A&p.neurophysiology.3

Front 1

what is the charge of the plasma membrane and why?

Back 1

its slightly negative because there is a slight excess of + charged ions outside the membrane and slight excess of - charged ions and proteins inside the membrane

Front 2

what is the transmembrane potential?

Back 2

unequal distribution of charges in membrane due to differences

Front 3

what does the transmembrane potential result from?

Back 3

-differences in the permeability of the membrane to various ions
-active transport mechanisms

Front 4

what is the resting potential?

Back 4

the transmembrane potential of a resting cell

Front 5

what do all neural activities begin with?

Back 5

a temporary, localized change in the resting potential caused by a typical stimulus

Front 6

what is a graded potential?

Back 6

the effect of the change in the resting potential by a typical stimulus; decreases with distance from the stimulus

Front 7

what triggers an action potential?

Back 7

if the graded potential is large

Front 8

what is an action potential?

Back 8

an electrical event that involves one location on the membrane; propagates along the axon toward the synaptic terminals

Front 9

what does synaptic activity do?

Back 9

produced graded potentials in the plasma membrane of the postsynaptic cell

Front 10

what does synaptic activity typically involve?

Back 10

the release of neurotransmitters (ACh) by the presynaptic cell

Front 11

what do the neurotransmitters released during synaptic activity do and what does this cause?

Back 11

they bind to the receptors on the postsynaptic plasma membrane which changes its permeability

Front 12

what does the response of a postsynaptic cell depend on?

Back 12

-what the stimulated receptors do
-what other stimuli are influencing the cell at the same time

Front 13

what is information processing?

Back 13

the integration of stimuli at the level of the individual cell

Front 14

what can changes in the transmembrane potential do?

Back 14

-trigger muscle contraction
-trigger gland secretion
-transfer information in the nervous system

Front 15

what does the cytosol contain?

Back 15

a lot of K+ ions and negatively charged proteins

Front 16

what determines what ions can pass through leak channels?

Back 16

size, shape, and structure of a leak channel; always open

Front 17

what does the negative sign on -70mV represent?

Back 17

the interior is negatively charged

Front 18

what do potassium ion gradients do?

Back 18

at resting potential, an electrical gradient opposes the chemical gradient for K+ ions; the net electrochemical gradient tends to force potassium ions out of the cell

Front 19

if the plasma membrane were freely permeable to potassium ions what would the equilibrium potential be?

Back 19

-90mV

Front 20

what do sodium ion gradients do?

Back 20

at resting potential, chemical and electrical gradients combine to drive Na+ into the cell

Front 21

what is a chemical gradient?

Back 21

concentration gradient for that ion across the plasma membrane

Front 22

what is an electrical gradient?

Back 22

created by the attraction between opposite charges or the repulsion between like charges

Front 23

what is equilibrium potential?

Back 23

a transmembrane potential in which the electrical and chemical gradients are equal and opposite and there is no net movement of ions across the membrane

Front 24

what does the high permeability to potassium ions cause on the resting potential?

Back 24

causes it to be close to -90mV, the equilibrium potential for K+

Front 25

what effect does Na+ have on the resting potential?

Back 25

it has only a smell effect on the resting potential because the membranes permeability to these ions is very low even though the electrochemical gradient for them is very large

Front 26

how do chemically gated channels operate?

Back 26

-they open when they bind specific chemicals

Front 27

what type of receptors bind in chemically gated channels?

Back 27

-ACh at the neuromuscular junction

Front 28

where are chemically gated channels most abundant?

Back 28

on the dendrites and cell body of a neuron

Front 29

where does most synaptic communcation occur?

Back 29

on the dendrites and the cell body of the neuron

Front 30

what is an excitable membrane?

Back 30

a membrane capable of generating and conducting an action potential

Front 31

where are voltage-gated channels found?

Back 31

areas of excitable membrane

Front 32

what do voltage-gated channels do?

