Chapter 2 - Neurons and Glia Flashcards
Cell theory
All tissue is composed of microscopic units called cells.
functions of glia
- insulates
- supports
- nourishes neurons
- aids in neuronal communication
functions of neurons
- process information
- sense environmental changes
- communicate changes to other neurons
- command body response
_____ discovered the Nissl stain
Franz Nissl
Where are nissl bodies located?
eER
the microscopic study of tissue structure
histology
- stains eER in cell body and dendrites
- facilitates the study of cytoarchitecture in the CNS
The Nissl Stain
central region containing the nucleus
perikaryon
What is the relationship between Nissl bodies and rER?
they’re the same thing, just different names.
soma
cell body
neurites
axons, dendrites
single neurite
- fast
- escape behaviour
- single processes (invertebrate)
- specialized segments
unipolar
two neurites
- dendrites carry information to cells
- axon transmits it to other cells
- specalized segments
Bipolar
more than two neurites
- dominate vertebrate nervous system
- given text book example of what neurons look like
- motor neurons
- complex cells (some will be myelinated)
multipolar
star-shaped neurons
stellate cell
pyramid-shaped neurons
pyramidal cells
what do spines do?
isolate chemical signals and are morphologically active events triggered by synaptic activation.
- each spine synapses with different cells
- these spines can change with regard to time
- these processes are believed to be the foundation of memory
- these changes that occur in neurons that allow for communication with other cells
- estrous cycle will change these
- complexity of cognition and behaviour - cells constantly changing.
nerves that transmit sensory information
primary sensory neurons
a nerve cell forming part of a pathway along which impulses pass from the brain or spinal cord to a muscle or gland.
- interacts with the peripheral system
motor neurons
a neuron that transmits impulses between other neurons, especially as part of a reflex arc.
interneurons
type of glial cell concerned with the production of myelin in the central nervous system
Oligodendrocyte
type of glial cell found in the peripheral nervous system.
- wrap around axon and nerons in different ways (entirely)
- insulate axons; speed action potential conduction
Shwann cells
type of glial cell. Most numerous glia in the brain.
- influence neurite growth
- regulate chemical content of extracellular space
- remove substances
- release substances
- supple metabolic substrate
- response to immune challenges (fighters)
- implicated in supporting normal function and responding to neurons
- release chemical signals that cell axons where to grow (growth factors)
- monitor extracellular environment (act like sponges)
astrocytes
the myelinating glia cells
Oligodendroglia (in CNA) Schwann cells (in PNS)
region where the axonal membrane is exposed
nodes of ranvier
astrocytes-neuron communication: metabolism
- store glucose as glycogen
- take up glucose from blood vessels
- glucose metabolized into glycogen
- supply neurons with alternative form of energy (ex: lactate)
- break down glycogen and supplies lactate and pyruvate to neurons (converts to energy)
small space (must more narrow than synapse ~ 2nm) between astrocytes that allow for fast communication
- low signal
- hemi-channels (connexon) : pre and post synaptic - 6 sub-units.
- large diameter pores
- voltage signal
- calcium wave
Astrocytic Gap Junction
are a type of glial cell that are the resident macrophages of the brain and spinal cord, and thus act as the first and main form of active immune defense in the central nervous system (CNS).
- phagocytes in CNS - suck up debris
microglia
watery fluid inside the cell
cytosol
membrane enclosed structures within the soma
organelles
contents within a call membrane (eg: fluid, organelles)
cytoplasm
where is genetic information held?
chromosomes in the nucleus
sequence of DNA that encodes a single polypeptide or protein
gene
structure of DNA
DNA is composed of two strands that twist together to form a helix. Each strand consists of alternating phosphate (PO4) and pentose sugar (2-deoxyribose), and attached on the sugar is a nitrogenous base, which can be adenine, thymine, guanine, or cytosine. In DNA, these bases pair; adenine pairs with thymine and guanine with cytosine. Hence, DNA is a ladder-like helical structure.
assembling of RNA information of the gene
RNA molecules are synthesized from the DNA template by RNA polymerase
transcription
RNA processing
splicing
messanger - carries information from the nucleus to the cytoplasm
mRNA
a polymerase that catalyzes the synthesis of a complementary strand of RNA from a DNA template
RNA polymerase
construction of proteins - occurring in the cytoplasm
Protein synthesis
each gene contains
1) promoter region
2) terminator region
promoter region
transcription is initiated
- RNA polymerase would bind to this region to initiate transcription
- controlled by transcription factors
- start signals for RNA synthesis: the site where RNA polymerase bind.
