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MBBCh 2- PHSL2004A > 9. Excitable Tissue (1) > Flashcards

9. Excitable Tissue (1) Flashcards

1
Q

What are excitable tissues? (2)

A
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2
Q

What is the plasma membrane?

A
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3
Q

Plasma membrane proteins
* integral proteins: (3)

A
  • Hydrophobic & hydrophilic regions
  • Spans the entire membrane
  • Ion channels and carrier proteins
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4
Q

Plasma membrane proteins
* peripheral proteins: (3)

A
  • Loosely bound to the membrane surface
  • Involved in cell communication & adhesion
  • Membrane bound enzymes
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5
Q

Ion channels: (2)

A
  • made from integral proteins
  • Channels are either LEAK or GATED
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6
Q

Ion channels
1. Leak channels : (2)

A
  • Channels are always open
  • Ions move down concentration gradients
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7
Q

Ion channels
2. Gated channels: (3)

A
  1. Ligand gated:
    Respond to a binding of a ligand (chemical messenger)
  2. Mechanically gated:
    Respond to stretch and pressure
  3. Voltage gated:
    Open or close due to change in membrane potential
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8
Q

Membrane transport:
Passive transport (3)

A
  • Moves molecules down a concentration and electrochemical gradient
  • No ATP required
  • Molecules will move from high to low concentration
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9
Q

Membrane transport:
Active transport (3)

A
  • Moves molecules against concentration and electrochemical gradient
  • from low to high concentration
  • Requires ATP
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10
Q

Membrane transport:
Vesicular transport (3)

A
  • Transports macromolecules too large to enter or leave the cell
  • Active method of transport
  • Two types: endocytosis & exocytosis
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11
Q

Endocytosis:

A

Plasma membrane surrounds the substance to be ingested, fuses over and pinches off a membrane enclosed vesicle

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12
Q

Exocytosis:

A

Membrane enclosed secretory vesicle fuses with the plasma membrane and releases its contents to the exterior

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13
Q

Electrical gradient:
* Membrane potential =
* Potential is measured in ______ (mV)

A

=difference in charge across the membrane
* millivolts (mV)

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14
Q
  • Electrical gradient —->
A

—> Positive ions are attracted to negative ions and repelled by other positive ions Ions move across membrane to reach electrical equilibrium (same amount of +’ve & -‘ve ions on each side)

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15
Q
  • Overall the body is electrically neutral—>
A

For every action there is a matching anion

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16
Q

Distribution of ion in ICF & ECF:

A
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17
Q

Distribution of ion in ICF & ECF:

A
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18
Q

Equilibrium potential: (2)

A
  • Membrane potential that exactly opposes a given concentration gradient
  • The membrane potential at which ion influx (K+ or Na+) and ion efflux is at electrochemical equilibrium
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19
Q

Equilibrium potential: (5)
Potassium (K+)

A
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20
Q

Equilibrium potential: (5)
Sodium (Na+)

A
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21
Q

Nernst potential: (2)

A
  • Potential level across a membrane that will prevent net diffusion of an ion
  • Used to calculate the equilibrium potential of a specific ion
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22
Q

E =
61 = constant
Z =
Co =
Ci =

A

E = Equilibrium potential (sometimes also Vm)
61 = constant
Z = ions valence. Z= 1 for K+ and Na+
Co = concentration of ion on outside of cell
Ci = concentration of ion on inside of ce

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23
Q
  • For Potassium Ek =
A

= (61) log 5mM/150mM = -90mV

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24
Q
  • For sodium Ena =
A

= (61) log 150mM/15mM = +60mV

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25
Q

Neither K+ nor Na+ exists alone, so equilibrium potentials are not present in the body cells. They exist only in _______ conditions. Both K+ and Na+ must be taken into account.

A

hypothetical

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26
Q

What are leak channels? (3)

A
  • Maintain membrane potential because they are always open
  • Relatively small net diffusion of Na+ ions inward
  • Relatively large net diffusion of K+ ions outward
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27
Q

Leak channels:
* No diffusion of __ ions across the membrane

A

A-

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28
Q
  • The cell membrane is more permeable to K+ ions so more potassium leaks out of the cell than sodium entering —->
A

RMP is more influenced by K+

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29
Q

Na+ - K+ ATPase pump: (2)

A
  • 3 Na+ out for every 2 K+ in
  • Maintains the concentration gradient
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30
Q

What is the process of resting membrane potential? (5)

A
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31
Q

What does it mean when the cell membrane is at rest? (3)

A
  • Refers to the electrical gradient across the cell membrane
  • Maintained by unequal distribution of charges
  • Intracellular-negative vs extracellular-positive
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32
Q

Resting membrane potential (RMP)=

A

= -70mV

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33
Q

How is the gradient maintained?

