Signal Reception and Integration

Question 1

How do receptors on the dendrites/cell body transduce an electrical signal?

Answer 1

Membrane bound receptors bind to a neurotransmitter, receptors transduce the chemical signal to an electrical signal by changing the ion permeability of the membrane.

Question 2

What is a graded potential?

Answer 2

A wave of depolarization through the cytoplasm

Question 3

What is conduction with decrement?

Answer 3

Magnitude of graded potential decreases with increasing distance from opened ion channel.

Question 4

What are the three causes of decrement?

Answer 4

leakage of charge ions across a membrane

electrical resistance of cytoplasm

electrical properties of membrane

Question 5

An inhibitory graded potential causes…

Answer 5

Hyperpolarization; K⁺ and Cl^-channels to open

Question 6

An excitatory graded potential causes…

Answer 6

Na⁺ nd Ca²⁺ channels to open

Question 7

What characterstic of the axon hillock is important in initiation of an action potential?

Answer 7

High density of voltage gate Na⁺ channels. An increased density lowers threshold and shortens relative refractory period.

Question 8

Action potentials occur only when…

Answer 8

membrane potential at the axon hillock reaches the threshold.

Question 9

What are the characteristics of action potentials?​

Answer 9

• triggered by a net graded potential at axon hillock (trigger zone)
• do not degrade over time or distance
• travel long distances through a membrane
• all or none
• must reach threshold potential to fire

Question 10

Define spatial summation

Answer 10

Graded potentials from different sites nfluence the net change.

Question 11

Define temporal summation.

Answer 11

Graded potentials that occur at slight different times inlfluence net change

Question 12

What does the strength of the graded potential depend on?

Answer 12

the amount of stimulation

Question 13

What are the 3 resisters of the area of the axon?

Answer 13

Rm, Re, Ri

Question 14

What is a capacitator?

Answer 14

stores electrical charge

Question 15

How does an axon behave like an electrical circuit?

Answer 15

• ions moving through VGCs causse current across membrane
• current spread electrotonically along axon
• some current leaks out of the axon and flows backards along the outside of axon, completing the circuit

Question 16

Higher resistance of intracellular and extracellular fluids cause…

Answer 16

greater decrease in voltage along the axon.

Question 17

Lower resistance of the membrane causes…

Answer 17

greater decrease in the voltage of the axon

Question 18

λ =

Answer 18

distance over which mebrane potential decreases to 37%

Question 19

When λ is large…

Answer 19

the change in potential degrades less with distance

Question 20

When λ is small…

Answer 20

the change in potential decreases more with distance

Question 21

Increasing λ, _______ velocity of the action potential

Answer 21

increases

Question 22

What three features affect capacitance?

Answer 22

• material properties
• ​area of two conducting surfaces
  
  • larger area increases capacitance
• thickness of insulating layer
  
  • increasing thickness decreases capacitance

​

Question 23

τ =

Answer 23

time over which membrane potential will decay to 37% of its maximal value

Question 24

What are the variables that affect τ?

Answer 24

• r_m
• C_m

τ = r_mc_m

Question 25

The higher τ is the ____ the conduction velocity.

Answer 25

the lower

Question 26

Define conduction velocity.

Answer 26

Rate at which an impulse is conducted along an axon

Question 27

How can you increase conduction velocity?

Answer 27

• increasing the diameter of the axon
• myelinating or insulating the axon

Question 28

How does myelin increase membrane resistance?

Answer 28

Local currents cannot leak out through the internode, must flow through the Node of Ranvier.

Question 29

How does myelin decrease membrane capacitance?

Answer 29

Capacitance is inversely relatied to the thickness of the insulating layer… decrease

Question 30

Describe how oligodendrocytes myelinate an axon?

Answer 30

• oligodendrocytes select axons with less than 0.2um in diameter
• neurons with electrical activity are selected for ensheathment
• during the peak of myelination, oligodendrocytes elaborate about 3X their weight in membrane per day
• high energy requirements
• high ion requirements

Question 31

What are the two types of damage to myelin?

Answer 31

• oxidative damage to oligodendrocytes and neurons - due to free radicals (ALS?)
• Immune-mediated damage

Question 32

How do the nodes of ranvier save energy?

Answer 32

• Results in about 1000x less active membrane
  
  • About 100 fold fewer Na⁺ entering the cell per impulse
  • Translates into an energy savings of about 2 orders of magnitude
    
    • Less need to restore post-impulse ionic balances

Question 33

What is the optimal distance between Nodes of Ranvier? Why?

Answer 33

200um to 2mm

Question 34

What is saltatory conduction?

Answer 34

Appears that electrical impulses jump fown the axon (APs only occuring at the nodes of ranvier)