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Year 2: NeuroBiology > Lecture 6: Chemical/Electrical Signals > Flashcards

Lecture 6: Chemical/Electrical Signals Flashcards

1
Q

characteristics of neurons

A

terminally differentiated epithelial cells

most have lost replicative capactities

different morphologies

communicate via electric and chemical signals

sensory = afferent, motor = efferent, and interneurons = integration and coordination

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2
Q

what cellular organs are contained in the soma

A

nucleus
rough ER
smooth ER
golgi apparatus
lysosome/peroxisome
mitochondria
cytoskeleton structures
cell membrane

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3
Q

describe the nucleus of a neuron

A

condensed

no replicative functions = no centrioles

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4
Q

function of rough endoplasmic reticulum and where in the neuron this takes place

A

protein and peptide synthesis in the Nissl body

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5
Q

smooth ER function

A

lipid synthesis

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6
Q

golgi apparatus function

A

modification of synthesized proteins and peptides and lipids for sorting

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7
Q

lysosome/peroxisome function

A

degrade metabolic waste

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8
Q

mitochondria function

A

power

produce ATP

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9
Q

function of cytoskeleton

A

made of neurofilaments

give shape to neuron

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10
Q

functions/purposes of the soma of a neuron

A

holds all cellular organs

synthesizes most molecules a neuron needs to survive

reception and summation of signals

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11
Q

what cellular organs can be found in the axon of a neuron as well as the cell body

A

mitochondria

lysosome/peroxisome

enzymes for synthesis/activation of neurotransmitters

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12
Q

what happens at the axon hillock

A

initiation of action potentials

APs are initiated by peripheral process in pseudounipolar neurons

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13
Q

how does the axon form synapses with target cells

A

release of neurotransmitters

transformed from electrical to chemical

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14
Q

what defines the type of neuron morphologically

A

number and location of the dendrites

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15
Q

multipolar neuron

A

multiple dendrites from the soma

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16
Q

bipolar neuron

A

dendrites mainly on one end of the soma

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17
Q

unipolar neuron

A

one hillock with dendrites on the axon

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18
Q

pseudounipolar neuron

A

one hillock then divides axon to 2 branches (1 branch like dendrites)

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19
Q

what type of neuron are most sensory neurons and their unique characteristics

A

pseudounipolar

unique characteristics = limited cellular organs, like axons, but has golgi apparatus extension

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20
Q

describe rapid delivery of molecules in the neuron and the 2 subtypes

A

active transportation

anterograde transportation = FROM soma TO dendrites/axons

retrograde = FROM dendrites/axons back TO soma

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21
Q

what proteins are involved in retrograde and anterograde transportation in the neuron

A

anterograde = kinesin

retrograde = dynein

viral and bacterial toxins can hijack these transportation mechanisms

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22
Q

the neuron cellular membrane is selectively permeable. What are some examples of this

A

water transporation across water channels facilitated aquaporin proteins

leaking and gated ion channels can be found in the membrane

sodium and potassium channels, controlled by ATP, found in the membrane as well

other molecules can enter only via transporters, receptors, etc

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23
Q

what is osmotic potential

A

numbers of ions and molecules

ratio

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24
Q

what is electric potential

A

positive and negative charges

ratio

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25
Q

what is the resting membrane potential of the neuron

A

negative

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26
Q

describe a ligand gated channel

A

neurotransmitter acts as a “ligand” (key)

ion channel acts as the receptor (key hole)

activation of channel causes a change in membrane potential

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27
Q

describe a voltage gated channel

A

opened when resting membrane potential increases to the threshold

no ligands needed

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28
Q

describe modality gated ion channels

A

can open or close via touch, heat, pressure, cold, light, sounds, etc

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29
Q

what ion is in charge of the resting membrane potential and how can it “freely” cross the cellular membrane

A

K+

can freely cross through leaking channels

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30
Q

what are the 5 phases of initiation of an action potential

A

numbers/thresholds vary, just using these as example values

resting potential (-70mv)

slow depolarization (>-70mv, mv increased via activation of modality/ligand gated Na+ channels; forms a graded potential)

fast depolarization (>-55mv, at threshold, result of voltage gated Na+ channel; action potential)

repolarization (back to -70mv; voltage gated K+ and pumps)

hyperpolarization (<-70mv; voltage gated K+ and pumps)

