Cellular Electrophysiology & Nerve Flashcards
1
Q
what are the roles of the cell membrane?
A
compartmentalisation, control of fluxes, attachment of enzymes/cytoskeleton/secondary messenger models, sensory receptors, binding sites for hormones, secretion by exocytosis, uptake by pinocytosis, endocytosis and phagocytosis
2
Q
what are the variables controlled by homeostasis?
A
concentration of ions, control of chemicals, physical characteristics of blood, concentration of blood gases, number of RBCs and WBCs, metabolic rate, body weight, bone density, muscle mass, temperature, heart rate
3
Q
what is gain?
A
amount of output signal per unit error
4
Q
what is a high gain?
A
large output from a small error
5
Q
what is a low gain?
A
small output from a large error
6
Q
what is feed-forward control?
A
predicted change in output necessary to maintain a constant level
7
Q
what is the cephalic phase of insulin release?
A
feed-forward stage, when food smelt/enters mouth insulin released- minimises rise in blood glucose
8
Q
what are the properties of hormones?
A
released into blood from endocrine glands, low concentrations so small changes have large effect, high specificity of binding, signal from 1 cell type to another
9
Q
what are the types of hormone receptor?
A
GPCRs and RTKs
10
Q
what type of receptor is the glucagon receptor?
A
a GPCR
11
Q
what type of receptor is an insulin receptor?
A
a RTK
12
Q
what is an ionotropic receptor?
A
coupled to ion channels, opens ion channel, used by fast neurotransmitters
13
Q
what is an autocrine signalling molecule?
A
signalling molecule released by same cell type it acts on
14
Q
what is a paracrine signalling molecule?
A
signalling molecule that acts locally via extracellular space on different cell type
15
Q
what is the adenohypophysis?
A
anterior pituitary
16
Q
what does the hypothalamus release in the cortisol release system?
A
CRH (corticotrophin releasing hormone)
17
Q
what does the pituitary release in the cortisol release system?
A
ACTH (adrenocorticotropic hormone)
18
Q
what does ACTH do?
A
inhibits CRH release, stimulates cortisol release and MSH release
19
Q
what causes CTH release from the hypothalamus?
A
stress, starvation
20
Q
what does CRH do?
A
stimulates ACTH release
21
Q
what releases cortisol?
A
the adrenal cortex
22
Q
what does the adrenal cortex do in cortisol release?
A
releases cortisol
23
Q
what does cortisol do?
A
increases blood glucose, reduces inflammation, inhibits CRH and ACTH release
24
Q
what happens in Addison’s disease?
A
adrenal gland can’t produce enough cortisol - leads to weakness, fatigue and hypotension, less inhibition so CRH and ACTH levels rise
25
what does MSH lead to?
more melanocytes so more pigmentation
26
what cause veterinary Cushing's
excess ACTH from pituitary gland causes high cortisol levels
27
what are the properties of water? (6)
high boiling point, density decreases when freezes, high specific heat capacity and latent heat of vaporisation, electrical dipole, dissociates spontaneously and reversible, can act as solvent for ions
28
what is charge?
quantity of electricity (measure in coulombs) due to atoms/molecules that have gained or lost electrons
29
what is voltage?
difference in charge relative to another region (in volts)
30
what is capacitance?
amount of charge stored per volt
31
what is current?
number of charged particles flowing past a point per unit time
32
what is resistance?
restriction of flow of current
33
what is Ohm's law?
voltage= current x resistance
34
what is resting potential?
potential across cell membrane at rest
35
what are excitable cells?
cells that can change their state from resting to excited and back again using bioelectricity
36
what is the cell membrane of nerve cells and muscle fibres composed of?
lipophilic phospholipid bilayer, transmembrane proteins that form ion channels and pumps and allow charged ions to move across the bilayer
37
what is a capacitor?
