Neurocytology Flashcards
How are axons classified? What is a typical neuron we think of?
Based on the number of processes coming off the cell body. Pseudounipolar = unipolar, only one connection to cell body. The typical neuron we think of is multipolar (due to dendrites coming off cell body)
What is the punctum adherens and where is that found?
Like the zonula adherens of epithelia, it is found at some synapses.
What are Nissl bodies made up of and where are they found?
Made up of rough ER, found in the perikaryon (around the nucleus)
What are two places where melanin can be found in neurons? Why?
- Substantia nigra - dopamine
- Locus ceruleus - norepinephrine
It is the breakdown product of catecholamine degradation
What is the general function of dendrites, and what unique processes can be found on them?
Tapering at acute angles to increase receptive membranes of the neuron.
Spines - appendages on the dendrites which further increase the surface area and may be involved in proliferating for learning and memory
Do all neurons have a single axon?
No, some have none (retinal amacrine cells), some have more than one (local circuit interneurons).
What is a branch off an axon called?
Collateral, always at a right or obtuse angle from parent cell.
How are unmyelinated axons organized in the CNS?
Astrocyte processes
What is the distal end of an axon called, and what does it contain?
Axon arborization, with individual axon varicosities. Contains mitochondria and synaptic vesicles.
How can you tell when a neurotransmitter is inhibitory in the synapse?
“more symmetrical” -> but honestly, the vesicles look more heterogeneous. They will be GABAnergic, vs glutaminergic is very heterogeneous and excitatory.
What at the three most common types of synapses?
pre: post
1. Axodendritic
2. Axospinous
3. Axosomatic
What are the rarer types of synapses and where are they normally found?
Dendrodendritic, somatosomatic, and axoaxonic. Axoaxonic in particular is normally found on the axon hillock, which has the largest effect on whether or not an action potential is generated. These are usually inhibitory.
What is the difference between a projecting and intrinsic axon?
Projecting = axon reaches a nearby nucleus (collection of cell bodies in CNS)
Intrinsic = Local circuit axon, an interneuron
What is the general function of an interneuron?
To form local synapses which are typically inhibitory
What are the types of macroglia, and what are they derived from?
Astrocytes: fibrous or protoplasmic
Oligodendrocyte
Epdendymal / tanycyte
All derived from NEUROECTODERM
What are microglia derived from?
Mesoderm
What are Schwann cells and Satellite cells derived from?
Neural crest
Where are the two types of astrocytes found most commonly, and what do their processes do? What do they look like in the nucleus?
Fibrous - most common in white matter
Protoplasmic - more compact and fuzzier, found in gray matter
Processes form “end feet” which sit on the outer perimeter of blood vessels
Look almost like plasma cells with marginated heterochromatin
How do astrocytes act in support?
During brain development, they are the radial glia which provide support + migration path for newly proliferated neurons
How do astrocytes help at synapses?
They isolate synapses, and also buffer potassium / act as a potassium sink in extracellular space after depolarization to quickly restore membrane potential
How do astrocytes contribute to the blood brain barrier?
Connect to the endothelial cells which form it, via gap junctions. Also help maintain the basal lamina on the outside.
Furthermore, they regulate the aquaporins on the blood brain barrier to regulate water passage
How do astrocytes serve in repair processes?
They proliferate and increase in size to wall off the injured area, and they also phagocytose neuronal parts.
How do astrocytes contribute to neural growth?
Secretion of growth factors like IGF, NGF (nerve growth factor), and BDNF (brain derived nerve factor)
What are the two different types of brain edema? How is this prevented?
- Vasogenic - too much water in extracellular compartment
- Cytotoxic - too much water in neurons
Prevented via aquaporin regulation of BBB via astrocytes
What is the most numerous cell type of the glia? How many things can they do?
Oligodendrocytes, can myelinate as many as 50 internodal flaps of myelin
What do microglia look like and what do they do?
They look very small, associated with blood vessels, with barbwire-like appendages. Mostly inactive, but are induced by cytokines during injury to phagocytose neuronal bits. Also called “gitter cells” by pathologists when they’ve eaten alot of debris
What is the difference between ventricular and choroidal ependymal cells?
They both line the ventricular system + central canal as epithelial cells. However, choroidal ependyma have occluding zonules since they form part of the CSF-brain barrier, whereas ventricular ependyma do not.
How do choroidal ependyma make the CSF?
They use ATP-ase dependent pumps, and much of the liquid / ions is brought in via fenestrated capillaries in the choroid plexus which are very leaky.
What is the role of tanycytes?
They are specialized ependyma which exist in areas where they is no blood brain barrier, like the hypothalamus. They function to absorb and release hormones from CSF into circulation.
What type of junctions are at lateral loops of myelinated axons (adjacent to nodes of Ranvier)?
Tight junctions
What cell type is present at the node of Ranvier in the CNS but not the PNS?
Astrocyte
What is the origin of most brain tumors?
Glial origin -> neuronal tumors are rare
What is the most malignant astrocytoma? How common is it?
Glioblastoma multiforme. Most common form of brain cancer, much more common that oligodendrogliomas
What type of tumor is an acoustic neuroma and where does it start?
Schwannoma, starts close to the cerebellopontine angle (CN8).
What is the most common oligodendroglial disease and what population is it found in?
Multiple sclerosis, autoimmune response to proteins in central myelin. More prevalent in females, rare near the equator.
