are Nissl bodies?
Basophilic masses consisting primarily of rough ER and ribosomes. Function is protein synthesis.
Positive Nissl stain indicates what 2 neuronal structures.
- Cell bodies
2. Proximal dendrites
Where is Nissl substance not found in neurons?
In the axon, beginning at the axonal hillock
Gray matter is _________ tissue and consists primarily of what two neuronal structures?
Unmyelinated; consists of Somas and Dendrites
White matter is ______ tissue; what neuronal structure does it primarily consist of?
Myelinated; consists of myelinated Axons
What organelles are present in the axonal hillock.
None!
What is the axonal initial segment?
Portion of axon from axonal hillock to beginning of myelination
Pseudounipolar neurons are typically found where?
In the PNS, as part of sensory neurons. Ex. - sensory neurons with cell bodies in the dorsal root ganglia
Where are multipolar neurons typically found
In the CNS. Ex. - pyramidal cells of cortical regions, Purkinje fibers of the cerebellum, or motoneurons
Local circuit interneurons, such as those in the retina are usually what type of neuron?
Bipolar
What type of cells integrate information and send long axons to other brain areas? Other two names for these?
Principal cells; also called projection neurons or Golgi type I cells
What is unique about interneurons? What other two names are they known as?
They do not send their axons out of the local brain area. Also called Local Circuit neurons or Golgi Type II cells (either no axon or short, local axon)
What are the two types of synaptic transmission?
Electrical and chemical
What structures are needed for electrical synapses to function?
Gap junctions
Most excitatory synapses in the brain are located on what structures?
Dendritic spines
What are the 4 types of synapse types?
- Axosomatic
- Axodendritic
- Axoaxonic
- Dendrodendritic
The neuromuscular junction is also one; axospinous is a subtype of axodendritic
What is unique about chemical synapses in vertebrates compared to electrical synapses?
Chemical synapses transmit information unidirectionally
What is the presynaptic bouton or axonal varicosity?
Portion at end of axon where synaptic vesicles containing NT reside
What are two examples of excitatory NTs?
Acetylcholine and glutamate
How do excitatory NTs work?
Depolarize the postsynaptic neuron to increase probability of firing
What are two main inhibitory NTs?
Glycine and GABA
What are two examples of modulatory NTs?
Dopamine and NE
Excitatory synapses are also called what? These are asymmetric, what does this mean?
Gray’s Type I. Asymmetric means they have a more pronounced density in the postsynaptic membrane than in the presynaptic membrane
Where are type I synapses normally found?
On dendrites
Gray’s type II synapses are what kind? Where are they found?
Inhibitory. Usually found on somas
What proteins are gap junctions composed of?
Connexons
What molecules make up connexons? How many?
Connexins. 6 connexins make up a connexon
What protein is responsible for anterograde axonal transport?
Kinesin
What protein is responsible for retrograde axonal transport?
Dynein
What cells provide myelination in the PNS?
Schwann cells
What cells provide myelination in the CNS?
Oligodendrocytes
What cells provide metabolic exchange and serve as a part of the BBB? What two types are there?
Astrocytes. Fibrous and protoplasmic types exist.
What cells serve as phagocytic and inflammatory cells in the CNS? What germ layer are they derived from?
Microglia. Derived from mesoderm, like monocytes.
What cells are the stem cells for glia and neurons?
Polydendrocytes
What cells line ventricles?
Ependymal cells. Are cuboidal to low columnar epithelial cells
How many internodes does a Schwann cell form? Does Schwann cell myelin contact the Schwann cell soma?
- (Schwann cells myelinate only one portion of one neuron). The Schwann cell myelin IS in contact with the Schwann cell soma
What is a Schmidt-Lanterman cleft, or incisure?
Small folds of cytosol that support the myelin; allow for continuity of cytoplasm despite the cell being wrapped tightly around the axon
What two Schwann cell pockets overhang the paranormal and nodal portion of the axon?
- Microvilli
2. Schwann cell pockets ( or paranormal loops)
What is endoneurium?
Thin layer of CT that surrounds each individual nerve fiber
What is perineurium?
CT layer covering entire nerve fascicle
How many internodes can one oligodendrocyte form? What similarity do they have to Schwann cells?
30-50 internodes, but like Schwann cells, oligodendrocytes can only form one internode per neuron. What is different is that they can myelinate several axons per oligodendrocyte.
What is different about unmyelinated neurons in the PNS compared to those in the CNS?
In the PNS, they are protected by Schwann cells (one Schwann cell can loosely envelope a few unmyelinated nerve, but they do not tightly wrap around, so don’t really insulate them). In the CNS, unmyelinated neurons are completely unprotected.
Other than maintenance of BBB, what 2 processes are astrocytes involved in?
- Angiogenesis
2. Synaptogenesis
What is the purpose of the metabolic exchange astrocytes carry out?
Maintain constant ionic concentrations for optimal neuronal function
What are Radial glia?
Sub population of astrocytes that provides direction and scaffolding for axon migration and development
How are astrocytes involved in the tripartite synapse?
They are involved in NT release into the synaptic cleft and also have NT receptors themselves
How do astrocytes communicate with each other?
Via Ca2+ release, spread by gap junctions
Which astrocytes are found in white matter?
Fibrous. These have vascular feet that connect them to outside of vascular walls
What astrocytes are found in grey matter?
Protoplasmic. These are the most common overall
What are two types of radial astrocytes that persist into adulthood?
- Mueller cells ( in retina)
2. Bergman glia ( cerebellum)
Which cells function as astrocytes in the PNS? What cells are they derived from?
Satellite cells. Derived from neural crest cells. Usually surround the entire soma of ganglia cells ( are around the pseudounipolar cells of peripheral ganglia). Are small cuboidal cells
Other than ventricles of the brain, what do ependymal cells line?
Central canal of spinal cord.
The apical surface of ependymal cells is covered by what?
Cilia and microvilli
What do the basal surfaces of ependymal cells contact?
Astrocytes
Why is it important that ependymal cells don’t have tight junctions?
Allows for free exchange between CSF and neural tissue
