1
Q
What are the principal functional units of the nervous system called?
A
Neurones
2
Q
Give examples of excitable cells.
A
Neurones, smooth, skeletal, cardiac muscle cells, secretory cells of the pancreas.
3
Q
Human N.S has how many neurons?
A
10^11-12
4
Q
Which non-neuronal cells produce the blood brain barrier?
A
Astroglia
5
Q
What do ependymal cells do?
A
- line the fluid-filled ventricles of the brain
- direct cell migration during brain development
6
Q
What is anterograde transport?
A
Movement of proteins from soma to terminal endings
7
Q
What is retrograde transport?
A
Movement from terminal endings to soma
8
Q
T or F. If the axon is severed the part distal to the cut degenerates.
A
T
9
Q
Changes in the cell body after injury-retrograde reaction?
A
- Chromatolysis- nissl bodies disappear
- Gogli apparatus and neurofibrils begin to disappear
- Cell body swells
- Nucleus is pushed to the side of the cell body
10
Q
How long does repair begin following injury and when does it complete?
A
Repair starts after 20 days following injury and completes in 80 days after injury.
11
Q
What is orthograde degeneration?
A
Or Wallerian degeneration- occurs distal to the site of injury-towards the terminal endings.
12
Q
What is retrograde degeneration?
A
occurs proximal to the site of injury-backwards degeneration to the cell body.
13
Q
What is regenerative sprouting?
A
Schwaan cells elongate and send processes outwards to the site of injury.
14
Q
After regeneration, the peripheral nerve normally achieves up to 90% of its original diameter. T or F.
A
F- it rarely achieves up to 80% of its original diameter.
15
Q
What is denervation hypersensitivity?
A
occurs when there’s increased responsiveness of the end-organ or muscle following injury of the peripheral nerve that was innervating it.
16
Q
Suggestions to explain denervation hypersensitivity? hint-theres 4
A
- Regenerative sprouting to new areas of the end-organ
- Lack of re-uptake of secreted neurotransmitters
- Denervated end-organ becomes hyper-responsive to neurotransmitters
- Up-regulation of receptors on the end-organ
17
Q
In neurons, the K+ conc is greater inside than outside. T or F.
A
T- & results in a K+ outward conc gradient when K-selective channels r open.
18
Q
What is the resting membrane potential?
A
the potential difference across the cell membrane of the neurone at rest & = -70mV.
19
Q
What does the Na/K ATPase pump do?
A
Extrudes 3 Na+ for every 2 K+ that comes in
20
Q
What is the equilibrium potential?
A
membrane potential at which the tendency to move against the electrical or conc. gradient is exactly balanced.
21
Q
EP for Na, K and Cl.
A
+61mv, -94.1mV and -70mV
22
Q
An increase in K conc on the outside of the cell results in a decrease in membrane potential. T or F.
A
T
23
Q
A decrease in membrane potential results in hyperkalemia. T or F.
A
T- decrease in MP results in increased nerve excitabilty (K+ conc on the outside increases)
24
Q
The membrane permeability to Na+ is greater. T or F.
A
F- K+ is greater
note: at rest the membrane is impermeable to Na+ but permeable to K+
25
What is the negative feedback process when generating AP
voltage gated K+ channels bring the AP to an end and cause closure of their gates.
26
What is the positive feedback loop when generating AP?
The entry of Na+ causes the opening of more voltage-gated Na+ channels and further depolarization
27
What happens when extracellular Ca2+ decreases?
There will be an increase in nerve excitability bcuz it will decrease the amount of depolarization needed to initiate the changes in Na+ and K+ conductance that produce the AP.
28
whats after-hyperpolarization?
Slight overshoot in the RMP in the hyperpolarizing direction. Cuz K+ channels close slowly & and increased efflux of K+ causes the MP to increase (be more negative), overriding the Na+/K+ ATPase pump.
Sidenote: after the channels finally close, the Na+/K+ ATPase pump will return the RMP back to -70mV
29
At what mV will the Na+ voltage gated channel activation start?
7 mV to 15 mV
30
Refractory period?
