Neurons and glia: Bear/Barr's Flashcards
1
Q
What is neurophilosophy?
A
No separation of mind and brain
2
Q
What do neurons do?
A
-process information
-sense environmental changes
-communicate changes to other neurons
-command body response
3
Q
What do glia/neuroglial/neuroglia do?
A
insulate, support and nourish neurons
4
Q
What is the purpose of scientists hardening the brain and how do they do it?
A
To create slices of the brain using microtome (precision cutting instrument), harden the brain my immersing in formaldehyde
5
Q
What is histology?
A
The microscopic study of the structure of tissues
6
Q
Describe the Nissl stain
A
-cationic dye
-binds to RNA and DNA
-stains nuclei of all cells
-distinguishes between neurons and glia
-enables histologists to study arrangement or cytoarchitecture of neurons in different parts of body
-the clump of material it shows is called Nissl bodies (rough ER)
7
Q
Describe Golgi stain and its purpose
A
-soaking brain in silver chromate solution (called Golgi stain) makes a small percentage of neurons become darkly coloured in their entirety
-shows 2 distinguishable parts: nucleus (cell body/soma) and neurites (axon and dendrites)
8
Q
What is the difference in lengths of axons and dendrites?
A
axons can extend over long distances (a metre or more), dendrites rarely longer than 2mm
9
Q
What was Cajal’s contribution?
A
The neuron doctrine (similar to cell theory): neurons are not continuous with each other, and communicate by contact not continuity, shown when electron microscope was invented because of resolving power; each neuron is a structural and functional unit
10
Q
What is the soma (cell body)?
A
-aka perikaryon
- contains the nucleus
-Roughly spherical central part of the neuron
- approx. 20 micrometres in diameter
- contains watery, salty, potassium-rich fluid called cytosol
11
Q
What are organelles?
A
- Membrane-enclosed structures
Some of them are: - Rough endoplasmic reticulum and smooth endoplasmic reticulum
- Golgi apparatus
- Mitochondria
12
Q
What is the cytoplasm?
A
Everything contained within the confine of the cell membrane, excluding the nucleus
13
Q
What is the Nucleus?
A
- spherical and centrally located
- 5-10 micrometres across
-contained within double membrane called nuclear envelop (has pores, about 0.1 micrometres across)
-Gene expression
-transcription
-RNA processing
14
Q
What are chromosomes?
A
-Within the nucleus
-contains genetic material DNA (deoxyribonucleic acid)
-each chromosome contains an uninterrupted double-strand braid of DNA
-humans have 46 chromosomes
15
Q
describe DNA
A
-blueprint of your entire body
-DNA in all of your cells in your body are the same
-What distinguishes cells from one another are the specific parts of DNA that are used to assemble the cell. These segments of DNS are called genes (0.1 to several micrometres in length)
16
Q
What is the “reading” of DNA called? and what is the final product of it?
A
gene expression, the final product is synthesis of molecules called proteins`
17
Q
What is protein synthesis and where does it occur?
A
The assembly of protein molecules, occurs in the cytoplasm
18
Q
Since DNA never leaves the nucleus how does genetic message get across the nucleus envelope?
A
An intermediary carried the genetic message to sites of protein synthesis in cytoplasm. This function is performed by messenger ribonucleic acid (mRNA)
19
Q
Describe mRNA
A
-Consists of 4 different nuclei acids strung together in various sequences to form a chain
-The detailed sequence of the nucleic acids in the chain represents the information in the gene. (just as a sequence of letters gives meaning to a written word
20
Q
What is the process of assembling a piece of mRNA that contains the information of a gene, and what is the result called besides mRNA?
A
Transcription, The resulting mRNA that comes from this is called the transcript
21
Q
What is a promoter?
A
One end of the gene, the region where the RNA-synthesizing enzyme, RNA polymerase, binds to initiate transcription.
22
Q
What are transcription factors?
A
The binding of polymerase to the promoter is tightly regulated by transcription factors
23
Q
What are terminators (stop sequence)?
A
Located at the end of the sequence of DNA, RNA polymerase recognises this as the end point for transcription
24
Q
What are intron?