Back 32

they open or close in response to changed in the transmembrane potential

Front 33

what are the three most important voltage-gated channels?

Back 33

sodium channels, potassium channels, and calcium channels

Front 34

sodium channels have two independently functioning gates, what are their functions?

Back 34

1. an activation gate that opens on stimulation, letting sodium ions into the cell
2. an inactivation gate that closes to stop the entry of sodium ions

Front 35

what do mechanically gated channels open in response to?

Back 35

to physical distortion of the membrane surface

Front 36

why are mechanically gated channels important?

Back 36

important in sensory receptors that respond to touch, pressure, or vibration

Front 37

are most gated channels open or closed at the resting potential?

Back 37

closed

Front 38

what are graded potentials?

Back 38

local potentials; changes in the transmembrane potential that cannot spread far from the site of stimulation

Front 39

what produces a graded potential?

Back 39

any stimulus that opens a gated channel

Front 40

what is depolarization?

Back 40

any shift from the resting potential toward a more positive value

Front 41

what is a local current?

Back 41

the movement of positive charges parallel to the inner and outer surfaces of the membrane

Front 42

as the distance away from the stimulus increases, what happens to the degree of depolarization and why?

Back 42

the degree decreases because the ions are entering in only one location but spreading in all directions

Front 43

what does the impact of the transmembrane depend on and why?

Back 43

the size of the stimulus because the intensity of the stimulus determines the number of open sodium channels

Front 44

what is the effect of more open channels?

Back 44

the more open channels there are, the more sodium ions enter the cell, the greater the membrane area affected, and the greater the degree of depolarization

Front 45

what happens when ACh is applied?

Back 45

chemically gated sodium ion channels open which leads to depolarization

Front 46

what is repolarization?

Back 46

occurs when the chemical stimulus is removed and the membrane returns to its normal resting potential

Front 47

what happens to the sodium ions during repolarization?

Back 47

the excess sodium ions are transported out of the cytoplasm

Front 48

what is hyperpolarization?

Back 48

occurs when chemically gated potassium channels are opened and results in a more negative transmembrane potential because the additional K+ ions leave the cytoplasm; a shift in the transmembrane potential past resting levels

Front 49

where is the transmembrane potential most affected?

Back 49

at the site of stimulation

Front 50

what type of channels does the resting potential depend on?

Back 50

leak channels

Front 51

what type of channels does the graded potential depend on?

Back 51

chemically gated channels

Front 52

what type of channes does the action potentials depend on?

Back 52

voltage-gated channels

Front 53

what is a threshold?

Back 53

where the voltage-gated sodium channels open due to a stimulus that initiated graded depolarization

Front 54

what is sodium channel inactivation?

Back 54

as the transmembrane potential approaches 30mV, the inactivation gated of voltage gated sodium channels close;coincides with the opening of voltage-gated potassium channels

Front 55

what is the absolute refractory period?

Back 55

when the membrane cannot respond to further stimulation
-voltage gated Na+ channels are open
-must return to resting state to reopen

Front 56

what is the relative refractory period?

Back 56

when the membrane can respond/AP can be generated only by a larger-than-normal stimulus
-interval following the absolute refractory period
-most Na+ channels returned to resting state but some K+ channels are still open

Front 57

what is the all-or-none principle?

Back 57

the concept in which a given stimulus either triggers a typical action potential, or it does not trigger one at all

Front 58

what is continuous propogation?

Back 58

occurs along unmyelinated axons; action potentials appears to "move" in a series of tiny steps that must be repeated along the entire cell; step by step depolarization and repolarization

Front 59

why cant continuous propagation occur along a myelinated axon?

Back 59

because myelin blocks the flow of ions across the membran so ions can only cross the plasma membrane at the nodes

Front 60

what is saltatory propagation?

