Cajal’s Neuron Dcotrine:
- neuron: neuron is the unit of the nervous system.
- synapse: neurons are separated by gaps
- connection specificity: each neuron contacts only specific target cells.
- dynamic polarization: impulses travel in one direction in a neuron.
what are the evidence for chemical transmission at the synapse?
- information appears flow in one direction from axon to dendrite
- some interaction appears to be inhibitory
- a delay of several milliseconds present
what are the excitatory neurotransmitters?
- acetylcholine (PNS)
- glutamate (CNS)
- noradrenaline
- dopamine
- serotonin
- ATP
- neuroactive peptides
what are the inhibitory neurotransmitters?
- GABA (in brain)
2. glycine (in spinal)
4 compartments in neurons?
- input compartment (dendrite & soma):
spines receive mainly excitatory inputs while soma receives mainly inhibitory inputs (one input can shut it all down) - integrative compartment (soma & axon initial segment):
- conductile compartment (axon)
- output compartment (axon terminal):
what are En Passant synapses?
where one neuron joins another at a place besides axon terminal
- in fact, en passant synapses are far more common in CNS than synapses that form at axon tips
- neurotransmitter release is not found along the entire length of the axon, but only at boutons and terminals
how is synapse size related to functional efficacy?
a larger synapse is a stronger synapse
microtubules to actin ratio in dendrites and axon?
- dendrites have a higher microtubule to actin ratio than axons.
- dendrites have less filamentous actin than axon.
microtubule polarity in dendrites and axon?
- dendritic microtubules are in both directions
2. in axons all the plus ends pointed distally.
Role of dynein and kinesins in axonal transport?
- kinesins move in anterograde direction
2. dyneins move in retrograde direction
which substances can be used as anatomical tracing?
- anterograde: lectins (wheat germ agglutinin –WGA)(it can jump synapse), phaseolus lectin (PHA-L)(purely anterograde), H3-Amino acids, Aden-associated virus, Herpes Simplex Virus
- retrograde: HRP, Fluorogold, Cholera toxin-gold, fluorescent microspheres, Rabies Virus(can jump synapses)
where do unipolar cells and pseudo unipolar cells located?
- unipolar cells are located in invertebrate nervous system
2. pseudo unipolar cells are in vertebrate nervous system
what are PSD composed of ?
the postsynaptic membrane contains a high concentration of glutamate receptors, associated signaling proteins, and cytoskeletal elements, all assembled by a variety of scaffold proteins into an organized structure called the postsynaptic density (PSD)
what are the microtubule associated proteins that axon and dendrite express?
- the MAP Tau is found exclusively in axons
2. MAP2 is found only in dendrites
summary: Axon vs. Dendrite
- propagation of electrical signals:
- passive input to dendrites
- active output from axon - synaptic components:
- postsynaptic density & spines
- synaptic neurotransmitter vesicles - different cytoskeletal components:
- MAP2 (dendrite) vs. MAP tau(axon)
- different filament polarity - different organelle organization and distribution: polyribosomes and Golgi outputs vs. actively transported cargo (vesicles and mitochondria)
which gene can cause elephant man disease?
NF1
glutamate receptors pass both K and Na upon binding glu. why does this cause depolarization?
by increasing the permeability to both ions, the new equilibrium potential will approach to the average of Na + and K+ equilibrium potential, which is about 0mV. this can cause an EPSP.
GABA can activate either GABA-A or GABA-B receptors. GABA-A receptors conduct Cl which transiently forces Vm down toward Ecl AND GABA-B indirectly causes more K channels to open, forcing Vm down toward Ek. if the resting Vm is higher than Ecl or Ek then GABA will result in an IPSP. but sometimes inhibition is still effect when, for example Ecl and Vm are the same why?
although the driving force for Cl- is small at rest, it becomes bigger when the cell is activated by an excitatory input (EPSP) and now effectively clamps the membrane at Ecl. this is known as shunting inhibition.
