Lecture 2 : Action potentials

Question 1

Resting state

Answer 1

-Na and K channels are closed
- leakage accounts for small movements of Na and K
- -70mv inside the cytoplasm
Cytoplasm is more negative that the plasma membrane

Question 2

Depolarization

Answer 2

Na gates are opened, K gates are closed
Na rushes in the cytoplasm and the charge is reversed to +30mv
Cytoplasm is postie and plasma membrane becomes negative
* if voltage is at threshold, AP will travel down the axon

Question 3

Repolarization

Answer 3

Na gates close, voltage sensitive K gates open
K exits the cell and the negative charge is restored.
-75mv

Question 4

Hyperpolarization

Answer 4

K gates remain open and causes leakage of K

Question 5

2 Functions of the Na/K pump

Answer 5

1. keep the cell polarized at rest
2. Return the ions to appropriate sides of membrane after AP
   3 Na out of the cell
   2K in

Question 6

Role of the Na/K pump

Answer 6

Repolarization- restores the electrical conditions of the neuron but does not restore the ionic conditions

Question 7

Threshold

Answer 7

change of about 15-20mV. in order to start AP change of 15-20mv has to occur

Question 8

Absolute Refractory period

Answer 8

-time from opening of the Na activation gates until the closing of inactivation gates

Question 9

Function of the Absolute Refractory period

Answer 9

• prevents the neuron from generation an AP
• ensures that each AP is separate
• enforces one way transmission of nerve impulses.

Question 10

Relative refractory period

Answer 10

happens after absolute refractory period

• Na gates are closed
• K gates are open
• Repolarization and hyperpolarization occurs

Question 11

Conduction Velocities of Axons

Answer 11

• rate of impulse propagation is determined by
  Axon diameter and presence of myelin sheath
  *** myelin increases the conduction velocities.

Question 12

Saltatory conduction

Answer 12

• current passes through a myelinated axon only at the nodes of ranvier.
• Voltage gated Na channels are concentrated at these nodes.

Question 13

Synapses

Answer 13

a junction that transfers information from one neuron :

• to another neuron
• to an effector cell

Question 14

Chemical synapses

Answer 14

release and reception of neurotransmitters

- has axon terminal of the presynaptic neuron and receptor region of the post synaptic neuron.

Question 15

Termination of Neurotransmitters

Answer 15

• are degraded by enzymes (AChE)
• are reabsorbed by astrocytes or the presynaptic terminals.
• diffuse from synaptic cleft

Question 16

Postsynaptic potentials

Answer 16

two types:
EPSP- excitatory post synaptic potentials
IPSP- inhibitory post synaptic potentials

Question 17

Summation

Answer 17

A single EPSP cannot include an action potential

EPSPs must summate temporally or spatially.

Question 18

Temporal Summation-

Answer 18

occurs when a single presynaptic neuron fires many times in succession causing the postsynaptic neuron to reach its threshold and fire

Question 19

Spatial summation

Answer 19

occurs when excitatory potentials from many different presynaptic neurons cause the postsynaptic neuron to reach its threshold and fire