Unit 5 Lecture 36

Question 1

Define propagation

Answer 1

The process by which an action potential spreads throughout the length of an axon to the axon terminal

Question 2

What is the 1st step of action potential propagation?

Answer 2

Na+ enters the membrane -> local (+) current inside cell

Question 3

How do currents spread during propagation?

Answer 3

ELECTRIC currents spread LATERALLY to depolarize adjacent membranes

Question 4

What effect does an increase of Na+ into the cell have on the membrane potential difference?

Answer 4

Depolarizes the membrane

Question 5

Explain continuous conduction

Answer 5

Na+ makes a (+) current -> depolarizes nearby membrane -> that new membrane reaches threshold and starts an AP -> Na+ makes a current in this new region -> depolarizes 3rd membrane -> AP -> Keeps going

Question 6

How does Na+ get through the membrane?

Answer 6

There was an initial local depolarization that opened voltage gated Na+ channels

Question 7

What is important about continuous conduction?

Answer 7

Axons do NOT have myelin sheaths

Question 8

What two factors effect the SPEED of propagation?

Answer 8

1. Size of axon

2. Myelination

Question 9

What is true about the size of an axon during propagation?

Answer 9

The BIGGER the axon diameter, the FASTER the current flow

Question 10

Why are bigger axons faster in propagating currents?

Answer 10

Resistance of current flow decreases as the size of the axon increases

Question 11

What is true about myelination during propagation?

Answer 11

Having myelin sheaths makes current flow FASTER bc Na+ channels open at each node

Question 12

What is myelin sheaths?

Answer 12

An insulating layer (sheath) around axons in the CNS and PNS

Question 13

What makes myelin sheaths?

Answer 13

Olgiodendrocytes in CNS

Schwann Cells in PNS

Question 14

Explain saltatory conduction

Answer 14

Na+ channels open at node of ranvier -> depolarizes adjacent node -> opens that node -> depolarizes 3rd node -> keeps going

Question 15

What are the differences between continuous conduction and saltatory conduction?

Answer 15

Continuous = NO myelin sheaths -> slower propagation

Saltatory = myelin sheaths -> faster propagation

Question 16

What are demyelination diseases?

Answer 16

Diseases which damages the myelin sheath of an axon in the central NS or peripheral NS

Question 17

Name two examples of demyelination diseases

Answer 17

Multiple sclerosis in CNS

Guillan-Barre in PNS

Question 18

How is an electrical signal (AP) transmitted from one excitable cell to another?

Answer 18

Synaptic Transmission

Question 19

Describe the basis of synaptic transmission

Answer 19

Same basic events that occur during neuromuscular transmission w/ a synapse

Question 20

Describe the events of synaptic transmission

Answer 20

1. Nerve impulse opens voltage gated Ca2+ channels and Ca2+ comes in
2. Ca2+ causes synaptic vesicles to bond w/ presynaptic terminal and releases neurotransmitter into the synapse
3. Neurotransmitters bind to proteins (receptors) on postsynaptic terminal which open Ligand-gated channels
4. EPSPs or IPSPs

Question 21

What are the two post-synaptic graded potentials?

Answer 21

1. Excitatory Post-Synaptic Potential (EPSP)

2. Inhibitory Post-Synaptic Potential (IPSP)

Question 22

Define excitatory post-synaptic potential

Answer 22

Depolarizes (if Na+ enters)

*Increase the likelihood of post-synaptic AP occurring

Question 23

Define inhibitory post-synaptic potential

Answer 23

Hyperpolarizes (if K+ leaves or Cl- enters)

*Decreases the likelihood of post-synaptic AP occurring

Question 24

What happens at the trigger zone of an axon?

Answer 24

Generates AP depending on the net summation of EPSPs and IPSPs

Question 25

Define spatial summation

Answer 25

• Many pre-synaptic neurons connect to one post-synaptic neuron
• Signals from many pre-synaptic neurons add up at the trigger zone

Question 26

Define temporal summation

Answer 26

• 1 pre-synaptic neuron connects to 1 post-synaptic neuron

- There is an increased repetition of AP from 1 pre-synaptic neuron