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31
Q

definition of an action potential

A

phase of potential above the threshold

lasts ~ 1mSec

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32
Q

what are the 3 stages of voltage gated sodium channels

A

resting state
activated state
inactivated state

never an instance where both gates will be closed at the same time

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33
Q

describe the resting state of voltage gated sodium channels

A

below threshold potential

activation gate closed

inactivation gate open

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34
Q

describe the activated state of voltage gated sodium channels

A

fast depolarization

both gates are open

35
Q

describe the inactivated state of voltage gated sodium channels

A

repolarization and hyperpolarization

activation gate is open

inactivation gate is closed

36
Q

what is the absolute refractory period related to voltage gated sodium channels

A

at both the activated and inactivated states

where you can not induce another AP

37
Q

what is the relative refractory period related to voltage gated sodium channels

A

when some channels have returned to resting state but not all

slightly earlier than hyperpolarization phase

can induce another AP with higher stimulation but increased threshold

38
Q

what defines the unidirectional conduction of APs

A

the refractory period

39
Q

describe repolarization of neurons

A

back to restong membrane potential

there is a compromised balance of electric and osmotic potentials

not just K+ that is flowing out of cell

40
Q

describe how sodium potassium pumps work

A

maintain the Na+ and K+ gradients

3 Na+ out and 2 K+ in

dependent on ATP; accounts for 20-40% of the energy consumed by the brain

41
Q

if an AP is produced in the middle of the axon, why might it spread bidirectionally when conduction of APs is generally unidirectional

A

both afferent and efferent tracts on one axon. if coming from the middle it can send both ways

42
Q

how do the voltage gated sodium channels aid in the unidirectional conduction of an AP

A

activated and then inactivated voltage gated sodium channels block backflow

absolute refractory period = unidirectional spread q

43
Q

what happens if there are multiple action potentials along one axon

A

the intensity of the stimuli is represented by frequency of the action potentials

repolarization follows the absolute refractory period

44
Q

what is a node of ranvier and what happens here in relation to AP conduction

A

small gap in the myelin sheath

only voltage gated sodium channels

there is no hyperpolarization secondary to an outflow of potassium (because there are no K+ channels present here)

only need regeneration of AP in the nodes; this gives a fast pass in the internodes (parts covered by myelin)

45
Q

where are potassium channels located on an axon

A

internodes- covered by myelin

46
Q

what is saltatory conduction

A

AP conduction jumping from one node to another

excitation occurs only at the nodes of ranvier

47
Q

what type of axons are fastest

A

larger diameter, myelinated

less resistance occurs

48
Q

`describe the giant axon of a squid

A

nonmyelinated, 800 micrometer diameter

aids in water jet propulsion; escape mechanism

diameter is almost 400 folds of 1 myelinated vertebrate axon

49
Q

describe the myelin sheath of most axons in the CNS

A

oligodendrocytes

covers multiple axons

for the few nonmyelinated axons in the CNS - astrocytes wrap around

50
Q

describe the myelin sheath in most axons of the PNS

A

schwann cells

only cover a single axon

nonmyelinated axons are bundled together and wrapped in schwann cells without myelin sheath

51
Q

describe communication between layers of myelin

A

gap junctions used for signal and molecule transportation

local ions replenish fast during repolarization

52
Q

what is multiple sclerosis

A

autoimmune injury

sporadic lesion (sudden/unpredictable)

affects the oligodendrocyte myelin in the CNS

causes problems/damage to olfactory bulb/tract and CN II (optic) in the diencephalon

53
Q

what guillain barre syndrome

A

autoimmune injury

affects schwann cell myelin of the PNS

54
Q

how do signals from neurons travel to target cells

A

neuron synapses with dendrites, soma or axons/terminals

signals sent to terminal functional cells of muscles, glands, etc

55
Q

components of electrical synapse

A

gap junction

AP bidirectional conduction

56
Q

components of a chemical synapse

A

presynaptic axon terminal contains vesicles with neurotransmitters

synaptic cleft (gap in between pre and post)

postsynaptic membrane contains receptors for neurotransmitters (logand gated and G protein coupled receptors)

57
Q

synapse definition

A

relat or transformation of electrochemical signals

58
Q

how is an electric signal turned into a chemical signal

A

AP arrives at presynaptic terminal of chemical synapse

depolarization opens the Ca2+ voltage gated channel

inflow of Ca2+ facilitates docking of vesicles on the presynaptic membrane

fuse vesicles with presynaptic membrane

neurotransmitters are released and then diffuse across synaptic cleft and bind to post synaptic membrane

59
Q

after neurotransmitters bind to the post synaptic membrane, what 2 responses can take place