A
  • Gradient maintained by Na+/K+ pump or ATPase pump
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34
Q
  • Removes __ Na+ and __ K+ into the cell
A

3
2

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35
Q
A

A,B,E

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36
Q

What are Graded potentials? (4)

A
  • Local changes in membrane potential
  • Depends on the strength and duration of triggering event
  • Serve as short-distance signals
  • Lose strength as they move along
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37
Q
  • If graded potential is large enough, can trigger an _____ _______.
A

action potential

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38
Q

What is an action potential? (2)

A
  • The rapid change in electrical potential that part of a nerve cell undergo when a nerve impulse is generated
  • If a graded potential is large enough to reach threshold then an action potential is generated
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39
Q

Action potentials
* Threshold —->
* Serve as long distant signals —->

A
  • Critical potential the membrane must depolarise to for an action potential to occur
  • Without losing strength as the move along
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40
Q

Membrane & ion channel changes during
an AP.

Voltage-gated Na+ channels:

A
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41
Q

Membrane & ion channel changes during
an AP.

Voltage-gated K+ channels:

A
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42
Q

What happens at resting potential? (3)

A
  • All activation gates are closed Na+ inactivation (h gate) is open
  • No Na+ moves into the cell for a high conc. in ECF to a low conc. in ICF
  • No K+ can move out of the cell for a high conc. in ICF to low conc. in ECF
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43
Q

What happens when the threshold is reached? (2)

A
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44
Q

How does the action potential begin?

A

Na+ enters cell, causing depolarization

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45
Q

What happens at the peak of action potential?

A
  • +30mV ——> Na+ inactivation gate closes & K+ gate opens
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46
Q

What happens during repolarisation? (3)

A
  • The permeability of Na+ falls
  • K+ activation gate opens K+ permeability
  • K+ leaves cell = repolarisation
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47
Q

What happens during hyperpolarisation? (3)

A
  • Na+ activation closes and inactivation gate opens
  • Further outward movement of K+ through still-open K+ channel = briefly hyper-polarises membrane
  • Closing of K+ channels Slow process which is why some K+ still leaks out of cell
48
Q

What happens after hyperpolarisation (return to
resting potential)?

A
  • Closing of K+ n gates = RMP (-70mV)
49
Q

What is the refractory period?

A
  • Distinguishes APs from graded potentials
  • Limits the rates at which signals can be transmitted from a neuron
  • Ensures the one way movement of action potentials from cell body to axon terminal
50
Q

Refractory period
* During repolarisation —>
* During hyperpolarisation —>

A
  • During repolarisation Na+ channels closes and cannot open
    Another AP cannot occur = refractory period
  • During hyperpolarisation Harder to generate an AP but not impossible = relative refractory period (because membrane is more negative)
51
Q

What is the role of Na+/K+ ATPase pump? (3)

A
  • For an AP to occur —–> Gradients of Na+ and K+ must be kept constant
  • if nothing replaced K+ inside cell & Na+ outside —-> Gradients would be destroyed
  • Pump maintains these gradients
52
Q

Extracellular ion concentration: effects
on RMP & AP

Normal:
Hypokalemia:
Hyperkalemia:

A
53
Q

Extracellular ion concentration: effects
on RMP & AP

Normal:
Hyponatremia:
Hypernatremia:

A
54
Q

Extracellular ion concentration: effects
on RMP & AP

Normal:
Hypocalcaemia:
Hypercalcaemia:

A
55
Q
A

B,C,D

56
Q

Neuron
Input zone:
Triggering zone:
Conducting zone:
Output zone:

A
57
Q

Determinants of conduction velocity:

A

Conduction velocities of neurons vary wide

58
Q

The rate of impulse propagation depends largely on three factor: (3)

A
  1. Axonal diameter
  2. Degree of myelination
  3. Temperature
59
Q

Determinants of conduction velocity:
1. Axonal diameter

A
60
Q

Determinants of conduction velocity: (2)
2. Degree of myelination

A
  • Unmyelinated axon
  • Myelinated axon
61
Q

Determinants of conduction velocity: (2)
3. Temperature

A
  • Decreased temperature= slower conduction
  • Increase Temperature= faster conduction
62
Q

