ch. 48 part 2

Question 1

action potentials

Answer 1

• carry electrical signals along an axon
• all-or-none - not graded
• actively propagated

Question 2

actively propagated

Answer 2

regenerates itself as it travels

Question 3

action potential sequences

Answer 3

1. graded potential depolarizes to threshold potential (-50mV)
2. voltage-gated Na+ channels open and trigger action potential
3. Na+ rapidly diffuses into cell causing spike
4. inactivation when gate in Na+ channel swings shut when membrane positively polarized

Question 4

threshold potential

Answer 4

-50 mV

Question 5

resting potential

Answer 5

-70 mV

Question 6

when do voltage-gated K+ channels open

Answer 6

1 sec later than Na+ channels

Question 7

opening of K+ channels for hyperpolarization

Answer 7

• voltage-gated K+ channels open by threshold potential
• K+ leaves cell and membrane becomes negative again
• membrane hyperpolarizes
• voltage-gated K+ channels close and resting potential restored

Question 8

where do graded potentials reach threshold potential

Answer 8

axon hillock

Question 9

what do graded potentials trigger just beyond the hillock region

Answer 9

opening of voltage-gated Na+ channels

Question 10

what does the sequential opening of Na+ channels do?

Answer 10

conduct a wave of depolarization from axon hillock to axon terminal

Question 11

what does the inactivation gate of Na+ channels do?

Answer 11

prevent backward movement toward cell body

Question 12

absolute refractory period

Answer 12

• while Na+ gate is closed, cell is unresponsive to another stimulus
• limit on frequency of action potentials
• ensures action potential does not move backward toward cell body

Question 13

relative refractory period

Answer 13

• K+ channels still open
• membrane hyperpolarizes
• graded potential would have to be huge to reach the threshold

Question 14

what does speed of conduction depend on

Answer 14

1. axon diameter
2. myelination

Question 15

axon diameter and speed

Answer 15

broad axons provide less resistance and action potential moves faster

Question 16

myelination and speed

Answer 16

• myelination faster than unmyelinated
• oligodendrocytes and Schwann cells
• gaps at nodes of Ranvier
• saltatory conduction

Question 17

saltatory conduction

Answer 17

action potential seems to “jump” from node to node

Question 18

synapses

Answer 18

junction where nerve terminal meets a neuron, muscle cell, or gland

Question 19

order at junction

Answer 19

• presynaptic cell sends signal
• synaptic cleft
• postsynaptic cell receives signal

Question 20

2 types of synapses

Answer 20

1. electrical
2. chemical

Question 21

electrical synapse

Answer 21

electric charge freely flows through gap junctions from cell to cell

Question 22

chemical synapse

Answer 22

neurotransmitter acts as signal from presynaptic to postsynaptic cell

Question 23

details of chemical synapse

Answer 23

• presynaptic cell contains vesicles of neurotransmitter
• exocytosis releases neurotransmitter into synaptic cleft
• diffuses across cleft
• binds to channels/receptors in postsynaptic cell membrane

Question 24

what does binding of a neurotransmitter at a chemical synapse do

Answer 24

change membrane potential of postsynaptic cell

Question 25

excitatory postsynaptic potential (EPSP)

Answer 25

- brings membrane closer to threshold potential - less negative - sodium channels opening

Question 26

inhibitory postsynaptic potential (IPSP)

Answer 26

- takes membrane farther from threshold (hyperpolarization) - more negative - opening of chlorine channels (Cl- enters cells)

Question 27

when does a synaptic signal end

Answer 27

when the neurotransmitter is broken down by enzymes or taken back into presynaptic cell for reuse

Question 28

where does the cell bod of a postsynaptic neuron receive input from

Answer 28

can be hundreds or thousands of synaptic terminals

Question 29

is a single EPSP strong enough to trigger an action potential in a postsynaptic neuron?

Answer 29

no - too small

Question 30

summation

Answer 30

ind. postsynaptic potentials can combine to produce larger potential

Question 31

temporal summation

Answer 31

if 2 EPSPs are produced in rapid succession

Question 32

spatial summation

Answer 32

EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together

Question 33

what can trigger an action potential

Answer 33

combination of EPSPs through spatial and temporal summation

Question 34

how can an IPSP counter the effect of an EPSP?

Answer 34

through summation

Question 35

what does the summed effect of EPSPs and IPSPs determine

Answer 35

whether an axon hillock will reach threshold and generate an action potential

Question 36

after a response is triggered, what does the chemical synapse do

Answer 36

return to its resting state - neurotransmitter molecules cleared from synaptic cleft

Question 37

nerve gas sarin

Answer 37

tiggers paralysis and death due to inhibition of the enzyme that breaks down the neurotransmitter controlling skeletal muscles

Question 38

metabotropic

Answer 38

movement of ions through a channel depends on one or more metabolic steps - can be metabotropic receptor on postsynaptic membrane

Question 39

what happens when a neurotransmitter binds to a metabotropic receptor

Answer 39

- activates signal transduction pathway in postsynaptic cell involving a second messenger - leads to amplification where many channels are opened/closed in response

Question 40

types of receptors for neurotransmitters

Answer 40

inotropic and metabotropic

Question 41

how many receptors can a single neurotransmitter bind to

Answer 41

can be more than a dozen - can excite postsynaptic cells expressing one receptor and inhibit postsynaptic cells expressing a different receptor

Question 42

acetylcholine

Answer 42

common neurotransmitter in vertebrates and invertebrates

Question 43

what is acetylcholine involved in

Answer 43

- muscle stimulation - memory formation - learning

Question 44

2 major classes of acetylcholine receptors in vertebrates:

Answer 44

1. ligand gated 2. metabotropic

Question 45

what can disrupt acetylcholine neurotransmission

Answer 45

number of toxins - like nerve gas sarin and botulism toxin produced by certain bacteria

Question 46

how many known neurotransmitters are there

Answer 46

over 100

Question 47

4 classes of neurotransmitters

Answer 47

1. amino acids 2. biogenic amines 3. neuropeptides 4. gases

Question 48

glutamate

Answer 48

one of several amino acids that can act as a neurotransmitter (vertebrates and invertebrates)

Question 49

glycine

Answer 49

acts as inhibitory synapses in parts of CNS outside the brain

Question 50

gamma-aminobutyric acid (GABA)

Answer 50

neurotransmitter at most inhibitory synapses in the brain

Question 51

biogenic amines include:

Answer 51

- norepinephrine - epinephrine - dopamine - serotonin

Question 52

what do biogenic amines do

Answer 52

central role in number of nervous system disorders

Question 53

Parkinson's disease

Answer 53

associated with lack of dopamine in brain

Question 54

neuropeptides

Answer 54

relatively short chains of amino acids that also function as neurotransmitters

Question 55

what do neuropeptides include

Answer 55

- substance P - endorphins - both affect perception of pain

Question 56

opiates

Answer 56

bind to same receptors as endorphins and can be used as painkillers

Question 57

nitric oxide (NO)

Answer 57

local regulators in PNS

Question 58

where is NO stores

Answer 58

- not stored in cytoplasmic vesicles like most neurotransmitters - synthesized on demand

Question 59

when can NO be broken down?

Answer 59

within a few seconds of production

Question 60

can CO be used as a neurotransmitter?

Answer 60

yes - body makes it in small amounts