A
-Gene that cannot be used to code for protein
-initial transcripts contain both introns and exons but then by a process called RNA splicing the introns removed and the remaining exons are fused together
25
What are exons?
The coding sequences, they are left behind after introns are removed.
26
What is alternatively spliced mRNA?
Specific exons are also removed with the introns, encodes different protein. Thus, transcription of a single gene can ultimately give rise to several different mRNAs and protein products
27
What are the building blocks of protein?
Amino acid, 20 different kinds.
28
What is translation?
The assembling of proteins from amino acids under direction of the mRNA
29
What is the "central dogma" of molecular biology?
DNA --Transcription--> mRNA --Translation--> protein
30
What is the human genome?
The entire length of DNA that comprises the genetic information in our chromosomes
31
What is gene copy number variations?
-Genetic basis for some diseases
-Long stretches of DNA that contain several genes are missing; in other, genes are duplicated, leading to overexpression of specific proteins.
-often occur at moment of conception
-some instances of serious psychiatric disorders, including autism and schizophrenia
32
What was mutations?
-can cause nervous system disorders/diseases
-"typographical errors"
-can be single nucleotide polymorphisms (minor "misspelling" like a single (e.g., color, colour) --> can affect protein function
33
What is genetic engineering?
Ways to change the organisms by design with gene mutations or insertions. Technology used in mice --> knockout mice- gene has been deleted "knocked out"
--> transgenic mice genes have been introduced and overexpressed, new genes called transgenes
-->knock-in mice: native gene is replaced with modified transgene
34
Where does protein synthesis occur?
-At dense globular structures in cytoplasm called ribosomes
- mRNA binds to the ribosomes and the ribosomes translate the instructions contained in the mRNA to assemble the protein molecule --> ribosomes use the blueprint provided by mRNA to manufacture proteins from raw material in the form of amino acids
- many ribosomes attached to stacks of membrane called rough endoplasmic reticulum (rough ER)
-Protein also produced by free-floating ribosomes -- several free ribosomes attached by a thread called polyribosomes.
35
What is the difference between protein synthesized on rough ER and those on free ribosomes?
Depends on intended fate of protein molecule:
-if destined to reside within the cytosol of neurons, then in free ribosomes
- if protein destined to be inserted in membrane, then synthesized on rough ER
36
What is smooth endoplasmic reticulum?
-continuous with rough ER but doesn't contain ribosomes
-heterogeneous and perform different functions in different locations
-some parts of smooth ER is site where proteins come out of rough ER are folded giving them 3-d shape
-other parts not involved in protein folding, but regulate internal concentrations of substances such as calcium
37
What is golgi apparatus?
-membrane enclosed disks in soma farthest from the nucleus
-site of extensive "post-translational" chemical processing of proteins
-sorts certain proteins that are destined for delivery to different parts of neurons (like neurites)
38
What is mitochondrion (plural: mitochondria)?
-very abundant organelle in soma
-about 1 micrometre long
-within the enclosure of their outer membrane are multiple folds of inner membrane called cristae
-between cristae is inner space called matrix
-site of cellular respiration
39
What happens when the mitochondrion "inhales"?
-Pulls in pyruvic acid (derived from sugars and digested proteins and fats) and oxygen --> both floating in cytosol
-pyruvic acid enters into complex series of biochemical reactions called Krebs cycle
-biochemical products of Krebs cycle provide energy that, in another series of reactions within the cristae (called electron transport chain), results in addition of phosphate to ADP, yielding ATP
40
What happens when the mitochondrion "exhales"?
17 ATP molecules released for every molecule of pyruvic acid taken in
41
What is energy currency of cell?
ATP (adenosine triphosphate)
42
Describe the neuronal membrane
-serves as barrier to enclose cytoplasm inside neuron and exclude certain substances
-about 5mm thick
-studded with proteins
-structure of discrete membrane regions influences neuronal function
-different is its soma, dendrite or axons membrane
43
Describe the cytoskeleton
-Gives neuron its shape
- the "bones" of cytoskeleton is microtubules, microfilements and neurofilaments
-not static
44
describe microtubules
-20nm in diameter
-involved in rapid transport of protein molecules and small particles in both directions of neurites
-relatively large (compared with neurofilaments and microfilaments) and run longitudinally down neurites
- wall of microtubule pipe composed of smaller strands braided like rope around hollow core
-each smaller strand consists of protein tubulin
-polymerisation and depolymerization of microtubules regulate shape of neuron (by various signals within neuron)
45
What is polymerization?
process of joining small proteins to form a long strand, resulting strand called polymer
46
What are MAPs?