Nerve fibre types, traits and functions:

A
63
Q

What is Multiple Sclerosis? (4)

A
  • Autoimmune disease: Immune system attacks myelin sheath
  • Nerve fibres throughout nervous system lose their myelin
  • Scar – “sclerosis” – forms at the site of damage and blocks action potential
    propagation
  • Leads to decreased conduction velocity
64
Q

The Synapse
Electrical synapse: (3)

A
  • Direct connection between two neurones
  • Conduct nerve impulses faster
  • Found in neural systems that require the fastest possible response, such as defensive reflexes
65
Q

The Synapse
Chemical synapse: (3)

A
  • Chemical messenger transmits information across a space separating the 2 neurons
  • Axon terminal form part of the pre-synaptic neuron
  • Dendrites form part of the post-synaptic neuron
66
Q

The Synapse:

A

The junction between one neuron and another neuron/muscle/gland.

67
Q

Presynaptic terminal:
Postsynaptic terminal:

A
68
Q

What is the process of synapsing? (4)

A
69
Q
A

A,E

70
Q

Ionotropic receptors: (3)

A
  • Ligand-gated ion channels
  • Allows ions to travel in and out of the cell
  • Rapid signalling between synapses
71
Q

Metabotropic receptors: (5)

A
  • Do not have a channel
  • Ligand binding activates the receptor = activates G-proteins on inside of cell membrane
  • G-protein. = activates 2nd messenger molecule
  • Slower
  • Effects last longer
72
Q

Post Synaptic Potentials: (3)
- Excitatory postsynaptic potential
- Graded potentials

A
  • Neurotransmitter binding to the receptor causes the opening of chemically gated Na+ channels
  • Net movement of positive ions into cell (Na+)
  • Depolarisation
73
Q

Post Synaptic Potentials: (3)
- Inhibitory postsynaptic potential

A
  • Neurotransmitter binding to the receptor causes opening of chemically gated K+ and Cl-
    channels
  • K+ flows out of cell, Cl- flows into cell (down concentration gradients)
  • Hyperpolarisation
74
Q

Summation:
* The sum of excitatory or inhibitory post synaptic potentials

A
75
Q

Temporal summation:

A
76
Q

Spatial summation:

A
77
Q

Neurotransmitters
* Biogenic amines: (6)

A
  • Acetylcholine
  • Dopamine
  • Adrenaline
  • Noradrenaline
  • Serotonin
  • Histamine
78
Q

Neurotransmitters
* Amino acids: (2x2)

A

Excitatory:
*Glutamate
* Aspartate
Inhibitory:
*Glycine
*Gamma-aminobutyric acid (GABA)

79
Q
  1. Other common transmitters
    Peptides:
    Lipids:
    Gases:
A

Peptides: GIT hormones e.g. CCK, VIP, gastrin.
Lipids: e.g. Anandamide (binds cannabinoid receptors) –euphoria.
Gases: NO (from arginine – vasodilation – erection)

80
Q

What is Glutamate? (3)

A
  • Most commonly found excitatory neurotransmitter in the brain
  • synthesised from a-ketoglutarate ( kerbs cycle intermediate)
  • Involved in most aspects of normal brain functioning i.e. cognition, memory, learning
81
Q

Glutamate:
* ______ from traumatic brain injury and stroke recovery

A

Disturbances

82
Q

What is Gamma amino butyric acid (GABA)?

A
83
Q

What does Gamma amino butyric acid (GABA) bind to?

A
  • Binds to 2 receptors GABA(A) (ionotropic) and GABA(B) (metabotropic)
84
Q
  • GABAA :
  • GABAB:
    *Responsible for reducing stress and anxiety
A
  • GABAA : increases influx of Cl- into cell – membrane potential becomes more negative
    (hyperpolarisation).
  • GABAB: increases K+ conductance out of cell
85
Q
  • GABAA :
  • GABAB:
    *Responsible for reducing stress and anxiety
A
  • GABAA : increases influx of Cl- into cell – membrane potential becomes more negative
    (hyperpolarisation).
  • GABAB: increases K+ conductance out of cell
86
Q

What is the formula of Acetylcholine?

