Module B-01 Flashcards
2 major cell types in CNS and PNS
1) Neurons
2) Glia
Functions of Glia
- Supportive
- Protective (cushion and ideal chemical environment)
- Regulatory
- Electrically Insulated
Define Neurites
axons and dendrites
Describe neuronal cell membrane
- Phospholipid bilayer with ion channels , receptors and other protein complexes
Describe neuronal nucleus
bilayered porous membrane that contains DNA
Nissl substance consists of_______ and produces______
RNA granules ; Proteins
Location of Nissl substance
Cell body and proximal regions of dendrites
describe mitochondria
Bilayered organelle involved in energy generation
Function of Golgi apparatus
- vesicular packaging
- modification and transport of products of Nissl substance
Lysosomes
scavenger vesicles loaded with degratory enzymes
3 types of Cytoskeleton filaments
1) Microtubules
2) Neurofilaments/Intermediate Filaments
3) MIcrofilaments
Functions of Cytoskeleton filaments
- Change shape during cell growth and regenration
- Maintain shape in Mature cell
- Transport of material
Microtubules are polymers of___________
alpha, Beta and Gamma tubulin
How do microtubules grow?
-addition of tubulin dimers which are the cross linked by Tau protein (alzheimer’s)
Function of microtubules
Forms Tracts for the 2 axonal transport
Anterograde transport aka
orthograde
Protein involved in anterograde axonal transport is ________ and retrograde is ________
Kinesin; Dynein
In which direction does Kinesin move on along the microtubules?
towards the positive end of the micortubule and becomes inactivated at nerve ending
What type of proteins are Kinesin and Dynein?
ATPases
In which direction does Dynein move on along the microtubules?
towards negative end of microtubule and becomes inactivated at the soma
Function of Retrograde transport
- NGF transport after endocytosis at teh nerve terminal towards the soma
- recycled vesicles and lysosomes
3 Types of Neurofilaments/Intermediate filaments
GFAP (glial fibrillary acidic protein)
nestin
vimentin
Function of Neurofilaments/Intermediate filaments
create scaffolding of cytoskeleton
Structure of Neurofilaments/Intermediate filaments
Highly polymerized with little turnover
Number of Neurofilaments/Intermediate filaments in neurons is dependant on _________
Axonal Diameter (radial development)
_________ is similar to myosin of muscle in that it has binding sites for large structures
Kinesin
Actin is a type of __________
Microfilament
Function of Microfilament
- participates in advancement of Growth Cone
- synaptic vesicle endocytosis during vesicle recycling (actin)
Location of Microfilaments
forms a network just below the cell membrane
How is dendritic transport different from axonal?
microtubule are in mixed orientation for selective movement to dendrites rather than axons
Rate of Axoplasmic flow
1mm/day
neuron with multiple dendrites
Multipolar
Multipolar neuron with long axons are called ________ and those with short axons are called ________
Golgi type I (Motor) ; Golgi type II (inhibitory)
Neurons with elongated cell body and two processes
Bipolar
Function of Bipolar
Special sensory systems like retina and CN 8 (visual and auditory)
neurons with 2 axonal processes that diverge from a stalk of the cell body
Pseudounipolar
Example of Pseudounipolar
sensory neurons that form the Dorsal Root ganglia and cranial nerve ganglia
Class A fibers
Myelinated neurons
Class C fibers
Unmyelinated neurons
Myelination _______ speed of conduction
increases
categorization of neurons according to myelination
Class A and C
Categorization of neurons according to Axonal diameter
Class I, II, III and IV
Class I
Largest diameter and most rapid conducting
Class II and III
intermediate diameter and intermediate conduction speeds
Class IV
Smallest, unmyelinated and slowest (Class C)
How do inhibitory neurons inhibit
release transmitter that polarize and stabalize membrane
What dictates whether a neuron has inhibitory or excitatory effect?
