Touch & Pain Flashcards
Why are receptors that respond to touch found?
They are embedded in the dermal layers of the skin
What are the types of receptors that respond to touch?
Pacinian corpuscles, Meissen corpuscles, Merkel’s disks and Ruffini endings
What do receptors do?
They have ion channels that open in response to mechanical deformation which triggers action potentials
What do Pacinian and Meissen corpuscles respond best to?
Rapidly changing indentations like sense of vibration and flutter
What do Merkel’s disk respond best to?
Sustained indentation of the skin like sense of pressure
What does Ruffini ending respond best to?
Slowly changing indentations
What is receptive field?
Area of skin to which each individual receptor responds
Which has a larger receptive field, Pacinian or Meissner corpuscles?
Pacinian corpuscles
How do receptors work?
Once they detect a stimulus, the receptors send impulses along the sensory nerves that enter the dorsal roots of the spinal cord. The axons connecting touch receptors are large myelinated fibres that convey information through the periphery towards the cerebral cortex extremely rapidly
How and what is the speed at which cold, warmth and pain are detected?
They are detected by thin axons with “naked” endings, which transmit more slowly
What is special about temperature receptors?
They show adaptation
How are touch relayed?
There are relay stations for touch in the medulla and the thalamus, before projection on the primary sensory area in the cortex call3d the somatosensory cortex
Which hemisphere is the right side of the body represented in and why?
The left hemisphere because the nerves crosses midline
What happens at the somatosensory cortex?
The input from the body is systematically mapped across the somatosensory cortex to form a representation of the body surface
What is the packing density like in the somatosensory cortex compared to our actual body?
In the somatosensory cortex, the packing density of neurons is uniform, which for body, the density is not uniform. Therefore, the map of the body surface on the cortex is very distorted
What is sensory homunculus?
Topographic distribution of sensory distribution of body found in the cerebral cortex
How to test different sensitivity across the body?
Using two-point discrimination test
Where is the ability to perceive fine details most highly developed?
Tip of fingers and lips
What is touch also involved in?
Active control of movement
Why is touch involved in the active control of movement?
Neurons in the motor cortex controlling muscles in your arm that move your fingers get sensory input from touch receptors in the finger tips
When do cross-talks happen between sensory and motor systems?
It begins at the first relays in spinal cord, including proprioceptive (stimuli produced) feedback on to motor neurons and continues at all level of the somatosensory system
Where are the primary cortex and motor cortices located relative to each other?
They are right beside beach other
What is crucial for the sense of touch?
Active exploration
Does the identification of textures or objects by touch involve one or different regions of cortex?
It involves different regions
What is something cool about the somatosensory area?
Map of the body in the somatosensory area can vary by experience
What is something about pain receptors?
The information conveyed by pain receptors provide little information about the nature of stimulus
What are nociceptors?
Sensory neuron that responds to damaging or potentially damaging stimuli by sending potentially threatening signals
What kind of receptors do noiceptors include?
Receptors that respond to heat above 46 degree celsius, tissue acidity and to the active ingredients of Chili peppers
What are the two class of peripheral fibres (sensory nerves) that respond to noxious stimuli?
Relatively fast myelinated fibres called A-delta fibres and very fine, slow, non-myelinated C fibres
How do the A-delta and C fibres work?
Both sets of nerves enter the spinal cord, where they synapse with a series of neurons that project up the cerebral cortex. They do so through parallel ascending pathways with A-delta dealing with the localisation of pain while the C fibre dealing with the emotional aspect of pain.
What areas do the C fibre pathway project to?
It projects to quite different areas that the somatosensory cortex, including the anterior cingulate cortex and the insular cortex
What is positron emission tomography (PET)?
A type of nuclear medicine procedure that radioactive substance to measure the metabolic activity of cells of tissue
Which part of the brain is activated during changes in experienced pain intensity?
Somatosensory cortex
Which part of the brain is activated during experience of pain unpleasantness?
Anterior cingulate cortex
Why is pain important?
- Action potentials in the nociceptive nerves entering the spinal cord initiate automate protective reflex such as withdrawal reflex
- pain also result in inhibition of activity, which is the rest that allows healing to occur after tissue damage
What is the first modulatory mechanism discovered to suppress pain for escape reactions?
Release of endogenous analgesics
How is the pain sensation suppressed?
Electrical stimulation of brain areas such as aqueductal gray matter causes a marked elevation in pain threshold and it is brought about by a descending pathway from the midbrain to spinal cord
What chemical transmitter is involved in the suppression of pain?
Endogenous opioids such as met-enkaphalin
What pain-killer act on the same receptor at which endogenous opioids act?
Morphine
What is the phenomenon of enchanced pain called?
hyperalgesia
What happens during hyperalgesia?
There is a lowering of pain threshold, an increase in intensity of pain, broadening of area over which pain is felt or even pain in absence of noxious stimulation
What does hyperalgesia involve?
The sensitisation of peripheral receptors as well as complex phenomena at various levels of ascending pain pathways, which includes the interaction of chemically mediated excitation and inhibition
What does hyperalgesia observed in chronic pain caused by?
Enhancement of excitation and depression of inhibition due to changes in responsiveness of neurons that process sensory information