Back 60

-In myelinated axon voltage hated channels clustered at Nodes of Ranvier
-the current is carried by Na+ and K+ flow across the membrane at nodes and the impulse appears to leap

Front 61

what is the only thing that can respond to a depolarizing stimulus?

Back 61

the nodes

Front 62

what is the fastest type of propagation?

Back 62

saltatory propagation

Front 63

what does the speed of propagation depend on?

Back 63

varies with axon diameter; the larger the diameter, the lower the resistance to ion movement, and the faster the current travels

Front 64

where are messages transferred to another neuron or effector cell?

Back 64

the synapse

Front 65

what is a chemical synapse?

Back 65

-rely on neurotransmitter release into synaptic cleft which travels by diffusion
-most abundant
-presynaptic and postsynaptic cells do not touch

Front 66

what is the most abundant type of synapse?

Back 66

chemical synapse

Front 67

what are cholinergic synapses?

Back 67

-typical chemical synapses that release acetylcholine
-widespread in CNS and PNS

Front 68

what is synaptic fatigue?

Back 68

once the synaptic knob is unable to keep pace with the demand for neurotransmitter

Front 69

after synaptic fatigue, when will the synapse be able to function normally again?

Back 69

once its supply of ACh is replenished

Front 70

what is a synaptic delay?

Back 70

.2-.5 msec; occurs between the arrival of the action potential at the synaptic knob and the effect on postsynaptic membrane

Front 71

why are reflexes important for survival?

Back 71

they involve only a few synapses and thus provide rapid and automatic responses to stimuli

Front 72

how do you eliminate synaptic dely entirely?

Back 72

directly couple the presynaptic neuron to the post synaptic cell at the electrical synapes

Front 73

why can the synaptic knob continue to function for an extended period of time?

Back 73

because neurotransmitters are reabsorbed and recycled

Front 74

what happens to presynaptic and postsynaptic membranes at an electrical synapse?

Back 74

this is where the presynaptic and the postsynaptic membranes are locked together by gap junctions

Front 75

in an electrical synapse, changes in the transmembrane potential of one cell will produce what?

Back 75

local currents that affect the other cell as if the two shared a common membrane

Front 76

where are electrical synapses located?

Back 76

the CNS and PNS; rare

Front 77

what happens to the action potential when it reaches an electrical synapse?

Back 77

AP conducts directly between adjacent cells and are propagated to the next cell; no synaptic cleft as we send message forward

Front 78

what does the adaptability of the nervous system result from?

Back 78

responses of a postsynaptic cell

Front 79

how do responses of a postsynaptic cell vary/depend on?

Back 79

the local chemical environment or the actives of synapses that release multiple neurotransmitters with varied effects

Front 80

what is an excitatory postsynaptic potential (EPSP)?

Back 80

a graded depolarization caused by the arrival of a neurtransmitter at the postsynaptic membrane that shifts the transmembrane potential closer to the threshold (~55 mV); FACILITAES the membrane

Front 81

what effect does the degree of facilitation have on the stimulus?

Back 81

the larger the degree of facilitation, the smaller the additional stimulus needed to trigger an action potential

Front 82

what is an IPSP?

Back 82

inhibitory postsynaptic potential; graded hyperpolarization of the postsynaptic membrane; suppresses AP generation

Front 83

what happens when membrane hyperpolarization occurs?

Back 83

the neuron is said to be inhibited because larger-than-usual depolarizing stiumus must be provided to bring the membrane potential to threshold

Front 84

what is summation?

Back 84

the integration of effects of graded potentials on a segment of the plasma membrane

Front 85

what do EPSP' and IPSP's result from?

Back 85

activation of different types of chemically gated channels

Front 86

if two diff neurotransmitters arrive simultaneously then what happens?

Back 86

both sets of channels open and the net effect may be no change in the membrane potential

Front 87

what are postsynaptic potentials?

Back 87

graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter

Front 88

what are the two major types of postsynaptic potentials and where do they develop?

