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Physiology > Exam 3: Nervous Tissue > Flashcards

Exam 3: Nervous Tissue Flashcards

1
Q

Resting membrane potential

A

Vm of a cell at rest (A cell that is not being stimulated or inhibited)
Negative value because there is a net negative charge on the inner lining of the membrane as compared to on the outer lining of the membrane
Established by the concentration gradients and permeabilities of Na+, K+ and Cl-

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2
Q

What is the concentration and permeability of sodium in a cell at rest?

A

[Na]i Intracellular sodium concentration: 15 mEq/L
[Na]o Extracellular sodium concentration: 145 mEq/L
PNa permeability of sodium: 0.05

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3
Q

What is the concentration and permeability of potassium in a cell at rest?

A

[K]i Intracellular potassium concentration: 135 mEq/L
[K]o Extracellular potassium concentration: 5 mEq/L
PK permeability of potassium: 1.0

Potassium is the most permeable and therefore plays the biggest role in determining resting membrane potential

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4
Q

What is the concentration and permeability of chloride in a cell at rest?

A

[Cl]i Intracellular chloride concentration: 8 mEq/L
[Cl]o Extracellular chloride concentration: 110 mEq/L
PCl permeability of chloride: 0.45

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5
Q

What dictates membrane potential?

A

The concentration gradients and permeabilities create an environment that dictates the relative movement of ions, which ultimately establishes Vm. Therefore, Vm is dictated by 2 separate factors: 1) magnitude of the concentration gradients of ions, and 2) permeabilities of the membrane to ions.

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6
Q

What primarily dictates resting Vm?

A

Passive movements of Na+, K+, and Cl-
Na+ and K+ concentration gradients maintained by the Na+/K+ pump. Actively transport 3 Na+ out of the cell and 2 K+ into the cell.
Cl- concentration gradient maintained as well.

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7
Q

Describe the passive movements of Na+.

A

Na+ leaks passively into the cell during resting conditions. At resting Vm, permeability of Na+ is small. Therefore, small amount of positive charge into cell.

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8
Q

Describe the passive movements of K+.

A

K+ leaks passively out of the cell during resting conditions. At resting Vm, permeability of K+ is the largest. Therefore, very large amount of positive charge out of the cell. Potassium has the greatest influence on resting Vm.

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9
Q

Describe the passive movements of Cl-.

A

Cl- leaks passively into the cell during resting conditions. At resting Vm, permeability of Cl- is large. Therefore, large amount of negative charge into cell.

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10
Q

Membrane potential (Vm)

A

Voltage (potential) generated via the difference between negative and positive charges lining the inner membrane and lining the outer membrane
The value is based on the inner membrane charges relative to the outer membrane charges
Measured in millivolts, present in all cells, established by movement of ions

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11
Q

Effect of increasing extracellular Na+

A

Causes Vm to become more positive (depolarize)
Increases the gradient for Na+ to leak into the cell
More Na+ leaks into the cell (more positive charge on inner membrane)

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12
Q

Effect of increasing extracellular K+

A

Causes a depolarization
Decreases the gradient for K+ to leak out of the cell
Less K+ leaks out of cell (more positive charge on inner membrane)

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13
Q

Effect of increasing extracellular Cl-

A

Causes Vm to become more negative (hyperpolarize)
Increases the gradient for Cl- to leak into the cell
More Cl- leaks into the cell (more negative charge on inner membrane)

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14
Q

Effect of decreasing extracellular Na+

A

Causes a hyperpolarization
Decreases the gradient for Na+ to leak into the cell
Less Na+ leaks into cell (less positive charge on inner membrane)

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15
Q

Effect of decreasing extracellular K+

A

Causes a hyperpolarization
Increases the gradient for K+ to leak out of the cell
More K+ leaks out of the cell (less positive charge on the inner membrane)

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16
Q

Effect of decreasing extracellular Cl-

A

Causes a depolarization
Decreases the gradient for Cl- to leak into the cell
Less Cl- leaks into cell (less negative charge on the inner membrane)

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17
Q

Effect of increasing intracellular Na+

A

Causes a hyperpolarization
Decreases the gradient for Na+ to leak into the cell
Less Na+ leaks into cell (less positive charge on inner membrane)

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18
Q

Effect of increasing intracellular K+

A

Causes a hyperpolarization
Increases the gradient for K+ to leak out of the cell
More K+ leaves out of the cell (less positive charge on inner membrane)