2 conductors separated by a non-conductor with different numbers of ions
38
what does membrane potential arise from?
different numbers of positive/negative charges across the membrane
39
what is a high resistance environment in terms of cell membranes?
no/closed ion channels
40
what are the 2 forces that determine movement of ions in solutions?
charge gradient and concentration gradient
41
when is ion flux at equilibrium?
when charge gradient and concentration gradient are balanced
42
what is the equilibrium potential of an ion?
the membrane potential at which the ion is at equilibrium
43
what is the Nernst equation used for?
to find the equilibrium potential of an ion
44
what is needed for the Nernst equation?
ideal gas constant (R), temperature (T in K), charge of the ion (Z), Faraday's constant (F), [C] outside (ref) and inside (rest) (C is ion)
45
what are the assumptions of the Nernst equation?
only 1 ion at a time, membrane completely permeable to ion, ion at equilibrium
46
what is the Nernst equation at room temperature (20 degrees)?
E= 58 x log([ion]out/[ion]in)
47
what is the Nernst equation at body temperature?
61 x log([ion]out/[ion]in)
48
what are the typical ion concentration of mammalian neurons inside vs outside?
high [K+], low [Na+], [Cl-], [Ca2+] inside vs outside
49
in resting state what ion is primarily moving across neuron membranes?
K+
50
in active state what ion is primarily moving across neuron membranes?
Na+
51
what provides the driving force for ions to move across membrane?
difference between potential and equilibrium potential
52
what are microelectrodes?
recording devices attached to a voltmeter
53
what is resting membrane potential usually between?
-60 and -80mV
54
what dis Hodgkin and Keynes find when comparing resting membrane potential to the Nernst equation for K+?
fit very well at high [K+], deviated at low [K+]
55
what did Hodgkin and Keynes suggest as an equation for membrane potential?
Goldman equation, taking into account Na+
56
what does the Goldman-Hodgkin-Katz equation account for?
K+, Na+, Cl-, relative permeability of the membrane to the ions
57
which is the most permeant ion across the cell membrane at rest?
K+
58
why do K+ ions tend to move out of the cell?
high conc in cell at rest, driving force to reach equilibrium potential which is around -90mV
59
what is the equilibrium potential of K+?
around -90mV
60
what is the equilibrium potential of Na+?
around +50mV
61
what are the changes in membrane potential during an AP
starts at around -70mV, increase to -55mV, rapid increase to around +40mV, decrease to almost -90mV, return to around -70mV
62
what experiment can be used to record voltage signals during an AP?
current clamp
63
what does axonal malfunction arise from?
injury, degeneration, demyelination
64
what is the time constant of a membrane?
how long it will take for the membrane to get to 1/e of its original charge/time to charge capacitance to 63%
65
what does the time constant depend on?
membrane resistance and membrane capacitance
66
how is the time constant calculated?
membrane resistance x membrane capacitance
67
what does a larger time constant mean?
changes in membrane potential will be slower
68
what is length constant?
distance over which voltage decays to 37% of its initial value
69
what is length constant dependent on?
membrane resistance, extracellular resistance (assumed to be negligible), intracellular resistance
70
what does a smaller length constant mean?
voltage signal decays over shorter distance
71
how can length constant be improved?
myelination
72
how does myelination improve the length constant?
increases membrane resistance
73
what is myelination in the PNS?
Schwann cells which wrap membrane around axon to form 20-160 concentric layers of membrane
74
what is myelination in the CNS?
oligodendrocytes wrap membrane around axon
75
what is between the segments of myelination?
unmyelinated nodes of Ranvier
76
how does myelination increase membrane resistance?
ions less likely to leak out of the membrane
77
why are action potentials 'all or none' events?
if threshold potential is reached, an action potential will occur, if not then it won't, size of action potential not changed by size of stimulus
78
what is the absolute refractory period?
state when sodium channels cannot be opened as they are in inactive state, so new AP can't be generated
79
what does the absolute refractory period do?
prevents transmission of impulse in both directions
80
what causes the relative refractory period?
