Synaptic Integration

Question 1

two types of summation

Answer 1

Temporal and spatial

Question 2

Temporal summation

Answer 2

occurs when a single presynaptic input fires repeatedly at high frequency

Question 3

Spatial summation

Answer 3

occurs when inputs from different presynaptic neurons arrive simultaneously

Question 4

Temporal summation depends on these two factors

Answer 4

frequency (how closely spaced these APs are)
decay time (how slowly the membrane potential returns back to base line)

Question 5

3 passive electrical properties of dendrites

Answer 5

1. Rm (membrane resistance) = 1/g
2. Cm (membrane capacitance)
3. Ri or Ra (internal or axial resistance)

Question 6

Is internal/axial resistance low or high in a dendrite? Why

Answer 6

The resistance of current down axial will be low, because dendrite is a good conductor, filled with salty solution (high conductance, g, = low resistance, 1/g)

Question 7

In absence of channels, the membrane resistance Rm is (high/low)

Answer 7

Fewer channels > low conductance > higher Rm

Question 8

What do capacitors store?

Answer 8

Electrical charge

Question 9

Ability to store an electrical charge

Answer 9

capacitance

Question 10

Effect of membrane capacitance

Answer 10

Changes in membrane potential are slower than changes in current (Because of time to charge and discharge the capacitance)

when open channel, immediately get current flowing through, but you get rounded change for membrane potential

Question 11

temporal summation constant and equation

Answer 11

time constant

tao = Rm x Cm

Question 12

Where is Cm relatively constant?

Answer 12

in dendrites

no myelin in dendrites!

Question 13

In axons, myelin increases/decreases Cm

Answer 13

Myelin reduces Cm (harder to store electrical charge when telephone book vs piece of paper)

Question 14

Rm depends on

Answer 14

of channels

Question 15

Short time constant =

Answer 15

short decay time for membrane potential

Question 16

How can you increase Rm? What is specific best target?

Answer 16

Close channels, specifically K channels

Question 17

Spatial summation constant and equation

Answer 17

length constant

lambda = square root(Rm/Ra)

Question 18

Explain Ra relation to diameter (thickness)

Answer 18

Ra is inversely proportional to diameter (thicker diameter, can carry more charge, less resistance)

Question 19

Determines how far the charge in membrane potential can passively spread out before dying

Answer 19

lambda constant

Question 20

Myelin (increases/decreases) conduction speed

Answer 20

increases

Question 21

Effects of myelin insulation on:

• Rm
• Cm

Answer 21

• increases Rm (myelin is an insulator, and thus fewer channels blocked by myelin, lowers g increases Rm)
• decreases Cm (capacitance depends on separation of charge. increasing that distance when wrap myelin around, so greatly reduce membrane capacitance / interaction bw outside and inside charges)

Question 22

Effects of myelin insulation on:

• Time constant
• Length constant

Answer 22

• decrease time constant = faster charging of membrane
  (time constant = Rm x Cm > myelin increases Rm, decreases Cm > Cm is more dramatic change)
  -increase length constant = greater distance between notes
  (length constant = square root(Rm/Ri) > myelin increases Rm, no effect on Ri > longer length constant

Question 23

The further you separate nodes, the faster the propagation down the axon. Why? How does myelin relate to this?

Answer 23

• Nodes= unmyelinated
• nodes require sodium voltage gated channels, which are active processes
• have to be placed to regenerate AP before it dies out
• channels are slower because take time to open and close.
• Area between nodes (myelinated) is passively spread, and passive spread is faster
• Unmyelinated is much slower because constantly opening channels.

Question 24

Dendrites integrate synaptic potentials:

• longer time constant = ?
• longer length constant = ?

Answer 24

longer time constant = better temporal summation

longer length constant = better spatial summation

Question 25

Axons faithfully propagate action potentials:

• shorter time constant = ?
• long length constant = ?

Answer 25

shorter time constant = faster conduction velocity

longer length constant = faster conduction velocity

Question 26

In axon, myelin leads to increased length constant, which means what?

Answer 26

greater distance between nodes

Question 27

In axon, myelin leads to decreased time constant, which means what?

Answer 27

Faster charging of membrane