Chapter 4 (MT2)

Question 1

What three questions did Descartes’ (incorrect) theory of information flow isolate?

Answer 1

(1) How do our nerves detect a sensory stimulus and inform the brain about it?

(2) How does the brain decide what response to make?

(3) How does the brain command muscles to move?

Question 2

Electricity

Answer 2

The flow of electrons from a body with a higher charge (more electrons) to one of lower charge (less electrons)

Question 3

Electrical stimulation

Answer 3

Passing an electrical current from the uninsulated tip of an electrode onto a nerve to produce behaviour— a muscular contraction

Question 4

When a single axon is stimulated, it produces a wave of excitation - what three things allowed us to record the wave and determine how it is produced?

Answer 4

Giant axon of the squid (~cm)
Oscilloscope (sensitive enough to measure tiny electrical signals)
Development of microelectrodes (small enough to place on/in an axon)

Question 5

What are embedded in semipermeable membranes that contribute to electrical activity?

Answer 5

Ion channels

Question 6

Neuronal electrical activity

Answer 6

The movement of ions through channels across membranes

Question 7

What conveys information throughout the nervous system?

Answer 7

Waves of electrical activity along membranes (allowed by the electrical activity in neurons)

Question 8

What does the intracellular and extracellular in/around a neuron contain - all of which contribute to forming the resting potential?

Answer 8

Na+
K+
Cl-
Protein molecules (-)

Question 9

What factors influence the movement of anions and cations into/out of the cells?

Answer 9

Diffusion
Concentration gradient
Voltage gradient

Question 10

Diffusion

Answer 10

Natural (no energy required) process of molecules to spread out from an area of high concentration to low concentration

Question 11

Resting potential

Answer 11

The inside of the membrane at rest is −70 mV relative to the extracellular side
The charge is a store of potential energy called the resting potential

Question 12

How does the semipermeable membrane contribute to maintaining the resting potential?

Answer 12

(1) Membrane is relatively impermeable to large molecules, so A- remain inside the cell

(2) Gated Na+ channels keep out Na+, and ungated K+ and Cl- allow K+ and Cl- to pass freely

(3) Na/K pumps force out Na+ from the intracellular fluid and bring in K+ (2 K+ in for 3 Na+ out)

Question 13

What does the unequal distribution of different ions in the axon cause?

Answer 13

Causes the inside of the axon to be relatively negatively charged

Question 14

Graded potentials

Answer 14

Small voltage fluctuations across the cell membrane

Question 15

Hyperpolarization

Answer 15

Increase in electrical charge across a membrane (more negative, eg. -70 to -73 mV)

• caused by an efflux of K+ ions or an influx of Cl- ions

Question 16

Depolarization

Answer 16

Decrease in electrical charge across a membrane (more positive, eg. -70 to -65 mV)

• caused by an influx of Na+ ions

Question 17

How long do graded potentials last?

Answer 17

A few milliseconds

Question 18

Action potential

Answer 18

A brief but very large reversal in an axon membrane’s polarity, that lasts about 1 ms (many can occur within one second)

• intracellular side becomes positive relative to the extracellular side

Question 19

What causes an action potential?

Answer 19

A large concentration of Na+ and then K+ cross the membrane rapidly (combined flow of Na/K)

• depolarization due to Na+ influx, then hyperpolarization due to K+ efflux
• Na+ rushes in, then K+ rushes out

Question 20

Threshold potential

Answer 20

Voltage on a neural membrane at which an action potential is triggered, happens when the cell membrane is depolarized to -50 mV

Question 21

What causes the upper limit for how frequently action potentials can occur?

Answer 21

Na and K channels

Question 22

Absolutely refractory

Answer 22

An axon cannot produce another action potential if it is stimulated during either the depolarization or repolarization phase

Question 23

Relatively refractory

Answer 23

An action potential can be induced if the axon membrane is SUFFICIENTLY (second stimulation must be greater than the first) stimulated during the hyperpolarization phase

Question 24

Nerve impulse

Answer 24

Each action potential propagates another action potential on the adjacent axon membrane

Question 25

All-or-none law

Answer 25

Action potentials do not dissipate - the size and shape of action potential remains constant (either generated completely or not at all)

Question 26

What do refractory periods do?

Answer 26

Limits the frequency of action potentials to one every 5 ms, or 200 per second

Prevent action potentials from reversing direction (they can travel in either direction, but are limited to one direction)

Question 27

Myelin

Answer 27

Produced by oligodendroglia (CNS) and Schwann cells (PNS)
Speed up neural impulses

Question 28

Nodes of ranvier

Answer 28

Uninsulated regions of axon that enable saltatory conduction
(action potentials cannot occur where it is wrapped in myelin)

Question 29

Saltatory conduction

Answer 29

Action potentials jump from node to node, increasing speed up to 120 m/s

Question 30

Consequences of myelin propagating action potentials

Answer 30

Propagation becomes energetically cheaper
Myelin improves conduction speed

Question 31

Multiple Sclerosis (MS)

Answer 31

MS results from a loss of myelin produced by oligodendroglia cells in the CNS. It disrupts the affected neurons’ ability to propagate action potentials via saltatory conduction. This loss of myelin occurs in patches, and scarring frequently results in the affected areas (hard scar/plaque forms at site of myelin loss, impaired functioning).

Question 32

How neurons receive information

Answer 32

Receiving neurons are bombarded with excitatory and inhibitory signals - through over 50,000 connections via dendritic spines, the cell body can also receive inputs

Question 33

Excitatory postsynaptic potential (EPSP)

Answer 33

Brief depolarization of a neuron membrane in response to stimulation
- small, move in same direction as action potential, toward the threshold (eg. -70 to -65 mV)
- depolarized neuron is more likely to produce an action potential
- associated with influx of Na+

Question 34

Inhibitory postsynaptic potential (IPSP)

Answer 34

Brief hyperpolarization of a neuron membrane in response to stimulation
- more negative, away from -50 mV threshold
- hyperpolarized neuron is less likely to produce an action potential
- associated with influx of Cl-, or an efflux of K+

Question 35

Temporal summation

Answer 35

The relationship between two EPSP’s or IPSP’s occuring close together or even at the same time (from a single neuron)

Question 36

Spatial summation

Answer 36

Occurs when two separate inputs (i.e. multiple neurons) are very close to each other both on the cell membrane and in time

Question 37

What does a neuron do with inputs?

Answer 37

It sums all inputs that are close together in time and space
- neuron analyzes inputs before deciding what to do
- ultimate decision is made at the initial segment (the region on the axon that initiates the action potential)

Question 38

How does summation relate to action potential?

Answer 38

To produce an action potential, the summed graded potentials—the IPSPs and EPSPs—on the cell body membrane must depolarize the membrane at the initial segment to − 50 mV

Question 39

Summary statement of how neurons transmit information as electrical signals

Answer 39

An action potential is generated, and then the impulse flows down an axon to the synapse