Neurocytology
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- What are the two basic cell types?
- Neurons and Glia
- What does the gray matter consist of?
- Mainly of neuronal bodies
- What does the white matter consist of?
- Main of neuronal processes
- Gray matter in the CNS forms:
- outer layers of the cerebral hemispheres and the cerebellum
- Gray matter in the PNS forms:
- Sensory ganglia including the dorsal root ganglia on roots of spinal nerves and sensory ganglia on roots of cranial nerves & autonomic ganglia (parts of the sympathetic system or parasympathetic system)
- Bundles of nerves may be referred to as:
- tracts, pathways, fasciculi, funiculi, or peduncles
- What are the three cell types of the CNS parenchyma? From what are they derived?
- Neurons, glia and ependymal cells which are derived from neuroectoderm.
- What are the other structures that are closely associated with the brain and spinal cord, however are not part of the neural parenchyma? From what are they derived?
- 1) the skull and vertebrae, 2)meningens covering the brain and spinal cord (dura, arachnoid, pia) and 3) blood vessels and their associated cells; all of which are derived from mesoderm
- What is stained by "Nissl" stain?
- Nissl stains react with phosphate groups of RNA and therefore stain nucleoli and ribosomes of rough ER, which is proiminent in the cytoplasm of nerve cell bodies nad dendrites.
- What do the components of H&E stain stain?
- Hematoxylin stains nucleic acids and primarly stains the large nuclei of large nerve cells. Eosin stains acidic proteins in the cytoplasm of both neuronal cell bodies and their processes.
- Which stain is preferred for viewing the general arrangement of the nerve cell bodies in the layers of the cerebral cortex and cerebellar cortices?
- The Nissl stain
- What is stained by neurofibrillar stains? How do they appear?
- This stain reacts with cytoskeletal elements in nerve fibers. The axon appears to be black and the myelin appears white.
- What is stained by myelin (osmium) stain and how do stained structures appear?
- This stain is based on osmium or dyes that bind lipids which appears black.
- Name the staining methods which stain only a few cells, but stain each cell completely.
- Golgi stains, microinjects, transport of label, and anitbody localization.
- Where is the final decision to fire an action potential made?
- At the start of the axon (axon hillock).
- Name the types of neurons based on the number of cytoplasmic processes.
- Multipolar, pseudounipolar, bipolar.
- What is the term used for neurons with short axons?
- Interneurons.
- what is the term used for neurons with long axons?
- Projection neurons.
- What are 2 common excitatory neurotransmitters?
- ACh and glutamate
- What is usually an inhibitory neurotransmitter?
- GABA (gamma-amino butyric acid)
- What is released by neurosecretory neurons (especially in the hypothalamus)?
- Peptide hormones rather than neurotrasmitter.
- Describe the DNA is the nucleus.
- Euchromatic. DNA is dispersed, consistent with a high rate of protein synthesis.
- Are ribosomes present in the axon?
- No.
- What stain is usedfor the cytoskeleton?
- Neurofibrillar stain.
- What cytoskeletal structures are found in both dendrites and neurons?
- Neurofilaments and mircrotubules
- What are neurofilaments composed of?
- They are composed of 3 proteins of the intermediate filament family.
- What are microtubules composed of and what is their function?
- They are composed of tubulin with associated proteins tau and MAP2. They are paths for axonal transport to and from the cell body (an active energy dependent process by which proteins and membrane synthesized in the cell body are transported to the endings).
- Describe lipofuscin.
- It is a yellowish pigment that accumulates in neurons with advancing age, commonly seen in the dorsal root ganglion cells. It probably represents insoluble residues of material that could not be degraded by lysosomes.
- Why can dendrites be seen with light microscopy?
- Because they usually contain Nissl bodies or dispered Nissl substance.
- What is considered the most distinctive and obvious feature of dendrites?
- The presence on their surfaces of numerous synaptic contacts with axon terminals from other neurons.
- Describe dendritic spines.
- They are present in many neurons but are best seen in Golgi-stained preparations. When present, these spious processes or "gemmules" are the main regions for synaptic contacts on the dendrites.
