Flashcards in Vertebrates 15 - Ion Channels Deck (23)
passive spread of signals (pass charge from atom to atom. Cable properties??. Occurs at dendrites, cell bodies, at synapses, EPSP, IPSP.
ie in retina, some parts of neuron. No action potentials.
Why do action potentials go more or less in one direction
Stimulus usually comes from dendrites so starts at one end, and Na channels shift to inactive so it can’t go backwards.
Speed of action potentials.
Increases with diameter of axon and myelination (Schwann cells and oligodendrocytes)
At notes Ranvier. b/w myelination. It passes along passively, decreases at it jumps along.
Signals b’w nerves
Electro and chem synapses. Neuromuscular junction, specialized synapse. Excite or inhibit
Electric synapses (in 1959)
Passive transmission via gap junctions. Faster than chemical. In vertebrate retina, CNS, Mauthner nerves. Bidirectional!
Chemical synapses experiment
Took solution from stimulated vagus nerve from one frog heart in dish and added to another heart with no nerve. Heart slowed in both. Basically found first NT (vagusstoff)
Chemical synapses description
Unidirectional. Lots of mito., Voltage gated calcium channels in abundance. Bouton wraps around post synaptic end. NT goes across synaptic cleft. NT receptors on post synaptic are highest concentration at the synapse
Chemical synapses process
1. Electrical signal arrives at bouton. 2. Causes Ca channels to enter. 3. Ca causes exocytosis of NT vesicles. 4. [NT] increases in cleft. 5. NT binds to receptor (ligand gated channel). 6. Channel opens up, allows Na or Ca to enter and depolarize OR Cl enters and inhibits excitation.
Movement of ions through ion channels at POSTSYNAPTIC membrane
excitatory post-synaptic potentials. Depolarize
inhibitory post-synaptic potentials. Hyperpolarizes
Integration of EPSP and IPSP
Generally have more EPSP than IPSP at one neuron.
Adding 2 input from same neuron really close together which increases voltage enough to depolarize. (time)
Adding 2 input from two neurons at same time which increases voltage enough to depolarize. Also possible to have inhibitory and excitatory
One of major and largest neurons in cerebellum. Has 200,000 inputs. Most are excitatory. Lots of summation to generate one action potential
Brain vs computer
Brain has more plasticity than computer; computer isn’t chemical
Modulation of synaptic communication
Changes in synaptic strength, synaptic density (not constant!). Signal transduction pathways activated / altered (PKA, CA, cAMP). Plasticity seen in Agnatha too
Long term potentiation - LTP (factor in plasticity)
Greater postsynaptic response to second AP stimulus (ie works better than before). Can last hours to weeks. Glutamate receptors role. Ca activates kinases in Postsyn., NT’s get (P)’d, and turn on genes so more receptors produced. Post. can release NO which affects Pre.
LTP basis of memory - possibly?
Both form quickly, last a long time. Learning, memory impaired when LTP abolished.
Long term depression
Opposite of LTP. Signals less strong than original. LTP and LTD both important.