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PRIN > PRIN 9 Excitable Membranes > Flashcards

PRIN 9 Excitable Membranes Flashcards

1
Q

What is Rhabdomyolysis?

A

breakdown of muscle fibers that leads to the release of muscle fiber contents (myoglobin) into the bloodstream.

Myoglobin is harmful to the kidney and often causes kidney damage.

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2
Q

How does the resting potential of a typical neuron differ from that of a cardiac/skeletal muscle cell?

A

Neuron:
-60 to -70 mV

Cardiac/Skeletal:
-80 to -90 mV

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3
Q

What is the role of a primary (Ia) sensory nerve fibre?

A

innervates nuclear bag and nuclear chain intrafusal muscle fibres.
Afferent - stretch reflex

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4
Q

What is the role of an α-motor neuron?

A

forms synapses with extrafusal muscles fibres and controls muscle contraction.

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5
Q

What is the term applied to a weak stretch that is not powerful enough to trigger depolarize?

A

receptor / generator potential

only causes a sub threshold stimulation
***graded phenomenon

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6
Q

What is the result of deformation of a Ia sensory fibre ending by stretching?

A

opens stretch-activated channels that conduct net inward Na+ current and cause the receptor potential

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7
Q

During the upstroke of the Action Potential, what predominates?

A

g-Na dominates over g-K (which is delayed)

K-Voltage channels respond more slowly to membrane depolarization

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8
Q

Status of voltage gated Na+ channels

A

Resting: CLOSED
Depolarizing; OPEN Conducting
Re-polarizing: OPEN - INACTIVATED
Hyperpolarizing: CLOSED - INACTIVATED

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9
Q

Status of voltage gated K+ channels

A

Resting: CLOSED
Depolarizing; CLOSED
Re-polarizing: OPEN CONDUCTING
Hyperpolarizing: OPEN CONDUCTING

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10
Q

What is the status of the Na+ and K+ voltage gated channels during the fall of the AP?

A

Na+ = Open Inactivated

K+ = Open Conducting

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11
Q

What is the definition of Threshold?

A

defined as the Vm at which inward Na+ current first exceeds outward K+ current.

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12
Q

Absolute VS Relative Refractoriness

A

ABS: impossible to re-stimulate AP

REL: we can make it fire, but it requires a bigger stimulus
threshold is higher

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13
Q

What causes Absolute Refractoriness?

A

the membrane is unexcitable

  • some NaV channels are still inactivated and thus are unavailable to conduct current even if the activation gate is opened
  • Some KV channels are still open and able to oppose the depolarizing effect of any Na+ current
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14
Q

What is meant by electrotonus?

A

ELECTRO-TONUS:

process by which electrical events propagate

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15
Q

What is meant by Electrotonic Decay?

A

process by which charge leaks outward, across the membrane, as current travels along the axon

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16
Q

Ra vs Rm

A

Ra = Axial Resis

Rm = Membrane Resis.

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17
Q

Formula for Length Constant (lambda)

A

lamda = square root of (Rm/Ra)

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18
Q

What happens to Ra as the diameter or the axon is increased?

A

Ra= Axial Resistance

As the “straw” becomes wider, Ra decreases.

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19
Q

Which way with the electrical current travel when Rm>Ra?

A

If the Membrane Resistance is greater than the Axial Resistance, then it will travel DOWN the axon since this is the path of least resistance

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20
Q

Which way with the electrical current travel when Ra>Rm?

A

If Axial Resistance is greater, then the current will simply leak out the membrane as there is less resistance there.

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21
Q

What TWO variables influence the rate of action potential propagation?

A

(1) DIAMETER OF FIBRE
Increasing Axon diameter decreases Ra

(2) AMOUNT OF MEMBRANE CAPACITANCE
Decreasing Capacitance decreases the time delay of voltage change across membrane

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22
Q

What forms the Myelin Sheath?

A

PNS: Schwann Cells

CNS: Oligodendrocytes

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23
Q

Where along the axon is the capacitance higher?

A

Capacitance is higher in the Nodes of Ranvier. This is where the Na+ channels are located.

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24
Q

Temporal Summation
VS
Spatial Sumation

A

TEMPORAL:
High frequency of a single input
(involves repetitive activation of a SINGLE synapse)

SPATIAL:
Simultaneous activation of multiple synapses

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25
Q

What are the two most common receptor subtypes that Glutamate acts on?

A

AMPA-gated channels:
allow Na, K.

NMDA-gated channels:
allo Na, K and Ca

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26
Q

At RMP, what is the status of the glutamate receptors?

A

AMPA-gated channels dominate

NMDA-gated channels blocked (don’t want Ca coming in at RMP)

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27
Q

What is the effect of GABA?

