Lec 9-10

Question 1

Channel and pump proteins allow for the passive and active
displacement of which key ions?

Answer 1

sodium, chlorine, and potassium

Question 2

What is the resting membrane
potential:

Answer 2

-70 millivolts (inside is 70mV lower than outside).
The resting potential is the voltage difference of the plasma membrane before any action potential

Question 3

Whar do we call the way information travels through the nervous system?

Answer 3

Propagation of an action potential

Question 4

The plasma membrane is modelled as an electrical circuit by… (model name)

Answer 4

Hodgkin-Huxley Model

Question 5

Draw and explain the Hodgkin-
Huxley Model. In this model what is represented by the components of the circuit?
◆ The caparictor represents…
◆ The resistors represent…
◆ The batteries represent…
◆ The current sources represent…

Answer 5

In this model:
◆ The lipid bilayer is represented by the capacitance (C)
◆ Voltage-gated ions channels are represented by the resistors (g)
◆ The electrochemical gradients driving ion flow are represented by the batteries (V)
◆ The active pumps are represented by the current source in the circuit (between
“Extracellular” and “Intracellular” above)

Question 6

Explain the “N-doped” area of the P-N (or N-P) junction.

Answer 6

In the “N-doped” area, group 5 elements are added in small quantities. The single fifth
electron will be mobile in the system.

Question 7

Explain the “P-doped” area of the P-N (or N-P) junction.

Answer 7

In the “P-doped” area, group 3 elements are added in
small quantities. The “gap” left by the missing valence electron will lead to current generation when free electrons from the N-doped region migrate to the P-doped region.

Question 8

The potential of a membrane can be computed using either the Nernst equation or Goldman equation. Whats the difference in how they should be used.

Answer 8

Goldman equation takes into account all ions, each with their difference in permeability across the membrane, whereas Nernst equation considers only the membrane potential of one ion.

Question 9

Describe what the patch clamp technique is.

Answer 9

This technique involves touching the membrane with a sharp pipette tip containing liquid. As
ions move in and out of the pipette, a small current can be measured. This allows for the study
of individual ion channels in the membrane.

Question 10

Lipid rafts form as a result of what?

Answer 10

The natural motion of the membrane and phase separation (the aggregation of similar molecules).

Question 11

Phase separation explains what model of the membrane?

Answer 11

Phase separation causes compartmentalization within membranes, creating the fluid mosaic model. It is split into actin-induced compartments each with its mesoscale raft domain.

Question 12

What ions tend to be outside the cell and which ones inside the cell in the resting membrane potential state? What is the charge on either side? Where is the charged concentrated?

Answer 12

Extracellular space: Na+, Cl- (net positive charge)
Intracellular space: A4- K+ (net negative charge)
The charge is concentrated along the cell membrane.

Question 13

What structures are used to allow facilitated diffusion?

Answer 13

Transmembrane integral proteins. Specifically ion channels.

Question 14

What structures are used to allow to transport ions aginst the concentration gradient?

Answer 14

Ion pumps.

Question 15

Describe how Resting K+ Channels work

Answer 15

Resting K+ Channels:
● Generate the resting potential across the
membrane

Question 16

Voltage-Gated Channels work?

Answer 16

Voltage-Gated Channels:
● Responsible for propagating action potential
along the plasma membrane in neurons
● A specific voltage (provided by a stimulus) is
needed to activate these channels

Question 17

How do Ligand-Gated Channels work?

Answer 17

Ligand-Gated Channels:
● Have a binding site for a specific
extracellular neurotransmitter, which
when bound activates the channel
● Respond to external stimuli

Question 18

How do Signal-Gated Channels work?

Answer 18

Signal-Gated Channels:
● Respond to intracellular signals
resulting from a neurotransmitter
binding to a distant receptor

Question 19

Which 2 types of channels are found on dendrites and cell bodies and are responsible for generating electric signals in
postsynaptic cells?

Answer 19

Ligand and Signal -Gated Channels:

Question 20

What stimuli open and close Ion channels of Sensory Neurons?

Answer 20

Ion channels open and close in response to
stimuli, such as light, temperature or pressure.

Question 21

What is Membrane potential?

Answer 21

An electrochemical
gradient caused by charged or polar
molecules across the cell membrane

Question 22

What is reversal potential of an ion?