A period of unresponsiveness
31
Excitability returns to 95% of its resting value in how much time?
10-30 msec
note: can reach full response again
32
Stimulus of a threshold intensity can elicit a 2nd AP in the relative refractory period. T or F.
F- only a stimulus of supra-threshold intensity will generate a 2nd AP- it will generate a shorter AP; some Na+ channels are inactivated so extracellular Na has decreased or smt.
33
Axon can conduct a nerve impulse in either direction away from stimulation, and it goes in both directions at a time. T or F.
F- can only go one direction at a time cuz of refractory period.
34
Orthodromic conduction?
normal conduction; AP moves towards the distal end of the axon.
35
Antidromic conduction?
AP moves towards the soma
36
Saltatory conduction?
Myelinated conduction; AP travels from node to node; high density of voltage gated channels at nodes.
37
Speed of conduction of an AP depends on?
Distance between the nodes and the thickness of the myelin sheath.
38
Primary demyelinating diseases?
MS and Guillain-Barre Syndrome
note: GB syndrome is due to demyelination in peripheral nerves and MS is due to patchy demyelination in the CNS.
39
Peripheral neuropathies?
Guillain-Barre Syndrome and Carpal tunnel syndrome
note: CT syndrome is due to compression of the median nerve.
40
Loss of myelin, like in MS, leads to what?
Leakage of K+ through voltage gated channels and failure to conduct APs; consequent slowing of nerve conduction
Note: MS is due to patchy demyelination in the CNS
41
Best way to avoid the limiting factors of fast conduction?
Long and thick myelinated fibres- lower core resistance and allows for better insulation (less loss of current).
42
Compound AP is All or none. T or F.
F- its not all All or none response
Its the maximal response reached when the maximal stimulus strength is reached.
43
Which fibre types are motor?
A alpha and A gamma i think
note: A beta is touch & press. and A delta is pain, cold & touch
also note: A fibres are myelinated and fast.
44
Hypoxia affects which fibre type the most?
B fibres, then A then C the least
BACH
45
Pressure affects which fibre type the most?
A fibres, then B then C is the least
ABC
46
Local anaesthesia affects which fibre type the most?
C fibres, then B then A is the least
backwards CBA
47
Slowly rising currents fail to induce an action potential because of adaptation. T or F.
T- AP is all-or-none
48
AP will increase if the stimulus intensity is greater than the threshold intensity. T or F
F- AP will stay the same
49
Whats the main cause of hyperkalemia?
- Impaired kidney function to excrete K+ due to renal failure, diabetes 1, dehydration etc.
- results in an increase in extracellular K+ conc
50
A single stimulus applied to a sensory neurone does not lead to a propagated AP in the post-synaptic neurone. T or F.
T- instead it leads to a transient partial depolarization or transient hyperpolarization.
note: need more than one stimulus
51
synaptic delay is what?
0.5 ms after afferent impulse
52
The initial depolarizing response of the first stimulus will increase the excitability of the neurone to the next stimulus leading to a fast excitatory postsynaptic potential (EPSP). T or F.
T
note: the EPSP due to one synaptic knob is small and wont depolarize the whole membrane but the depolarizations from multiple synaptic knobs will summate.
the Na+ and Ca2+ channels open in the post-synaptic membrane
53
Whats the IPSP (inhibitory post-synaptic potential)?
- Due to hyperpolarizing responses where an initial hyperpolarizing response will decrease the excitability of the neurone to the next stimulus.
- note: the Cl- channels open in the post-synaptic membrane leading to a negative charge inside the cell, increasing the membrane potential.
- The movement of MP away from the firing level is what cause decreased excitability.
- K+ channels may open or Na+ and Ca2+ channels may close.
54
Summation of the EPSPs will generate a full-fledged AP. T or F.
T
55
Occlusion?
Decrease in expected response due to pre-synaptic neurons sharing the same post-synaptic neurons
56
Summation?
The response to the combined presentation of 2 stimuli equals the sum of those produced when each stimulus is given separately
57
Facilitation?
