Lecture 4: Electrical Signals to Transmit Info

Question 1

What is the composition of intracellular fluids?

Answer 1

Positive ions: Na+, K+

Negative ions: Cl+

Question 2

List factors that influence ion movement:

Answer 2

1. Concentration gradient (differences in concentration of a substance within a certain space)
2. Diffusion (movement of particles from high to low concentration in order to reach equilibrium - passive process that requires no energy)
3. Charge (ions move down a voltage gradient from area of high charge to low charge to reach equilibrium - same as concentration gradient)

Question 3

Describe ion movement through a semi permeable membrane in a neuron cell

Answer 3

There is a phospholipid bilayer that possesses some cracks and crevices that allow some substances to pass through. Allows for partial movement of ions between interior and exterior of cell via protein channels. Channels are specific to certain substances (some channels only accept Cl-, or Na+, etc). Once some substances are pulled through, they remain attracted to the opposite charge of the other substances left behind, resulting in the creation of voltage

Question 4

When does a voltage across the cell membrane occur?

Answer 4

When the concentration gradient is equal to the voltage gradient, creating a negative charge on one side and a positive on the other. One side is more “charged” than the other

Question 5

Describe action potential

Answer 5

One side of the cell membrane is more “charged” than the other. The difference between charges creates the action potential.

Question 6

Describe resting potential

Answer 6

When there is no activity, the voltage at rest is -70mV. This is the difference between one side of the cell and the other. The charge of extra cellular space is positive, while the inner is negative, at -70mV - relative to the outside. If outside is 0, then inside is -70.

Question 7

Describe distribution of ions in the extra cellular and intracellular space

Answer 7

Unequal distribution of four particles creates membrane potential; however protein and potassium ions are only within the cell, while Chlorine and Sodium are extra cellular but can enter via channels

Question 8

How is resting potential maintained?

Answer 8

Via sodium/potassium pump. Sodium is always primed to enter the cell but can only enter via gated channels. The pump extrudes sodium from inside the cells. It takes three sodium ions out and brings two potassium ions in. Sodium is negative while potassium is positive. Cells keeps 20% more potassium inside to offset negative charge. This is NOT a passive process. It’s an active process using 66% of cell’s energy.

Question 9

What is graded potential

Answer 9

Small voltage fluctuations in the restricted vicinity of the axon - only lasts a few milliseconds.

Question 10

What are two forms of graded potential?

Answer 10

1. Hyperpolarization: membrane potential is exaggerated by a greater difference in charge. More charged - further from zero.
2. Depolarization: membrane potential is diminished as the difference in charge moves closer to 0mV. Less charged.

Question 11

What did Descartes believe was the flow of information?

Answer 11

The pineal gland caused CSF to flow through ventricles which led to muscles contractions, thus movement. It was incorrect

Question 12

What questions did Descartes’ theory give rise to?

Answer 12

1. How do our nerves detect sensory stimulus and then inform the brain
2. How does the brain formulate a response from the stimulus
3. How does the brain communicate with the muscles to create movement and produce observable behaviour

Question 13

Describe Stephan Gray’s experiment from 1731.

Answer 13

Gathered electrons on a metal rod via woollen cloth. He touched a boy’s feet to transfer electrons, then observed a piece of metal foil bend when approaching the boy’s nose.

Question 14

What were important discoveries made from Stephan Gray’s experiment?

Answer 14

That the transfer of electrons happened without the boy’s conscious sensation. Therefore this transfer must be a natural phenomenon - first notion that electricity must pass through body on regular basis.

Question 15

What did Luigi Galvani discover?

Answer 15

Electrical stimulation - that passing an electrical current from an electrode into a nerve causes muscle contraction

Question 16

Who first stimulated the neocortex with an electrode?

Answer 16

Fritsch and Hitzig - brains of several animal species including humans and observed movement in arms and legs

Question 17

What study did Roberts Bartholow do?

Answer 17

First to write reports on brain stimulation in 1874. Caused a lot of kerfuffle due to death of a subject after her brain was stimulated. He left the city and moved to another to continue his work.

Question 18

Describe difference between electrical stimulation and electrical recording

Answer 18

Stimulation involves inserting electrode and producing a current in order to create a nerve stimulation. Recording involves observing and measuring the electrical current of the brain using a voltmeter.

Question 19

Who was first to measure electrical current in the brain?

Answer 19

Richard Catan, using a voltmeter

Question 20

What did Von Heimholtz observe?

Answer 20

The time between stimulation to contraction is much slower than conventional electrical flow, meaning that there must be additional processes occurring

Question 21

What was Bernstein’s contribution in 1886?