Back 88

they develop at neuron-neuron synapses:
1. excitatory postsynaptic potentials
2. inhibitory postsynaptic potentials

Front 89

what determines how a neuron responds from moment to moment?

Back 89

the net effect on the transmembrane potential at the axon hillock

Front 90

why does the net effect on the transmembrane potential at the axon hillock determine neuron responces?

Back 90

1. because axon hillock is closest to the initial segment and granded potentials are what trigger the action potentials
2. the threshold

Front 91

what does the axon hillock do?

Back 91

integrates the excitatory and inhibitory stimuli affecting the cell body and dendrites at any given moment nd determines the rate of action potential generation at the initial segment

Front 92

where and how many voltages does the EPSP produce a depolarization?

Back 92

.5mV at the postsynaptic membrane

Front 93

why wont an EPSP result in an action potential?

Back 93

because before an action potential will arise in the intial segment, local currents must depolarize that region by atleast 10 mV

Front 94

what are the two forms of summation?

Back 94

temporal and spatial

Front 95

when does temporal summation occur?

Back 95

when a signle synapse is active repeatedly

Front 96

what does spatial summation involve?

Back 96

multiple synapses are active simultaneously

Front 97

why are the effects of spatial summation cumulative on the transmembrane potential?

Back 97

because each active synapse opens gated channels that allow ion movement in or out of the cell

Front 98

what does the depolarization at the initial segment depend on?

Back 98

1. how many excitatory synapses are active at any given moment
2. how far the are from the initial segment

Front 99

when does an action potential result from a temporal summation?

Back 99

when the transmembrane potential at the initial segment reaches threshold

Front 100

what changes a neurons sensitivity to stimulation?

Back 100

1. changes in body temperature
2. changes in the availability of oxygen or nutrients
3. the presence of abnormal chemicals

Front 101

when are regulatory neurons involved and why?

Back 101

when there are higher levels of information processing because they facilitate or inhibit the activities of presynaptic neurons

Front 102

in what two ways do regulatory neurons facilitate or inhibit the activities of the presynaptic neurons?

Back 102

-by affecting the membrane of the cell body
-by altering the sensitivity of the synaptic knobs

Front 103

what indirect effects on ion channels do many important neurotransmitters usually involve?

Back 103

binding to G proteins

Front 104

what are G proteins?

Back 104

receptor proteins

Front 105

what do activated G proteins trigger?

Back 105

the formation or release of second messengers

Front 106

what do second messengers do?

Back 106

-alter conditions in the cytoplasm
-change the activity of the postsynaptic cell

Front 107

how is the messages propagated by action potentials across the synapse often interpreted?

Back 107

solely on the basis of the frequency of action potentials

Front 108

what two things are proportional to the frequency of an action potential?

Back 108

-strength of the motor response
-degree of sensory stimulation

Front 109

what does a graded potentials variance in amplitude depend on?

Back 109

the strength of the stimulus which determinds how many ion channels are opened/closed and how long they remain that way

Front 110

what two things does the strength of the stimulus control?

Back 110

1. how many ion channels open or close
2. how long they remain opened or closed

Front 111

what effect does diffusion have on graded potentials

Back 111

they travel short distances and die out quickly

Front 112

where are the sensory receptors and neurons located?

Back 112

the presynaptic cell

Front 113

what two type of potentials are in the presynaptic cell?

Back 113

receptor and generator

Front 114

what are receptor potentials?

Back 114

receptor cells

Front 115

what are generator potentials?

Back 115

sensory neurons

Front 116

what is the goal of graded potentials?

Back 116

to change RMP enough to send the info down the axon (~55mV) at the axon hillox

Front 117

what does the response to a neurotransmitter depend on?

Back 117

the nature of the receptor

Front 118

how does distance affect the strength of an AP?

Back 118

it doesnt; its the same thing along the axon

Front 119

in the generation of AP, what phase is Na+ channels involved in?