Receptors on postsynaptic neurons , not the transmitter
6 types of glia
- Astrocytes
- Microglia
- Oligodendrocytes
- Ependymal cells
- Tanycytes
- Choroidal epithelial cells
Most numerous cell type in CNS
Astrocytes
Functions of Astrocytes
- Maintain ionic homeostasis
- Maintain synaptic homeostatis
- Regulate cerebral blood flow
- Protect neurons from oxidative damage
- Supply lactate to glucose-deprived neurons
- Direct differentiation of neuronal precursors (releasing growth factors)
- Release cholesterol (a component of the lipid structure of membranes)
- Increase numbers of synapses
- Release gliotransmitters
- Uptake of excess K+ through ion channels
What transmitters do astrocytes take up at the synaptic cleft?
glutamate, glycine and monoamines
What Gliotransmitters do Astrocytes release?
Glutamate, D-serine and ATP
Which 2 types of glial cell forms Gliotic scar (gliosis) during Brian and Spinal cord damage?
Astrocytes and ependymal cells
Effect of high extracellular K+ levels on neuron
Depolarizes the neuron
What is spatial buffering or potassium siphoning?
When astrocytic K+ ion channels that take up the excessive extracellular ions for shunting to neighboring astrocytes via gap junctions
__________ are Neuronal, astrocytic and oligodendrocytic progenitors
Radial Glia
2 locations where Radial glia persist
- Bergman glia in cerebellum
- Müller cells of the retina
Function of Microglia
Immunocompetent and phagocytic
- Protect neurons from micro-organisms and toxic effects of cellular debris
- Secrete neurotrophic or neuron survival factors upon activation
- contribute to initiation of pathological neuronal degernation
- Release cytotoxic molecules
Types of cytotoxic molecules released by microglia
o Proinflammatory cytokines
o Reactive oxygen intermediates
o Proteases
_________ myelinate axons of CNS neurons
Oligodendrocytes
Function of ependymal cells
Produce CSF
form CSF-brain barrier
produce neurons and glial cells after stroke
Location of Ependymal cells
walls of ventricles
Function of Choroid plexus epithelial cells
- Secrete cerebrospinal fluid (CSF)
- transfer molecules from blood into CSF
Tanycytes are derived from
Radial Glia
Function of Tanycytes
Interface between CSF and Blood
allow sampling by homeostatic areas
Where do Schwann cells originate from
neural crest cells (both myelinated and unmyelinated)
Functions of Schwann cells
- myelination in PNS
- clearing cellular debris by phagocytosis
What happens to schwann cells of damaged axons
regress to immature state to support regeneration
Enteric glial cells are similar to _______
astrocytes
Where are satellite glia found?
in sensory, sympathetic and parasympathetic ganglia
what type of glia are schwann cells, satellite and enteric glial cells?
PNS glia
Function of satellite cells
surround neurons to to regulate chemical environment
What happens during axonal transection of PNS
o Distal axonal segment degenerates
o Proximal axonal segment may form sprouts
o Schwann cells Proliferate, forming a guide tube
Release nerve growth factors, encouraging axonal regeneration
Re-myelinate the regenerating axon
Target cells may die unless reinnervated within denervated
cells may die after 3 weeks
Rate of axon growth in remyleination
about 2 mm/day
Define Chromatolysis
Post traumatic neuronal swelling and dilution of of organelles
Anterograde transneuronal degeneration
death of denervated (postsynaptic) cell or neuron
Retrograde transneuronal degeneration
death of the cell presynaptic to the damaged cell
Wallerian degeneration
degeneration of the disconnected axon and terminal
Why doesn’t regeneration occur in CNS?
- not enough NGF is secreted by the glial cells
- oligodendrocytes don’t form guide tubes as Schwann cells
- Gliotic scars block axonal regrowth
All Tumors of the PNS are_________
Schwannomas
__ of tumors of brain and ____ of spinal cord are glial origin
50%; 25%
2 demyelinating autoimmune diseases
- Guillain Barre Syndrome (peripheral demyleinating)
- Multiple Sclerosis
