Healthy Nervous Sytem 2 Flashcards
1
Q
What is a synapse?
A
• Refers to the place of connection together of two cells where an impulse is transmitted two cells where an impulse is transmitted, usually referring to two neurones
2
Q
What are the three types of synapse?
A
• Electrical (or electronic) • Chemical • Mixed
3
Q
Explain electrical synapses and how they work?
Examples of there occurrence?
A
- Reduced extracellular space (2nm)
- cytoplasmic continuity between pre- and post synaptic cell.
- Mediating agent is ionic current.
- Little or no synaptic delay
- Typically bidirectional
- Egs- particularly in invertebrates and lower vertebrates. Lateral vestibular nucleus, inferior olive, molecular layer of the cerebellum, retina and a few junctions in the cerebral cortex.
4
Q
Approximately how many boutons does a single neurone have?
A
10,000
5
Q
Explain what chemical synapses are
A
- Increased extracellular space (30-50nm); no cytoplasmic continuity.
- Mediating agent is a chemical messenger.
- Significant synaptic delay (0.3-5msec). Contributions include the time required for opening of Ca2+ channels include the time required for opening of Ca2+ channels, secretory process at presynaptic terminal, diffusion across synapse, interaction with postsynaptic receptor and in some cases production of second messengers.
- Unidirectional
- Egs-majority of synapses in the CNS
6
Q
What factor is referred to when synapses are describes as symmetric or asymmetric
A
distribution of electron dense material
7
Q
What is the difference between Gray type I and II synapses?
A
See diagram on page three of synapse lecture
- Type I: large active zone. Type IIpu
: smaller active zones
-Type I end on shaft or spine while type II often end on often end on soma
8
Q
6 anatomical classes of synapse?
A
Anatomical classification of synapses describes the part of the presynaptic cell in contact with the part of the postsynaptic cell thus:
•axodendritic - between axon and dendrite •axosomatic - axon and cell body
•axoaxionic - axon to axon
•dendrodendritic - dendrite to dendrite
•somatosomatic -cell body to cell body
•somatodendritic - cell body to dendrite
9
Q
2 forms of axodendritic synapse?
A
Spine synapse
Shaft synapse
10
Q
Is there often segregation of afferent input onto cells according to their source?
A
Yes
11
Q
Give a summary of events occurring during neurotransmission at chemical synapses
A
- Action potential in presynaptic cell.
- Depolarisation of the plasma membrane of the presynaptic axon terminal.
- Entry of Ca2+ into presynaptic terminal.
- Release of transmitter by the presynaptic terminal.
- Chemical combination (binding) of the transmitter with specific receptors on the plasma membrane of the postsynaptic cell.
- Transient change in the conductance of the postsynaptic plasma membrane to specific ions.
- Transient change in the membrane potential of the postsynaptic cell.
- Points 6 and 7 are true for ionotropic receptors, metabotropic receptors have a diffferent mechanism
12
Q
How does Ca2+ dependent NT release work?
A
See diagram on page 5 of synapse lecture
13
Q
What type of molecules associated with synaptic vesicles allow docking and NT release?
A
A complex of proteins allows docking and neurotransmission release
14
Q
What is a type of synapse that is particularly lost in Alzheimer’s?
A
Glutamergic
15
Q
2 classes of NT action?
A
Direct gating and 2nd messenger systems
16
Q
How are NT signals terminated?
A
• Metabolism to non-active compounds eg acetylcholine is broken down to acetate and choline by acetylcholinesterase.
• Reuptake of neurotransmitter into the presynaptic terminal or glia in the case of glutamate.
• A combination of both in the case of 5-HT and dopamine
(See diagram on page 6 of synapse lecture)
17
Q
Which NTs are Biogenic amines?
A
Acetylcholine noradrenaline adrenaline dopamine serotonin (5-HT)
18
Q
Which NTs are amino acids?
A
Glutamate
aspartate
gamma-aminobutyric acid (GABA)
glycine
19
Q
Which NTs are peptides?
A
Somatostatin endorphins enkephalins dynorphins bradykinin substance P etc
20
Q
What ‘other’ NTs do you know?
A
ATP
adenosine
nitric oxide (NO)
21
Q
What are the results of the presence of a variety of receptors for a single NT on the same neurone?
A
NTs have:
• different effects at receptors on different neurones
• different effects at receptors on the same neurone
• similar effects at different receptors on the same neurone.