A

allows influx of Cl-

Prevents cell from causing an AP by clamping it back down to -70mV

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28
Q

How wide is the synaptic cleft?

A

50 nm

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29
Q

Within the post-synaptic membrane, where are the voltage-gated Na+ channels located?

A

Peri-junctional membrane

“shoulders” of each fold

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30
Q

What is the site of muscle AP initiation?

A

Peri-junctional Zone

located in the depths of the Peri-junctional Folds

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31
Q

Describe the Nicotinic ACh receptors…

A

5 subunits
requires 2 molecules of ACh
open pore conducts Na & K

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32
Q

What is the role of Synaptogamin?

A

Senses a local rise of Ca2+ in the pre-synaptic bouton and triggers the exocytosis of docked vesicles

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33
Q

What are Fasciculations?

A

VISIBLE “twitches”
Motor unit fires in response of spontaneous a-MN APs
Motor unit functional

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34
Q

Fibrillation

A

occurs after complete denervation
**Motor unit NON-functional
**individual muscle fibers spontaneously contract
NON-Visible

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35
Q

What has gone wrong in polio?

A

Virus kills cell bodies in ventral horn
Death of a-MN cell body causes Paralysis as ason degenerates and NM transmission is blocked
Some motor muscle mass is maintained

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36
Q

Guillan-Barre Syndrome

A

PNS disorder

Autoimmune Cells attack on Schwann cells degrading myelin

37
Q

What does Botulism do?

A 
Acts on PRE-synaptic mechanism
Disrupts SNARE proteins, prevents ACh release
Flaccid Paralysis (hangs limp)
38
Q

What does the Simpson Plus Test diagnose?

A

Myasthenia Gravis

39
Q

What is meant by Safety Factor

A

large amounts of vesicles ready to go

Ensures MUCH more ACh is released what what is actually required to trigger AP in muscle cell

40
Q

Myasthenia Gravis

A

Most common post-synaptic NMJ disorder

Reduces ACh binding and EPP safety factor

41
Q

How can muscle contraction be evoked?

A

(1) Volitionally
(2) Tendon Tap (brief muscle stretch)
(3) electrical stimulation of nerve
(4) direct stimulation of muscle fibres

42
Q

What comprises a motor unit?

A

a-MN and all the muscle fibres it innervates

43
Q

EMG?
EEG?
ECG?

A

EMG = Electro-myo-graphy
(electrical activity of skeletal muscles)

EEG = Electro-encephalo-graphy
(brain)

Electrocardio-graphy (heart)

44
Q

What is CMAP?

A

Compound Muscle AP

CMAP is the extracellular correlate of near-synchronous AP discharge in a number of muscle fibres

We used surface electrodes to detect fibrillations and fasciculations

45
Q

What is the Hoffman Reflex?

A

Only H-wave is evoked

Produced by using stimulation with a low intensity electric current such that only the largest Ia sensory axons are evoked

46
Q

How can the M-wave be increased?

A

M-wave will increase as stimulus is turned up

47
Q

How can propagation speed be increased?

A

(1) increase axon diameter
(2) increase transverse resistance of the cable (myelin)
(3) Decrease the capacitance of the cable

48
Q

What is the difference between the H-reflex and the spinal stretch reflex?

A

H-reflex bypasses the muscle spindle

49
Q

Orthodronic
VS
Antidromic

A

Orthodromic = Hand to Brain

Antidromic = Brain to hand

50
Q

What is CSNAP?

A

Ccompund Sensory-Nerve AP

*Represents the signal generated by AP discharge in a number of sensory axons

51
Q

Normal Nerve Conduction Velocities

A

50-70 m/s = Normal myelinated large fibre nerve

<40m/s = Damaged / demyelinated nerve

52
Q

What are muscle spindles?

A

Muscle spindles are sensory receptors within the belly of a muscle

detect changes in the length of this muscles and allow for coordinated movements

53
Q

What clinical conditions affect spinal motor neurons and/or cortico-spinal neurons?

A

ALS

Polio

54
Q

What is MEPP?

A

Motor End Plate Potential

55
Q

Describe Actin

A

Each actin filament (F-actin) is composed of a helix of globular actin (G-actin) monomers.

Each G-actin monomer has a binding site for myosin which, during rest, is covered by tropomyosin.

56
Q

What is the effect of Ca2+ in muscle cell?

A

Toponin C binds Ca2+. This causes a conformational change such that Tropomyosin gets moved out of the way.
This exposes actin’s myosin binding site.

57
Q

What is the effect of myosin head binding to the actin filament?

