PBL 2 - Sub Arachnoid Haemorrhage Flashcards
Difference Between Pain and Nociception
Pain:
- Perceptual phenomena - The consequence of Nociception - A subjective feeling - Defensive mechanism
Nociception:
- Signalling in the nervous system resulting from tissue damage
You can have tissue damage/nociception without pain/psychological distress
What are Mirror Neurons?
Activated by watching another person experience something
What are the steps involved in detecting nociception?
1) Origin of nociception is the process of tissue damage
2) Local effects and Signal generation - Leads to local effects (axon reflex) - Nociceptors convert mechanical or chemical signals into afferent neural action potentials 3) Transmission - Ascending neural pathways to the brain 4) Perception and emotions from higher centres 5) Antinociceptive signals sent back down - intrinsic opioid compounds
What is the Axon Reflex?
- Release of chemical mediators from local axon terminals
- Activation of immune system locally
- Degranulation of mast cells
- Arteriole dilation
- Smooth muscle contraction
- Plasma extravasation from nearby vessels
What are the different types of Pain receptors?
3 Classes of pain receptors
- Thermo - Chemo - Mechanical (associated with sharp prickling pain) - Polymodal ( acitvated by a variety of stimuli and found in almost all tissues)
What substances activate Nociceptors?
Alogenic chemicals include:
- Potassium (from damaged cells) - Serotonin (From Platelets) - Bradykinin (From Plasma) - Histamine (From Mast cells) - Prostaglandins (From damaged cells - arachidonic acid) Capsaicin (From chilli- has their own receptors)
What is the Nociceptor Reflex?
- Motor action performed automatically without involvement of consciousness
- Nociceptive information enters the Dorsal Horn of the spinal cord
- Information decussates as normal to the ascending pathway to the brain
- Some synapses in the local interneurons in the anterior horn to facilitate movement
- In the Anterior spinal cord there are alpha motor neurons that control skeletal muscles
This allows for motor movement that will remove the body part from the nociceptive stimulus.
How does Pain information get to the brain?
- Nociceptive information gets to the brain via the Spinothalamic pathway
- Initial stimulus is detected by terminal nociceptors
- This then travels through the Dorsal Root Ganglion
- Enters the spinal cord through the dorsal horn
- Synapses with the second order Neuron in the dorsal horn of the spinal cord
- Second order neuron decussates immediately to the anterior contralateral side of the spinal cord
- Ascends via the spinothalamic pathway to the brain- reaches the thalamus and also branches to the amygdala
- The 2nd order neuron synapses with the 3rd order neurone in the thalamus
The 3rd order neuron then takes the information to the somatosensory cortex (post central gyrus)
What is the Paleospino thalamic Pathway?
What type of pain does it produce? What type of fibre does it use? What Neurotransmitter does it use? What is the localisation of the pain? Where does it project the nociceptive information to in the brain?
Paleospino-thalamic pathway
Type of pain:
Produces aching, dull or burning pain
Type of Pain Fibre:
Travels via C fibres to DEEPER dorsal horn of spinal cord
Neurotransmitter:
- Transmits via substance P (slow sustained action)
Localisation:
- Passes to brain and produces poorly localised and usually distressing pain
Location in the brain and outcome:
- Most go to reticular formation, and then to the thalamus - producing increased alertness and arousal
The Neospino thalamic pathway
What type of pain does it produce? What type of fibre does it use? What Neurotransmitter does it use? What is the localisation of the pain? Where does it project the nociceptive information to in the brain?
Neospinothalamic pathway
Type of pain:
Produces Sharp, pricking pain from mechanical and fast thermal nociceptors
Type of Pain Fibre:
Travels via A delta fibres to the SUPERFICIAL dorsal horn of the spinal cord
Neurotransmitter:
- Transmits via Glutamate (Rapid and precise action)
Localisation:
- Passes to brain and produces well localised painful stimuli
Location in the brain and outcome:
- Most go to Somatosensory cortex and produce highly localised sensations
What is the Periaqueductal gray?
Where is it located?
What is its function in relation to pain?
- It is the gray matter located around the cerebral aqueduct within the tegmentum of the midbrain
- Receives information from the hypothalamus or limbic cortex regarding pain
- functions as an inbuilt anti nociceptive system to produce endogenous analgesics
- Has enkephalin producing cells that secrete in response to pain and act as a suppressant
- Projects to the Nucleus raphe magnus via the pontine noradrenergic neurons
Endogenous opiods are released
Explain Nociceptive pain
What stimulates it?
Is inflammation present in the cns?
Is it adaptive?
- No nervous system lesion or CNS inflammation
- Stimulus dependent pain
- Adaptive- protects by signalling potential tissue damage
- Has physiological stimuli such as mechanical, thermal or chemical
Explain Inflammatory pain What stimulates it? Is inflammation present in the cns? Is it adaptive? What can cause it?
- Active inflammation is present
- Can be spontaneous pain or stimulus dependent
- Can be evoked by stimulus that is usually not pain producing (light touch)
- It is adaptive and reversible - protects itself by producing hypersensitivity during healing
- Has peripheral and central amplification through inflammtory mediators
- Caused by : surgical inflammation, tissue trauma, joint inflammation
Explain Dysfunctional pain What stimulates it? Is inflammation present in the cns? Is it adaptive? What can cause it?
- No known structural nervous system lesion or active peripheral inflammation
- Spontaneous as well as stimulus dependent pain
- Present even with a lack of stimulus
- It is maladaptive and potentially persistent
- Caused by :
○ Fibromyalgia - sensitization of CNS nociceptive pathways
Primary Erythermalgia- mutation in Na channel leads to increased excitability of nociceptors
Explain Neuropathic pain
What stimulates it?
Is inflammation present in the cns?
Is it adaptive?
- Nervous system lesion or disease is present
- Marked neuroimmune response
- Spontaneous as well as stimulant derived pain
- There is sensory amplification maintained independent of the disease
Commonly perisistant and maladaptive
