CNS 2 Flashcards
Neuroglia in CNS
- astrocytes
- oligodendroglia
- microglia (latent phagocytes)
- ependymal cells (line ventricles/CSF production)
Neuroglia in PNS
- Schwann cells (cover/myelenate the axon)
- satellite cells (cover the cell body)
pyramidal cells
- a type of multipolar neuron of cerebral cortex classified by dendrites
- makes up about 75% of neurons
- Primary excitation unit of frontal cortex
- Excited by: glutamate and aspartate
- Inhibited by: GABAA
Stellate or granule cells
- neuron type in cerebral cortex
- makes up about 25%
- excitatory amino
- acid (glutamate or aspartate)
-
most are inhibitory
- y-aminobutyric acid (GABA) transmitter
Myelination
- allows for faster conduction
- increases the effective membrane resistance (by decreasing the amt of Na that leaks out)
- decreases the capacitance
- restricts action potential generation to only the nodes of Ranvier
capacitance
the ability of a system to store an electric charge
functional benefits of myelination
- efficiency
- fast reflexes
- complex mental processing
- lower metabolic requirements
Synaptic Signaling
- classic neuron-neuron junction
- electrical (gap junctions)
- chemical (neurotransmitter)
- Neuron- Glial
- Ligands to G protein receptors in glial cells
- Extra-synaptic
- Neurotransmitters sneak out and hit other axons
electrical synapses/ gap junctions
- low resistance pathway that allows current to flow from one cell to another
- allows exchange of small molecules between cells
- bidirectional
- Gap junctions regulated by:
- voltage, intracellular pH, Ca, and G protein coupled receptors
SNARE
- the protein that mediates vessicle fusion
- brings the vessicle to the terminal edge of the axon
astrocytes
- BBB
- K+ uptake
- SVR of small vessels
- ACh recycling
- communication
oligodendroglia
myelination of the CNS
(multiple different axons)
microglia
- phagocytic cells of the CNS
- since Ab don’t cross BBB
Ependymal
- CSF production
- line the ventricles
bipolar neurons
- type of neuron classified by number of neurites
- two processes
- axon and dendrite
- retina/olfactory epithelium only–not common
pseudo unipolar neurons
- type of neuron classified by number of neurites
- sensory only
- One axon, two branches
- branches serve the function of both axon and dendrite
- one branch in CNS, one in PNS
- cell body in the dorsal root ganglion
multipolar neurons
- Type of neuron classified by number of neurites
- by far most common
- one axon and multiple dendrite
stellate cells
- type of neuron classified by dendrites
- star shaped
- 25% of CNS
- Ex: inhibitory, GABA or some excitatory, aspartate or glutamate
v-SNARES
are incorporated into the membrane of the transport vesicles
t-SNARES
associated with the nerve terminal membrane
types of SNARE proteins
synaptobrevin
syntaxin
SNAP-25
synaptotagmin
- binds to the Ca++ and SNARE complex and allows for exocytosis to occur
4 mechanisms of Ca++ entry and exit
- Ca++ pump
- Ligand gated Ca++ channel
- Voltage gated Ca++ channel
- Na+/Ca++ exchanger
***remember Ca++ concentration gradients are HUGE!!
criteria for a neurotransmitter
- must be present in presynaptic terminal
- cell must be able to synthesize the substance
- must be released upon depolarization of presynaptic membrane
- there must be a specific receptor on the postsynaptic membrane (some go to extrasynaptic locations)
***over 100 neurotransmitters currently identified
Class 1 Neurotransmitter
Acetylcholine
Class II Neurotransmitters
Biogenic Amines
- Norepinephrine
- Epinephrine
- Dopamine
- Serotonin
- Histamine
Class III Neuro transmitters
Amino Acids
- Gamma-aminobutyric acid (GABA)
- Glycine
- Glutamate
- Aspartate
Class IV Neurotransmitters
- Neuropeptides/Peptide transmitters
- i.e. hormones, Angiotensin II, Insulin, Oxytosin
Gaseous Neurotransmitters
- Are not released from “vesicles”
- able to diffuse out at any point and may travel far before encountering receptor
- Ex: NO, CO
Glutamine-Glutimate cycle
aka
Glutamate Recycling
- Axon terminal is depolarized and glutamate is released by vesical out of axon terminal
- Glutamate hits receptors on other side of synaptic cleft. Once it is released or if it never bound, glutamate gets taken up by glial cells and converted back into glutamine.
- Glutamine gets released by the glial cells and it goes back into the axon.
- Glutaminase turns the glutamine into glutamate and it gets repackaged into vesicle and ready for next release.
Acetylcholine Recycling
- Acetylcholine is made from choline and Acetyl CoA
- after being released from Axon terminal, acetylcholine is quickly broken down by acetylcholinesterase.
- Choline is transported back into the axon terminal and is used to make more ACh.
Ion current equation
Ix = gx*(Vm-Ex)
Ix = total current
gx = conductance of individual ion channel
Vm = resting membrane potential
Ex = Nerst potential for that ion
**Ion current flow direction depends on electrochemical gradients of permeant ions
MEPP
- Miniature end plate and potential
- small <0.5 mV depolarizations of postsynaptic membrane
- reflect spontaneous release of a single synaptic vesicle
- too small to reach threshold so no action potential occurs
EPSP
- Excitatory response
- increased Na+ influx
- decreased Cl- influx or K+ efflux
- change in receptor expression or enzymatic/metabolic activity
- lasts about 15 milliseconds, must have multiple within this time for an AP to occur
IPSP
- Inhibitory response
- Increased Cl- influx or K+ efflux
- pre synaptic
- post synaptic
- change in receptor expression or enzymatic metabolic activity
changes in pH affect on synaptic transmission
- alkalosis- greatly increases neuronal excitability
- acidosis- greatly depresses neuronal activity
- hypoxia- severely decreases neuronal excitability
A alpha sensory
- large, myelinated, fast
- primary golgi