A

(1) reduces the affinity for ADP and Pi and so it gets released.
(2) Myosin head rotates 45 degrees
(3) ATP binds and mediates release of actin from myosin

58
Q

What is the triad?

A

Sandwich of:
SR lateral sac
T-tubule
SR lateral sac

Triads are the location where translation of the action potential into an intracellular calcium transient occurs

59
Q

What are T-tubules?

A

extensions of ECM, relays AP through cells

ensures that the action potential is carried quickly and deeply into the muscle

60
Q

Order of Receptors / Molecules connecting AP from T-Tubule into SR

A

DHPR
ryr1
Triadin
Calsequestrin

61
Q

What is DHPR

A

Dihydro-pyridine Receptor
voltage gated calcium channel

located in the cell membrane
(myoplasm on inside // ECM t-tubule on outside)

62
Q

What is the role of Calsequestrin in the SR?

A

binds/stores 50 mol calcium/mol of protein in the lumen of the SR

63
Q

Coupled VS Non-coupled ryr1

A

COUPLED ryr:
only every other ryr receptor is coupled with a DHPR

UN-COUPLED ryr:
open in response to calcium released from the coupled receptors
(get activated in response)

64
Q

What happens to Calsequestrin during an AP?

A

(1) change in configuration of ryr is transmitted via triadin to calsequestrin
(2) calsequestrin changes from a random coil to a more linear configuration
(3) Calsequestrin then releases Ca into the lumen of the SR,
(4) calcium exits into myoplasm through open ryr

65
Q

What is summation?

A

Additional stimuli, delivered prior to the time at which force has returned to baseline, causes re-opening of the ryr and superposition of the next contraction on top of the declining phase of the previous contraction

66
Q

What is Tetanus?

A

summed contractions caused by fast summation

67
Q

What causes the mrapid increase in muscle mass of body builders?

A

the CNS has been trained to increase the firing rate to maintain tetanus
maxed at about 4 weeks … plateau

68
Q

What is Hypercapnia?

A

elevated CO2

69
Q

How do we treat hypercapnia?

A

Hyperventilation

70
Q

How do we treat MH?

How do this work?

A

Dantrolene
**blocks up RYR pore and prevents Ca@+ from escaping the SR lumen
(like a cork in a bottle)

71
Q

How do we treat Acidosis?

A

NaHCO3 infusion

deliver bicarbonate

72
Q

How do we treat Hyperkalemia?

A

INSULIN
drives K+ into cells
promotes GLUT4 for glucose (irrelevant) but also stimulates Na+/K+ pumps

73
Q

What’s the problem with Hyperkalemia?

A

BAD for heart - cardiotoxic

74
Q

What is the first sign of MH?

A

increased CO2 & HR

75
Q

Under normal physiological conditions the equilibrium potential for Ca2+ (across the plasma membrane) is:

A

Positive

76
Q

When does recovery from Na channel inactivation occur?

A

during the after-hyperpolarization (AHP)

77
Q

d-tubocurarine, pancuronium and rocuronium cause skeletal muscle paralysis by:

A

acting as competitive antagonists of the nicotinic cholinergic receptor at the motor end-plate

78
Q

How does Hyperkalemia affect the RMP?

A

Hyperkalemia causes the RMP to become LESS negative because it causes the equilibrium potential for potassium to become LESS negative.

79
Q

Creatine
vs
Creatinine

A 
Creatine
...broken down to...
Creatinine
...taken to .... 
kidneys
80
Q

What does Creatine Kinase do?

A

Catalyses the reaction that transfers a phosphate group to Creatine to make a high energy compound

(skeletal muscle)

81
Q

When is the potassium conductance (gK) of the membrane larger than then sodium conductance (gNa)?

A

(1) at RMP …. and

(2) during the after hyperpolarization

82
Q

A unique and distinguishing feature of smooth muscle cells is:

A

dense bodies and caveolae

83
Q

What IS the sarcolemma?

A

Simply the cell membrane of the a skeletal muscle cell

84
Q

Which region within the sarcomere contains both Myosin & Actin?

A

A Band

85
Q

Which region within the sarcomere contains only myosin?

A

H zone

86
Q

What is the MOA of paralytic shellfish poison and other such toxins?

A

blocks voltage-gated Na channels in nerves.

depolarization can’t occur

87
Q

Hyperkalemia
VS
Hypokalemia

What is the effect of each on RMP?

A

Hyperkalemia will increases likelihood of depolarization
(make RMP less negative)

Hypokalemia will decrease likelihood
(make RMP more negative)

88
Q

How are non-depolarizing NMBA drugs eliminated?

rocuronium, mivacurium …

A

plasma cholinesterases

PRIN (13 decks)

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