-microtubule-associated proteins, one class of proteins that participate in regulation of microtubule assembly and function
-anchor microtubules to one another
-pathological changes in an axonal MAP, called tau, implicated in the dementia that accompanies Alzheimer's disease
47
describe microfilaments
-5nm in diameter (same as cell membrane)
-found throughout neurons but particularly numerous in neurites
-braid of 2 thin strands of polymers of protein actin
-constantly undergoing assembly and disassembly (regulated by signals in neuron)
-closely associated with membrane, anchored to membrane by attachment with meshwork of fibrous proteins that line the inside of membrane like spider web
48
describe neurofilaments
-10nm diameter (intermediate size between microtubules and microfilament)
-exist in all cells of body as "intermediate filament" only in neurons called neurofilaments
-consists of multiple subunits (building blocks) that wound together into a rope like structure
each strand of rope consists of individual long protein molecules, making neurofilaments mechanically very strong
-when gathered in bundles called neurofibrils
49
where does the axon begin?
-The axon hillock, tapers away (gets smaller) from the soma from initial segment of the axon proper
50
What are the features that distinguish axon from soma
-no rough ER extend into the axon, few if any free ribosomes in mature axons
-protein composition of axon membrane different from soma
51
Where do the proteins that are in the axon come from?
no ribosomes in axons means proteins in axons originate from soma
52
What are axon collaterals?
The axons that branch out
53
What are recurrent collateral?
an axon collateral returns to communicate with the same cell that gave rise to the axon or with the dendrites of neighbouring cells
54
What is the end of axon?
The axon terminal or terminal bouton
55
what is the terminal arbor?
axons have many short branches at their ends, each branch forms synapse one dendrite of cell bodies in same region, these branches collectively called terminal arbor
56
what is, to provide innervation or innervate?
axons form synapses at swollen regions along their length and then continue on to terminate elsewhere. when a neuron make synaptic contact with another cell
57
How does the cytoplasm of axon terminal differ from that of axon?
-microtubules do not extend into terminal
-terminal contains synaptic vesicles (50nm in diameter)
-inside surface of membrane that faces the synapse has particularly dense covering of proteins
-axon terminal cytoplasm has numerous mitochondria, indicating a high energy demand
58
What are the 2 sides of the synapse?
Presynaptic and postsynaptic
59
What does the presynaptic and postsynaptic side of synapse generally contain?
presynaptic generally contain axon terminals, postsynaptic may be dendrite or soma
60
What is the chemical signal of synapse and where is it stored?
neurotransmitter, stored and released from synaptic vesicles within terminals
61
What are the parts of the axons?
-axon hillock (beginning)
-axon proper (middle)
-axon terminal (end)
62
What does synaptic transmission dysfunction lead to?
mental disorders
63
What is Wallerian degeneration?
The degeneration of axons that occurs when they are cut from the soma - normal flow of material from soma to axon terminal is interrupted
64
What is axoplasmic transport?
movement of material along the axon
65
What is fast axoplasmic transport?
material enclose within vesicles with then "walk down" the microtubules of axon. The "leg" are provided by a protein called kinesin, process fuelled by ATP
66
What is slow axoplasmic transport
Transport of material at rate of 1-10 mm per day
67
What is anterograde transport?
Soma to terminal
68
What is retrograde transport?
-terminal to soma
-provides signals to soma about changes in metabolic needs of axon terminal
- the "legs" for retrograde different from that of anterograde, uses dynein instead.
69
What are the dendrites of a single neuron collectively called? and also each branch of the tree
dendritic tree, each branch called dendritic branch
70
how do the dendrites detect neurotransmitters in synaptic cleft?
have specialised protein molecules called receptors
71
What are dendritic spines?
-receive some types of synaptic input, look punching bags hanging off the dendrite.