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19
Q

Effect of increasing intracellular Cl-

A

Causes a depolarization
Decreases the gradient for Cl- to leak into the cell
Less Cl- leaks into the cell (less negative charge on inner membrane)

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20
Q

Effect of decreasing intracellular Na+

A

Causes a depolarization
Increases the gradient for Na+ to leak into the cell
More Na+ leaks into the cell (more positive charge on the inner membrane)

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21
Q

Effect of decreasing intracellular K+

A

Causes a depolarization
Decreases the gradient for K+ to leak out of the cell
Less K+ leaks out of the cell (more positive charge on inner membrane)

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22
Q

Effect of decreasing intracellular Cl-

A

Causes a hyperpolarization
Increases the gradient for Cl- to leak into the cell
More Cl- leaks into the cell (more negative charge on inner membrane)

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23
Q

The concentration of what ion has the greatest effect on resting Vm?

A

Changing the concentration of K+ will have the greatest effect on resting Vm because the cell is most permeable to K+ at rest

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24
Q

Effect of increasing the permeability of Na+

A

Increases the movement of Na+ into the cell

More positive charge on the inner membrane (depolarization)

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25
Q

Effect of decreasing the permeability of Na+

A

Decreases the movement of Na+ into the cell

Less positive charge on the inner membrane (hyperpolarization)

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26
Q

Effect of increasing the permeability of K+

A

Increases the movement of K+ out of the cell

Less positive charge on the inner membrane (hyperpolarization)

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27
Q

Effect of decreasing the permeability of K+

A

Decreases the movement of K+ out of the cell

More positive charge on the inner membrane (depolarization)

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28
Q

Effect of increasing the permeability of Cl-

A

Increase of the movement of Cl-into the cell

Negative charge on the inner membrane (hyperpolarization)

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29
Q

Effect of decreasing the permeability of Cl-

A

Decreases the movement of Cl- into the cell

Less negative charge on the inner membrane (depolarization)

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30
Q

Action potential

A

Local, very large and very rapid depolarization followed by repolarization
Only a few cells generate action potentials, neurons and muscle cells
Allows for communication
Threshold is a depolarized Vm that must be reached to elicit an action potential
All or none response if threshold is met or not met, respectively

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31
Q

Generation and dynamics of an action potential in a neuron (Part 1)

A

Neuron is stimulated to cause the Vm to depolarize/Threshold is reached/Voltage gated Na+ channels open rapidly/Na+ permeability increases/Rapid movement of Na+ into the cell/Causes a very large and very rapid depolarization of Vm/Action potential passes through zero towards ENa/Large depolarization causes voltage gated Na+ channels to inactivate/Na+ movement into cell stops, ENa never reached/Action potential reaches its peak

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32
Q

Generation and dynamics of an action potential in a neuron (Part 2)

A

Voltage gated K+ channels open but less rapidly, K+ permeability increases/Rapid movement of K+ (but not as rapid as Na+) out of the cell/Causes Vm to repolarize towards resting Vm after peak of action potential/Vm continues towards EK (voltage gated K+ channels close slowly)/Produces an afterhyperpolarization of Vm/Vm is more negative (hyperpolarized) than resting Vm
Resting Vm re-established by leak channels

33
Q

Refractory period

A

Period of time when a cell fails to respond to a threshold stimulus

34
Q

Absolutely refractory period

A

Occurs from the peak of the action potential and repolarization phase, Due to inactivation of Na+ channels
Period of time when no action potential can be elicited regardless of the stimulus intensity

35
Q

Relative refractory period

A

Occurs during the afterhyperpolarization phase
Most Na+ channels begin to activate
Most K+ channels can be opened or are still open
Possible to elicit an action potential during this time; however, greater stimulus is needed
Cell is further away from threshold during this time

36
Q

Action potential frequency

A

Maximum frequency dictated by the refractory period
Shorter refractory period=greater number of action potentials
Directly proportional to the stimulus strength
The greater the stimulus, the greater the action potential frequency

37
Q

Sub-threshold stimulus

A

Very small stimulus that does not cause a cell to reach threshold, no action potential elicited

38
Q

Threshold stimulus

A

Stimulus that causes a cell to reach threshold, one action potential elicited

39
Q

Submaximal stimulus

A

Greater than threshold stimulus but less than maximal stimulus
Greater than one action potential but less than the number of action potentials elicited with a maximal stimulus

40
Q

Maximal stimulus

A

Stimulus that causes the maximum action potential frequency

41
Q

Supramaximal stimulus

A

Greater than maximal stimulus
Action potential frequency does not increase despite larger stimulus because we cannot go beyond a maximum action potential frequency