The response to the combination of 2 stimuli exceeds the sum of responses to separate presentations.
58
what is a motor unit?
the number of muscle fibres being innervated by a single motor neuron.
59
motor endplate?
specialized portion of sarcolemma of muscle fibre innervated by a single motor nerve ending.
60
Cholinergic transmission is Ca2+ independent. T or F.
F- Ca2+ dependent
61
Arrival of a nerve AP leads to the opening of Ca2+ voltage gated channels in the terminal endings. T or F.
T- which in turn causes Ach choline to be released and bind to the nicotinic receptors- produce endplate potential- which summate to produce muscle AP- then muscle contracts
62
What happens after Ca2+ channels open (note: AP causes this)?
- Ca2+ binds to calmodulin and synaptotagmin
- Ca-calmodulin kinase is formed which phosphorylates synapsin I.
- This causes synaptic vesicles to loosen from the cytoskeleton attachments
- vesicles then migrate to and dock at active zones then release the neurotransmitter.
- Ach diffuses to the nicotinic receptors which allows for the entry of Na+ which produces an endplate potential. This summates to produce muscle AP then muscle contraction.
63
Myasthenia gravis?
- autoimmune disease where antibodies destroy some of the nicotinic receptors on skeletal muscle
- causes muscle weakness, paralysis and eventually death
64
Lambert-Eaton Syndrome?
- antibodies destroy Ca2+ channels in the nerve endings at the neuromuscular junction decreasing Ach release
- causes muscle weakness
65
miniature endplate potential is due to what?
- spontaneous release of small quanta of Ach
- not enough to generate AP
- results in large endplate potentials being formed to initiate muscle AP
66
SNARE proteins?
- Synaptobrevin
- Syntaxin
- SNAP-25
- Rab 3
67
which part of the neurone is the most excitable?
axon hillock
68
what is wallerian degeneration?
occurs due to axonal injury/severance and the distal part to the cut degenerates.
injury like trauma or ischaemia
69
regeneration after injury only occurs if the nucleus is retained. T or F.
T
70
regeneration does not normally occur in the CNS. T or F.
T
71
K+ has a tendency to leak in the cell due the net negative charge inside. T or F.
T- down its electrical gradient
72
an increase in K+ conc (outside) will result in what?
a decrease in RMP (more positive) which increases nerve excitability
hyperkalemia
73
rapid changes in the Na+ n K+ permeability are primarily responsible for signal transmission in nerves. T or F.
T
74
whats after-depolarization?
- slower increase in the m.p
- coincides with -55 mV on the other side
- point at which re-stimulation can occur
75
whats after-hyperpolarization?
- slight overshoot of RMP in the hyper-polarizing direction (increase in RMP)
- K+ efflux overrides the Na+/K+ pump
- last approx 40 ms
76
whats depolarization?
- a decrease in membrane potential from its resting value (more positive)
- Na+ is moving in the cell- its permeability increases
- +35 mV
77
whats repolarization?
- membrane potential returns to resting level
-membrane becomes more permeable to K+ and it becomes more negative (K+ efflux)
78
whats the absolute refractory period?
- starts from firing level to 1/3 of repolarization
- cannot elicit a 2nd AP
79
whats the relative refractory period?
- starts from 1/3 of repolarization to resting level
- a suprathreshold intensity can elicit a 2nd AP here- but it'll be shorter
80
nerve membrane is polarized at rest. T or F.
T- inside is more negative
81
what are the limiting factors to fast conduction?
- core resistance: increases with length
- loss of current to myelin sheath: not a good insulator; need thicker myelin
82
Synthesis of Ach?
- acetyl CoA + choline
- by choline acetyltransferase
83
functions of synaptotagmin?
- Ca2+ sensor for release of neurotransmitter
- allows for vesicle fusion proteins to bind during exocytosis
- involved in docking, binding and endocytosis of synaptic vesicles
84
what does tetanus toxin do?
block presynaptic neurotransmitter release in the CNS and leads to spastic paralysis
85
what does botulinum toxin do?
block Ach release at the neuromuscular junction and causes flaccid paralysis
Neuro
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