Neurophysiology Flashcards
1
Q
What is pain?
A
An unpleasant sensory and emotional experience associated with actual tissue damage OR described in terms of such damage
2
Q
What function does acute pain typically serve?
A
Protective
3
Q
What is nociceptive pain?
A
An appropriate physiological response to painful stimuli via an intact nervous system
4
Q
What is neuropathic pain?
A
An inappropriate response due to nervous system dysfunction
5
Q
What is allodynia?
A
Pain from a non-noxious stimulus
6
Q
What is hyeralgesia?
A
Excessive pain from a painful stimulus
7
Q
Shingles, surgery, trauma, diabetes, amputation and idiopathic pain are what type - Nociceptive or Neuropathic?
A
Neuropathic
8
Q
What is the first step of the WHO Analgesic Ladder?
A
Non-opioids:
- NSAIDs
- Paracetamol
9
Q
What is the second step of the WHO Analgesic Ladder?
A
Weak opioids: - Codeine - Tramadol - Oxycodone (low dose) \+/- Non-opioids \+/- Adjuvants
10
Q
What is the third step of the WHO Analgesic Ladder?
A
Strong opioids: - High dose morphine - Fentanyl \+/- Non-opioids \+/- Adjuvants
11
Q
What adjuvants are available for pain management?
A
Antidepressants: - Amitryptiline (1st) - Duloxetine (3rd) Anticonvulsants: - Gabapentin (Alternative 1st) - Pregabalin (2nd) Topical analgesics: - Capsaicin - Lidocaine 5% plaster (4th)
12
Q
What pain do NSAIDs mainly act on?
A
Nociceptive
13
Q
What are the side effects of NSAIDs?
A
GI irritation/bleeding
Renal toxicity
Drug-drug interactions
CVS side effects (due to COX-2)
14
Q
How does paracetamol work?
A
Inhibits central prostaglandin synthesis
15
Q
What pain do opioids mainly act on?
A
Nocieptive
Some effect on neuropathic pain
16
Q
What are the side effects of opioid analgesics?
A
Nausea and vomiting Constipation Dizziness/Vertigo Somnolence Dry skin and pruritus
17
Q
How do opioid analgesics work?
A
- Stimulate limbic system receptors (eliminate subjective pain)
- Affect descending paths that modulate pain
- Decrease ascending pain signals
18
Q
When are tricyclic antidepressants useful in pain management?
A
Neuropathic pain
Complex Regional Pain Syndrome
Tension headache
19
Q
How do tricyclic antidepressants work?
A
Inhibit neuronal NA and 5-HT reuptake
20
Q
What are the side effects of tricyclic antidepressants?
A
Constipation Dry mouth Somnolence HR and rhythm abnormalities Insomnia Increased appetite
21
Q
Which is better in relieving neuropathic pain, SNRIs or SSRIs?
A
SNRIs
22
Q
How do SNRIs and SSRIs work?
A
Selectively inhibit 5-HT and/or NA reuptake
Intensify descending inhibition -> Analgesia
23
Q
What are the side effects of SNRIs and SSRIs?
A
Nausea and vomiting Constipation Somnolence Dry mouth Increased sweating Decreased appetite
24
Q
How does gabapentin work?
A
Binds to presynaptic voltage-dependant calcium channels
25
How does pregabalin work?
Interacts with special N-type calcium channels
26
How does carbamazepine?
Blocks sodium and calcium channels (presynaptic)
27
What are the side effects of anticonvulsants in pain management?
```
Sedation
Dizziness
Ataxia
Peripheral oedema
Nausea
Weight gain
```
28
How do topical analgesics work?
Reduce pain impulses transmitted by:
- A delta fibres
- C fibres
29
What are the side effects of topical analgesics?
Local:
- Rash
- Pruritus
- Erythema
30
What is an opiate?
Substance extracted from opium or of a similar structure
31
What is an opioid?
ANY agent that acts upon an opioid receptor?
32
What brain regions are involved in pain perception and the emotional response that is projected to medulla and spinal cord?
Cortex
Amygdala
Thalamus and hypothalamus
33
What is the function of the periaqueductal grey (PAG)? What drugs can excite it?
Excitation produces profound analgesia
Enkephalins and morphine:
- Inhibit inhibitory GABAergic interneurones
34
What neurones compose the nucleus raphe magnus (NRM)?
Serotonergic and Enkephalinergic
35
What drug can excite the nucleus raphe magnus?
Morphine
36
What neurones compose the locus coeruleus (LC)?
Noradrenergic
37
How do the PAG, NRM and LC work?
1. Electrical stimulation and opioids excite the PAG
2. PAG excites NRM (as do opioids) and LC
3. NRM and LC inhibit nociceptive transmission in dorsal horn
38
How do the axons of the NRM and LC project?
Via the dorsolateral funiculus
39
Opioid action is mediated by what class of receptors?
G-protein coupled receptors (Gi/Go)
40
What opioids bind to opioid receptors, what occurs?
Postsynaptic potassium channels open
| Hyperpolarisation and reduced excitability
41
What are mu opioid receptors responsible for?
Most analgesic action via opioids
42
What side effects do mu opioid receptors cause?
Respiratory depression
Constipation
Euphoria/Sedation/Dependence
43
What do delta opioid receptors do?
Contribute to analgesia
44
What is a side effect of delta opioid receptor binding?
Potentially pro-convulsant
45
What do kappa opioid receptors do?
Spinal and peripheral analgesia
46
What effect does the ORL1 receptor have?
Anti-opioid effect
47
When is morphine used?
```
Acute severe pain (IV/IM/SC)
Chronic pain (PO)
```
48
When is diamorphine used?
Post-operative pain
49
When is fentanyl used?
```
Maintenance analgesia (IV)
Chronic pain (transdermal patch)
```
50
When is buprenorphine used?
Chronic pain (patient-controlled injection systems)
51
When is pethidine used?
Acute pain esp. labour (IV/IM/SC)
52
What drugs can pethidine not be used with and why?
```
Monoamine oxidase inhibitors
Can cause:
- Excitement
- Convulsions
- Hyperthermia
```
53
How does tramadol mainly work?
Potentiates NRM and LC systems
54
Apart from at the mu opioid receptor, where else does methadone work?
Potassium channels
NMDA receptors
Some 5-HT receptors
55
Why is methadone used to treat opioid (heroin) withdrawl?
Longer half-life and it is given PO (no need for injection)
56
When is etorphine used?
Veterinary medicine (large animal sedation)
57
When is naloxone used?
To reverse opioid overdose
58
How does naloxone work?
Competitive antagonist at mu-receptors
59
What are signs of opioid toxicity that would warrant naloxone used?
Respiratory and/or neurological depression
60
When might naloxone be given to a newborn?
Respiratory distress due to pethidone given during labour
61
Naloxone has a short half-life, why is this useful?
Helps avoid further toxicity
| Easier to titrate dose and frequence
62
Etoricoxib, Celecoxib and Lumiracoxib are examples of what?
COX-2 selective inhibitors
63
What do COX-1 and COX-2 do?
Produce endoperoxides (Prostaglandin, Thromboxane-A2 and Prostacyclin [PGI2])
64
Which COX is induced in inflammation?
COX-2
65
How do COX-1 inhibitors cause GI toxicity?
Reduced production of PGE2 results in decreased protection against acid and pepsin
66
What is the analgesic effect of paracetamol due to?
N-acetyl-p-benzoquinoneimine
67
What are some serious side effects of COX-2 inhibitors?
Nephrotoxicity
| Prothrombic
68
What subunit of the calcium channel to gabapentin and pregabalin effect?
Alpha-2-delta
69
What drugs can be used in migraine prophylaxis?
1st line:
- Amitryptiline OR
- Propanolol
2nd line is Gabapentin
70
What is the first line treatment for trigeminal neuralgia?
Carbamazepine
71
What is the perikaryon?
The soma/cell body of a neurone
72
What is the Nissl substance?
RER in a neurone
73
Where is the 'all-or-nothing' AP initiated?
Axon hillock
74
What viruses can exploit retrograde (presynaptic terminal to soma) transport to infect neurones?
Herpes
Polio
Rabies
75
What are the main structure type of neurones in the peripheral autonomic system?
Unipolar
76
What are the main structure type of neurones in the retinal system?
Bipolar
77
What are the main structure type of neurones in the dorsal root ganglia?
Pseudounipolar
78
What are the main structure type of lower motor neurones (motoneurones)?
Multipolar
79
What staining method allows visualisation of individual neurones?
Camillo Golgi's
80
What are Golgi type i neurones?
Long axons (eg. Projection neurones from dorsal horn to brain)
81
What are Golgi type ii neurones?
Short axons (eg. Local interneurones in CNS)
82
What causes the upstroke in an AP?
Sodium influx
83
What is the typical membrane potential of threshold?
-60mV
84
What is the typical resting membrane potential?
-70mV
85
What is the typical membrane potential reached by overshoot?
+40mV
86
What causes the downstroke in an AP?
Potassium efflux
87
What is the typical membrane potential reached by undershoot?
-80mV
88
Membrane resistance (rm) aims to prevent what?
Current leaking from axon back to the extracellular space
89
What does membrane leakage generate?
Membrane potential change (delta-Vm)
90
The distance over which current spreads passively is know as the length constant (lambda). What does it depend on?
Membrane resistance (rm) and axial resistance of the axoplasm (ri)
91
How can we calculate the length constant?
Lambda = (rm/ri)^0.5
| ie the square root of rm/ri
92
What does a longer length constant indicate?
Greater local current spread
93
How can we increase passive conduction?
Decreasing ri by increasing axon diameter
| Increasing rm by insulatin axon with myelin
94
What cells produce myelin in the PNS? What axonal distribution do these have?
Schwann cells
| Many around one axon
95
What cells produce myelin in the CNS? What axonal distribution do these have?
Oligodendrocytes
| One around many axons
96
What does myelin result in?
Saltatory conduction
97
What channels are located in the Nodes of Ranvier?
Voltage-activated sodium channels
98
Give an example of a disease resulting in CNS demyelination?
MS
99
Give an example of a disease resulting in PNS demyelination? What can precipitate this?
Guillian-Barre:
- Gastroenteritis
- Respiratory tract infection
100
What is the most common CNS excitatory neurotransmitter?
Glutamate
101
What is the most common CNS inhibitory neurotransmitter?
GABA (or glycine)
102
What does glutamate activate?
Post-synaptive, cation-selective, ionotropic glutamate receptors
103
What does GABA activate?
Post-synaptic, anion-selective, ionotropic GABAa receptors
104
How wide is the typical synaptic cleft?
20-50nm
105
What is the diameter of a typical vesicle?
50nm
106
How can we differentiate between the pre-synaptic membrane and the post-synaptic membrane?
Pre:
- Active zones where vesicles cluster
Post:
- Postsynaptic density with neurotransmitter receptors
107
What is spatial summation?
Many inputs converge upon a neurone to determine its output
| eg. 1 epsp + 2 ipsp = Net inhibition
108
What is temporal summation?
A single input can alter output by varying AP frequency
109
What are the three main amino acid neurotransmitters?
Glutamate
GABA
Gylcine
110
How can we tell if a neurotransmitter is an amine?
Typically ends in -ine (eg. Ach, dopamINE, histamINE, NA)
| OR -in as in serotonIN
111
Apart from amino acids and amines, what other groups of neurotransmitter is there?
Peptides
112
What type of channels can glutamate, GABA, glycine, Ach and 5-HT activate? What speed of transmission does this permit?
Ionotropic, ligand-gated ion channels
| Fast
113
What is the only neurotransmitter that cannot activate GPCRs? What speed of transmission do these receptors permit?
Glycine
| Slow
114
What neurotransmitters are in all cells?
Glycine and glutamate
115
What neurotransmitters need to be specifically synthesised?
GABA and amines
116
What is the process by which peptide neurotransmitters are synthesised and stored?
1. Precursor peptide synthesis by ribosomes at RER
2. Precursor cleaved in Golgi - Active neurotransmitter
3. Secretory granules bud off from Golgi
4. Granules transported to terminal by fast axoplasmic transport along microtubules
117
What is the typical extracellular ion concentrations of the following:
- Sodium
- Potassium
- Chloride
- Calcium
```
Sodium = 145 mM
Potassium = 4 mM
Chloride = 123 mM
Calcium = 1.5 nM
```
118
What is the typical intracellular ion concentrations of the following:
- Sodium
- Potassium
- Chloride
- Calcium
```
Sodium = 12 mM
Potassium = 155 mM
Chloride = 14 mM
Calcium = 10^-7 M (0.0001 nM)
```
119
Ionotropic receptors allow for what type of gating?
Direct (receptor is also channel)
120
Metabotropic receptors allow for what type of gating?
Indirect (receptor and channel are distinct molecules)
121
Via what type of receptors can glutamate potentially be inhibitory?
Metabotropic
122
How can ionotropic glutamate receptors be classified?
Via their response to non-endogenous glutamate mimics
123
What can non-NMDA receptors bind?
Kainate and AMPA (agonists)
124
What do non-NMDA receptors permit?
Fast excitatory transmission via sodium and potassium channels
125
What do NMDA receptors permit?
Slow excitatory transmission via sodium, potassium and calcium
126
How can NMDA receptors promote neurotoxicity?
High calcium permeability
127
What can block NMDA receptors?
Ketamine and psychomimetric agents (eg. Phencyclidine)
128
What do GABAa receptors do? What type of receptor are they?
Operate a chloride channel
| Ionotropic
129
What do GABAb receptors do? What type of receptor are they?
Operate a potassium channel
| Metabotropic
130
How do benzodiazepines work?
Positive allosteric modulators of GABAa:
- Enhance chloride entry
- Hyperpolarisation
- Even further enhancement in presence of GABA
131
How do barbituates work?
Similar to benzodizapeines
| Potentiate effect of GABA at GABAa
132
How does baclofen work?
GABAb agonist:
- Enhances potassium efflux
- Hyperpolarisation
133
How does glycine work?
Acts on an ionotropic glycine receptor:
| - Gates a chloride channel
134
Where is glycine released and what neurones does it usually affect?
Interneurones in spinal cord
| Inhibits antagonistic muscle motoneurones
135
What do ionotropic receptors essentially act as?
ON-OFF switches
136
What is a quanta?
The amount of transmitter in 1 vesicle
137
How can we increase quanta release?
Extensive innervation:
- eg. Purkinje cell (Inferior Olivary Neurone Synapse_
- eg. Inhibitory basket cell (Cerebellum, hippocampus, cortex)
Mega humongous presynapse:
- eg. Calyx of Held synapse
138
What are Hermann currents and what do they trigger?
Local current flow
| Trigger -all-or-nothing' APs
139
What do low threshold mechanoreceptors mediate?
Touch
Vibration
Pressure
140
What do low threshold thermooreceptors mediate?
Cold and cool
Indifferent
Warm and hot
141
What do thermal nociceptors respond to?
Extreme temperatures:
- >45 degrees celcius
- 10-15 degrees celcius
142
What do chemical nociceptors respond to?
Substances found in tissues in inflammation
143
What info do slowly adapting tonic/static adaptation responses provide? What is this important in?
Position
Stretch
Force
Important in posture
144
What info do rapidly adapting phasic/dynamic adaptation responses provide? What is this important in?
Detect changes in stimulus strength eg. rate of motion
Examples:
- Some muscle spindle afferents
- Hair follicle afferents
145
What info do very rapidly adapting very phasic/dynamic adaptation responses provide? What is this important in?
Respond only to very fast movements eg. Rapid vibration
| Eg. Pacinian corpuscle
146
Which axon types have the thickest myelin and the biggest diameter from the skin and their equivalent from muscles/tendons?
A-alpha
| Group i
147
Which axon types have the thinest myelin and the second smallest diameter from the skin and their equivalent from muscles/tendons?
A-delta
| Group iii
148
Which axon types are unmyelinated and have the smallest diameter from the skin and their equivalent from muscles/tendons?
C
| Group iv
149
What is the function of A-alpha fibres?
Proprioception of skeletal muscle
150
What is the function of A-beta fibres?
Mechanoreceptors of skin
151
What is the function of A-delta fibres?
Pain and temperature
152
What is the function of C fibres?
Temperature, pain and itch
153
What is the receptive field (RF)?
The RF of an afferent neurone is the region that, when stimulated, adequately causes a response in that neurone.
The peripheral terminal of primary afferent neurones
154
How is the size of an RF evidenced?
By two point discrimination:
- ~2mm on fingertips
- ~10mm on palms
- ~40mm on forearms
155
How does decreasing the RF size affect discriminative capacity?
Increases it
156
Where are Meissner's corpuscles most abundant and absent?
Most abundant where 2 point discrimination highest
| Absent in hairy skin
157
Where are Merkel's discs most abundant and present?
Similar distribution as Meissner's corpuscles and some present in hairy skin
158
How are Merkel's discs grouped?
In Iggo domes:
- Multiple discs innervated by a single myelinated fibre
- Both cell and fibre are mechanosensitive
159
What do both the cell and fibre express in Merkel's discs?
Piezo2
160
Where are Krause end bulbs found?
At border of dry skin and mucous membranes
161
Where are Ruffini endings found?
Within dermis and joint capsules
162
Where are Pacinian corpuscles found?
Within dermis and fascia
163
What cutaneous receptors are encapsulated?
Meissner's corpuscles
Ruffini endings
Pacinian corpuscles
164
What fibre group do Meissner's corpuscles transmit to and what modality does it detect?
A-beta
| Stroking/Flutter (rapidly adapting)
165
What fibre group do Merkel disc receptors transmit to and what modality does it detect?
A-beta
| Pressure and texture (slowly adapting)
166
What fibre group do Pacinian corpuscles transmit to and what modality does it detect?
A-beta
| Vibration (very rapidly adapting)
167
What fibre group do Ruffini endings transmit to and what modality does it detect?
```
A-beta
Skin stretch (slowly adapting)
```
168
What fibre group do Hair (G) guard (long) transmit to and what modality does it detect?
A-beta
| Stroking/Flutter
169
What fibre group do Hair (D) down (short) transmit to and what modality does it detect?
A-delta
| Light stroking
170
What fibre group do C mechanoreceptors transmit to and what modality does it detect?
C
| Stroking, social and erotic touch
171
What are the grey matter subdivisions?
Horns (dorsal and ventral)
| 10 distinct Laminae of Rexed
172
In which laminae do nociceptors (A-delta/C fibres) terminate in the spinal cord?
Laminae i and ii
173
In which laminae do low threshold mechanoreceptors (A-beta) terminate in the spinal cord?
Laminae iii, iv, v and vi
174
In which laminae do proprioceptors (A-alpha) terminate in the spinal cord?
Laminae vii, viii and ix
175
What sensations does the Dorsal Column Medial Lemniscus (DCML) pathway transmit?
Discriminatory touch
Pressure
Vibration
Conscious proprioception
176
What sensations does the Spinothalamic Tract (STT) transmit?
```
Pain (lateral)
Thermosensation (lateral)
Crude touch/Pressure (ventral)
Itch (ventral)
Tickle (ventral)
```
177
Where does the Dorsal Column Medial Lemniscus decussate?
Brainstem (great sensory decussation)
178
Where do the first order neurones of the DCML end?
Brainstem
179
Where do the second order neurones of the DCML ascend and end?
Medial lemniscus to ventral posterolateral nucleus of thalamus
180
Where do the third order neurones of the DCML end and via where?
Primary sensory cortex (S1) via posterior internal capsule
181
Where does the Spinothalamic Tract decussate?
At each level of the spinal cord (anterior white commissure) close to point of entry via Lissauer's Tract
182
Where do the first order neurones of the STT end?
Ipsilateral spinal cord (at each level)
183
Where do the second order neurones of the STT end?
Thalamus
184
Where do the third order neurones of the STT end?
Primary sensory cortex
| Also cingulate and insular cortices
185
What sensations does the Spinocerebellar Tract transmit?
Proprioceptive info from:
- Muscle spindle (dorsal)
- Golgi tendon organs (ventral {and dorsal])
186
In what part of the DCML do sensations from the lower limb (up to T6) travel?
Fasciculus gracilis (gracile tract) - more medial
187
In what part of the DCML do sensations from the upper limb (above T6) travel?
Fasciculus cuneatus (cuneate tract) - more lateral
188
Where are the soma of trigeminal sensory neurones?
Trigeminal sensory ganglion
189
Where do the 2nd order neurones of the trigeminal system start?
Either the:
- Chief sensory nucleus (general tactile)
- Spinal nucleus (pain and temperature)
190
Where do the 2nd order neurones of the trigeminal system decussate and project to?
Ventroposteriomedial nucleus of thalamus via trigeminal lemniscus
191
Where do the 3rd order neurones of the trigeminal system relay info to?
Cortex via thalamocoritcal neurones
192
Where is the primary sensory cortex (S1) located?
Post-central gyrus of the parietal cortex
193
What is the primary sensory cortex immediately posterior to?
Central sulcus (SI)
194
What is the primary sensory cortex adjacent to?
Posterior parietal cortex (S2)
195
What Brodmann areas makes up the primary sensory cortex?
3a, 3b, 1 and 2 (from anterior to posterior)
196
Where do inputs to the primary sensory cortex come from?
Venteroposterior thalamus:
- ~70% to Brodmann areas 3a and 3b
- ~30% to Brodmann areas 1 and 2
197
What sensory input does Brodmann area 3a deal with?
Proprioception
198
What modality sensitivity is Brodmann area 3a responsible for?
Body position
199
What sensory inputs does Brodmann area 3b deal with?
Cutaneous (Merkel's and Meissner's) AND
| Brodmann area 3a
200
What modality sensitivity is Brodmann area 3b responsible for?
Touch (texture, shape, size)
201
What sensory inputs does Brodmann area 1 deal with?
Cutaneous (rapid mechanoreceptors)
| Brodmann area 3b
202
What modality sensitivity is Brodmann area 1 responsible for?
Texture discrimination
203
What sensory inputs does Brodmann area 2 deal with?
Joint afferents
Golgi tendon organs
Deep tissues
Brodmann areas 3a and 3b
204
What modality sensitivity is Brodmann area 2 responsible for?
Object perception (size and shape - Stereognosis)
205
In what cell layer of the somatosensory cortex do thalamic inputs mainly terminate in?
iv - Lamina granularis interna
206
From superficial to deep, what are the six cell layers of the somatosensory cortex?
```
Lamina i - Lamina molecularis
Lamina ii - Lamina granularis externa
Lamina iii - Lamina pyramidalis externa
Lamina iv - Lamina granularis interna
Lamina v - Lamina pyradmidalis interna
Lamina vi - Lamina multiformis
```
207
What does the posterior parietal cortex do?
Receives and integrates info from S1 and other cortical areas (visual, auditory) and sub-cortical areas (thalamus)
208
Damage to the posterior parietal cortex causes what symptoms/signs?
Agnosia
Asterognosia
Hemispatial neglect syndrome
209
Where are upper motor neurones found?
Within the brain
210
Where are the lower motor neurones found?
Soma in the brain stem
| Some in ventral column of spinal cord
211
Apart from UMNs, where else do LMNs receive inputs from?
Proprioceptors and interneurones
212
What do LMNs command?
Muscle contraction
213
What neurones comprise LMNs? What are their functions?
Alpha-motor neurones:
- Innervate the bulk of muscle fibres that generate force
Gamma-motor neurones:
- Innervate muscle spindles
214
Where are there more motor neurones? Why?
```
Cervical enlargements (C3-T1) for arms
Lumbar enlargement (L1-S3) for legs
```
215
What is the motor unit comprised of?
The alpha-motor neurone and all the muscle fibres it supplies
216
What is a motor neurone pool?
The collection of alpha-motor neurones innervating a single muscle
217
Force of contraction of a muscle is graded by what 2 main principles?
- AP frequency of alpha-motor neurones (each cause a twitch)
| - Recruitment of synergistic motor units
218
Are LMNs innervating axial muscles located more medially or laterally to those supplying distal muscles?
Medially
219
Are LMNs innervating flexors located more dorsally or ventrally to those supplying extensors?
Dorsally
220
What are the three inputs to an alpha-motor neurone?
Central terminals of dorsal root ganglion cells
UMNs
Spinal interneurones
221
For fine movements, what is the size of a motor unit? Where might these units be present?
Small (few fibres)
| Extraocular eye muscles
222
For postural muscles, what is the size of a motor unit? Where might these units be present?
Large (100s - 1000s)
| Leg muscles
223
How are alpha-motor neurones innervating fast motor units different to those innervating slow units?
Larger
| Faster conducting axons
224
Usually, there is one motor axon endplate (NMJ) per muscle fibre. Where is this untrue?
Extraocular eye muscles
225
Where are motor axon endplates usually located on a fibre?
Near centre
226
There are fast and slow skeletal muscle types. How do they differ?
How fast myosin ATPase splits ATP to provide energy for cross-bridge recycling
227
Where do Type i (slow-oxidative) fibres get ATP from?
Oxidative phosphorylation
228
Why are Type i fibres fatigue resistant?
Slow contraction and relaxation
229
Why are Type i fibres red?
Rich in myoglobin
230
Where do type iia (fast) fibres get ATP from?
Oxidative phosphorylation
231
Are Type iia fibres fatigue resistant or not?
They are
232
What colour are Type iia fibres?
Red
233
Where do Type iib/x fibres get ATP from?
Glycolysis
234
Are Type iib/x fibres fatigue resistant or not?
They aren't
235
What colour are Type iib/x fibres?
Pale
236
What are the features of a fast-fatiguing motor unit?
Very high tension
Large alpha-motor neurones
Type iib/x fibres
237
What are the features of a fatigue resistant motor unit?
High tension
Intermediate alpha-motor neurones
Type iia fibres
238
What are the features of a slow motor unit?
Low tension
Small alpha-motor neurones
Type i fibres
239
How does increasing the muscle load affect the contraction velocity?
It decreases it
240
What is the Henneman Size Principle?
The susceptibility of an alpha-motor neurone to discharge an AP is a function of its size
241
Which alpha-motor neurones are more easily activated and trained?
Smaller alpha-motor neurones
242
What is the myotatic reflex?
When a skeletal muscle is pulled, it pulls back
243
Change in length (and rate of change) of a muscle is registered by what structure? What does this contribute to?
Muscle spindle
| Non-conscious proprioception
244
What does a muscle spindle consist of?
A fibrous capsule
Intrafusal muscle fibres
Sensory afferents:
- Type ia class (myelinated and very fast)
Gamma-motor neurone efferents (innervate intrafusal fibres)
245
What is the process by which a muscle responds to stretch?
1. Muscle spindle stretches
2. Activation of Ia afferents
3. Excitatory transmission in spinal cord (glutamate)
4. Activation of alpha-motor neurone (extrafusal fibre innervation)
5. Homonymous muscle contraction
246
What type of reflex in the myotatic reflex?
Monosynaptic (only one in the body)
247
In what muscles in the myotatic reflex more prominent?
Extensor muscles
248
The supinator (wrist) reflex assesses what spinal levels?
C5-C6
249
The biceps (elbow) reflex assesses what spinal levels?
C5-C6
250
The triceps (elbow) reflex assesses what spinal levels?
C7
251
The quadriceps (knee) reflex assesses what spinal levels?
L3-L4
252
The gastrocnemius (ankle) reflex assesses what spinal levels?
S1
253
What part of muscle spindle intrafusal fibres do Ia sensory neurones innervate?
A non-contractile equatorial region
254
What part of muscle spindle intrafusal fibres do gamma-motor neurones innervate?
Contractible polar ends
255
Where are the cell bodies of gamma-motor neurones located?
Ventral horn
256
What does gamma-motor neurone stimulation result in?
Spindle contraction
257
Why is the muscle spindle kept taut?
Maintains its sensitivity
258
What are dynamic/bag 1 nuclear bag fibres responsible for?
Very sensitive to rate of muscle length change
259
What are static/bag 2 nuclear bag fibres responsible for?
More sensitive to overall muscle length
260
What are chain fibres sensitive to and what innervates them?
Absolute muscle length
| Static gamma-motor neurones
261
What do type Ia afferents form around an intrafusal fibre?
A primary annulospiral nerve winding around the centre
262
What do type II afferents form on an intrafusal fibre?
Flowerspray endings (except on dynamic bags)
263
Type Ia afferents are more sensitive to what?
Rate of length change
264
Type II afferents are more sensitive to what?
Absolute intrafusal fibre length
265
Only static gamma-motor neurones are activated during what activities?
Where muscle length changes slowly and predictably:
- Sitting
- Standing
- Slow walking
266
When are both dynamic and static gamma-motor neurones activated?
Where muscle length changes rapidly and unpredictably
267
Where are Golgi tendon organs located?
Muscle-tendon junctions
268
What do Golgi tendon organs do?
Monitor muscle tension (in series with extrafusal fibres)
269
What fibres innervate Golgi tendon organs?
Ib sensory afferents
270
What is the function of Golgi tendon organs?
Regulate muscle tension in order to:
- Protect muscle from overload
- Keep tension in an optimal range
271
What is the course of a group Ib afferent?
Enter spinal cord
Synapse with inhibitory interneurones:
- Synapse upon alpha-motor neurones of same muscle
272
What reflex is the result of group Ib afferent firing?
Inverse myotatic reflex - Muscle relaxation
273
Where are free nerve endings located in joints?
Capsule
| Connective tissue
274
Where are Golgi type units located in joints?
Ligaments
275
Where are Paciniform endings located in joints?
Periosteum near articular attachments
| Also in fibrous part of capsule
276
Where are Ruffini endings located in joints?
Joint capsule
277
What are the most numerous sensory units in joints?
Free nerve endings
278
What is the function of free nerve endings in joints? What is the threshold and adaptation rate of these?
Nociceptive
| High-threshold and slowly-adapting
279
What is the function of Golgi type units in joints? What is the threshold and adaptation rate of these?
?Protection
| High-threshold and slowly-adapting
280
What is the function of Paciniform endings in joints? What is the threshold and adaptation rate of these?
Detect acceleration
| Low-threshold and slowly-adapting
281
What is the function of Ruffini endings in joints? What is the threshold and adaptation rate of these?
Static position and movement speed
| Low-threshold and slowly-adapting
282
What do inhibitory interneurones mediate?
Inverse myotatic reflex
| Reciprocal inhibition between extensor and flexor
283
What is reciprocal inhibition?
Voluntary contraction of an extensor stretches the antagonising flexor - Myotatic reflex
284
What do the descending paths of reciprocal inhibition do?
Activate extensor alpha-motoneurones
Inhibit flexor alpha-motoneurones
Results in unopposed extension
(The opposite can occur)
285
What do excitatory interneurones mediate?
Flexor reflex
| Crossed extensor reflex
286
What is the flexor reflex?
Flexion due to noxious stimuli
287
What is the crossed extensor reflex?
Extension due to noxious stimuli
288
What is the function of the crossed extensor reflex?
Enhances postural support:
| - When injured foot withdraws, supporting leg extends to prevent falling over
289
What activity do excitatory interneurones display
Oscillatory/Pacemaker
290
In a simplistic motor control hierarchy, what is the function of the highest levels?
Strategy (what is the aim of the movement)
291
What do the highest levels in a simplistic motor control hierarchy involve?
Neocortical association areas
| Basal ganglia
292
In a simplistic motor control hierarchy, what is the function of the middle levels?
