Physiology Of Pain And Sensation Flashcards
1st/2nd/3rd sensory neurons
Function to conduct sensory information
1st order = is the primary sensory afferent neuron. Start with the receptor on the target and synapses on relay nuclei at the brainstem or spinal cord
2nd order = interneuron that connects the relay nuclei from the brain stem/ spinal cord -> the relay nuclei in the thalamus
3rd order = take infromation from the relay nuclei in the thalamus -> the cerebral cortex
-also represent local interneurons that excite/inhibt signal is within the cerebral cortex.
4th order = resides in the sensory cerebral cortex area specifically. Takes the final relay signal and brings it to the cortex for interpretation
Review of the two major pathways for somatosensory information
1) DCML pathway
- processes the sensations of fine touch/pressure/2 point discrimination/ vibration and proprioception
- 2nd order location = brain stem
- 3rd order location = thalamus
2) anterolateral system
- processes sensations of pain/temperature and light touch
- 2nd order location = spinal cord
- 3rd order location = thalamus
Difference between nucleus gracillis and cuneatus
both are part of DCML pathway
Gracillis = lower body information
Cuneatus = upper body information
Are somatic sensations primarily conscious or sub conscious?
Conscious
- except for muscle length/tension and proprioception
Differences physiologically between types A and C nociceptive fibers
A - faster conduction velocity - myelinated - large diameters - A(beta) = touch/joint positioning, mild pressure and vibration - A(delta) = cold sensations and acute pain C - slower conduction velocity - non-myelinated - small diameters - warm sensations and chronic pain
- type B isnt pain but only visceral afferents and autonomic fibers*
Differences physiologically between group 1/2/3/4 afferent fibers
Group 1:
- largest diameter
- fastest conduction
- myelinated
- conduct proprioception from spindle endings of muscles and in golgi tendon organs
Group 2:
- middle of the pack diameter and conduction
- myelinated
- conducts propose potion of muscle spindles and touch/pressure in skin and deep tissues
Group 3:
- smaller diameter and conduction speeds
- myelinated
- conducts pain from skin and joints as well as shape pain,heat, cold and touch/pressure
Group 4:
- slowest conducting speed
- smallest diameter
- unmyelinated
- conducts slow burning pain and visceral pain from skin and muscles
6 types of tactile receptors in the skin
Pacinian corpuscle
- rapid adaptation
- senses vibration
- encapsulated with a layered capsule
Meissner corpuscle
- same as pacinian except senses touch
Ruffini ending
- slow adaptation
- senses pressure
- encapsulated with a thin capsule
Endings around the Hairs
- rapid adaptation
- senses touch
- nonencapsulated
- has accessory structures
Merkel endings
- slow adaptation
- senses touch
- nonencapsulated
- has accessory structures
Free nerve endings
- variable adaptation
- senses pain/temp/itch/touch
- nonencapsulated
- has no accessory structures
Free nerve endings purpose
Nonspecific responses to touch/pressure/pain and temperature
Most common receptors in the skin
children and adults with type 1 diabetes have abnormal cold thermal perception thresholds
Root hair plexuses purpose
Monitors distortions and movement of the hair follicle via sensory dendrites and rapid action potentials
Very good at adaptation
Tactile discs and Merkel cells purpose
Continuously sensing applied touch sensations
Extremely sensitive and found throughout the skin
tactile disc = Merkel cell + nerve terminal
Meissner corpuscles (Tactile corpuscles)
Provides sensation of fine touch/pressure/ low-frequency vibration
Rapid adaptation and possess thin layers
One of the larger receptors
Pacinian corpuscles (lamellated corpuscles) purpose
Receives sensations of deep pressure
- most sensitive to pulsating or high-frequency vibration
Very fast adaptation
Large receptors as well
Found in
- dermis of fingers, genitalia and mammary glands
- superficial deep fascia and joint capsules
- viscera
- action potential magnitude is directly proportional to the amount of pressure applied to the receptor*
Ruffini corpuscles purpose
Sensative to pressure and distortion (stretch) of deep/reticular dermis
Tonic receptors that dont adapt much
Capsule is surrounded by collagen
Muscle spindle vs golgi tendon organs
Muscle spindles
- detect muscle length/sudden stretch and positioning
- also important for the muscle stretch reflex
- usually excites and does and causes a variety of responses
Golgi tendon organ
- detects excessive tension and positioning.
- important for the Golgi tendon reflex
- usually inhibts and causes muscle relaxation
Transient receptor potential (TRP)
A protein family that are so far hypothesized to be the transducers of thermal sensations
TRPA 1/8 = cold
- 1 is activated by capsaicin
TRPV 3/4 = medium
- 3 is activated by camphor
TRPV 1/2 = hot
