Pain : Peripheral Mechanisms & Central Pathways Flashcards
Explain the process of sensation
1- Stimulus activates receptor in skin
2- action potential is elected in the dorsal route ganglion nerves
3- AP enters the spinal cord and synapses onto ascending nerve in Dorsal route horn
4- nerves travel across spinal cord, cross over and ascend into brain usually via thalamus
5- signal travels to sensory cortex and is processed
Where is the sensory cortex located
Outer area of the cerebrum and closely aligned to motor cortex
Explain what are somatic senses ( give examples )
Senses that aren’t dependent on a specialized organ. For ex: thermoception, magnetoception, proprioception, nociception, equilibrioception.
Explain what are interoceptive senses
Senses perceived from internal organs.
What are the two components of pain
1- nociception: unconscious detection of harmful stimuli using sensory receptors
2- emotional and subjective response to to the nociception
What is the Nociceptor
The receptor type associated with pain. Has a simple free nerve ending.
Where are nociceptors located
Located all throughout the skin, arterial walls, joint surfaces. Sparsely distributed throughout deeper body tissue.
Where are the nociceptors in the Brian
in the walls of the blood vessels and the meninges
What fibres are associated with nociceptors
1- A delta: myelinated nerve fibres that have rapid conduction velocity
2- C : unmyelinated fibres with slow conduction
Activity in the A delta fibres results in which sensations
Sharp, immediate pain that is highly localized.
Activity in the C fibres results in which sensations
Dull pain that is hard to locate, lingers and occurs after slow delay. ( SLOW pain )
What can evoke A delta fibre and C fibre pain
A : mechanical or thermal stimuli
C: mechanical, thermal or chemical stimuli
Where is Fast pain not felt
In most deep tissue
What are the chemical mediators of pain
1- Potassium and Histamine bradykinin are released from damaged cells to activate nociceptors
What is histamine bradykinin responsible for
characteristic changes occurring during inflammation
Explain the process of chemical mediator release as nociceptor activators ( 5 different chemicals )
1- IgE coated antigens attach to the surface of mast cells and basophils
2- K+ and histamine bradykinin are released from the mast cells and basophils
3- Tissue damage stimulates prostaglandins production = increases sensitivity. of nociceptors without activating them
4- Excess H+ during high intensity exercise can elicit pain
5- 5-HT ( serotonin ) is released from activated platelets when they aggregate at a site of blood vessel damage. Activate nociceptors
What Can activate nociceptors other than chemicals
1- extreme temperature
2- strong pressure
What channels are involved with pain responses and how
Transient Receptor Potential ( ion )channels
1- TRPV1 : sensitive to high temp, H+ and mechanical stimuli and post burn allodynia
2- TRPM8 : methanol and cold receptor
3- TRPAA1: irritant and cold receptor
What is Allodynia
A type of pain where a person is extremely sensitive to touch. pain in response to something not normally painful. Ex: post burn allodynia
What is Gracile fasiculus and how does it work
A tracts that carries visceral pain signals ( kidney stones, stomach ache ).
1- Tract carries A delta fibres up spinal cord without crossing over and into the gracile nucleus in the medulla oblongata.
2- Crosses over before traveling to thalamus and cortex
How do the facial pain signals reach the brain
1- Travel primarily via the trigeminal nerve , through the pons and to the medulla.
2- second order neurones, usually C fibres bring the signal through the thalamus and to the cortex ,
Explain what happens when a nociceptor in the torso or limbs is activated
1- first order pain fibres carry the signal from affected tissue to dorsal horn of spinal cord
2- single synapses onto second order neurons that crossover and ascend into spinothalamic or spin-reticular tracts
3- If spinothalamic tract: nerve synapses in thalamus and then to somato-sensory cortex
4- If in spin-reticular tract: nerve synapse in reticular formation in the Brian stem and then to somato-sensory cortex
Branches of the spin-reticular third order nerves innervate which structures
The hypothalamus and the limbic system
What is released by C fibres to pass on signal
Glutamate and substance P