-sensitive to type and amount of synaptic activity.
-unusual changes in spines have been shown to occur in brain in individuals with cognitive impairments
72
describe the cytoplasm of dendrites?
-resembles that of axons
-filled with cytoskeletal elements and mitochondria
- one difference is polyribosomes observed in dendrites, often right under spines
73
What is the classification of neurons based on number of neurites?
-single neurite -- unipolar
-2 or more neurites -- bipolar (2), multipolar (more than 2)
74
What is the classification of neurons based on morphology od dendrites and soma (or the spines)?
In cerebral cortex:
-stellate cells (star shaped)
-pyramidal cells (pyramid shaped)
neurons can be classified according to whether their dendrites have spines:
-spiny
-aspinous
75
What are primary sensory neurons?
-information delivered to NS by neurons that have neurites in the sensory surfaces of body such as skin and the retina of eye
76
What are motor neurons?
Neurons have axons that form synapses with muscles and command movement
77
What are interneurons?
neurons in NS form connections only with other neurons -- most of neurons in NS
78
What are Golgi type I neurons?
(projection neurons)
long axons that extend from one part of brain to the other
79
What are Golgi type II neurons?
(local circuit neurons)
neurons that have short axons that do not extend beyond the vicinity of cell body
80
What is a transgenic mouse?
genetically modified mouse
81
Are neurotransmitters used to classify neurons and how?
Yes, transmitter difference arise because of differences in expression of proteins involve in transmitter synthesis, storage and use.
e.g., motors neuron that command voluntary movements all release acetylcholine at their synapses, there classified as cholinergic
82
What are the most numerous glia in the brain?
astrocytes, fill most of spaces between neurons, the space that remains between neurons and astrocytes about 20nm wide
83
What is the role of astrocytes?
-influence whether a neurite can grow or retract
-regulating chemical content of extracellular space
-have special proteins in their membranes that actively remove transmitters from synaptic cleft
-astrocytic membranes possess transmitter receptors that can trigger electrical and biochemical events inside the glial cells
-regulates extracellular potassium concentrations
-cytoplasm contains intermediate filaments composed of glial fibrillary acidic protein (GFAP)
84
What is the role of the glial oligodendroglial and Schwann cells? and their differences
-provides layers of membrane that insulae axons
-called myelin
- oligodendroglia found only in CNS
-Schwann cells found only in PNS
-oligodendroglial cells contribute myelin to several axons, whereas Schwann cell only myelinates single axon
85
What is myelin?
(the oligodendroglia and schwann cells)
-spirals around the axons
-myelin sheath describes entire covering
-sheath interrupted periodically, leaving short length where axonal membrane is exposed --> this region called node of Ranvier
-serves to speed propagation of nerve impulses down the axon
86
What are ependymal cells?
line fluid-filled ventricles within brain and play a role in directing cell migration during brain development
87
What are microglia?
-Phagocytes, remove debris left by dead or degenerating neurons and glia
-involves in remodelling synaptic connections by gobbling them up
-can migrate into brain from blood stream
88
What are the vasculatures of brain?
arteries, veins and capillaries that deliver, via the blood, essential nutrients and oxygen to neurons
89
What's is gray matter?
Contains the cell bodies of neurons, each with a nucleus, embedded in a neuropil made up predominantly of delicate neuron and glial processes
90
What is white matter?
consists of mainly long processes of neurons, the majority being surrounded by myelin sheaths, cell bodies are lacking here
91
What do both gray and white matter contain?
large numbers of neuroglial cells and a network of blood capillaries
92
what is a variation in size of cell bodies?
5 micrometre - 135 micrometres
93
Where do neurons occur in the PNS and the CNS?
ganglia in the PNS and either in laminae (layers) or groups of nuclei in the CNS
94
What are principal cells?
The large neurons of a nucleus or comparable region; their axons carry the encoded output of information from the region containing their cell bodies to other parts of the NS; the dendrites of these are contacted by axonal terminals of several other neurons --> these neurons include principal cells of other areas and nearby small neurons
95
What do stains for myelin rely on? and what do they reveal
The affinities of certain dyes for hydrophobic proteins and protein-bound phospholipids. reveal major tract of fibres
96
What are receptors?
protein molecules that respond to specific chemical stimuli, typically causing the opening of associated channels
97
What are lysosomes?