A
87
Q

Acetylcholine
* Location: (2)

A
  • Plays important role in the Peripheral Nervous System
  • Acts as the neurotransmitter at neuromuscular junction
88
Q

Acetylcholine
* Nicotinic receptors : Ionotropic (2)

  • Muscarinic receptors: Metabotropic (2)
A
  • Nicotinic receptors:Ionotropic
  • Produce excitatory responses
  • (Increase Na+ influx – depolarisation
  • Muscarinic receptors: Metabotropic
  • Both excitatory and inhibitory
  • Muscarinic blocker: Atropin
89
Q

How is Acetylcholine (Ach) degraded? (2)

A
  • Degraded by acetylcholinesterase into acetic acid and choline
  • Choline transported back into presynaptic terminal
90
Q

How is Adrenaline/Noradrenaline made?

A
91
Q

Where is Adrenaline/Noradrenaline found?

A
  • Found throughout CNS and at junction between nerves and smooth muscle in ANS
92
Q

Adrenaline/Noradrenaline:
* Excitatory and inhibitory effects on post-synaptic membrane and _______.

A

metabotropic

93
Q

How is Adrenaline/Noradrenaline binded?

A
  • 2 receptors that NA can bind to: α-adrenergic and β-adrenergic receptors – further studied in ANS
94
Q

How is Adrenaline/Noradrenaline degraded?

A
  • Degradation by MOA (monoamine oxidase) and COMT ( catecholamine methyl transferase)
95
Q
A

A,D,E

96
Q

What is Skeletal muscle? (4)

A
  • Multinucleated
  • The number of fibres innervated by a single motor neurone varies
  • On motor unit activation —–> All fibres contract
  • Each muscle consists of numerous intermingled motor units
97
Q

What is Motor unit recruitment in skeletal muscle? (3)

A
  • The mor motor units are stimulated/ recruited the stronger the contraction
  • increased stimulus strength = more motor units recruited = stronger contractions
  • This allows for gradation in strength of contraction
98
Q

Skeletal muscle structure:

A
99
Q

Scarolemma:
Sarcoplasmic reticulum:
Transverse (T) tubule:

A
100
Q

Skeletal muscle: neuromuscular junction
How is an action potential generated? (7)

A
101
Q

Action potential: Skeletal muscle
* RMP of skeletal muscle is even more _____ than that of a neurone since skeletal muscle is even less permeable to ____
* Skeletal muscle has less Na+____ channels
* RMP of skeletal muscle is closer to the equilibrium potential of ____
* _______ potential is lower than that of a neurone

A

negative
Na+
leak
K+
Threshold

102
Q

Excitation-contraction coupling in skeletal muscle: (8)
Process in which muscle AP initiate calcium signals which activate a contraction/ relaxation cycle —-> Muscle twitch

A
103
Q

Skeletal muscle contraction: (3)

A
104
Q

Cross bridge cycle:
STEP 1

A
105
Q

Cross bridge cycle:
STEP 2

A
106
Q

Cross bridge cycle:
STEP 3

A
107
Q

Cross bridge cycle:
STEP 4

A
108
Q

Skeletal Muscle: Steps in contraction &
relaxation

CONTRACTION: (7)

A
109
Q

Skeletal Muscle: Steps in contraction &
relaxation

RELAXATION: (3)

A
110
Q

Interpret the diagram:

A
111
Q

Drugs and Poisons affecting Muscle Contraction
- Curare (tubocurarine): (4)

A

– ACh antagonist
– Binds strongly to ACh receptor on motor end plate
(nicotinic)
– AP cannot occur in muscle – paralysis occurs
– Death from respiratory failure

112
Q

Drugs and Poisons affecting Muscle Contraction
- Organo-phosphates: (3)

A

– Inhibit AChE
– As ACh is not destroyed / no re-uptake, ion channels in end-plate remain open, producing a maintained
depolarization of the end plate and muscle.
– Therefore, muscle cannot contract in response to
subsequent nerve stimulation —> Paralysis; death (lung muscles).

113
Q

Drugs and Poisons affecting Muscle Contraction
- Botulinum Toxin: (4)

A
  • Blocks synapsin 1
  • Blocks release of Ach in response to motor neurone AP
  • Botulism = form of food poisoning
  • Diaphragm can’t contract = respiratory failure
114
Q

Drugs and Poisons affecting Muscle Contraction
- Myasthenia gravis: (4)

A

– Caused by abnormal antibodies carried in blood.
(Autoimmune neuromuscular disease)
– Antibodies bind to cholinergic (nicotinic) receptors at NMJ.
– Decrease in # of ACh receptors.
– Progressive fatigue & generalized weakness

115
Q
A

B,C,E

MBBCh 2- PHSL2004A (19 decks)

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