K+ channels are delayed in closing so hyperpolarisation of membrane occurs- greater depolarisation required for new AP as further from threshold value
81
what does increasing size of stimulus current do?
increases frequency of action potentials
81
where are voltage gated ion channels concentrated in myelinated axons?
at Nodes of Ranvier
82
what is saltatory conduction?
rapid jumping of current from node to node
83
how are axons classified?
speed of conduction, myelination, diameter of axon, function
84
what is the general rule for characteristics of large diameter neurons?
heavily myelinated, low thresholds for electrical stimulation, rapid conduction
85
what did Cole and Curtis observe in 1939?
AP clearly over-shot 0mV and change in membrane resistance during AP
86
what did Hodgkin and Huxley find about the AP using squid giant axon?
AP overshot to around +40mV, sodium movement responsible for AP
87
what are examples of conditions involving damage to axons?
prolapsed intervertebral disc, poliomyelitis, motor neurone disease, hypo-myelinating neuropathy
88
what is the C fibre afferent?
type of sensory afferent fibre that is important for alerting brain to harmful stimuli
89
what are local anaesthetics?
class of drugs that can cross membrane and block VGNaCs from inside- shut down APs in pain fibres
90
why do voltage gated ion channels have selective permeability?
due to amino acids
90
what are the reversal potentials for closing VG ion channels?
the Nernst equilibrium potential for the permeant ion
91
what is capacitive current? (voltage clamp experiment)
current needed to be injected
92
what is the command voltage? (voltage clamp experiment)
the membrane potential decided by the experimenter
92
how is the command voltage reached in the membrane? (voltage clamp experiment)
microelectrodes record actual membrane potential, compare it with command voltage, then inject current into axon to change it to command voltage
93
what is the recording taken in the voltage clamp experiment?
how much current had to be injected to reach command voltage- and if positive or negative- shows current passing through the open membrane channels at the command voltage
94
what is the current injected equivalent to when command voltage is made more positive in voltage clamp experiment?
the current moving across the membrane during the depolarisation phase of an AP
95
what is seen in the voltage clamp experiment?
rapid capacitative current (current injection), rapid transient inward current, delayed outward current
96
what is seen in the control experiment for voltage clamp experiment (membrane potential changed in opposite direction by same amount)?
only capacitative current and no ionic current
97
what does voltage clamp experiment prove?
currents 'gated' by specific voltage change
98
what suggested that the rapid transient inward current in the voltage clamp experiment may be due to Na+ ion flux?
initially got larger with more depolarisation, as membrane potential approached +50mV (equilibrium potential of Na+) started to get smaller
99
what suggested the delayed outward current was due to K+ in the voltage clamp experiment?
increased with more depolarisation suggesting equilibrium potential of ion moving was more negative
100
how was the importance of Na+ for the transient inward current proved?
by removing the Na+ in the seawater bathing the axon or by blocking the VGNaC conductance using tetrodotoxin
101
how was the importance of K+ for the delayed outward current proved?
by using TEA to block VGKCs- can't change intracellular K+ concentration
102
what are channelopathies?
clinical conditions associated with non-functional mutated ion channels
103
what is the structure of the VGNaC?
single α-subunit polypeptide with associated β-subunits
104
what key functional features are present in the α-subunit of VGNaCs?
sensitivity to voltage, selectivity to Na+ ions
105
how many repeating domains do VGNaCs have?
4
106
how many membrane spanning regions do the domains of VGNaCs contain?
6 (S1-S6)
107
how are the 4 domains of VGNaCs arranged?
around a central ion channel pore
108
where is the voltage sensor located in VGNaCs?
around S4
109
what is the ion channel pore formed from in VGNaCs?
the linker sequence between S5 to S6
110
how long after opening will the VGNaC inactivate?
1ms
111
what region of the VGNaC determines selectivity?
loop between S5 and S6
112
how is the intracellular pore of VGNaCs opened?
when S4 detects voltage S5 moves, opening the pore
113
what happens in the inactivated state of the VGNaC?
intracellular loop blocks channel
114
what causes a positive feedback cycle of VGNaCs opening?
if nearby VGNaCs are close enough for the resulting depolarisation from 1 opening to be at threshold value they will also be opened
115
what is the difference between the structure of VGNaCs and VGKCs?
the α-subunit in VGKCs is equivalent to a single domain of the VGNaC so 4 α-subunits are needed to form VGKCs
116
what were the 2 theories of transmission between neurons and targets?
electrical and chemical
117
what did Dale and colleagues show in 1913?