22
Q
How many types of 5-HT (seratonergic) receptor are there?
A
7
23
Q
What drugs act on gamma-aminobutyric acid (GABA)?
A
Hypnotics and anxiolytics (benzodiazepines)
anticonvulsants (phenobarbitone)
anaesthetics (halothane?)
24
Q
What drugs act on seratonin (5-HT)?
A
Anxiolytic (buspirone)
antidepressants (MAOI, tricyclics, SSRIs)
stimulants (MDMA)
hallucinogens (LSD).
25
What drugs act on NA?
Antidepressants (MAOI, tricyclics)
26
What drugs act on/modulate dopamine?
Anti-Parkinson drugs (levodopa, bromocriptine)
neuroleptics (phenothiazines)
stimulants (amphetamine, cocaine).
27
What drugs act on/modulate peptide NTs?
Analgesics (enkephalins, dynorphins)
28
What drugs act on/modulate glutamate?
Anti-ischemia (NMDA antagonists)
anticonvulsants (phenytoin)
cognitive enhancers (memantine, D-cycloserine).
29
What drugs act on/modulate Ach?
Anti-dementia (tacrine, Aricept, cholinesterase inhibitors).
30
In somatosensory receptor terminals such as in the skin, what type of potential occurs in response to a stimulus?
Whatever the stimulus, activation of the receptor causes a graded potential to occur in the nerve terminal that may by either transient or sustained
31
What 2 factors give information about the intensity (how big) and kinetics (how fast) of the sensory stimulus?
The frequency and pattern of the action potentials in the nerve fibre
(The frequency and pattern of the action potentials that constitute the 'signal' are produced by generator potentials in the sensory receptors)
32
What is a phasic response to a sensory stimulus and what is a tonic response?
phasic response: adapting response that typically signals a change of state.
tonic response: sustained response that usually encodes information about the status quo.
33
What type of relationship exists between the strength of a response to a stimulus and the strength of that stimulus?
Which law describes this phenomenon?
Hyperbolic
| Weber's Law
34
How are generator potentials produced?
Generator potentials are produced by changes in the behaviour of ion channels. The TRP ion channel family are a good example.
e.g. TRPV1, the capsaicin receptor (activated at T > 45oC).
35
At what temperatures are the different receptors of the TRP family
activated?
TRPV1, the capsaicin receptor (activated at T > 45oC)
TRPV2 (activated at T > 52oC) TRPV3 (activated at T > 34oC) TRPV4 (activated at T > 27oC) TRPM8 (activated at T < 25oC) TRPA1 (activated at T < 17oC)(and by mustard oil) ??
36
What can activate the TRPV1 ion channels?
T > 45oC (threshold for tissue damage)
pH < 6.0
some lipids capsaicin
(TRPV1 is especially interesting because it is found in high levels in nociceptors and may be involved in generating pain responses.)
37
What is the rough membrane potential of the receptor nerve terminals?
c.-50 mV
38
For somatic sensations it is likely that generator potentials are produced by what type of channel?
non-specific cation' channels that are opened by specific environmental stimuli i.e. ion channels that are opened by mechanical stress or deformation of the nerve membranes, by low or high temperatures or by chemicals. There are many such ion channels expressed in the sensory nervous system
39
What is the job of generator potentials?
• To initiate action potentials in the neuronal axon
40
What are four characteristics of generator potentials?
* Usually associated with non-specific cation channels (which can be found in non-neuronal cells too).
* modality specific: mechanoreceptors (high or low threshold), thermoreceptors (hot or cold), chemoreceptors, osmoreceptors, polymodal receptors (nociceptors), photoreceptors etc
* graded potentials
* transient (phasic, adapting) or sustained (non-adapting)
41
What are 2 strengths of generator potentials?
* localized: information on location of stimulus
| * graded: information on intensity of stimulus
42
In what way are generator potentials limited?
• Although generated by specific modalities graded generator potentials do not contain modality specific information: modality-specific sensation requires labelled lines
43
What is the job action potentials and what 3 characteristic features?
* highly co-ordinated activity of voltage-gated Na+ and K+ ion channels
* all or nothing
* brief: usually ~2 - 5 ms
44
2 strengths of APs?
* signal size is maintained over distance and axonal branches
* Versatility of information coding: frequency encoding + pattern encoding
45
2 limitations of APs?
* membrane must be hyperpolarized to start
| * system must be reprimed after use (refractory period)
46
What type of cation channels do post synaptic NT receptors tend to open?
