Neurophysiology Flashcards
describe the basic pathway of pain to the brain
- Stimulus activates a receptor (Temperature, pain, touch & pressure receptors)
2) Action potential (AP) elicited in nerve
(called Dorsal Route Ganglion nerves or DRG)
3) AP enters spinal cord and synapses onto an ascending nerve in the Dorsal Route Horn.
4) Nerves travels across the spinal cord (crosses over) and ascends to the brain (usually via the thalamus).
5) Signal travels to the sensory cortex where it is processed and acted upon
describe the difference in myelinated and unmyelinated neurones in pain
Myelinated neurones (A δ):
- Rapid conduction velocity (6 to 30 m/s)
- fast pain
- Sharp
- Seems immediate
- Highly localised
- Superficial tissue
Unmyelinated neurones (C)
- Slow conduction velocity (0.5 to 2 m/s)
- slow pain
- Dull
- Delay (tends to linger)
- Hard to locate
- Superficial and deep tissue
briefly describe the Gracile fasciculus - A δ fibres nociceptor pathways
pain in kidneys
sends signal to spine
but it travels up the same side of the spine that the pain is - only crosses over the. it gets to the nucleus in the medulla
hard to tell exactly where the pain is
Facial nerves (Trigeminal) - C fibres - describe their nociceptor pathway
unmeyelinated
duller pain - pain in gums teeth and in jaw
pathway leads directly into the brain - doesn’t pass through spinal cord
Why would it be advantageous to inform the hypothalamus of injury when a person is in a potentially harmful situation?
fight or flight, descending analgesic pathway
The hypothalamus is part of the limbic system, which is associated with emotion, does this area therefore contribute to nociception or pain perception?
pain perception
describe referred pain and its cause
pain felt in “wrong area”
pain felt where there isn’t a problem
cause:
- nerve from organ and skin enter dorsal root ganglion close together
- when the signal is sent to the brain it can’t discriminate between the two
- so associates the pain in the organ with the skin of the nerve
difference between acute and chronic pain
ACUTE: Physiological: - Nociceptive and inflammatory - Sudden onset in response to a discrete event - Recedes during healing
CHRONIC:
Pathological:
- Neuropathic
- Persists long after recovery (> 3 months)
- Often difficult to tie to a specific event
- Often unresponsive to analgesics
describe neuropathic pain
Occurs as a result of a lesion or disease in the P/CNS – change in neurone not the tissue
Eg diabetic neuropathy, multiple sclerosis, fibromyalgia or spinal cord injury
May be associated with allodynia or hyperalgesia
Hyperalgesia – increased intensity of pain sensation for a given nociceptive stimulus
Allodynia – sensation of pain in response to something not normally painful in nature – eg light touch near a wound
Due to sensitization of peripheral and central neurones
Peripheral sensitization:
- Increased sensitivity of C and Aδ fibres due to prostaglandin release
- Increased voltage dependent Na+ channel expression - more likely to form an action potential to send pain
Central sensitization:
- Increased glutamate release because of peripheral sensitization
- Increased expression of glutamate receptors (NMDA receptor subtype)
o Hyperalgesia
- Sprouting of Aβ (mechanoreceptor) fibres to make new connections
o Normal sensation of pressure now perceived as painful
o Allodynia
Phantom limb pain:
- A type of neuropathic pain
- Reorganization of cortex - confusing because then sensors from other parts of the body like the face or feet start sending signals to the part of the brain that used to hold info for the arm - so therefore person may be actually stimulated on their face but they feel the pain in their face and also their ‘arm’ even though their arm is no longer there
- Sensitization
Question: How could the increased expression of Na+ channels cause an increase in nociceptor sensitivity?
Increased likelihood that the threshold potential will be reached
describe phantom limb pain
Phantom limb pain:
- A type of neuropathic pain
- Reorganization of cortex - confusing because then sensors from other parts of the body like the face or feet start sending signals to the part of the brain that used to hold info for the arm - so therefore person may be actually stimulated on their face but they feel the pain in their face and also their ‘arm’ even though their arm is no longer there
- Sensitization
describe the levels of integration of the brain/spinal cord
So reflexes integrated on a spinal level are simple, concerned with basic survival of the animal such as homeostasis, basic locomotory circuits, postural control and stereotypical behaviour.
Step up one level to subcortical reflex integration and things are a little more advanced. Feeding and drinking behaviours are integrated here, our sexual and instinctual activities being strongly influenced by this more primitive brain area.
Finally humans and other primates have large cerebral cortices. Neural control integrated on a cortical level is quite advanced. The cerebral cortex of man, one could opine, is the apogee of evolution, being the seat of intellect, art, literature, philosophy and science. It certainly is the highest level of neural integration in the healthy human.
describe what the hippocampal system is made up of and its function
Limbic cortex, Hippocampus, fornix, mamillary body
Cognition and interface of intellect and emotion
Memory formation
describe what the amygdaloid system is made up of and its function
Amygdala, Olfactory bulbs, medial forebrain bundle
- more central than hippocampal
Emotional expression, sexual drives
Strengthen memories
- Smells
- Emotions
Motivation and reward
Describe the descending pathway and explain how its activation causes analgesia
Identify circumstances when analgesia may be naturally effective
Identify four types of pharmacological analgesics and explain how they work
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