IV injection of ACh inhibits heartbeat of cat, as does parasympathetic nerve stimulation, suggesting parasympathetic nerve stimulation could be chemical
118
what did Otto Loewi find in 1921?
put 2 beating hearts in 2 containers filled with Ringer's solution. stimulated vagus nerve in one, heart rate slowed. took solution from this container, put in other container- heart rate of other heart slowed- seemed a substance released by vagus nerve slowed heart rate- chemical
119
who used microelectrodes to directly record chemical synaptic transmission at the NMJ?
Katz
120
where are neurotransmitters stored?
in vesicles in the presynaptic axon terminals
121
what is an advantage of chemical over electrical transmission?
diversity of neurotransmitters and their receptors in the post-synaptic membrane produces different types of response
122
what does an AP cause when it reaches the axon terminal?
activation of VGCaCs so rapid influx of Ca2+
123
what is the structure of VGCaCs similar to?
VGNaCs
124
what is intracellular concentration of Ca2+ like and why?
kept very low by buffers/transporters/pumps
125
what are examples of proteins that keep intracellular Ca2+ concentration low?
the Na+/Ca2+ exchanger, the calcium pump (pumps 1 Ca, 2 H ion out, uses 1 ATP)
126
what does influx of Ca2+ cause?
the neurotransmitter containing vesicles to fuse with the presynaptic membrane and release the neurotransmitter by exocytosis
127
how is the vesicle membrane recovered after neurotransmitter release?
endocytosis
128
what are electrical synapses called?
gap junctions
129
how are gap junctions formed?
a connexon on the pre and post-synaptic membrane form a gap junction channel, conducts ions if there is depolarisation in 1 of the neurons to the 2nd neuron
130
what forms a connexon?
6 connexins
131
what enzyme is used to synthesis ACh?
choline acetyltransferase (ChAT)
132
what are end plate potentials?
depolarisations when ACh binds to receptors at the post-synaptic region of the muscle cell in the NMJ
133
what do EPPs cause?
depolarise the muscle membrane enough to open VGNaCs in the muscle cell membrane causing a muscle AP
134
why will an AP in the motor neuron reliably produce an AP in the muscle cell?
AP in the motor neuron causes the release of sufficient ACh to open VGNaCs in the muscle cell
135
what enzyme inactivates ACh in the synaptic cleft?
acetylcholinesterase (AChE)
136
what are MEPPS?
miniature EPPs- represent the smallest unit of chemical synaptic transmission- spontaneous small depolarisations at endplate when motor neuron not being stimulated
137
what is the quantal theory of synaptic transmission based on?
neurotransmitter is released in parcels (quanta), giving rise to MEPPs; EPP amplitudes correspond to the sum of MEPPs
138
what is 1 quantum (MEPP) equivalent to?
1 vesicle of neurotransmitter
139
what is the model for number of MEPPs?
number of quanta x probability of release
140
what happens if the NMJ is bathed in low Ca2+ solution?
EPPs are much smaller in amplitude- fewer quanta released
141
what is the post-synaptic receptor for ACh on the NMJ?
nicotinic ACh receptor
142
what is curare?
antagonist of the nAChR- reduces amplitude of EPPs
143
where are nAChRs found in the post-synaptic membrane?
junctional folds
144
what is the function of junctional folds?
increase the SA available for synaptic transmission at the NMJ
145
what sort of protein is the nAChR?
ligand-gated ion channel
146
what does ACh binding to the nAChR cause?
opening of an integral ion channel pore in the receptor protein
147
what is the pore of the nAChR permeable to?
Na+ ions and K+ ions
148
what is the sodium pump coupling ratio?
