9. Excitable Tissue (1) Flashcards
1
Q
What are excitable tissues? (2)
A
2
Q
What is the plasma membrane?
A
3
Q
Plasma membrane proteins
* integral proteins: (3)
A
- Hydrophobic & hydrophilic regions
- Spans the entire membrane
- Ion channels and carrier proteins
4
Q
Plasma membrane proteins
* peripheral proteins: (3)
A
- Loosely bound to the membrane surface
- Involved in cell communication & adhesion
- Membrane bound enzymes
5
Q
Ion channels: (2)
A
- made from integral proteins
- Channels are either LEAK or GATED
6
Q
Ion channels
1. Leak channels : (2)
A
- Channels are always open
- Ions move down concentration gradients
7
Q
Ion channels
2. Gated channels: (3)
A
- Ligand gated:
Respond to a binding of a ligand (chemical messenger) - Mechanically gated:
Respond to stretch and pressure - Voltage gated:
Open or close due to change in membrane potential
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
9
Q
Membrane transport:
Active transport (3)
A
- Moves molecules against concentration and electrochemical gradient
- from low to high concentration
- Requires ATP
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
11
Q
Endocytosis:
A
Plasma membrane surrounds the substance to be ingested, fuses over and pinches off a membrane enclosed vesicle
12
Q
Exocytosis:
A
Membrane enclosed secretory vesicle fuses with the plasma membrane and releases its contents to the exterior
13
Q
Electrical gradient:
* Membrane potential =
* Potential is measured in ______ (mV)
A
=difference in charge across the membrane
* millivolts (mV)
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)
15
Q
- Overall the body is electrically neutral—>
A
For every action there is a matching anion
16
Q
Distribution of ion in ICF & ECF:
A
17
Q
Distribution of ion in ICF & ECF:
A
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
19
Q
Equilibrium potential: (5)
Potassium (K+)
A
20
Q
Equilibrium potential: (5)
Sodium (Na+)
A
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
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
23
Q
- For Potassium Ek =
A
= (61) log 5mM/150mM = -90mV
24
Q
- For sodium Ena =
A
= (61) log 150mM/15mM = +60mV
25
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.
hypothetical
26
What are leak channels? (3)
* Maintain membrane potential because they are always open
* Relatively small net diffusion of Na+ ions inward
* Relatively large net diffusion of K+ ions outward
27
Leak channels:
* No diffusion of __ ions across the membrane
A-
28
* The cell membrane is more permeable to K+ ions so more potassium leaks out of the cell than sodium entering ---->
RMP is more influenced by K+
29
Na+ - K+ ATPase pump: (2)
* 3 Na+ out for every 2 K+ in
* Maintains the concentration gradient
30
What is the process of resting membrane potential? (5)
31
What does it mean when the cell membrane is at rest? (3)
* Refers to the electrical gradient across the cell membrane
* Maintained by unequal distribution of charges
* Intracellular-negative vs extracellular-positive
32
Resting membrane potential (RMP)=
= -70mV
33
How is the gradient maintained?
* Gradient maintained by Na+/K+ pump or ATPase pump
34
* Removes __ Na+ and __ K+ into the cell
3
2
35
A,B,E
36
What are Graded potentials? (4)
* 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
37
* If graded potential is large enough, can trigger an _____ _______.
action potential
38
What is an action potential? (2)
* 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
39
Action potentials
* Threshold ---->
* Serve as long distant signals ---->
- Critical potential the membrane must depolarise to for an action potential to occur
- Without losing strength as the move along
40
Membrane & ion channel changes during
an AP.
Voltage-gated Na+ channels:
41
Membrane & ion channel changes during
an AP.
Voltage-gated K+ channels:
42
What happens at resting potential? (3)
* 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
43
What happens when the threshold is reached? (2)
44
How does the action potential begin?
Na+ enters cell, causing depolarization
45
What happens at the peak of action potential?
* +30mV ------> Na+ inactivation gate closes & K+ gate opens
46
What happens during repolarisation? (3)
* The permeability of Na+ falls
* K+ activation gate opens K+ permeability
* K+ leaves cell = repolarisation
47
What happens during hyperpolarisation? (3)
* 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
What happens after hyperpolarisation (return to
resting potential)?
* Closing of K+ n gates = RMP (-70mV)
49
What is the refractory period?
* 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
Refractory period
* During repolarisation --->
* During hyperpolarisation --->
* 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
What is the role of Na+/K+ ATPase pump? (3)
* 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
Extracellular ion concentration: effects
on RMP & AP
Normal:
Hypokalemia:
Hyperkalemia:
53
Extracellular ion concentration: effects
on RMP & AP
Normal:
Hyponatremia:
Hypernatremia:
54
Extracellular ion concentration: effects
on RMP & AP
Normal:
Hypocalcaemia:
Hypercalcaemia:
55
B,C,D
56
Neuron
Input zone:
Triggering zone:
Conducting zone:
Output zone:
57
Determinants of conduction velocity:
Conduction velocities of neurons vary wide
58
The rate of impulse propagation depends largely on three factor: (3)
1. Axonal diameter
2. Degree of myelination
3. Temperature
59
Determinants of conduction velocity:
1. Axonal diameter
60
Determinants of conduction velocity: (2)
2. Degree of myelination
* Unmyelinated axon
* Myelinated axon
61
Determinants of conduction velocity: (2)
3. Temperature
* Decreased temperature= slower conduction
* Increase Temperature= faster conduction
62
Nerve fibre types, traits and functions:
63
What is Multiple Sclerosis? (4)
* 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
The Synapse
Electrical synapse: (3)
* Direct connection between two neurones
* Conduct nerve impulses faster
* Found in neural systems that require the fastest possible response, such as defensive reflexes
65
The Synapse
Chemical synapse: (3)
* 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
The Synapse:
The junction between one neuron and another neuron/muscle/gland.