42
Q

Action potential conduction

A

Propagation/spread of action potentials along a membrane
Action potential does not move across a membrane
Stimulates the production of another in an adjacent region (Analogous to dominoes toppling, one after another)
Velocity in axons depends on fiber diameter and myelin
Larger axons have greater surface area with more voltage gated ions so they conduct action potentials faster
Myelinated axons conduct action potentials faster (More myelin=faster conduction)

43
Q

Continuous conduction

A

Unmyelinated axons and membranes of excitable cells
Action potential in one region stimulates another in adjacent region
Conduction velocity is less than 2 m/s
Positive current from action potential flows to adjacent region, causes depolarization of membrane
When threshold is met, another action potential is elicited
Spread of action potentials continues in one direction, ensured by the refractory period

44
Q

Saltatory conduction

A

Solely in myelinated axons
Action potentials elicited at nodes of Ranvier where there is a high concentration of voltage gated Na+ and K+ channels
Conduction velocity is anywhere from 3 to 120 m/s
Positive current from action potential flows toward adjacent node, causes depolarization of membrane
Myelin sheath allows the flow of current to be rapid
When threshold is met, another action potential is elicited
Spread of action potentials continues in one direction, ensured by the refractory period

45
Q

Synapse

A

Junction between two cells that allows communication between those two cells
Two types are electrical and chemical

46
Q

Electrical synapse

A

Communication between two cells via gap junctions; allows for rapid passage of information between adjoining cells
Formed via 2 connexons (one from each adjoining cell)
Connexon formed from proteins called connexins (6 connexins form 1 connexon)
Molecules flow freely through gap junctions when open

47
Q

Chemical synapse

A

Communication between two cells via release of chemicals
Neurotransmitters (chemicals) released from presynaptic cell (membrane at the synapse that is carrying the info) to postsynaptic cell (membrane at the synapse that is receiving the info)
Neurotransmitters are most commonly produced and then stored in synaptic vesicles
Gaseous neurotransmitters are produced and released when needed; therefore, they are not stored

48
Q

Synaptic cleft

A

Small space between presynaptic and postsynaptic membranes

49
Q

Synaptic transmission (Option 1)

A

Action potential travels to synapse terminal of presynaptic membrane
Causes voltage gated Ca+ channels to open, intracellular Ca+ concentration increases and causes synaptic vesicles to fuse with membranes of synaptic knob
Neurotransmitter is released into synaptic cleft via excytosis, diffuses across synaptic cleft
Binds to specific receptors of the postsynaptic membrane
Modulates ion channels in the postsynaptic membrane
Info transmitted from one cell to the other

50
Q

Synaptic transmission (Option 2)

A

Causes production of gaseous neurotransmitter
Neurotransmitter released from presynaptic cell via diffusion
Diffuses across synaptic cleft, diffuses into postsynaptic cell, has some effect within the postsynaptic cell
Info transmitted from one cell to the other

51
Q

Fate of Neurotransmitter

A

Reuptake of chemical Neurotransmitter by presynaptic membrane
Gaseous neurotransmitters are metabolized by postsynaptic cell

52
Q

Postsynaptic potential

A

Vm change in postsynaptic membrane due to neurotransmitter

53
Q

Excitatory postsynaptic potential (EPSP)

A

Caused by depolarizing currents through the postsynaptic membrane
Influx of cations (Na+) or efflux of anions (Cl-)

54
Q

Inhibitory postsynaptic potential (IPSP)

A

Caused by hyperpolarizing current through the postsynaptic membrane
Influx of anions (Cl-) or efflux of cations (K+)

55
Q

Summation of postsynaptic potential

A

Integrated sum of EPSPs and IPSPs
Determine Vm change (if any)
Two types are Spatial and Temporal

56
Q

Spatial summation

A

When multiple postsynaptic potentials from different synapses converge at about the same time

57
Q

Temporal summation

A

When multiple postsynaptic potentials from the same synapse converge at about the same time

58
Q

Synaptic plasticity

A

Ability of some component of a synapse to change
Decrease or increase in neurotransmitter release, receptor sensitivity, the number of receptors
Occurs if the stimulus to do so is large and/or sustained

59
Q

List the neurotransmitters

A

Acetylcholine (ACh)
Monoamines (Serotonin/5-HT, Norepinephrine, Dopamine)
Amino Acids (GABA, Glutamate, Glycine)
Neuropeptides (Endorphins & Enkephalins, Substance P)
Gaseous neurotransmitters (Carbon monoxide, nitroc oxide)