Contain enzymes that catalyse the breakdown of unwanted large molecules
98
What are the 2 types of pigment granules?
lipofuscin - yellow-brown pigment formed from lysosomes that accumulate with aging
Neuromelanin - black pigment seen only in neurons that use catecholamines (dopamine or noradrenaline) as neuroransmitters
99
What is saltatory conduction?
AP jumps electrically from one node to the next, so signalling is much faster in myelinated than unmyelinated axon
100
What is a nerve fibre?
axon together with myelin sheath, if present, and the ensheathing glial cells
101
What is a neuromodulator?
modifying the responsiveness to transmitters
102
What are ionotropic receptors?
ion channels that open in response to the binding of a neurotransmitter
103
What are metabotropic receptors?
-aka G-protein-coupled-receptor
-require G proteins and second messengers to indirectly modulate ionic activity in neurons
104
Describe electrical synapses
- common in invertebrates and lower vertebrates (have been observed at few sites in mammalian NS)
-Each consists of close apposition (2nm) of pre- and post-synaptic membranes
-across the cytoplasm's of 2 cells they are joined by numerous "connexons", formed from transmembrane protein of both cells
- water and small ions and molecules move freely through the connexons
-low resistance and no delay
-cluster of connexons that joins cells called "gap junction"
105
What is chromatolysis?
a reactive change that occurs in the cell body of damaged neurons, involving the dispersal and redistribution of Nissl substance
106
What is transneuronal degeneration?
-is the death of neurons resulting from the disruption of input from or output to other nearby neurons
-causing the dysfunction of that neuron (either damaging it or killing it) which drives neighbouring neurons into metabolic deficit, resulting in rapid, widespread loss of neurons
107
What is axonal regeneration in PNS?
If axon of a large neuron is transected halfway along its length, cell loses more than half of its cytoplasm. Lost part of neuron can be regrown with injury occurs within territory of the PNS
108
What do phagocytes do to residual bits of axon and myelin after they've been separated from cell body?
remove residual bits and prepare the nerve to receive any axons that might regenerate into its distal stump
109
What are endfeet?
Astrocytic processes closely applied to capillary blood vessels
110
What makes up the external and internal glial limiting membranes?*
external- endfeet are applied to the pia mater at external surface of the CNS
internal- end feet applied beneath the single layer of ependymocytes the lines the ventricular system
111
What are the 2 extreme types of astrocytes that are easily recognised by light or electron microscope?
Fibrous astrocytes and protoplasmic (or velate) astrocytes
112
What are fibrous astrocytes?
occur in white matter and have long processes with coarse bundles of GFAP filaments
113
What are protoplasmic (or velate) astrocytes?
found in gray matter, processes are greatly branching and flattened to form delicate lamellae around the terminal branches of axons, dendrites and synapses
-Muller cells (in retina) and pituicytes are varieties of protoplasmic astrocytes
114
What are olfactory ensheathing cells?
Occur in the olfactory nerves and in the olfactory bulb of the forebrain. They are derived from the olfactory placode and have properties in common with both astrocytes and Schwann cells
115
Can astrocytes absorb neurotransmitters?
Yes, notably glutamate
- Thus the protoplasmic astrocytes that surround synapses and nodes terminate their actions on the postsynaptic membrane
116
What does the absorption of potassium by astrocytes around the synapses, unmyelinated axons and nodes of ranvier do?
Restrains the spread of electrical disturbances within bundles of axons and regions of neuropil. The dissipation of potassium ions and other small molecules is further enhanced by the existence of gap junctions between adjacent astrocytes.
117
What are Corpora amylacea?
-Spherical bodies 25 - 50 micrometres in diameter
-seen in brains and spinal cords of most middle-aged and elderly people
-formed by accumulation of glycoproteins and lipoproteins within processes of astrocytes
-often extremely abundant, especially in white matter of spinal cord
- at sites of degeneration of the cerebral cortex, a locally increased abundance of corpora amylacea sometimes occurs --> not thought to be involved in causation of disease
118
What are oligodendrocytes?