Answer 21

That electrical signals are similar to the form of waves, and have a chemical basis. Believed that signals can be detected as they pass an electrode that is touching the axon

Question 22

How were waves of information in an axon studied?

Answer 22

1. A giant axon like that in a North Atlantic squid
2. An oscilloscope - extremely sensitive voltmeter
3. Micro electrode to stimulate the cell

Question 23

Describe Hodgkin and Huxley’s discovery

Answer 23

That nerve impulses are a result of changes in ion concentration across a membrane. It is the movement of intracellular and extra cellular ions that are positively and negatively charged.

Question 24

What causes graded potential?

Answer 24

The protein channels/gates permit ions to move creating the change in potentials.

Question 25

What is the drug that blocks potassium channels?

Answer 25

Tetraethylammonium - prevents hyperpolarization

Question 26

What is a drug that blocks sodium channels?

Answer 26

Tetrodotoxin - prevents depolarization. (Found in puffer fish, which can stop action potential therefore causing death)

Question 27

Define action potential

Answer 27

A brief but large reversal in polarity in the axon’s membrane. A charge may go from -70 to +30 mV.

Question 28

What causes an action potential?

Answer 28

An influx of sodium and a efflux of potassium, the changes in voltage. Inside of cell becomes more positive as more sodium floods in. Eventually potassium begins to leave the cell. Time scale is 2 milliseconds.

Question 29

What is the threshold for the action potential?

Answer 29

-50millivolts.

Question 30

What occurs when an axon has been stimulated to -50mV?

Answer 30

Once the threshold has been met, no further stimulation is required because the sodium ions will continue to flood the channels (depolarization) until the voltage reaches +30mV. (Relative to the outside of the membrane)

Question 31

What are voltage fated ion channels?

Answer 31

Channels in the cell membrane that are activated by voltage. They are specific to the kind of ion that passes through: potassium, sodium, calcium, etc.

Question 32

Which voltage gated channel opens first?

Answer 32

Sodium because it’s more sensitive to charges.

Question 33

When does the potassium voltage gated channel open?

Answer 33

When the polarity reaches -50mV

Question 34

What is a nerve impulse?

Answer 34

The propagation of an action potential along an axon from one end to the other

Question 35

How does an action potential move?

Answer 35

A massive change in voltage causes other voltage gated channels to open along the axon, causing a chain reaction all the way down the axon. The closing of gates during the refractory period causes the signal to move forward away from point of origin

Question 36

Describe the all or none rule

Answer 36

Action potentials expend the same amount of energy at each point along the axon - the strength of signal does not dissipate. It is generated completely or not at all. It happens all the way down the axon or not at all.

Question 37

Which cells insulate the axon in myelin?

Answer 37

Schwann cells in the PNS

Oligodendroglia in the CNS

Question 38

What are node of Ranvier?

Answer 38

Spots along the axon where there is no myelin, and the voltage gated ions exist

Question 39

What is the speed of a myelinated axon? Un myelinated axon?

Answer 39

Myelinated axons can reach up to 120 meters per second. Un myelinated axons max out at 30 meters per second, and are often incomplete signals

Question 40

What is an Excitatory Postsynaptic Potential?

Answer 40

Brief depolarization of an neuron in response to stimulation. More likely to produce action potential but hasn’t hit threshold yet

Question 41

What is an inhibitory Postsynaptic potential?

Answer 41

Brief hyperpolarization (increasing negative charge), opening chloride channels, neuron is less likely to fire, therefore it “shits off the neuron”

Question 42

How does the neuron decide which EPSP or IPSP to do?

Answer 42

More positive ions result in an EPSP, while more negative ions result in an IPSP.

Question 43

What is temporal summation?

Answer 43

When graded potentials occur close enough together (roughly at the same time) they are summated into a single, large occurrence

Question 44

What is spatial summation?

Answer 44

When the location of stimulation on the membrane is close together (stimulation coming from dendrites located side by side) then the graded potential is summated.

Question 45

Explain significance of the axon hillock

Answer 45

It is rich in voltage gated channels, and the summed EPSPs and IPSPs that reach it must exceed the -50 threshold. It is the beginning point of signal transmission. Inputs near the hillock have more control over reaction than ones further away

Question 46

Describe steps from sensory stimulation to action potential

Answer 46

1. Receive info via sensory organs: tactile, auditory, visual or chemical receptors.
2. Receptors have ion channels in their membranes, similar to neurons
3. A dendrite may wrap itself about the receptor, and stretches when the receptor is activated
4. Stretch sensitive channels open on the dendrite and create a sodium influx (depolarization)