60
Q

Acetylcholine (ACh)

A 
CNS and PNS
Excitatory or inhibitory
Arousal, sleep, attention, memory
Stimulates skeletal muscle
Neurotransmitter of the ANS
Loss of ACh producing neurons implicated in memory loss with Alzheimer's (Treat with ACh reuptake inhibitors)
61
Q

Monoamines

A

Serotonin/5-HT, norepinephrine, dopamine

62
Q

Serotonin/5-HT

A

CNS and PNS, mostly in gut (Stimulates gut)
Excitatory or inhibitory
Temp regulation, sleep, mood, nausea, vomiting
Low levels linked to depression, anxiety, OCD (treat with selective serotonin reuptake inhibitors (SSRIs) such as Prozac, Paxil, Zoloft, Celexa, Lexapro or treat with psychotherapy such as talk therapy, cognitive behavioral therapy, exposure therapy)
MDMA (Ecstasy) causes serotonin release and inhibits serotonin reuptake

63
Q

Norepinephrine

A

CNS and PNS
Excitatory or inhibitory
Decision-making, attention, mood
Neurotransmitter of the sympathetic nervous system
Low levels linked to depression, ADD (treat with norepinephrine reuptake inhibitors such as Wellbutrin or Ritalin or psychotherapy)

64
Q

Dopamine

A

CNS
Excitatory or inhibitory
Movement, attention, motivation, pleasure
High levels linked to Tourette’s, schizophrenia and psychosis (treat with dopamine receptor antagonist)
Low levels linked to depression, ADD, addictive behavior (treat with dopamine reuptake inhibitors such as Wellbutrin, Ritalin, Chantix or psychotherapy)
Loss of dopamine producing neurons leads to Parkinson’s disease

65
Q

Amino acids

A

GABA, glutamate, glycine

66
Q

Glutamate

A

CNS
Major excitatory neurotransmitter in the CNS
Has many functions including learning and memory
High levels cause seizures and neural degeneration (treat with drugs that block glutamate release and receptors)

67
Q

GABA

A

CNS
Major inhibitory neurotransmitter in the CNS
Drugs that increase GABA (GABAergic drugs) used to treat epileptic activity
Death of GABA producing cells leads to Huntington’s disease (treat with GABAergic drugs)

68
Q

Glycine

A

Found primarily in the CNS

Inhibitory neurotransmitter

69
Q

Neuropeptides

A

Endorphins and enkephalins, substance P

70
Q

Endorphins and enkephalins

A

Found in the CNS and PNS
Opioid compounds
Inhibitory
Important in regulation of pain and gut motility, diminishes pain and slows the gut
Morphine and Demorol are agonists to endorphin receptors

71
Q

Substance P

A

CNS and PNS
Excitatory
Importance in the regulation of pain, anxiety, nausea and breathing
Inhibiting substance P receptors reduces pain and prevents nausea

72
Q

Gaseous neurotransmitters

A

Cannot be stored, produced as they are needed

Nitric oxide, carbon monoxide

73
Q

Nitric oxide

A

Found in the CNS and PNS
Excitatory or inhibitory
Thought to be involved in memory
Involved in many processes such as erection, blood vessel tone, neurotransmitter release

74
Q

Carbon monoxide

A

Found in the CNS and PNS
Excitatory or inhibitory
Thought to be a co-neurotransmitter with nitric oxide
Similar functions to nitric oxide

75
Q

Sensory memory

A 
Very short-term retention of sensory input
Info that is scanned, evaluated and acted upon; one does not realize this is happening
Last less than a second, electrical in nature (changes in Vm), gone if it is ignored
If perceived (not a conscious act), it is stored in short-term memory
76
Q

Short-term memory

A

Last seconds to approximately a minute, electrical in nature, forgotten if an effort is not made to retain it or an impression is not made

77
Q

Long-term memory

A

Last minutes to hours and as long as a lifetime
Info stored when an effort is made or an impression is made
synaptic in nature (synaptic plasticity)
-Long term potentiation (increased neurotransmitter release, receptor sensitivity, number of receptors)
-new synapses formed
2 types: declarative/explicit (retention of events, people, places, facts) and procedural/implicit (development of skills, conditioned reflexes)

78
Q

Areas of the brain involved in memory

A

Hippocampus, prefrontal cortex, amygdala, striatum, mammillary bodies

Physiology (3 decks)

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