-Nuclei small
-cytoplasm conspicuous because of its high electron density and much granular endoplasmic reticulum and many ribosomes
-filaments and glycogen absent, but numerous microtubules are present in the processes
119
What are interfascicular oligodendocytes?
Occur in rows among myelinated axons, where their cytoplasmic processes form and remain continuous with the myelin sheaths
120
What is satellite oligodendrocytes?
-Closely associated with the cell bodies of some large neurons
-called “satellite cells” when they are found next to neuron cell bodies in gray matter
121
What is ependyma?
-simple cuboidal-columnar epithelium that lines the ventricular system
-3 types: Ependymocytes, Tanycytes, choroidal epithelial cells
122
What are Ependymocytes?
-Type of ependyma -->majority
-cytoplasm contains all the usual organelles as well as filaments similar to those in astrocytes
-most bear cilia and microvilli on the free or apical surfaces
-bases of cells have cytoplasmic processes that mingle with astrocytic end feet of the internal glial limiting membrane
-line ventricular system, in contact with CSF
-not connect by tight junctions, and molecules of all sizes freely exchange's between CSF and the adjacent nervous tissue
123
What are Tanycytes?
-type of Ependyma
-differ from ependymocytes in having long basal processes
-most occur in floor of 3rd ventricle
-basal processes end on pia mater and blood vessels in median eminence of hypothalamus
-tanycytes of ventral hypothalamic region respond to changing levels of blood-deprived hormones in CSF by discharging secretory products into the capillary vessels of the median eminence --> may be involved in the control of endocrine system by the anterior lobe of pituitary gland
124
What are choroidal epithelial cells?
-type of Ependyma
-cover surfaces of choroid plexus
-have microvilli at apical surfaces and invaginations at basal surfaces which rest on a basement membrane
-adjacent cells joined by tight junctions, thus preventing passive movement of substances from blood into CSF.
-metabolically active in controlling chemical composition of CSF
125
what are "resting" microglia?
-5% of total neuroglial population in CNS
- normally "resting" therefore called resting microglial cells
-small elongated nuclei, scanty (small) cytoplasm, several short-branched processes with spiny appendages.
-evenly spaced throughout the gray and white matter with little overlapping and intertwining of their processes
-Can acquire phagocytic properties when the CNS is afflicted by injury or disease
- may also be involved in protecting the nervous tissue from viruses, microorganism, and the formation of tumours
126
What is hypertrophy?
-when brain or spinal cord injured the astrocytes near lesion undergo hypertrophy
-cytoplasmic processes become more numerous and are densely packed with GFAP filaments
-may also be small increase in number of cells caused by mitosis of mature astrocytes (gliosis) --> occur in many pathological conditions, and sometimes the reactive astrocytes acquire phagocytic properties
127
What are reactive microglial cells?
-cells with structural and staining properties similar to those of resting microglial cells appear in large numbers at the sites of injury or inflammatory disease in the CNS
-formed from resting microglial cells, which retract their processes, divide, exhibit amoeboid movement, and acquire phagocytic properties.
128
What are gitter cells?
Reactive microglial cells that are distended (swollen) with lipid-rich phagocytosed material
129
What are schwann cells (neurolemmocytes)?
-tubular cells with elongated nuclei intimately ensheath all axons in all parts of PNS
-Each axons suspended in the cytoplasm of its Schwan cell by double layer of surface membrane --> mesaxon
-one schwann cells ensheaths either 1 myelinated axon or surrounds several unmyelinated axons
- the surface of an unmyelinated axon is in contact with extracellular fluid along its whole length, through the cleft between the layers of its mesaxon
-outside surface of each schwann cell, basal lamina present
130
What are satellite cells (ganglionic gliocytes)?
-In sensory and autonomic ganglia, these cells intimately surround the neuronal somata
-ganglia also contain Schwann cells around axons
-The enteric NS consists of small ganglia and interconnecting strands of mostly unmyelinated neurites in the wall of the gut.
-The neuroglial cells in this system have structural and chemical features in common with both astrocytes and ganglionic gliocytes
(no special name for enteric glial cells)
