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Human Physiology > Neuronal Physiology > Flashcards

Neuronal Physiology Flashcards

1
Q

Factors affecting ion flux across membranes

A
  1. Ion (membrane) conductance
  2. Ion gradient
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2
Q

Renal systems maintains?

A

Near constant internal environment, so ion gradient changes are minimal

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3
Q

Unexcitable membrane

A

Dendrite and cell body
- don’t contain voltage-gated channels

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4
Q

Excitable membrane

A

Axon hillock and axon
- contain voltage-gated channels

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5
Q

Axons can be what in length?

A

up to feet

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6
Q

When we open channels…

A

Generate ion flux which changes membrane potential

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7
Q

Action potential syn

A

Nerve impulse, spike

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8
Q

Axon syn

A

Nerve fiber

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9
Q

Axon terminal syn

A

Synaptic knob, terminal bouton, presynaptic terminal, axon knob

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10
Q

Cell body syn

A

Soma

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11
Q

Cell membrane/Plasma membrane syn

A

Axolemma

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12
Q

Two types of disrupting events

A
  1. Graded potentials
  2. Action potentials
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13
Q

Graded potentials

A

A change in membrane potential that varies in size
a. Magnitude of response is directly proportional to the magnitude of stimulus
b. Does not transmit over long distances (decremental conduction)
c. Effects can be summated, added together
- found in unexcitable membrane
- either ligand-gated or mechanically-gated channels

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14
Q

Graded potential is relative to?

A

Resting potential

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15
Q

Graded potentials decrease in?

A

Strength as they spread out from the point of origin due to current leak out of the cell

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16
Q

Additive effect

A

Na+ influx and Ca2+ influx
- calcium is similar to sodium as it depolarizes the cell and has a driving force into the cell

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17
Q

Action potential

A

Change in a membrane potential of excitable membrane
a. Action potential are “All-or-nothing”, magnitude is “fixed” after threshold
b. Capable of transmitting over long distances (> 1m)
c. Do not summate
- found in neurons & some are non-neural tissue (ex: muscle)

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18
Q

Threshold

A

The MINIMUM stimulus necessary to elicit a response (action potential)

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19
Q

An above threshold stimulus applied to the membrane can cause a change in?

A

Voltage, resulting in the opening of voltage-gated channels
ex: during the rising phase of an AP, gNa (mem. conductance for Na+) can increase 600x over resting values

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20
Q

Membranes also possess voltage-gated K+ channels which open in response to?

A

Changes in membrane potential, but are 10x slower than Na+ channels
- increased K+ conductance results in K+ efflux & repolarization
- K+ channels only close when membrane potential returns to normal (-70mV)

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21
Q

K+ has a huge driving force…

A

Outside of the cell

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22
Q

Refractory period

A

Time period after an action potential in which Na+ gates may be inactive and the K+ channels may be open so that a second AP is impossible

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23
Q

Voltage-gated Sodium Channel

A
  1. Closed but capable of opening at first
    —at resting potential (-70mV)
    2 Then open (activated)
    —from threshold to peak potential (-50mv to +30mV)
  2. Closed/locked and not capable of opening (inactivated)
    —from peak to resting potential (30mV to -70mV)
    Essentially takes on 3 shapes
    - Na+ has a huge driving force into cell
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24
Q

Triggering event takes cell to?

A

Threshold

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25
Q

Voltage-gated Potassium Channel

A
  1. Initially closed
    —At resting potential; delayed opening triggered at threshold; remains closed to peak potential (-70mV to 30mV)
  2. Then opened
    —From peak potential through after hyperpolarization (30mV to -80mV)
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26
Q

Rising phase

A

Caused by Na+ influx
- depolarizing

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27
Q

Falling phase

A

Caused by K+ efflux
- repolarizing

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28
Q

Na+ movement

A

Essentially going down the membrane
- works on patches, moves adjacently
- lots of action potentials happening in chunks of axon and moved along

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29
Q

Action potential recurring

A

Positive feedback loop

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30
Q

Because of refractory period…

A

action potential only moves one direction

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31
Q

For a depolarization to occur…

A

Na+ (or Ca2+) influx must exceed K+ efflux
- disproportionate ion flux

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32
Q

Rate of transmission is dependent on?

A

Axon diameter
- wider diameter has lower resistance

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33
Q

AP’s usually begin at?

A

Excitable tissue of the axon hillock

34
Q

AP is unidirectional due to?

A

Refractory period
- however, leakage of charge occurs during transmission

35
Q

Local current flow

A

Movement of AP from one region to neighboring region (moving down axon)
- limitations = slow
- all muscle cells use this

36
Q

Myelin sheath

A

Insulator for axon
- multiple layers of cell mem
- wrap around & suck out cytoplasm
- membranes generally don’t let ions in

37
Q

AP is open for?

A

4-5 msec

38
Q

Neuroglial (glial) cells

A

Assist cells for neurons
- Schwann
- Oligodendrocytes
- Astrocytes
- Microglia

39
Q

Schwann cells

A

Myelin forming cells of PNS
- help to prevent leakage of charge

40
Q

Oligodendrocytes

A

Myelin forming cells of CNS
- help to prevent leakage of charge
- extends & wraps several cells (1:4 & 1:6)

41
Q

Astrocytes

A

Star shaped cells that surround unmyelinated cells that give structural support

42
Q

Microglia

A

????
- modified immune cells
- act as scavengers

43
Q

Myelinated cells each have to be what?

