Lecture 10

Question 1

Stages of the Action Potential

Answer 1

1. Stimulus is received, meaning a large
   number of voltage-gated channels
   have opened. The membrane must
   depolarize to at least -55 millivolts.
2. Depolarization: Na+ channels open,
   voltage spikes to +40 millivolts,
   transmitting the signal onward
   (unidirectionally).
3. Repolarization: K+ channels open,
   and Na+ channels close, reversing
   the disruption
4. Hyperpolarization: The membrane
   potential overshoots resting potential,
   dipping down near -80 mV, as the K+
   channels are slow to close.
5. Refractory Period: During
   hyperpolarization, the neuron cannot fire
   another action potential.
6. Resting State: -70 mV

Question 2

Myelination

Answer 2

Myelinated neurons transmit information faster than unmyelinated
neurons.

Question 3

Schwann Cells

Answer 3

The cells that are responsible for myelination

Question 4

Node of Ranvier

Answer 4

Schwann cells place myelin in specific locations along the axon
to allow channels to open at these specific nodes.

Question 5

Saltatory Conduction

Answer 5

The nodes of Ranvier allow the action potential to jump
from node to node.

Question 6

Synapses

Answer 6

● At the end of a neuron, the action potential must be communicated to
the following neuron
● Synapses use neurotransmitters to transmit the action potential, which
is a form of chemical communication

Question 7

Connexons

Answer 7

● Connexons use electric
impulses to transmit
information, which form of
electrical communication.
● Connexons do not require the
diffusion of neurotransmitters,
making them a faster method
for communication
● Connexons are made of
connexin subunits
● Used for signals related to
touch and dull pain

Question 8

Describe the saltatory
conduction of the action
potential.

Answer 8

● Myelinated axons only allow action potentials to occur at the unmyelinated nodes of
Ranvier. Due to this, saltatory conduction propagates an action potential along the
axon of a neuron much faster than in unmyelinated axons.
● Although the action potential appears to jump along the axon, this phenomenon is
actually just the rapid, almost instantaneous, conduction of the signal inside the
myelinated portion of the axon.
● If the entire surface of an axon were insulated, there would be no place for current to
flow out of the axon and action potentials could not be generated.

Question 9

Highlight the main similarities
and differences between
synapses and connexons

Answer 9

Similarities:
● Both are methods of communication between one neuron and the next
Differences:
● Synapses
○ Form of chemical communication between axons
○ Synaptic cleft found between axon terminal and dendrites
○ More efficient for long signal transmission
● Connexons
○ Form of electrical communication between axons
○ Found in cell membrane
○ Faster communication method
○ Also plays a role in intracellular signalling