Answer 22

The membrane potential at which there is no net flow of that particular ion from one side of the membrane to the other

Question 23

Why are voltage-gated ions channels are represented by resistors in the Hodgkin-Huxley Model?

Answer 23

The diagonal arrow across the
diagram of the resistor indicates
that the value of the resistance is
not fixed, but changes depending
on whether the ion channel is
open or closed.

Question 24

How are semiconductors found in P-N
junctions if electricity can’t really flow through these
materials?

Answer 24

Introducing impurities to the intrinsic (pure) lattice structure.
●There exist two types of doping, n-type and p-type

Question 25

Give 2 examples of n-type materials

Answer 25

Group V materials like arsenic or phosphorus

Question 26

Give 2 examples of p-type materials

Answer 26

Group III materials such as boron or gallium

Question 27

Explain why the lipid bilayer can be modelled as a capacitor.

Answer 27

A capacitor consists of two conducting surfaces, separated by an insulator. Capacitors are used to store charge in electric circuits. The phospholipid bilayer is an excellent insulator separating the intracellular and extracellular ionic (conducting) media, it is functionally equivalent to a capacitor.

Question 28

Explain how resting potential forms.

Answer 28

1) [K+] inside > [K+] outside. 2) Creating a net (+) charge outside. 3) At some point K+ can no longer diffuse out because the charge there is too (+). This is a state of equilibrium. 4) [Na+] inside < [Na+] outside. 5) Na+ diffuses in. Lowering the net (+) charge outside. But it diffuses in less due to closed channels. 6) Na+/K+ ATPase pumps 3Na+ out for each 2K+ in, thus pumping 1+ charge out percycle. This lowers internal potential to -70mV.

Question 29

Explain how action potential leads to a unidirectional propagation of the signal in a neuron.

Answer 29

1) Sufficiently large stimulus is received => large number of voltage-gated channels open => membrane depolarizes to at least -55 millivolts. (Action potential is triggered) 2) A massive depolarization occurs => +40 millivolts, transmitting the signal onward (bidirectional). 3) The voltage-gated channels close to repolarize the membrane potential. 4) The membrane potential overshoots resting potential, dipping down near -80 millivolts hyperpolarization. 5) The potential climbs back to -70 millivolts. The neuron cannot fire another action potential until the resting potential is reached (refractory period) thus making the propagation of action potential unidirectional.

Question 30

Speed of propagation of the signal along nerves depends heavily on _____?

Answer 30

Myelination (the addition of myelin on the neuron’s axon)

Question 31

What do Schwann cells do?

Answer 31

They add myelin at just the right locations along the axon to allow sodium channels to open at specific nodes, called Nodes of Ranvier

Question 32

Describe saltatory conduction.

Answer 32

Propagation of the signal from node to node is called saltatory conduction or “jumping conduction”. 1) The influx of Na+ ions associated with an action potential at one node => depolarization of that region of the axonal membrane. 2) Depolarization moves rapidly down the axon because the excess positive ions cannot move outward across the myelinated portion of the axonal membrane. 3) The buildup of these cations causes depolarization at the next node => induces an action potential at that node.

Question 33

How is action potential must communicate between neurons?

Answer 33

This is done through synapses and connexons.

Question 34

Explain how Synapses work.

Answer 34

Synapses use neurotransmitters to transmit the action potential. This is a form of chemical communication. Do we need to know all the steps?

Question 35

How do Synapses prevent signals from travelling backwards?

Answer 35

There are no receptors for the neurotransmitters at the end of the neuron (Axonal Terminal). They only exist on dendrites.

Question 36

What do connexons do? What are they made of?

Answer 36

Connexons use electric impulses to transmit information( electrical communication) Connexons are made of connexin subunits. Connexons form gap junctions.

Question 37

Why are connexons faster at transmitting signals than synapses?

Answer 37

The diffusion of neurotransmitters is slow. Connexons open or close, modulating signal transmission directly.

Question 38

Why are thicker sensory fibres fast than thin ones?

Answer 38

They have more myelin. Very thin nerves have no myelin at all.

Question 39

What is Electrodiagnosis

Answer 39

Electrodiagnosis is the use of electrical signals to obtain information about diseases. Various stimuli are used to trigger electrical signals in the body. These signals can then be measured.

Question 40

Three examples of electrodiagnosis are:

Answer 40

◆ Electrocardiography (ECG) ◆ Electroencephalography (EEG) ◆ Electromyography (EMG)