A

Individually taken care of
- uses a lot of energy

44
Q

Node of Ranvier

A

Section of unmyelinated axon membrane b/t two Schwann cells
- only space consisting of VG channels

45
Q

Schwann cell nucleus

A

Pushed to outside of myelin sheath

46
Q

Saltatory conduction

A

AP propagation by “jumping” from node to node in myelinated fibers
- moving along an axon
- normal nerve conduction in myelinated axons

47
Q

Loss of myelination results in loss of?

A

AP signal
- causes multiple sclerosis (MS)

48
Q

Large axons

A

Offer less resistance to current flow, but occupy space
- 0.8 mm diameter (pencil lead size)

49
Q

Small myelinated axons

A

Conduct AP’s as rapidly as large unmyelinated axons

50
Q

Largest cells in our body are

A

A-alpha
- part of our somatic nervous sys

51
Q

Somatic nervous system goes to?

A

Skeletal muscles

52
Q

Myelin comes at a cost, but…

A

Is also a benefit as it is faster
- size & myelin both have effects

53
Q

Synapse

A

Anatomically specialized junction b/t 2 cells, where the electrical activity of one cell influences the excitability of another

54
Q

Two types of synapses

A
  • Electrical (ions)
  • Chemical (messenger): neurotransmitter flow b/t a neuron & an adjacent cell
55
Q

Gap junctions are synapses found in?

A

Cardiac

56
Q

Once an AP reaches the end of an axon, how is the signal transmitted to adjacent cells?

A
  1. AP travels down axon to terminal bouton
  2. Depolarization open voltage-gated calcium channels leading to calcium influx
  3. Calcium influences cytoskeleton & causes fusion of neurotransmitters filled vesicles w/ plasma membrane
  4. Neurotransmitter (NT) released into synaptic cleft * diffuse across to postsynaptic mem
  5. NT binds to receptors on postsynaptic mem leading to graded potential
    — dealing w/ unexcitable membrane (ligand-gated channels)—> open a channel (NTs)
57
Q

Fast postsynaptic graded potentials

A

a. Excitatory Post-Synaptic Potential (EPSP)
b. Inhibitory Post-Synaptic Potential (IPSP)

58
Q

Excitatory Post-Synaptic Potential (EPSP)

A

Depolarizing graded potential in postsynaptic neuron
- Na+ pr Ca2+ influx
- Does not necessarily meet threshold

59
Q

Inhibitory Post-Synaptic Potential (IPSP)

A

inhibits depolarization in postsynaptic neuron
- makes it hard to depolarize postsynaptic neuron
–hyperpolarization from K+ efflux
–stabilization by Cl- channels opening

60
Q

Grand Post-Synaptic Potential (GPSP)

A
  • The cumulative change in mem potential
  • All EPSPs + IPSPs
61
Q

Two methods to enhance GPSP to initiate an AP

A
  1. Temporal summation
  2. Spatial summation
62
Q

Temporal summation

A

Summation of 2 stimuli from the SAME neuron that follow one another in time

63
Q

Spatial summation

A

Summation of graded potentials from several sources
- also close in time, NOT from same neruon

64
Q

Common neurotransmitters

A
  1. Acetylcholine (Ach)
  2. Biogenic Amines
  3. AA
  4. Misc.
65
Q

Acetylcholine (Ach)

A

In a class by itself
- An ester & choline
- most abundant NT

66
Q

Biogenic Amines

A

AA derivatives
a. Primary catecholamines: Epi, NorEpi, Dopamine (both a hormone & NT, based on the way it travels)
b. Others:
—serotonin is made from tryptophan
—histamine is made from histidine

67
Q

AA

A

a. Glutamate: excitatory
b. Asparate
c. GABA
d. Glycine

68
Q

Misc

A

a. Neuropeptides (substance P, opioid pep.)
b. Purines (AMP & ATP)
c. Gases (NO & CO)
d. Lipids (Eicosanoids)

69
Q

All post-synaptic (in NS) work either by:

A
  • Ligand-gated ion channels
  • GPCR
70
Q

Postsynaptic receptors

A
  1. Cholinergic
  2. Adrenergic
71
Q

Cholinergic

A

Respond to Ach
a. nicotinic
b. muscarinic

72
Q

Nicotinic

A

Receptor acts as Na+ (and K+) channel
- monovalent cationic channel (+1)
- biggest effect is Na+ influx = depolarization = excitation
- found on skeletal muscle (somatic NS)
- found in autonomic PNS
- found in CNS

73
Q

Muscarinic

A

Utilizes G-protein & 2nd messenger sys
- mult. subtypes of receptor
- found in autonomic PNS
- found in CNS
(NOT in skeletal muscle)

74
Q

Adrenergic

A

Respond to Epi/NE
a. Alpha 1,2
b. Beta 1,2

75
Q

Alpha 1,2

A

Utilize 2nd messenger sys. (PL-C & cAMP)

76
Q

Beta 1,2

A

Utilize cAMP 2nd messenger sys

77
Q

Enzymes that degrade NTs

A
  • Ach degraded by: Acetylcholinesterase (Ache)
  • Epi/NE degraded by: monoamino oxidase (MAO) & catechol-o-methyltransferase (CoMT)
78
Q

Enzymes are outside of?

A

postsynaptic cell

79
Q

No summation

A

Two graded potentials will not cause an action potential if they are far apart in time

80
Q

Summation causing action potential

A

If two subthreshold potentials arrive at the trigger zone within a short period of time, they may sum and create an action potential

81
Q

Convergence

A

Neurons are constantly being influenced/impacted by other neurons

82
Q

Divergence

A

Same messenger, but can have diff responses depending on diff receptors
- Our axon can split
- Not limited to one or two
- Colateral = AP goes down both axons

Human Physiology (8 decks)

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