Physiology Flashcards
What is neuropathic pain?
Nerve damage causing pain
What is spontaneous pain?
Pain in the absence of a stimulus
Two Major types of pain fibres and their properties?
A fibres - Fast, myelinated
C Fibres - Slow unmyelinated
What type of pain are C fibres involved in transmitting?
Aching, burning pain
What type of pain are A fibres involved in transmitting? the four types of fibre?
A alpha fibres - muscle pain
A beta fibres - mechanical
A gamma fibres - muscle and pressure
A delta - sharp pain
What do substance P and CGRP do at peripheral synapses?
Lead to flare and oedema
The two types of ascending pathways that transmit pain in the peripheries, their properties?
Spinothalamic (neospinothalamic)
- Direct
- immediate, exact location
Spinoreticulothalamic (Paleospinothalamic)
- Indirect
- Involve limbic structures (amygdala included)
- Emotional and visceral pain
- descending suppression of pain
What fibres are involved in descending suppression of pain? What do they release?
C Fibres release glutamate and substance P
How do glial cells respond to painful stimuli?
What can this lead to?
They release mediators to sensitise the post-synaptic receptor e.g.
IL 1 and 2 TNF NO Prostaglandins Glutamate ATP
This can lead to central sensitisation
Two types of sensitisation?
Central
Peripheral
What mostly leads to central sensitisation?
Repetitive input
What does repetitive input produce?
Wind-up
What is wind up?
Increased electrical activity that results in increased excitability of second order neurones in the spinal cord
What two things can central sensitisation cause?
Define them
Allodynia - Pain from a stimulus that is not usually painful
Hyperalgesia - increased sensitivity to painful stimuli
What are the three main mechanisms of central sensitisation?
Increase of membrane excitability
Synaptic facilitation
Disinhibition (less inhibitory neurotransmitters)
Where does central modulation occur?
The dorsal horn
One main example of how central modulation works?
The gate theory
What is the gate theory?
the theory that descending pathways inhibit pain fibres
A beta fibres inhibit pain fibres in the dorsal horn
Two main types of synapses in the CNS?
Electrical and chemical
What type of synapses are gap junctions?
Electrical
What type of synapses involve the SNARE complex?
Chemical
What is the SNARE complex?
A complex in the pre-synaptic cell that changes in the presence of high intracellular calcium.
In the presence of high calcium the SNARE complex allows a pore to be formed between the vesicles and the cell membrane which allows neurotransmittors to be released.
Three types of chemical synapse?
Axo-dendritic
Axo-somatic
Axo-axonic
What is the one type of chemical synapse that is excitatory as well as inhibitory, also the most common by far?
Axo-dendritic
What is the speed of ionotropic receptors compared to metabotropic receptors?
Ionotropic - Fast
Metabotropic - Slow
Two main ways neuronal transmission is modulated?
G-protein coupled receptors (through second messengers)
Co-transmitters - excitatory and inhibitory (neuropeptides)
How do neuropeptides (co-transmitters) modulate neuronal activity?
Through their action on G-protein coupled receptors
They are only released in high Ca concentration
An example of a neuropeptide involved in pain? what does it do?
Substance P, increases pain transmission
What does enkephalin do?
Reduces pain through reduction of substance P and Glutamate
As each synapse releases on average 1 vesicle each (there are 10,000+) What are the two types of synaptic integration (summation)?
Temporal - summation at the same synapse
Spatial - from several different synapses
What is the loss of both temporal fields of the eye called?
Bitemporal hemianopsia
What area is damaged to cause bitemporal hemianopsia, example of what can cause this damage?
Optic chiasm
Pituitary tumour
Where would damage have occured to cause loss of vision in one eye? examples?
optic nerve
MS
Glioma
Head trauma
What artery would be damage to give one eye full vision loss
Anterior cerebral artery
Haemorrhage of what artery would cause bitemporal hemianopsia?
Anterior cerebral artery (anterior communicating artery)
What would loss of vision to the left temporal visual field and the right nasal field be called?
Left homonymous hemianopsia
Where would damage have occurred to cause left homonymous hemianopsia? Causes?
Optic tract (right side) OR optic radiations
Tumour
What artery would be damaged to cause left homonymous hemianopsia?
Posterior Cerebral Artery
What is left superior quadrantopsia? Causes?
Both superior left quadrants damaged
Temporal lobe tumour