- What is meant by "Dendritic spines are labile?"
- they may disappear with aging, disease, deafferentation, or sensory deprivation. They may increse with the increased neuronal input resulting from a stimulating environment.
- What is the most obvious feature of the axon hillock using light microscopy?
- The absence of Nissl staining due to the absence of free ribosomes and RER.
- What is the most obvious feature of the axon hillock using electron microscopy?
- Microtubules and Neurofilaments extending from the perikaryon into the initial segment.
- What does the initial segment lack?
- It lacks ribosomes and rough ER.
- What does the electron-dense undercoating of the initial segment consist of?
- It consists of cytoplasmic proteins that are associated with a high concentration of membrane proteins (voltage-gated channels).
- Why does the initial segment have the lowest threshold of excitability?
- The concentration of voltage-gated channels.
- What type of ion channels are concentrated at the nodes of Ranvier?
- Voltage-sensitive ion channels
- What is present in the axonal membrane between the nodes?
- Sodium pump proteins
- What region lies just lateral to the node of Ranvier and what is its characteristic?
- The paranodal region where loops of myelin lie apposed to the axon membrane
- What region lies between sucessive paranodal regions?
- Internodal regions
- Of what type are most CNS synapses and what are they characterized by?
- Chemical synapses which are characterized by thickened pre- and postsynaptic membranes separated by a narrow "synaptic cleft" synaptic vesicles within the presynaptic terminal. They also contain mitochondria.
- The thickened appearance of pre- and postsynaptic membranres is due to _________.
- Proteins (Ca channels) that are specific to the synapse. These channels can be seen as distinctive collections of intramembrane particles in synapses viewed by freeze-frame.
- Describe the series of events involving chemical transmission.
-
1. some synaptic vesicles dock at the active zone
2. an action potential causes an local influx of calcium through voltage-controlled calcium channels which triggers a complex process leading to fusio of synaptic vesicles with the presynaptic membrane.
3. The neurotransmitter molecules diffuse across the cleft to postsynaptic membrane where they interact with specific receptors.
4. Membrane is retrieved from the presynaptic membrane by coated vesicles and used to form more synaptic vesicles. - What always excites the presynaptic axon?
- An action potential.
- Chemical synapses are called ____ or ______
- Excitatory or inhibitory.
- Describe the different appearances of the vesicles.
- Round, flattened (inhibitory), clear (ACh), or having an electron-dense core (catecholamines).
- How is communication carried between cells in an electrical synapse?
- By channels in gap junctions.
- List the classifications of synapses based on their distribution on the postsynaptic cell.
- Axospinous, axodendritic, axosomatic, and axoaxonal (often inhbitory)
- Peripheral nerves are covered by:
- Epineurium, perineurium and endoneurium
- Name the 2 types of glial cells in the PNS.
- Schwann cells, and satellite cells
- Name the 4 types of glial cells in the CNS.
- Astrocytes, oligodendrocytes, microglia, and ependymal cells
- What defines the boundaries of the nervous system?
- Astrocytes and their interfaces.
- Besides using the Golgi stain, how else can astrocytes be stained?
- By staining for glial fibrillary acidic protein (GFAP)
- What are the two types of astrocytes?
- Fibrous and protoplasmic
- Describe fibrous astrocytes.
- Found in white matter and have long, slender, unbranched processes containing many delicate fibrils (made of GFAP).
- Describe protoplasmic astrocytes.
- Found in gray matter and have shorter, high branched processes (made of GFAP).
- Using EM, what is always present in astrocytes?
- Golgi apparatus (lysosomes and glycogen granules are common)
- What is the most distinctive organelle of the astrocyte?
- the "glial filaments" found in most processes of astrocytes.
- Name the three limiting membranes formed by astrocytes.
- Internal limiting membrane (ependymal cells), external limiting membrane (pia), and perivascular limiting membrane (blood)
- List the functions of astrocytes.
-
1. provide structural support
2. take up neurotransmitters
3. maintain ionic balance
4. guide axonal outgrowth during development
5. may contribute to immune response
6. play a key role in removing neuronal debris and sealing off damaged brain tissue.