terminator region
RNA polymerase recognizes the signal to end transcription
segments of genes that do not code for proteins
introns
segments of the gene that do code for proteins
exons
the process of removing introns and splicing together exons
RNA splicing
assembling of proteins from amino acids
translation
major site for protein synthesis
rER
site for preparing/sorting proteins for delivery to different cell regions (trafficking) and regulating substance.
smooth ER and golgi (in soma)
Epigenetic mechanisms
- Histone remodeling
2. DNA methylation
involves modifications to a histone protein (around which DNA is coiled) and can either decrease or increase gene expression
Histone remodeling
involves the attachement of a methyl group to DNA and tensds to reduce the expression of adjacent genes
DNA methylation
nuture can alter genes - control mechanisms in which things are turned on and off.
Many changes can change gene expression and pass down through generations
ex: smoking
Epigenetic mechanisms
Each nerve cell makes only 3 classes of proteins
1) Proteins synthesized in the cytosol - and stay there
2) Proteins synthesized in the cytosol but later incorporated into the nucleus and mitochondria
3) proteins synthesized in association with membrane systems.
a) remain attached to the membrane of the rER and golgi (and vesciles)
b) remain in the organelle (eER or GA) - not attached to the membrane
c) transported by means of vesicles from the golgi or other organelles - can become secretory products (eg: neuropeptides)
site of cellular respiration
Mitochondria
energy cycle
Krebs cycle
cells energy course
ATP
_____ pulls in pyruvic acid and oxygen
inhale
17 APT molecules released for each pyruvic acid molecule
exhale
internal scaffolding of neuronal membrane
cytoskeleton
3 bones in cytoskeleton
microtubules (20nm) - made out of tublin
neurofilaments (10 nm)
microfilament (5nm)
structure of the axon
axon hillock (beginning) axon proper (middle) axon terminal (end)
differences between axon and soma
ER does not extend into the axon
Protein composition = unique (different from soma)
differences between the cytoplasm of axon terminal and axon
No microtubules in terminal
Presence of synaptic vesicles
Abundance of membrane proteins
Large number of mitochondria
axo-dendritic
spine
axo-somatic
presynaptic axon synapsing on cell body
axo-axonic
rare
- if you have a region where you have a pre and post synaptic cell - likely to be next to presynaptic side
modulating axons
is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other cell parts (i.e. organelles) to and from a neuron’s cell body, through the cytoplasm of its axon
- membrane and secretory proteins are actively transported
axoplasmic transport
1) FAST axonal transport
- anterograde
- retrograde
2) SLOW axonal transport
large particles move in a saltatory manner dependent on ATP (energy consuming) independent of cell body microtubules tract kinesins form cross-bridges little feet walking along microtubules
Two motor heads, neck linkers with tether to organelle/vesicle
Motor movement of kinesin
Motor head has ADP molecule bound
Binding of motor head to microtubule causes
ADP release
Molecule of ATP now binds, triggers neck linker zipper action onto the core
Throws the second motor head forward to further bind to the microtubule (ATP hydrolyzed back
to ADP)
Active process: 1 ATP molecule step/ 2 ATP molecules cycle
FAST axonal transport
the motor molecule
Kinesin
Motor movement of kinesin
Motor head has ADP molecule bound
Binding of motor head to microtubule causes
ADP release
Molecule of ATP now binds, triggers neck linker zipper action onto the core
Throws the second motor head forward to further bind to the microtubule (ATP hydrolyzed back
to ADP)
Active process: 1 ATP molecule step/ 2 ATP molecules cycle
returning materials to cell body (degradation, reuse)
packaged in large membrane-bound organelles
slow but still fast
dynein - motor molecule
virus infections and labelling
Retrograde Fast Transport
retrograde labelling
horseradish peroxidase labelling
practicalities of Retrovirsues
- tracing studies similiar to HRP
- also becomes a method of incorporating proteins (enzymes, transcription factors etc) into cells
- cytoskeleton elements and soluble proteins and some metabolic enzymes
2 components: - slow: carried components of microfilaments and parts of microtubules
- fast: some actin (microfilaments)
does not occur in the retrograde direction
slow axoplasmic transport