The ion channels are non-selective cation channels and can allow both Na+ and K+ ions to pass
Some ligand-gated ion channels e.g. the NMDA receptor also allow Ca2+ ions to enter the cell
47
What are 2 relatively unusual but important factors in the termination of glutamate as a NT?
Uptake of glutamate into glial cells is thought to be especially important in determining the decay of some glutamate evoked synaptic potentials.
in synapses where glutamate acts at AMPA receptors to evoke an EPSP the decline of the EPSP is thought to be due partly to desensitization of the AMPA receptors
48
Are EPSPs all or nothing or graded?
Graded
49
What 3 factors does the amplitude of an EPSPs rely on?
1. Amount of neurotransmitter released
2. Number of receptors
3. State of receptors
50
What 4 factors will the decay of EPSPS rely on?
1. Dissociation of ligand
2. Diffusion and uptake (e.g. glutamate)
3. Desensitization (AMPA-type glu receptors)
4. Enzymatic destruction (ACh)
(First two are more common)
51
What is the job of EPSPs (excitatory post-synaptic potentials)?
EPSPs contribute to somatic depolarization leading to generation of an action potential at the axon hillock of the neuron
52
Characteristic features of EPSPs?
• usually EPSPs are fast but slow EPSPs also occur:
• fast EPSPs ( ~ 10 - 100 ms) are usually due to activation of ligand-gated non-specific (pass Na+, K+ and sometimes Ca2+) cation channels e.g. glu (AMPA, lj
NMDA), ATP (P2X), ACh (nicotinic).
53
Advantages of EPSPs?
* versatility: different transmitters can act on the same postsynaptic cell using different receptors
* versatility: different receptors/ion channels can be regulated independently
* versatility: independent postsynaptic and presynaptic control of synaptic 'strength'
54
2 limitations I'd EPSPs?
* Metabollically expensive
| * Vulnerable to chemical attack (drugs and toxins)
55
What is the no of IPSP?
• IPSPs prevent somatic depolarization and generation of an action potential at the axon hillock
56
Characteristic features of IPSPs?
* EPSPs are graded - they are not all or none
* usually EPSPs are fast but slow EPSPs also occur:
* fast IPSPs ( ~ 10 - 500 ms) are usually due to activation of ligand-gated anion (Cl-) channels by GABA at GABAA receptors or glycine.
57
Advantages of IPSPs?
* versatility: different transmitters can act on the same postsynaptic cell using different receptors (e.g. mixed epsp and ipsp)
* versatility: different receptors/ion channels can be regulated independently
* versatility: independent postsynaptic and presynaptic control of synaptic 'strength'
58
2 limitations of IPSPs?
* Metabollically expensive
| * Vulnerable to chemical attack (drugs and toxins)
59
Explain the concept of convergence?
Different presynaptic neurones send inputs to a single postsynaptic neuron and that neuron will fire or not depending on whether the epsps and ipsps at any moment add together to cause sufficient depolarization of the axon hillock to make the postsynaptic neuron fire.
60
Synchronous activation of many inputs to a single neurone can give rise to a complex synaptic potential that involves the activity of many different types of ion channel - see diagram on page 4 of information transmission lecture
-
61
Describe the relationship between convergence and divergence within the CNS
Neuronal networks are functional hierarchies where signals from multiple inputs can converge on neurons within a 'nucleus' and be integrated. Integrated output signals then diverge to provide inputs to the next level of the hierarchy.
62
How is signal divergence controlled in the CNS?
Inhibitory processes
Inter neurons
- 'surround' inhibition by negative feedback
63
Different configurations of interneurons are possible e.g. in the spinal cord most of the following configurations have been postulated........
1. Descending inhibition produced via interneurones by an axo-somatic pathway
2. Descending inhibition produced via interneurones by a pre-synaptic axo-axonic pathway
3. Feed-forward inhibition
4. Feedback inhibition
5. Recurrent inhibition
See final diagram on page 4 of the formation transfer lecture
64
In what meningeal layer/space do nerve roots travel?
Subarachnoid
65
What are found in tue dorsal root ganglia?
Cell bodies of primary sensory neurones
66
Laminae are divisions of which part of the spinal cord?
| Eg.s?
Grey matter
| Eg.s- Lissauer's tract, Substantia gelatinosa, Clarke's column
67
What type of information does the Dorsal column-medial lemniscus pathway carry and from what type of receptors?
