CHAPTER 4

Question 1

What did Galvani discover?

Answer 1

Galvani discovered that the muscles of dead frogs legs twitched when struck by electricity

Question 1

Electricity:

Answer 1

A flow of electrons from a body that contains a higher charge (more electrons) to a body that contains a lower charge (fewer electrons)

Question 2

Electrical Potential:

Answer 2

An electrical charge measured in volts; the ability to do work through the use of stored potential electrical energy

Question 3

Hermann von Helmholtz

Answer 3

Measuring electric nerve impulses in frog leg nerves
Conclusion: Flow of information in the nervous system is too slow to be a flow of electricity!

Question 4

Measuring the electric potentials (i.e. membrane voltage

Answer 4

–Recording electrode is inside the nerve fiber
–Reference electrode is outside the fiber
–Difference in charge between them is about -70 to -80 mV in the steady state (resting membrane potential ,RMP)

Question 5

Cations

Answer 5

Positively charged ions
Examples: Sodium (Na+),
potassium (K+)

Question 5

How do the movement of ions create electrical potentials in neurons

Answer 5

Diffusion & Concentration Gradient:

Question 6

Anions

Answer 6

Negatively charged ions Examples: Chloride (Cl-), protein molecules (A-)

Question 7

Diffusion

Answer 7

Movement of ions from an area of higher concentration to an area of lower concentration

Question 8

How do the movement of ions create electrical potentials in neurons - cont.

Answer 8

Electric Potential: Difference in electrical charge between two regions – Oppositechargesattract
– Similarchargesrepel

Question 8

Concentration Gradient:

Answer 8

Differences in concentration of a substance from an area of higher concentration to an area of lower concentration

Question 8

The Movement of Ions is caused by two major forces:

Answer 8

– Chemical force (Diffusion): the tendency for molecules to distribute themselves equally within a medium
– Electric potential: the difference in electrical charge across the membrane

Question 9

what do these forces make together

Answer 9

electrochemical gradient

Question 10

Net effect:

Answer 10

high concentration (potential) of Na+ ions outside and negativeproteinsA-andK+ inside.Theresultingmembranepotential is about -70 mV

Question 11

Action Potentials are triggered at the

Answer 11

Axon Hillock

Question 11

Voltage-Sensitive (gated) Ion Channels

Answer 11

• Gated protein channel that opens or closes only at specific membrane voltages (typically at about -65 mV
• Sodium (Na+) and potassium (K+)
• Closed at membrane’s resting potential

Question 12

Action potentials occur when

Answer 12

Permeability of the membrane changes (e.g. due to opening of touch sensitive sodium channels in a receptor neuron)
* If the excitation (i.e., the depolarization of the membrane) is strong enough it reaches a threshold which activates voltage sensitive sodium (Na+) channels
* The Neuron will then further depolarize very fast due to the influx of more and more sodium ions

Question 13

Continuous conduction

Answer 13

action potential propagation in unmyelinated axon

Question 14

All-or-none law

Answer 14

the strength of the action potential is independent of the intensity of the stimulus that elicits it

Question 14

How does the action potential encode information about the intensity of a stimulus?

Answer 14

All-or-none law & (rate law)

Question 15

Saltatory Conduction:

Answer 15

Action potential propagation in myelinated axon

Question 16

rate law

Answer 16

Coding of intensity is by the firing rate (rate law) of a neuron and by the number of neurons firing.

Question 17

Neural impulse

Answer 17

The propagation of an action potential along an axon.

Question 18

The axon depolarizes in a sequential fashion from the axon hillock to the presynaptic terminal.

Answer 18

The neural impulse occurs only one way because of the absolute refractory period.
Speed of transmission varies due to thickness of the axon, presence or absence of myelination, and number of synapses.

Question 19

Properties of action potentials

Answer 19

Action potentials remain the same size
* The only coding possible on a neuron is by variation firing
rate (AP/s)
* Increase in stimulus intensity can increase the firing rate of neurons
* Refractory period is 1 ms - upper firing rate is 500 to 800 impulses per second
* In some neurons, spontaneous activity of action potentials occurs without stimulation

Question 20

Graded Potentials

Answer 20

Small voltage fluctuations in the cell membrane where ion concentrations change

Question 21

Hyperpolarization

Answer 21

– Increase in electrical charge across a membrane (more
negative)
– Usually due to the inward flow of chloride ions or outward flow of potassium ions
– Can be blocked: Tetraethylammonium (TEA), Curare

Question 22

Depolarization

Answer 22

– Decrease in electrical charge across a membrane (more
positive)
– Usually due to the inward flow of sodium
– Tetrodotoxin

Question 23

Excitatory Postsynaptic Potential (EPSP)

Answer 23

– Brief depolarization of a neuron membrane in response to an input
– Neuron is more likely to produce an action potential

Question 24

Inhibitory Postsynaptic Potential (IPSP)

Answer 24

– Brief hyperpolarization of a neuron membrane in
response to an input
– Neuron is less likely to produce an action potential

Question 24

• Temporal Summation

Answer 24

– Pulses that occur at approximately the same time on a membrane are summed

Question 24

The Axon Hillock

Answer 24

• Junction of cell body and axon
• Rich in voltage-sensitive
  channels
• Where EPSPs and IPSPs are
  integrated
• Where action potentials are
  initiated

Question 25

• Spatial Summation

Answer 25

– Pulses that occur at approximately the same location on a membrane are summed

Question 26

How Nerve Impulses Produce Movement

Answer 26

Acetylcholine
Ligand (Transmitter)-sensitive channel
* End plate

Question 27

Acetylcholine

Answer 27

– The first neurotransmitter discovered in the peripheral and central nervous systems
– Activates skeletal muscles

Question 28

Ligand (Transmitter)-sensitive channel

Answer 28

– Receptor complex that has both a receptor site for a chemical and a pore through which ions can flow

Question 29

• End plate

Answer 29

– On a muscle, the receptor–ion complex that is activated
by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron