Eileen - Motor control, PD and functional anatomy of learning Flashcards
(154 cards)
1
Q
Describe declarative memory
A
- Factual information
- Life events
- Available to the consciousness
- Easily formed and forgotten
2
Q
Describe non-declarative memory.
A
- Procedural memory
- Motor skills
- Not available to the consciousness
- Less easily formed and forgotten
3
Q
Describe ballistic movements
A
Movement based on pre-programmed instructions
Rapid, but at the expense of accuracy - can’t accommodate unexpected changes
4
Q
Describe visual feedback movements.
A
- Motor command continually updated according to sensory feedback (e.g. Visual)
- Highly accurate - can be modified in progress
- Slow
5
Q
Out of ballistic and visual feedback movements, which is used more often in the body?
A
A mixture of both
6
Q
What does stimulation of the primary motor cortex do?
A
Elicits muscle twitches/movements depending on the amount of stimulation
7
Q
What is the somatotrophic map?
A
Certain areas of the motor cortex specifically control certain areas of the body
8
Q
How is the somatotrophic map distorted?
A
Face, hands and digits receive larger representation in the primary motor cortex - due to more through the required for fine control
9
Q
If there is a stroke or haematoma in or near the primary motor cortex, what (motor) effect will be had on the body?
A
Paralysis and loss of sensation on the side contralateral to the pathology
10
Q
What sensory information is crucial for co-ordinated movements?
A
- Proprioception - feedback from peripheral sensory reports on the positions and movements of limbs
- Vision - eyes, visual system, visual cortex
- Vestibular - feedback from organ of balance
11
Q
What are the main non-cortical structures required for movement?
A
- Basal ganglia
- Cerebellum
12
Q
What is the input and output from the basal ganglia?
A
- Input - prefrontal motor cortex (intended movement)
- Output - premotor area of the thalamus
13
Q
What are the functions of the basal ganglia?
A
- Initiation of movement - puts motor plan into action
- Planning of complex voluntary movement
14
Q
What is the input and output for the cerebellum?
A
- Input - sensory cortex
- Output - primary motor cortex (via the thalamus)
15
Q
What are the functions of the cerebellum?
A
- Co-ordination and smooth execution of movements
- Motor learning
- Error detection
16
Q
What does damage to the cerebellum do?
A
Causes cerebellar ataxia - poor co-ordination
17
Q
What are the lateral descending motor pathways?
A
Corticospinal and rubrospinal - pyramidal neurons in primary motor cortex project to the spinal cord (corticospinal) and red nucleus (rubrospinal)
18
Q
What are the functions of the lateral motor pathways?
A
Control of voluntary movements - e.g. Fine control of the hand by distal muscles
19
Q
What is the function of the vestibulospinal tract?
A
Balance and posture
20
Q
What is the function of the reticulospinal tract?
A
- Medial path facilitates voluntary movement and increased muscle tone
- Lateral path inhibits voluntary movements and decreases muscle tone
21
Q
What is the function of the tectospinal tract?
A
Co-ordinates movements in the head in relation of visual stimuli
22
Q
What evidence is there for function of the supplementary motor cortex?
A
Imaging studies show your primary motor cortex, premotor cortex and supplementary motor cortex are involved involved in moving a finger. However, only the SMA is involved in THINKING about moving the finger (but not actually moving it)
23
Q
What are the symptoms of Parkinson’s disease?
A
- Resting tremor
- Bradykinesia
- Shuffling gait
- Muscular rigidity
- Progression to general cognitive decline
24
Q
What are the two treatments for Parkinson’s?
A
- Levodopa - and carbidopa to prevent peripheral breakdown
- Deep brain stimulation
25
What is Huntington's disease?
Suppression of activity in the basal ganglia
26
What are the symptoms of Huntington's disease.
* Choreas
* Difficulty speaking and swallowing
* General cognitive decline
27
How do intrinsic circuits of the spinal cord produce the rhythmic motorneuron activity which drives stepping?
* Alternating activity in flexor and extensor muscles co-ordinated across two limbs
* Two sets of pattern generating neurons project to flexor and extensor motorneuron pools respectively
* Reciprocal inhibitory connections between the two sets of pattern generating neurons help to co-ordinate their activity - alternating excitement of flexors and extensors
28
Motorneuron pools of each muscle form columns in the ventral horn, what are they called?
Motornuclei
29
What is the most important mechanism for grading motor force?
Recruitment of motor neurons
30
Describe the effect of action potential frequency in motor axons on muscle fibre contraction.
* The more action potentials, the stronger the muscle contraction
* No rest period means each action potential increases contraction form an already elevated level
31
What does the frontal lobe do?
* Reasoning
* Behaviour
* Mood
* Movement
32
What is the function of the temporal lobe?
* Hearing
* Memory (hippocampus)
* Semantics
33
What is the function of the parietal lobe?
Sensory - pain, pressure, temperature
34
What is the function of the occipital lobe?
Sight
35
What is the corpus callosum.
Connects the cerebral hemispheres and allows communication between them
36
What is the amygdala and what does it do?
* It is a group of neurons located deep to the medial temporal lobes
* Processing and memory of emotional reactions
37
What is the general role of the limbic system?
Supports a variety of functions including emotion, behaviour and long-term memory
38
What is the function of the basal ganglia?
Co-ordinates gross, automatic muscle movements and regulates muscle tone
39
Which brain regions make up the diencephalon?
* Epithalamus
* Thalamus
* Hypothalamus
* Subthalamus
40
What is the function of the epithalamus?
* Consists of the - pineal gland (melatonin secretion - biological clock and sleepiness)
* Habenular nuclei (emotional response to olfaction)
41
What is the function of the thalamus?
* Relays sensory information to the cerebral cortex
* Includes nuclei involved in voluntary, motor and arousal actions
* Anterior nucleus functions in emotions, memory, cognition and awareness
42
Describe the function of the subthalamus
Contains
* subthalamic nuclei
* portions of basal substantia nigra
* portions of red nucleus
Helps control body movements
43
Describe the function of the hypothalamus
* Controls and integrates ANS and pituitary gland activities
* Regulates emotional and behavioural patterns
* Controls body temperature
* Regulates eating and drinking behaviour
44
What structures make up the midbrain?
* Midbrain
* Superior colliculus
* Inferior colliculus
45
What is the function of the midbrain?
* Relays motor impulses from cerebral cortex to the pons
* Relays sensory impulses from the spinal cord to thalamus
46
What is the function of the superior colliculus?
Co-ordinates movement of the eyeballs in response to visual and other stimuli
47
What is the function of the inferior colliculus?
Co-ordinates movement of the head and trunk in response to auditory stimuli
48
What brain parts make up the hindbrain?
* Cerebellum
* Pons
* Medulla oblongata
49
What is the function of the cerebellum?
* Co-ordinates smooth and complex movements
* Regulates posture and balance
50
What is the function of the pons?
* Relays impulses from one side of cerebellum to the other, and from medulla to midbrain
* Contains nuclei of origin for CNV, VI, VII, and VIII
51
What is the function of the medulla oblongata?
* Relay between brain and spinal cord
* Reticular formation functions in consciousness and arousal
* Vital centres regulate heartbeat, breathing and blood vessel diameter
* Other centres co-ordinate vomiting, swallowing, coughing, sneezing and hiccuping
* Contains nuclei of origin for CNIX, X, XI and XII
52
What does the vestibulocochlear nerve do?
Sensory- hearing and equilibrium
53
What is the function of the primary motor cortex?
Generates nerve impulses that control the execution of movement
54
What is the function of the posterior parietal cortex?
* Transforms visual information into motor commands
* Sends this information to premotor and supplementary motor cortex areas
55
What is the function of the premotor cortex?
* Sensory guide of movement
* Controls more proximal and trunk muscles
56
Describe the function of the supplementary motor cortex.
Planning and co-ordination of complex movements
57
What is the input and output for the striatum of the basal ganglia?
* Input - brain regions - motor cortex, premotor cortex
* Output - globus pallidus internal (inhibitory neurons)
58
What are the components of the basal ganglia?
* Dorsal striatum - caudate nucleus and Putamen
* Substantia nigra
* Globus palidus - internal and external
* Subthalamic nuclei
* Thalamus
59
What is the input and output for the globus palidus internal of the basal ganglia?
* Input - inhibitory neurons of the striatum
* Output - stops inhibiting the thalamus
60
What is the input and output for the substantia nigra of the basal ganglia?
* Input - excitatory neurons of the subthalamic nucleus
* Output - dopaminergic neurons that excite the inhibitory messages the striatum is sending to the globus palidus internal
61
What is the input and output for the subthalamic nucleus of the basal ganglia?
* Input - excitatory neurons from the motor cortex and inhibitory neurons from the substantia nigra
* Output - excitatory neurons to the substantia nigra
62
What is the substrate for dopamine synthesis?
Tyrosine
63
In the cytoplasm a of the dopaminergic neuron, what is tyrosine converted to?
DOPA via the action of tyrosine hydroxylase
64
How is DOPA converted to dopamine?
DOPA-decarboxylase
65
How is dopamine transported into storage vesicles?
Active transport carried out by the vesicular transporter mechanism
66
What is dopamine re-uptake 1?
When dopamine is released into the synaptic cleft and is then actively transported back into the neuronal terminal (this happens to 50% of dopamine in cleft)
67
What happens to the dopamine in the neuronal terminal that isn't transporterd into vesicles for storage and release?
It's broken down by the mitochondrial enzyme monoamine oxidase
68
What is re-uptake 2?
When some of the dopamine (10%) in the synaptic cleft is actively transported into the effector cell
69
How is dopamine inactivated in the effector cell?
Inactivated by the enzyme catchol-o-methytransferase (COMT)
70
What happens the 40% of dopamine still left in the synaptic cleft?
Diffuses into the circulation and is broken down by monoamine oxidase and COMT in the liver
71
What are the end products of dopamine metabolism?
Organic acids and alcohol - excreted in the urine
72
What are the four main dopaminergic pathways in the brain?
1. Nigrostriatal pathway
2. Mesolimbic pathway
3. Mesocortical pathway
4. Tuberhypophyseal system
73
What is the name of the bundle of monoamine containing fibres that the nigrostriatal, mesolimbic and mesocortical system travel in?
Medial forebrain bundle
74
Where are the cell bodies found in the nigrostriatal pathway?
In the substantia nigra
75
Where are the cell bodies for the dopaminergic neurons in the mesolimbic pathway?
In the midbrain ventral tegmental area (VTA) adjacent to the substantia nigra
76
Where do the neurons in the mesolimbic pathway project to?
Parts of the limbic system- especially the nucleus accumbens and amygdaloid nucleus
77
Where are the cell bodies of the neurons in the mesocortical pathway found?
In the midbrain ventral tegmental area (VTA)
78
Where do the neurons of the mesocortical pathway project to?
Frontal cortex
79
Where do the neurons of the tuberohypopyseal system start and terminate?
Run from the ventral hypothalamus to the median eminence and pituitary glands
80
What is the function of the tuberohypopyseal system of dopamine action?
Controls secretions of the pituitary gland
81
Which dopamine receptors are in the D1 receptor family?
D1 and D5
82
Which dopamine receptors are in the D2 receptor family?
D2, 3 and 4
83
Which areas are D1 receptors found in?
* Striatum
* Limbic system
* Thalamus
* Hypothalamus
84
Which areas of the brain are D2 receptors found in?
* Striatum
* Limbic system
* Thalamus
* Hypothalamus
* Pituitary gland
85
What are the function of D2 receptors?
Inhibitory autoreceptors
86
What are the effects in the periphery that dopamine receptors (D1) exert?
* Renal vasodilation
* Increased myocardial contractility
87
What is the function of dopamine in the nigrostriatal system?
* Excites the inhibitory messages being sent to the globus palidus.
* Fine tunes motor movements
88
What is the function of dopamine in the mesolimbic and mesocortical systems?
* Mediates the pleasure system in the brain (reward pathway)
* Allows motivational and emotional responses
89
What is the function of dopamine in the tuberohypopyseal system?
Acts on lactotrophs in the pituitary gland to inhibit release of prolactin.
90
Where do neurons of the noradrenergic system arise from?
Neurons of the locus coeruleus - on one each side of the pons
91
List the places in the brain that the neurons from the locus coeruleus (noradrenergic neurons) innervate?
* All the cerebral cortex
* Thalamus
* Hypothalamus
* Olfactory bulb
* Cerebellum
* Midbrain
* Spinal cord
92
What is the function of the noradrenergic system?
Regulates attention, arousal, sleep-wake cycles, leaning, memory, anxiety, pain, mood and brain metabolism
93
Where do the serotonin-containing neurons originate?
The nine-raphe nuclei
94
Where do the more caudal (medulla) of the nine raphe nuclei project?
The spinal cord - modulate pain-related sensory signals
95
Where do the more rostral (those in the pons and midbrain) of the nine raphe nuclei innervate?
Most of the brain, in the same diffuse way as the locus coeruleus neurons
96
When do serotonin neurons fire the most rapidly?
Fires the most during wakefulness (when aroused and active) - most quiet during sleep - so involved in the sleep-wake cycles
97
Describe the reticular activating system.
Includes the raphe nuclei and the locus coeruleus Included the reticular core of the brainstem in the processes that arouse and awaken the forebrain
98
Define Parkinson's disease.
Progressive degenerative disorder of the basal ganglia that results in variable combinations of tremor, rigidity and bradykinesia
99
What is the pathology that causes Parkinson's?
Dopamine depletion resulting from a degeneration of the dopamine nigrostriatal system
100
What are some other reasons (apart from dopamine depletion) that can cause Parkinsonism.
* Postencephalitic syndrome
* Side effects of anti-psychotic drugs (block dopamine receptors)
* Toxic reaction to a chemical agent
* Outcome of severe CO poisoning
101
What are the pathological processes that destroy the nigrostriatal system.
* Oxidative stress
* Apoptosis
* Mitochondrial disorders
* Auto-oxidation of dopamine may injure the neurons
102
Describe what happens in alpha-synuclein mutations to cause Parkinson's.
Alpha-synuclein are a member of a family of proteins found mostly in the substatia nigra
Mutations cause an autosomal dominant form of the disease - mutation can cause this protein to form Lewy bodies (eosinophilic cytoplasm inclusions found in surviving neurons)
103
Name the two mutations associated with Parkinson's disease.
Alpha-synuclein mutations
Parkin mutations - autosomal recessive early onset form of Parkinson's
104
Describe the tremors associated with Parkinson's disease.
* Affects distal segments of limbs - hands, feet, head, neck, face, lips and tongue
* Rhythmic flexion and contraction
* Usually unilateral
* Occurs when limb is supported/at rest
* Disappears in movement or when sleeping
105
Describe the rigidity associated with Parkinson's disease.
* Resistance to movement of flexors and extensors
* Most evident during passive joint movements- cogwheel rigidity- requires lots of energy to perform
* Flexion contraction occur due to rigidity
* Starts unilateral - becomes bilateral
106
What is bradykinesia?
* Slowness in initiating and performing movements
* Difficulty with sudden, unexpected stopping of voluntary movements
* Unconscious movements occur in a series of disconnected steps - not in a smooth manner
107
Describe problems bradykinesia causes.
* Difficulty initiating walking and turning
* Feet may freeze in place while walking
* Lean forward when walking to maintain centre of gravity
* Small, shuffling steps without swinging arms
108
Describe some of the later stage Parkinson symptoms.
Loss of postural reflexes
Voluntary/emotional face movements become limited - mask like face
Loss of blinking reflex
Tongue, palate and throat muscles become rigid = drooling
Speech becomes slow and monotonous - no modulation and poorly articulated
Excessive sweating, sebaceous gland secretion and salivation - due to basil ganglia involvement with ANS - also causes lacrimation, dysphagia , orthostatic hypertension, thermal regulation, constipation, impotence and urinary incontinence
109
What are the later stage cognitive problems of Parkinson's?
* Cognitive dysfunction occurs in 20-30% of people
* Deficits in executive function disappear first - difficulty planning, starting and carrying out tasks
* Dementia
* Slower rate of decline than in Alzheimer's
110
How does L-DOPA medication help people with Parkinson's?
L-DOPA is a precursor to dopamine
Administering more substrate will increase the amount of dopamine being synthesised in the remaining 20% of healthy dopaminergic neurons
111
What is the disadvantage of L-DOPA?
It only manages symptoms - doesn't fix the destroyed nigrostriatal pathway
Only works while it is present in the body
Only works if there are enough healthy neurons left to convert it into dopamine- doesn't work in late stage Parksinon's because the degeneration has progressed too far
112
Which drugs is often co-administered with Levodopa, and why.
Carbidopa - a DOPA decarboxylase inhibitor - can't cross the blood brain barrier- reduces nausea and vomiting often found with L-DOPA administration
113
Why is levodopa given to patients rather than dopamine?
Dopamine can't cross the blood brain barrier, so would remain in the periphery
114
Why are such large amount of levodopa given to patients?
Because a lot is converted to dopamine in the periphery before it can enter the brain
115
Describe the mechanism of action of carbidopa.
Inhibits dopa decarboxylase, so prevents the peripheral conversion of levodopa to dopamine
Lowers levodopa dose needed by 5-fold
Decreases severity of side effects - vomiting and nausea
116
Define attention
A global/domain specific cognitive process, encompassing multiple sensory modalities, operating across sensory domains.
Global = driving
Domain specific = visual awareness
117
What cognitive processes make up attention?
1. Arousal - a general state of wakefulness + responsivity
2. Vigilance - capacity to maintain attention over prolonged periods of time
3. Divided attention - ability to respond to more than 1 task at once
4. Selective attention - ability to ficus on 1 stimulus while suppressing competing stimuli
118
What is the consequence of breakdown of global attention?
Delirium/acute confusional state - impaired arousal -\> drowsiness - impaired vigilance -\> impersistence - impaired divided/selective attention -\> distractible
Due to a problem with the ascending reticular activating system
119
What is the consequence of breakdown of domain specific attention?
- visual inattention - sensory inattention - neglect
Could be due to e.g. non-dominant hemisphere stroke -\> problem in prefrontal cortex/parietal cortex/limbic cortex
120
What divisions does the prefrontal cortex have? What function are they responsible for?
1. Dorsolateral - Attention
2. Ventrolateral - Behaviour & Judgement
3. Orbitofrontal - Emotional reponses
121
What structures make up the parietal cortex? What is its function?
Functions to recieve + process sensory info from body & skin (somatosensory info) -\> transmits info to other parts of brain -\> co-ordinates info from other parts of brain.
Alsom involved in visual attention + spatial reasoning
122
What are the components of the limbic system? What is its function?
- cingulate gyrus
- hippocampus
- fornix
- amygdala
- orbital + prefrontal cortex
- mamillary bodies
Function:
- memory, learning
- emotion: aggressive + sexual behaviour
- homeostasis mainentance by hypothalamus
123
What makes up the ascending reticular activating system? Function?
- brainstem nuclei
- thalamic nuclei
- cortex
Functions to:
- recieve fibres from sensory pathways via long ascending spinal tracts
- alertness, maintenance, wakefulness, attention
124
What happens in disorders of ascending reticular activating system function?
- impaired arousal/delirium
- metabolic disturbances
- neurodegernative diseases
125
How do you test attention?
1. orientation in time + place?
2. serial 7s (count down from 100 in 7s)
3. digit span + digits backwards (repeat back or write down a series of no's)
4. months of the year/days of the week in reverse
5. stroop test (say the name of the colour written not filled in)
6. star cancellation test
7. trail making test
126
How is memory classified?
Into long term & immediate/working memory
127
What are the features of working memory?
- immediate recall of smal amounts of verbal/spatial info
- functions independently of long-term memory
Central executive function in the dorsolateral prefrontal cortex splits into:
- visual sketchpad (parieto-occipital lobe) -\> spatial info
- phonological store -\> words, numbers, melodies
128
What are the divisions of long-term memory?
129
Describe episodic memory
- a form of explicit/declarative memory: availabel for conscious access + reflection
- personally experiences, temporally specific events
Involves:
- extended limbic system (medial temporal lobe, hippocampus, entorhinal cortex, diencephalon, mamillary bodies, thalamic nuclei)
- dorsolateral prefrontal cortex (for temporary organisation of episodic memory + interaction with structures within the extended limbic system)
- impairment by e.g. Korsakoff's, amnesia, subarachnoid haemorrhage, can lead to acute (delirium) or chronic (dementia) results
130
How do you test episodic memory?
1. Recall complex verbal info
2. Word-list learning
3. Recognition of newly encountered words + faces
4. Recall of geometric figures
131
Describe semantic memory
- another form of explicit/declarative memory: availabel for conscious access + reflection
- factual info/general knowledge & vocab
- independant of context, time, personal relevance (as opposed to episodic)
- storage, maintenance + retrieval are NOT based on limbic system
- info initially process via episodic memory systems, then repeated rehearsal -\> semantic storage
Involves:
- left hemisphere anterior temporal lobe
- anterior temporal cortex + angula gyrus integrate incoming info
Clinical damage could be: herpes simplex, right temporal lobe atrophy, alzheimer's dementia
132
How do you test semantic memory?
1. Test general knowledge + vocab
2. Fluency (e.g. name as many animals as possible in 60secs)
3. Object naming to confrontation
4. Test of verbal knowledge (e.g. what colour is a banana)
5. Person-based tasks (e.g. name photos of famous people)
133
Describe implicit/procedural memory
- no conscious access to implicit memory stores
- we progressively acquire motor skills to perform tasks, but we cannot explain them (e.g. riding a bike, playing an instrument)
- Korsakoff's -\> amnesia
- Involves basal ganglia, cerebellum
134
What are ballistic movements?
Movement based on a set of pre-programmed instructions - rapid delivery but at expense of accuracy
135
What are pursuit/visual feedback movements?
- motor command continually updated according to sensory feedback -\> high accuracy as movement can be modified while in progress BUT slow
136
What are the areas of the brain involved in planning + instructing voluntary movement?
137
Why does the face & hands have the largest representation in the motor homuculus?
Because they're used in fine control
138
Describe the motor pathway
139
Describe the sensory pathway
140
Describe proprioception
Feedback from peripheral sensory receptors on the positions & movement of limbs - somatic sensory cortex
141
What is the input & output of the cerebellum?
Input - Sensory cortex
Output - Primary motor cortex (via thalamus)
142
What is the function of the ventromedial descending motor pathway?
control of proximal + axial (trunk) muscles -\> maintain posture
- descending systems synpase on motor neurones/ interneurones in the spinal cord
143
Describe the knee jerk reflex
Tapping the tendon stretches the muscle to which it is attached -\> a monosynaptic reflec which produces contraction of the stretched muscle:
- muscle spindle is stretched -\> nerve activity increases -\> a motor neuron activity increases -\> muscle fibres contract -\> resist stretching
144
Define motoneuclei
Collections of motor-neurones in the VENTRAL HORN.
Collections formed from columns of all the different motor-neurons of each muscle
(a-motor neurons0
145
Describe 2 methods of non-invasive brain stimulation - used for diagnosis + therapy
1. Transcranial electrical stimulation
2. Transcranial magnetic stimulation
146
Define muscle recruitment
When the nervous system adjusts the number of motor axons firing, which controls the number of twitching muscle fibres
147
Define muscle summation
When the nervous system varies the frequency of action potentials via the motor axons to be between 200-75 ms -\> Ca2+ in the muscle is still above baseline levels from a previous action potential = the muscle fibre is not completely relaxed so the next contraction is stronger than normal
148
Define muscle tetanus
When muscle fibres are stimulated at very high frequencies, the muscle has not time to relax between successive stimuli -\> a smooth contraction many time stronger than a single twitch
149
Define 'motor point'
Points on the muscle which are more sensitive to electrical stimulation than the rest of the muscle.
- usually lie over where the nerve ENTERS the muscle (muscle belly) -\> muscle contraction produced by stimulation of innervating nerve
150
Why does electrical stimulation of an area sometimes cause pain?
At these places, a cutaneous sensory nerve is being stimulated. If the left wrist is being stimulated this is being sent to the right somatosensory cortex etc
151
Curare is a nicotinic acetylcholine receptor antagonist. What effect do you think do you think this drug would have on electrical stimulation of an arm muscle?
What clinical use can Curare provide?
As it would block the ACh receptor, the nerve would not be able to pass the signal on to the muscle so the muscle would not respond to the stimulus.
Clincally:
It could be used as a neuromuscular blocker – sometimes called a “muscle relaxant”, e.g. in the treatment of tetanus, as part of general anaesthesia or in intensive care – to allow assisted ventilation. as a paralysing poison. There are other classes of drugs also sometimes called muscle relaxants, these are anti-spasmodics, used for treatment of spacticity, for example in multiple sclerosis. These latter have different mechanisms of action.
152
Describe how radial nerve compression can cause damage
Compression of the nerve occurs in the spiral groove of the humerus - Normally compression of the nerve causes tingling and pain to alert the sleeper, however after alcohol the warning symptoms may not be noticed. The compression continues for a longer period, resulting in damage to the nerve.
Motor fibres would be affected BEFORE pain fibres
153
Describe the mechanism of damage to a body part due to compression of a nerve
There's both mechanical compression + ischaemia.
## Footnote
- External compression restricts blood supply of nerves in the vasa nervorum. The ischaemia affects transmission of action potentials.
- If compression continues, demyelination occurs which can cause a conduction block.
- Finally continued ischaemia causes axonal damage.
- Compression initially affects the large motor fibres -\> pain fibres
- Effects irreversible if ischaemia occurs for \>8hrs
154
What symptom can compression of the common peroneal nerve result in?
Foot drop - weakness in dorsiflexing foot