3Na pumped out for 2K pumped in
149
what is the resting MP of the endplate of a muscle cell?
around -100mV
150
what is the threshold for an AP in skeletal muscle?
around -65mV
151
where are VGNaCs located in the endplate?
at the bottom of junctional folds
152
what is myasthenia?
muscle weakness
153
what is an autoimmune cause of myasthenia gravis?
immune system attacking the nAChR
154
what is the main treatment for autoimmune myasthenia gravis?
prolonging duration of ACh activity in the synapse
155
what is a large difference between electrical and chemical synapses?
in electrical membrane of the 2 neurons very close together, in chemical larger synaptic cleft
156
what is a motor unit?
1 motor neuron plus all the muscle fibres it stimulates
157
what is a neuromuscular junction?
synapse between motor neuron and skeletal muscle end plate
158
what is the electron microscopy evidence for the quantal theory of synaptic transmission?
vesicles shown near membrane at rest and fusing with membrane after stimulation
159
what does postsynaptic response amplitude depend on?
amount of NT released and number of NT receptors
160
in a reflex response where is the 'decision' to contract a muscle made?
at the sensory afferent synapses onto the motor neuron
161
in voluntary movements where in the 'decision' to contract a muscle made?
at the level of cortical brain neurons
162
difference between synapses in the CNS vs NMJ?
many different NTs in CNS, just ACh in NMJ; synapses can be excitatory or inhibitory in CNS, just excitatory in NMJ; axons can contact different parts of neurons in CNS; neurons contact other neurons in CNS; an EPSP in excitatory neurons in the CNS doesn't always cause an AP- an AP depends on input of all the different neurons; voltage changes produced at most synapses in CNS smaller than EPPs at NMJ
163
why are voltage changes produced at most synapses in the CNS smaller than EPPs at the NMJ?
NMJ is a larger synapse with more vesicles of ACh in the presynaptic terminal of the motor neuron, more nAChRs in junctional folds, than CNS synapses
164
what is an EPSP?
an excitatory postsynaptic potential
165
why is it beneficial for strong signals to be required to evoke a response in CNS post-synaptic neurons?
ensure energy isn't wasted generating non-essential signals in brain and spinal cord, keeps good levels of response specificity
166
what neurotransmitter are EPSPs due to at most CNS synapses?
glutamate
167
what are the receptors for glutamate on post-synaptic receptors?
AMPA receptors, NMDA receptors, Kainate receptors
168
what are IPSPs in CNS synapses in the brain mediated by?
GABA
169
what are IPSPs in CNS synapses in the spinal cord mediated by?
glycine
170
how can glutamate cause excitation and inhibition?
causes excitation via AMPA receptor, and inhibition via GPCR
171
how does the knee jerk reflex work?
sensory afferent fibres from the muscle synapse with efferent extensor motor neuron, projects back to quadriceps muscle. glutamate released from pre-synaptic terminal of sensory neuron, binds to AMPA receptors in dendrites of the motor neuron. AMPA receptor activation leads to a depolarisation of the motor neuron dendrites. glutamate also binds to AMPA receptors present on inhibitory interneurons in spinal cord, excite the interneuron, which releases glycine to bind to glycine receptors on the motor neuron to the antagonist (flexor) muscle causing this muscle to be inhibited so both muscles don't contract simultaneously against each other
172
what is synaptic integration?
combining of all the synaptic inputs in the dendrites of a CNS neuron
173
what is temporal summation?
when a single presynaptic neuron is activated several times to cause multiple rounds of neurotransmitter released- if response to the rounds of release occurs before 1st response fully decayed they add together to generate a larger EPSP
174
what is spatial summation?
when more than 1 presynaptic neuron is activated near-simultaneously causing neurotransmitter release at multiple sites, each EPSP adds together to generate a larger EPSP
175
what is shunting inhibition?
when an IPSP happens in the path of an EPSP- inward Cl- movement effectively pulls positive current out of the dendrite reducing the EPSP
176
what is primary active transport?
energy provided directly by ATP
177
what is secondary active transport?
energy provided from the Na+ or H+ gradients set up by ATP pumps