Tactics (sequence of extension and flexion)
293
What do the middle levels in a simplistic motor control hierarchy involve?
Motor cortex
| Cerebellum
294
In a simplistic motor control hierarchy, what is the function of the lowest levels?
Execution (activate motor pools - movement)
295
What do the lowest levels in a simplistic motor control hierarchy involve?
Medulla
| Spinal cord
296
Where are the cell bodies of the corticospinal (pyramidal) tracts located?
Motor cortex (~2/3):
- Brodmann areas 4 and 6
Somatosensory areas of parietal cortex (~1/3):
297
Where do axons of the corticospinal tract course after leaving their site of origin?
Base of medulla - Medullary pyramid
298
Where do the fibres of the corticospinal tract decussate? What tracts do these form?
```
Pyramidal decussation:
- 75-90% of fibres
- Lateral corticospinal tract
More caudally (in spinal cord):
- 10-25% of fibres
- Initially stay ipsilaterally as the ventral corticospinal tract
```
299
What is the function of the lateral corticospinal tract?
Controls fine movement of limbs
300
Damage above the pyramidal decussation will cause what lateral corticospinal deficits?
Contralateral motor deficits
301
Damage below the pyramidal decussation will cause what lateral corticospinal deficits?
Ipsilateral motor deficits
302
What is the function of the ventral corticospinal tract?
Axial muscles of the trunk
303
Where does the rubrospinal tract originate?
Magnocellular red nucleus
304
Where does the rubrospinal tract receive inputs from?
Motor cortex
| Cerebeullum
305
Where do axons of the rubrospinal tract decussate?
Ventral tegmental decussation
306
Where does the rubrospinal tract descend in relation to the lateral corticospinal tract?
Ventrolateral
307
What is the function of the rubrospinal tract?
Controls flexors
308
What are the lateral descending spinal tracts?
Corticospinal tract
| Rubrospinal tract
309
Generally, what do lesions of the lateral tracts result in?
Loss of 'fractioned' movements:
- ie. Shoulder, elbow, wrist and fingers can't move independently
Slowing and impairment of accuracy of voluntary movements
310
What do lesions of the lateral tracts have little effect on?
Posture
311
The rubrospinal tract, if not damaged, can take over some functioning of the lateral corticospinal tract if lesioned. What functioning can't it restore?
Distal flexors
| Independent finger movements
312
Where do the soma of the vestibulospinal tracts reside?
Vestibular nuclei
313
Where do the soma of the vestibulospinal tracts receive input from?
Vestibular labyrinths via CN VIII
| Also cerebellum
314
Where does the lateral vestibulospinal tract originate from?
Lateral vestibular nucleus (Deiter's nucleus)
315
Does the lateral vestibulospinal tract descend ipsilaterally or contralaterally?
Ipsilaterally
316
What is the function of the lateral vestibulospinal tract?
Help with posture:
- Facilitate extensor motor neurones
- In antigravity muscles (eg. legs)
317
Where does the lateral vestibulospinal tract end (roughly)?
Lumbar spinal cord
318
Where does the medial vestibulospinal tract originate from?
Medial vestibular nucleus
319
Where does the medial vestibulospinal tract end (roughly)?
Cervical spinal cord
320
What is the function of the medial vestibulospinal tract?
Control neck and back muscles:
| - Head movements
321
Where do the soma of the tectospinal tracts reside?
Superior colliculus (aka optic tectum)
322
Where does the tectospinal tract receive inputs from?
Direct input from retina
Input also from:
- Visual cortex
- Afferents conveying somatosensory and auditory info
323
Where do the axons in the tectospinal tract decussate?
Dorsal tegmental decussation
324
Is the tectospinal tract more medial or lateral?
Medial (close to midline)
325
Where does the tectospinal tract end?
Cervical spinal cord
326
What is the function of the tectospinal tract?
Influences muscles of the:
- Neck
- Upper trunk
- Shoulders
327
Where do the reticulospinal tracts originate?
Reticular formation
328
Where is the origin of the reticulospinal tracts located?
Along the length and at the core of the medulla
329
Does the pontine (medial) reticulospinal tract descend ipsilaterally or contralaterlly?
Ipsilaterally
330
What is the function of the pontine (medial) reticulospinal tract?
Enhances postural neck reflexes
Maintains standing posture:
- Helps facilitate lower limb extensor contraction
331
Does the medullar (lateral) reticulospinal tract descend ipsilaterally or contralaterlly?
Neither - Bilaterally
332
What is the function of the medullar (lateral) reticulospinal tract?
Opposes actions of pontine tract
| Helps relax antigravity muscles
333
What controls both reticulospinal tracts?
Descending signals from cortex