Back 119

the depolarizing phase

Front 120

in the generation of AP, what phase is K+ channels involved in?

Back 120

repolarizing phase

Front 121

what four steps are involved in the sequence of rapidly occuring events of the AP?

Back 121

1. depolarizing phase
-when NA+ channels open
2. repolarizing phase
-when NA+channels inactivating and K+ channels open
3. hyperpolarizing phase
-some K+ channels remain open and Na+ channels reset
4. after the AP is complete, the sodium potassium pumps put the ions back in place

Front 122

what happens during AP propagation?

Back 122

the influx of Na+ establishes local currents depolarizing adjacent membrane which changes the membrane potential from -55 to +30mV

Front 123

what is a refractory period?

Back 123

the period of time, after an action potential begins, in which the cell cannot generate another action potential

Front 124

why dont graded portentials have a refractory period?

Back 124

so spatial and temporal summation can occur

Front 125

why is there no summation in an action potential?

Back 125

because it involves a refractory period

Front 126

what factors affect the speed of propagation across the axon diameter?

Back 126

1. myelinated- faster
2. unmyelinated- slower

Front 127

why is the speed across an unmyelinated axon slower than myelinated?

Back 127

because you have to open every individual channel

Front 128

how does the size of the diameter effect the speed of the propagation across an axon?

Back 128

the larger the diameter the faster the speed

Front 129

what are the three different types of fibers, their size, and how long the propagation across the axon takes place?

Back 129

1. type A fiber- 5-20um; 12-13msec
2. type B fiber- 2-3um; 15msec
3. type C fiber- <2um, 2msec

Front 130

what are type A fibers?

Back 130

-life-threatening
-myelinated (faster)
-sensory: touch, pressure, pain, heat; information from skin and skeletal muscle
-motor: information going from sensory to skeletal
-motor: information going from sensory to skeletal

Front 131

what sensors are involved in type A fibers and where do they get this information from?

Back 131

touch, pressure, pain, heat; information is from skin and skeletal muscle

Front 132

what is the motor function of type A fibers?

Back 132

information goes from sensory to skeletal

Front 133

what are type B fibers?

Back 133

-intermediate
-Myelinated
-Sensory viscera to brain and spinal cord- from organs
-ANS motor neurons from brain and spinal cord to ANS relay stations (autonomic ganglia)- organs and glands

Front 134

where is sensory viscera in type B fibers from and where are they transported to?

Back 134

from organs to brain and spinal cord

Front 135

in type B fibers, ANS motor neurons are from where and are sent to where?

Back 135

from brain and spinal cord to ANS relay stations (autonomic ganglia) such as organs and glands

Front 136

what is type C fibers?

Back 136

-Unmyelinated- smooth muscles
-Sensory: pain, touch, pressure, heat, cold from skin and pain from -Motor: autonomic motor fibers from autonomic ganglia to heart, smooth muscle and glands
-Not life-threatening
-Majority traveling from outside to CNS

Front 137

what sensory is involved in type C fibers?

Back 137

pain, touch, pressure, heat, cold, pain

Front 138

in type C fibers where is the sensory cold from and pain from?

Back 138

cold is from the skin and pain is from viscera

Front 139

what motor functions does type C fiber have?

Back 139

autonomic motor fibers from autonomis ganglia to heart, smooth muscle, and glands

Front 140

where are majority of type C fibers traveling?

Back 140

traveling from outside to CNS

Front 141

what are the three neuron to neuron synapse locations?

Back 141

1. axodendritic
2. axosomatic
3. axoaxonic

Front 142

what is axodendritic?

Back 142

from axon to dendrite

Front 143

what is axosomatic?

Back 143

from axon to cell body

Front 144

what is axoaxonic?

Back 144

from axon to axon; voltage gated channels open immediately

Front 145

what type of synapse location is the most common?

Back 145

axosomatic

Front 146

what type of synapse location is the least common?

