Week 2: Nociception Flashcards
When a noxious stimuli occurs eg a nail penetrating our skin, the nociceptors are stimulated they will then propagate this information about this pain to the spinal cord nearby. Where in the spinal cord does this information go?
It is brought into the spinal cord from the dorsal horn (back of the spinal cord). This is because the sensory fibres are at the dorsal side of the spinal cord
What are the two types of nociceptors?
A-delta fibres & C fibres
What do a-delta fibres do?
Produce fast, well localised sharp pain (myelinated)
What do c-fibres do?
Produce slow & poorly localised pain (burning/throbbing) - unmyelinated
What is the area in the brain that is associated with sensation (ie feeling of touch)? Along this region are specific areas related to specific parts of the body, what is this related to?
Somatosensory cortex - the location of where the pain has occurred correlates to the area of the somatosensory cortex. The homunculus.
What part of the brain does the 2nd order neuron pass the information onto?
The thalamus
What are a-beta fibres? Provide examples
Mechanoreceptors. Light touch, non-noxious, rapid, sharp.
Pacinian corpuscle (Deep dermis - Glabrous)
Merkel cells (Basal layer of epidermis - Glabrous)
Ruffini (Dermis - glabrous)
Meissner corpuscle (Dermal Papillae - Glabrous)
How are nociceptors classified?
- Receptor type: polymodal or high threshold mechanical
- Fibre characteristics: Velocity (speed of transmission), myelination & diameter (these two affect velocity!)
There are lots of new pathways starting in the dorsal root ganglion. Provide examples…
Nociceptors
Mechanoreceptors
Proprioceptors
What happens at the dorsal horn?
Site where the primary afferent fibre synapses with second order neurons.
Explain the pathway from the DRG to the brain (brief)
Lots of new pathways starting in the dorsal root ganglion. These get into the dorsal horn (spinal cord). The message reaches the grey matter and goes via the 2nd order neuron to the brain (allows complex interaction between excitatory and inhibitory interneurons (connects one neuron to another)
Which laminae are important area for modulation and localisation of pain?
Laminae II and V
What laminae do A-beta fibres synapse with? What are these fibres associated with? What neurons do they synapse with and in what laminae? What C-fibre laminae do they directly terminate with?
Laminae III-V. Light touch and vibration. Synapse directly with terminals of unmyelinated c-fibres in lamina II
What laminae do A-delta fibres synapse with? What neurons do they synapse with?
Laminae I-V. Synapse directly with 2nd order neurons.
What laminae do c-fibres synapse with? What neurons do they synapse with?
Laminae I, II, V, X. Synapse indirectly with 2nd order neurons via internueorns
True or False - the dorsal root of the spinal nerve is always for sensory neurons?
TRUE
Provide examples of stimuli that the sensory afferent fibres detect?
Touch, pain and pressure
The first order neuron/nociceptor will release pain neurotransmitters at the dorsal horn which is received by the 2nd order neuron. Explain this process further….
Calcium channels from 1st order neurons release neurotransmitters into the synaptic cleft.
What are the neurotransmitters released by the 1st order neuron? These neurotransmitters
Glutamate (major excitatory amino acid)
Substance P (peptide)
Calcitionin-gene-related peptide (peptide)
Somatic Nociceptive Pain
* Nociceptive pain has an important ….. role because it evokes a ….. sensation that draws immediate ……
* The …. reflex protects the organism from further injury.
Protective, painful, attention
Withdrawal
Nociceptors are specialised ….. that detect and respond to potentially …… forms of …… — ….., ….., and chemical.
Neurons
Damaging
Energy
Heat
Mechanical
The process by which harmful energy is converted into ionic currents is known as ….
Sensory transduction
After, the action potential has been propagated through the axon. Calcium channels from 1st order neurons release neurotransmitters into the synaptic cleft. What are these neurotransmitters?? What is there purpose?
These neurotransmitters act on receptors on 2nd order neurons. What are these receptors called?
What are these neurotransmitters? GSC
- Glutamate (excitatory)
- Substance P
- Calcitonin gene related peptide (CGRP)
They are carrying the action potential to the 2nd order neuron.
The receptors are called AMPA and NMDA
What happens once the information reaches the 2nd order neuron?
The action potential travels to the brain via the spinothalamic pathway (takes it to the thalamus in the brain).
NOTE: There is a third order neuron in the brain. This is where the discrimination of pain then occurs.
Describe the descending pathway
- Sympathetic nervous system activated via hypothalamus
- Inhibition begins in the periaqueductal gray (grey matter in the midbrain - more specifically the brainstem)
- PAG receives pain information via spinomescencephalic tract, processes nociceptive info & relays it to the rostral ventral medulla
- Neurons in the RVM send a signal down the dorsal horn of the spinal cord and activates the endogenous opiate system to suppress pain
In the descending pathway the …. modulates pain perception through direct connections with the descending pain inhibitory system.
Amygdala
TRUE OR FALSE - the PAG is involved in both ascending and descending pathways
TRUE
….. …… is a nucleus in the ….. and is the major producer of …… (the noradrenergic system) to modulate ……
Locus Coeruleus, pons, noradrenaline, nociception
Rostroventromedial Medulla (RVM) receiving a dense innervation from the …… and ….. and projecting to the dorsal horn.
PAG & LC
…… projections also excite opioid interneurones that can ….. the excitatory interneurones and/or inhibit presynaptic receptors on the primary nociceptor. All these can act to turn the volume of nociception to higher centers ……
GABAnergic, inhibit, down
