Vertebrates 15 - Ion Channels

Question 1

Graded potentials

Answer 1

passive spread of signals (pass charge from atom to atom. Cable properties??. Occurs at dendrites, cell bodies, at synapses, EPSP, IPSP.

Question 2

Non-spiking neurons.

Answer 2

ie in retina, some parts of neuron. No action potentials.

Question 3

Why do action potentials go more or less in one direction

Answer 3

Stimulus usually comes from dendrites so starts at one end, and Na channels shift to inactive so it can’t go backwards.

Question 4

Speed of action potentials.

Answer 4

Increases with diameter of axon and myelination (Schwann cells and oligodendrocytes)

Question 5

Saltatory conduction

Answer 5

At notes Ranvier. b/w myelination. It passes along passively, decreases at it jumps along.

Question 6

Signals b’w nerves

Answer 6

Electro and chem synapses. Neuromuscular junction, specialized synapse. Excite or inhibit

Question 7

Electric synapses (in 1959)

Answer 7

Passive transmission via gap junctions. Faster than chemical. In vertebrate retina, CNS, Mauthner nerves. Bidirectional!

Question 8

Chemical synapses experiment

Answer 8

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)

Question 9

Chemical synapses description

Answer 9

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

Question 10

Chemical synapses process

Answer 10

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.

Question 11

Synaptic current

Answer 11

Movement of ions through ion channels at POSTSYNAPTIC membrane

Question 12

EPSP

Answer 12

excitatory post-synaptic potentials. Depolarize

Question 13

IPSP

Answer 13

inhibitory post-synaptic potentials. Hyperpolarizes

Question 14

Integration of EPSP and IPSP

Answer 14

Generally have more EPSP than IPSP at one neuron.

Question 15

Temporal Summation

Answer 15

Adding 2 input from same neuron really close together which increases voltage enough to depolarize. (time)

Question 16

Spatial summation

Answer 16

Adding 2 input from two neurons at same time which increases voltage enough to depolarize. Also possible to have inhibitory and excitatory

Question 17

Purkinje cell

Answer 17

One of major and largest neurons in cerebellum. Has 200,000 inputs. Most are excitatory. Lots of summation to generate one action potential

Question 18

Brain vs computer

Answer 18

Brain has more plasticity than computer; computer isn’t chemical

Question 19

Modulation of synaptic communication

Answer 19

Changes in synaptic strength, synaptic density (not constant!). Signal transduction pathways activated / altered (PKA, CA, cAMP). Plasticity seen in Agnatha too

Question 20

Long term potentiation - LTP (factor in plasticity)

Answer 20

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.

Question 21

LTP basis of memory - possibly?

Answer 21

Both form quickly, last a long time. Learning, memory impaired when LTP abolished.

Question 22

Long term depression

Answer 22

Opposite of LTP. Signals less strong than original. LTP and LTD both important.

Question 23

Long term memory

Answer 23

LTD and LTP involved in short term. Long term memory deals with change in synaptic density etc.