Back 146

axoaxonic

Front 147

what are chemical synapses filled with?

Back 147

interstitial fluid

Front 148

what happens at a chemical synapses?

Back 148

the postsynaptic cell recieved chemical signal by diffusion

Front 149

what results from a chemical synapse?

Back 149

a postsynaptic potential (graded potential)

Front 150

how long is the delay of a chemical synapse?

Back 150

0.5 msec

Front 151

what are the two advantages of electrical synapses?

Back 151

1. faster because it doesnt have the time travel across the cleft
2. synchronication- fire off at almost the same exact time

Front 152

explain the ion flow in electrical synapses and where are they common?

Back 152

-ions flow from pre-postsynaptic cell through connexons
-common in visceral smooth muscle, cardiac muscle, developing embryo, and the CNS (rare)

Front 153

what are connexons?

Back 153

membrane proteins

Front 154

where is it rare to fine electrical synapses?

Back 154

the CNS

Front 155

what two classifications are made for ACh and what does it depend on?

Back 155

excitatory or inhibitory; it depends on the site recieving ACh

Front 156

how does ACh act directly? indirectly?

Back 156

acts directly through an ion channel or indirectly through a second messenger

Front 157

what is a typical electrical synapse?

Back 157

gap junction

Front 158

what is a typical chemical synapse?

Back 158

neuromuscular junction

Front 159

what are the four steps of a typical chemical synapse?

Back 159

1. AP arrives at synaptic knob (end of the telodendria) which opens voltage gated channels for Ca+
2. Extracellular Ca2+ enter synaptic knob facilitating fusion of synaptic vesicles with presynaptic membrane; releases neurotransmitter by exocytosis
3. ACh binds receptors; protein receptors in the muscle cell; ligand connection because it is opening up a channel and in the excited cell depolarization takes place or graded potential; Sodium ion enter by open chemincally-gated channels
4. ACh is removed by acetylcholinesterase (AChE)- breaks it down → retrograde transport (brings it back to the beginning)

Front 160

what are the three ways to remove a neurotransmitter?

Back 160

1. diffusion
2. enzymatic degradation
3. uptake by cells

Front 161

how does diffusion move a neurotrasmitter?

Back 161

it diffuses out into the interstitial fluid to neuroglia cells around it and becomes concentrated; there are no receptors out there so it does not fire anything off

Front 162

how are neurotransmitters removed by uptake by cells?

Back 162

-by neurotransmitter transporters (membrane proteins): these can also cause reuptake; drugs block reuptake of neurotransmitter so it prolongs the neurotransmitters activity
-by neuroglia: by uptake

Front 163

what are neural circuits and what do they create?

Back 163

they are functional groups of neurons that process specific types of information and create a network between other cells/neurons

Front 164

what are the four different types of neural circuits?

Back 164

1. diverging circuit
2. converging circuit
3. reverberating circuit
4. parallel after-discharge circuit

Front 165

what is a diverging circuit?

Back 165

it involves a single presynaptic neuron and several postsynaptic neurons

single cell --> many cells

-amplifies signal

Front 166

what is a converging circuit

Back 166

its a high graded potential that involved several presynaptic neurons and a single postsynaptic neuron

many --> one

-provides more information

Front 167

what is a reverberating circuit?

Back 167

-branches from later neurons synapse with earlier ones
-information coming in, keep the info going, it increases the length of time of the message until we stop it

Front 168

what is parallel after-discharge circuit?

Back 168

-single presynaptic cell stimulates group of neurons
-group of synapses with single postsynaptic neuron

Front 169

what is the important function of the diverging circuit?

Back 169

amplifies signal

Front 170

what is the important function of the converging circuit?

Back 170

provides more information

Front 171

what is the important function of the reverberating circuit?

Back 171

increases length of time message is transmitted

Front 172

what happens to the last neuron in the parallel after-discharge circuit?

Back 172

it exhibits multiple EPSP's or IPSP's