A

excitation: excitatory postsynaptic potential (EPSP)
- depolarization of postsynaptic membrane
- doesnt necessarily mean AP initiation

inhibition: inhibitory posy synaptic potential (IPSP)
- hyperpolarize postsynaptic membrane
- doesnt mean AP will necessarily be inhibited

60
Q

what are ionotropic receptors of the postsynaptic membrane

A

ligand gated ion channels

fast, point to point, and specific

one AP is enough

small vesicles with different neurotransmitters sent to synaptic gap

causes depolarization or hyperpolarization of postsynaptic membrane

61
Q

what are metabotropic receptors of the postsynaptic membrane

A

GPCR, 2nd messenger system

slow, can be point to area, nonspecific

need multiple APs (longer Ca2+ opening)

small vesicles with different neurotransmitters sent to synaptic cleft

large vesicles release neurotransmitters through exocytosis

binding of neurotransmitters release G protein subunit

initiates multiple responses

62
Q

describe single postsynaptic membrane potentials

A

graded potentials

either EPSP or IPSP

dissipate due to distance and time (spatiotemporal effects)

63
Q

what is temporal summation

A

stimuli from same lcation or locations with different time frame

64
Q

what is spatial summation

A

stimuli from different locations simultaneously

65
Q

what are the results of AP summation

A

if over resting potential but lower than threshold = no AP

over threshold = AP initiated

lower than resting potential = inhibitory; hyperpolarized and refractory to be activated

66
Q

what is NMJ

A

neuromuscular junction

specialized button shaped synapes

67
Q

describe what takes place at the NMJ

A

APs arrive at motor neuron acon terminal

depolarization; opem terminal voltage gate Ca2+ channel

vesicle fuses with presynaptic membrane

Aacetylcholine is released

ACh binds to receptor on aplha subunit

this causes Na+ channels to open

depolarization of postsynaptic membrane

if above threshold, AP initiated

result = muscle contraction

68
Q

what are NMJ channelopathies

A

disorders that impair channels around the synapses

autoimmune antibodies can block or initiate degradation of channel molecules

69
Q

what is lambert eaton syndrome

A

voltage gated calcium channels affected

diminshed Ca2+ channel function = impaired fusion of ACh vesicles with membrane

result = weakness and flaccidity

70
Q

what is isaacs’ syndrome

A

affects voltage gated potassium channels

blocked K+ channel = impaired depolarization

result = continuous release of ACh = spasm

71
Q

what causes myasthenia gravis

A

directly affects ACh receptor involved in sodium channels

indirectly affects ACh receptor localization (ACh must be concentrated in the postsynaptic membrane by stabilizers MuSK and LRP4)

72
Q

what is myasthenia gravis/S&S

A

most common NMJ pathology

weakness; eye muscles often effected the worst

treatment = block acetylcholinesterase

73
Q

possible “fates” of neurotransmitters

A

reuptake
degradation
diffusion away
endocytosis by postsynaptic membrane

74
Q

two types of ACh receptors

A

nicotinic: ionotropic
- in PNS; fast EPSP
- point to point, specific, fast

Muscarinic: metabotropic, GPCR based
- in PNS: slow IPSP in smooth and cardiac muscle; point to point, specific, slow
- in CNS: modulating functions; point to area, nonspecific, slow

75
Q

what is muscarine

A

agonist of ACh receptors in brain/PNS (parasympathetic); deadly poison

76
Q

describe anterograde transportation of neurotransmitters for small molecular neurotransmitters

A

enzymes needed are synthesized in the soma

transport to terminals

synthesize small molecular neurotransmitters in terminal

77
Q

describe anterograde transportation of neurotransmitters for peptide neurotransmitters

A

prepeptide synthesized in soma

transport with enzymes to terminal

degrade to form active neurotransmitter

78
Q

describe retrograde transportation of neurotransmitters

A

molecules are recovered from terminals

transported back to cell body for reuse

79
Q

4 categories of neurotransmitters

A

amines
amino acids
neuropeptides
other small molecules and ions

80
Q

medication for agonist of Leukotriene

A

aspirin

81
Q

medication for antagonist of ACh

A

curare

82
Q

how do receptors on the postsynaptic membrane define functions of neurotransmitters

A

fast vs slow

excitatory vs inhibitory (depends on receptor and transmitter)
- i.e. glutamate can be either for different bipolar neurons in the visual system

83
Q

what are the 3 amines that overlap in their function of maintaining arousal and alert status via the ARAS

A

norepinephrine
seratonin
dopamine

84
Q
A

Year 2: NeuroBiology (10 decks)

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