Biopsych Lecture 3

Front 1

Parts of the potential

Back 1

Threshold
Subthreshold
Resting potential
Afterpotential
Refractory period
Regeneration

Front 2

Speed of conduction is dependent on...

Back 2

diameter, and if mylenated

(passive current flow - active prop. only occurs at nodes of ranvier)

Front 3

Stuff to know about giant squid axon

Back 3

1) Easy to use in experiments (Which is why Hodgekin/Huxley/Katz used it)
2) Unmyelinated
3) Very large diameter for fast AP propagation rate

Front 4

Name another model system?

Back 4

Motor neuron in anterior horn of spinal chord

Front 5

Intracellular recording from brain slice/ record + stimulate axon slides

Back 5

You can use glass micro-pipettes to stimulate/record along axon

You find that hyperpolarizations provide no active response, but depolarization will result in action potentials

Front 6

Action potentials vs graded potentials re:strength down axon

Back 6

strength remains same! (why?) All or nothing!

Graded potentials fade over axon

Front 7

Why is there a threshold?
Why does action potential reverse?
Why is there a hyperpolarizing afterpotential?

Back 7

1) Threshold due to Voltage gated Na+ channels (only open at certain depolarization)
Action potentials a function of voltage sensitive protein channels
2) depolarizes in both directions IF stimulated by electrode, because there's only a RELATIVE refractory period. Naturally, the absolute refractory period prevents it from going backward
3) Because K+ gates are slow, take a while to close

Front 8

Voltage gated protein channels, provide another example

Back 8

Determine the electrical properties of cells, evolve, differ across tissue types, animals, etc.
Different cells are more or less active

Cardiac sodium channel

Front 9

Explain how action potentials propagate (are regenerated) along the axon

Back 9

1) Ionic current flows between neighboring membrane in inside/outside of cell (outside -> positive sides go to inner negative action potential, inside - positive action potential goes in both sides

2) Active membrane excites (depolarizes) neighboring inactive membrane - +ions move to either side

3) Refractory part (behind AP) remains unaffected

4) depolarization causes another AP

Front 10

Absolute Refractory period

Back 10

Part where Na+ is inactivated (BUT DOES NOT CLOSE - this doesn't happen till it returns to resting potential)

Front 11

Explain what happens to action potential at terminals

Back 11

1) action potential travels down axon
2)Voltage gated Ca channels open, Ca2+ enters
3) Synaptic vesicles fuse with membrane/ release NT into cleft
4) Transmitter activates postsynaptic receptors
5) This triggers ionic currents (EPSP/IPSP)
6) Transmitter inactivated/removed, may activate presynaptic autoreceptors to decrease release

Front 12

EPSP

Back 12

excitatory postsynaptic potential - produces a small local depolarization pushing the cell closer to threshold

Front 13

IPSP

Back 13

inhibitory postsynaptic potential - produces a small hyperpolarization pushing cell away from threshold

NEGATES EPSP!

Front 14

Postsynaptic potentials are..
what do their effects depend on (what does reaching threshold depend on?)

Back 14

SMALL (much less than presynaptic recording), the summation of their charges (NET effect)

Front 15

What triggers postsynaptic neurons (2 things)? Explain how

Back 15

Electrical signals (not covered)

Neurotransmitters!
1) Activate (attach to) ligand gated ion channels
2) allow Na+ to move through channel into cell
3) Can trigger IPSP or EPSP

Front 16

Equilibrium potential of Cl-

Back 16

is near resting potential, negative

Front 17

Temporal summation

Back 17

Summing of potentials at axon hillock that arrive at different times

Closer together in time they arrive = greater sumation/possibility of AP

So, pattern of APs matter

Front 18

Location of inputs (Spatial summation) - explain.

How does evolution relate?

Back 18

More near cell body = more potent

Near synapse = most potent

More inputs simultaneous = stronger

Evolution of neural morphology reflects this property (Betz cell layer 5 - very large = receives gigantic input from large area, can integrate a lot of info)

Front 19

Striatial/subthalamic innervation of pallidal cells

Back 19

Example of spatial summation - how potent nerve can be depending on neuroanatomy

1) striatal inputs gives small terminal to each pallidal cell
2) Subthalamic innervates its terminals around all palidal cells, very potent (wraps itself around)
3) Striatal cells pick and choose which pallidal cells to innervate
4) Subthalamic neurons aim for max innervation

Front 20

Betz cell/ Striatal and subthalamic innervation of pallidal cells

Back 20

Striatal neurons seem to pick
and choose particular dendrites on GPi cells to influence more
than others

STN iuputs to GPi wrap around
target dendrites to
maximize influence

Front 21

Name 2 adaptive properties of most neural circuits, explain then

Back 21

Convergence: Where many cells send signals to one cell

Divergence: One cell sends signals to many cells

Parallel, sequential, lateral interactions across units

Front 22

Example of convergence/divergence

Back 22

Convergence from retinal receptor cell, bipolar cell, retinal ganglion cell (EYE)...across optic nerve...Divergence across thalamic and cortical cell (BRAIN)

Front 23

GABA

Back 23

A neurotransmitter that activates Cl- channels, Concentration of Cl- is high outside so they move out of cell to inside.

Hyperpolarizes cell closer to resting potential (inside becomes more negative), so it is harder for a EPSP to make it reach threshold

Front 24

5 subunits of a gaba receptor

Back 24

1) Benzodiazepine site
2) Picrotoxin site
3) GABA site
4) Neurosteroid site
5) Barbiturate site
(6) Alcohol/steroid sites

Front 25

IF too much K+ in blood, you feel...

Back 25

not great, go to hospital (why?)

Front 26

Relative refractory period

Back 26

How K+ hyperpolarizes beyond resting potential, so a larger depolarization is needed (but AP is still possible, compared to absolute refractory period)

Front 27

Difference between spatial summation and convergence

Back 27

Spatial summation is more local (regards one neuron) than convergence (which is more general, talks about system)

Front 28

Which ions provide excitatory input, which are inhibitory

Back 28

Na+ = excitatory
K+ = excitatory?
Cl- = inhibitory