- fine discriminative touch
- vibration
- proprioception
- mechanoreceptors
68
What type of information does the spinothalamic pathway carry and from what type of receptors
- pain (‘fast' pain)
- temperature
- crude touch
- nociceptors
- thermoceptors
- mechanoreceptors
69
Spino-reticulothalamic pathway?
(Spino-reticulothalamic pathway – evolutionarily older, ‘slow' dull aching pain)
70
What type of information is carried by the Spinocerebellar pathways (dorsal and ventral)?
- proprioception
| - touch
71
What is the only type of sensory information that does not go to the thalamus?
Olfactory
72
What passes through the internal capsule?
All somatosensory pathways to cortex and motor axons going down to the spinal cord
73
What would be the effect of a lesion to the dorsal column?
- loss of fine touch, proprioception and vibration sense - location: below the lesion ipsilaterally
(Ataxia, unsteady gait
Rombergs side - stand up straight with eyes closed - cant stay upright)
74
What would be the effect of a lesion to medial lemniscus in brainstem Lesion to medial lemniscus in brainstem?
- loss of fine touch, proprioception and vibration sense
| - location: below the lesion contralaterally
75
What would be the effect of a lesion to the spinothalamictract?
- loss of crude touch, pain and temperature sense - location: several spinal segments below the lesion contra-laterally
76
At what vertebral levels is cystic enlargement of the central canal most likely are what tract ascending tract does it compress?
- common at cervical level
| - compression of spinothalamic tract axons
77
What do you know about Tabes Dorsalis?
Tertiary syphilis - dorsal spinal roots & dorsal columns
Loss of proprioception - high step, unsteady gait - sensory ataxia
Romberg's sign - worse with eyes shut; can fall over backwards
78
What do you know about Subacute combined degeneration of the cord?
B12 - cyanocobalamin deficiency- pernicious anaemia Degeneration of dorsal columns. Also lateral columns (“combined”) - weakness and spasticity of limbs
79
What effect can MS have on the central columns?
Many effects in CNS Fasciculus cuneatus (above T6) - loss of proprioception in hands and fingers
Loss of dexterity; inability to identify shape & nature of objects -astereognosis
80
What do you know about Syringomyelia?
Central canal enlarged by gelatinous syrinx
Decussating 2nd order pain/temperature neurons anteriorly compressed
Dissociated cutaneous loss of pain and temperature – light touch preserved
81
What is Cordotomy/tractotomy?
Elective surgical lesion of tracts for the relief of intractable pain
82
What results from cerebellar damage?
Ataxia; incoordination; intention tremor
Ipsilateral effect
(Cerebellum - comparator of input from sensory and output to motor from cortex
Posture etc from input from vestibulocochlear)
83
What is Friedreich's ataxia?
Inherited degeneration of system
84
What is Brown Séquard syndrome and what does it lead to?
hemisection of the spinal cord
leads to - contralateral spastic paralysis below the lesion ipsilateral loss of fine touch, proprioception, vibration below the lesion contralateral loss of pain and temperature sense several segments below the lesion several segments below the lesion
85
What causes syringomyelia and what does it lead to?
tubelike enlargement of spinal canal – usually cervical/thoracic
leads to - ipsilateral flaccid paralysis if ventral horns are affected – weakness and atrophy of hand muscles
spinothalamic tract may be first affected due to proximity of crossing fibres to central canal – loss of pain and temperature sense bliaterally in arms and shoulders
86
What embryological part of the neural tube is the cerebral hemispheres derived from?
Telencephalon
| Differentiation as early as 5 weeks gestation
87
How is the forebrain subdivided?
```
THE FOREBRAIN - parts
CEREBRAL HEMISPHERE CEREBRAL
- Cerebral cortex
- Basal ganglia
- Various small nuclei
```
OLFACTORY BULB
DIENCEPHALON
- Thalamus
- Subthalamus
- Hypothalamus
- Epithalamus
88
What is the epithalamus involved in?
Circadian rhythm
| Seratonin
89
What are the meaning of neocortex and allocortex?
New cortex - neo-cortex - most mass
| Aloe- cortex a old - less - more primitive function, olfaction
90
How many layered does the neocortex have?
6 layers
| See page 134 of neuroanatomy
91
How many layers does the allocortex have?
3
| (Hippocampus and other parts of the temporal lobe - limb if