67
Presynaptic terminal:
Postsynaptic terminal:
68
What is the process of synapsing? (4)
69
A,E
70
Ionotropic receptors: (3)
* Ligand-gated ion channels
* Allows ions to travel in and out of the cell
* Rapid signalling between synapses
71
Metabotropic receptors: (5)
* 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
Post Synaptic Potentials: (3)
- Excitatory postsynaptic potential
- Graded potentials
* Neurotransmitter binding to the receptor causes the opening of chemically gated Na+ channels
* Net movement of positive ions into cell (Na+)
* Depolarisation
73
Post Synaptic Potentials: (3)
- Inhibitory postsynaptic potential
* 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
Summation:
* The sum of excitatory or inhibitory post synaptic potentials
75
Temporal summation:
76
Spatial summation:
77
Neurotransmitters
* Biogenic amines: (6)
* Acetylcholine
* Dopamine
* Adrenaline
* Noradrenaline
* Serotonin
* Histamine
78
Neurotransmitters
* Amino acids: (2x2)
Excitatory:
*Glutamate
* Aspartate
Inhibitory:
*Glycine
*Gamma-aminobutyric acid (GABA)
79
3. Other common transmitters
Peptides:
Lipids:
Gases:
Peptides: GIT hormones e.g. CCK, VIP, gastrin.
Lipids: e.g. Anandamide (binds cannabinoid receptors) –euphoria.
Gases: NO (from arginine – vasodilation – erection)
80
What is Glutamate? (3)
* 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
Glutamate:
* ______ from traumatic brain injury and stroke recovery
Disturbances
82
What is Gamma amino butyric acid (GABA)?
83
What does Gamma amino butyric acid (GABA) bind to?
* Binds to 2 receptors GABA(A) (ionotropic) and GABA(B) (metabotropic)
84
* GABAA :
* GABAB:
*Responsible for reducing stress and anxiety
* GABAA : increases influx of Cl- into cell – membrane potential becomes more negative
(hyperpolarisation).
* GABAB: increases K+ conductance out of cell
85
* GABAA :
* GABAB:
*Responsible for reducing stress and anxiety
* GABAA : increases influx of Cl- into cell – membrane potential becomes more negative
(hyperpolarisation).
* GABAB: increases K+ conductance out of cell
86
What is the formula of Acetylcholine?
87
Acetylcholine
* Location: (2)
* Plays important role in the Peripheral Nervous System
* Acts as the neurotransmitter at neuromuscular junction
88
Acetylcholine
* Nicotinic receptors : Ionotropic (2)
* Muscarinic receptors: Metabotropic (2)
* Nicotinic receptors:Ionotropic
- Produce excitatory responses
- (Increase Na+ influx – depolarisation
* Muscarinic receptors: Metabotropic
- Both excitatory and inhibitory
- Muscarinic blocker: Atropin
89
How is Acetylcholine (Ach) degraded? (2)
* Degraded by acetylcholinesterase into acetic acid and choline
* Choline transported back into presynaptic terminal
90
How is Adrenaline/Noradrenaline made?
91
Where is Adrenaline/Noradrenaline found?
* Found throughout CNS and at junction between nerves and smooth muscle in ANS
92
Adrenaline/Noradrenaline:
* Excitatory and inhibitory effects on post-synaptic membrane and _______.
metabotropic
93
How is Adrenaline/Noradrenaline binded?
* 2 receptors that NA can bind to: α-adrenergic and β-adrenergic receptors – further studied in ANS
94
How is Adrenaline/Noradrenaline degraded?
* Degradation by MOA (monoamine oxidase) and COMT ( catecholamine methyl transferase)
95
A,D,E
96
What is Skeletal muscle? (4)
* 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
What is Motor unit recruitment in skeletal muscle? (3)
* 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
Skeletal muscle structure:
99
Scarolemma:
Sarcoplasmic reticulum:
Transverse (T) tubule:
100
Skeletal muscle: neuromuscular junction
How is an action potential generated? (7)
101
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
negative
Na+
leak
K+
Threshold
102
Excitation-contraction coupling in skeletal muscle: (8)
Process in which muscle AP initiate calcium signals which activate a contraction/ relaxation cycle ----> Muscle twitch
103
Skeletal muscle contraction: (3)
104
Cross bridge cycle:
STEP 1
105
Cross bridge cycle:
STEP 2
106
Cross bridge cycle:
STEP 3
107
Cross bridge cycle:
STEP 4
108
Skeletal Muscle: Steps in contraction &
relaxation
CONTRACTION: (7)
109
Skeletal Muscle: Steps in contraction &
relaxation
RELAXATION: (3)
110
Interpret the diagram:
111
Drugs and Poisons affecting Muscle Contraction
- Curare (tubocurarine): (4)
– ACh antagonist
– Binds strongly to ACh receptor on motor end plate
(nicotinic)
– AP cannot occur in muscle – paralysis occurs
– Death from respiratory failure
112
Drugs and Poisons affecting Muscle Contraction
- Organo-phosphates: (3)
– 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
Drugs and Poisons affecting Muscle Contraction
- Botulinum Toxin: (4)
* 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
Drugs and Poisons affecting Muscle Contraction
- Myasthenia gravis: (4)
– 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
B,C,E
