Lecture 11: Sensory Physiology Flashcards
Sensory Aα What is its classification of afferent fibers? Is the fiber diameter large of small? What is its conduction velocity? What receptors does it supply?
Ia and Ib
large
80-120 m/s (fast)
Primary muscle spindles and Golgi tendon organs
Sensory Aβ
What is its classification of afferent fibers?
What receptors does it supply?
II
Secondary muscle spindles, skin mechanoreceptors
Sensory Aδ
What is its classification of afferent fibers?
What receptors does it supply?
III
Skin mechanoreceptors, thermal receptors, and nociceptors
Sensory C What is its classification of afferent fibers? Is the fiber diameter large of small? What is its conduction velocity? What receptors does it supply?
IV
small
0.5-2 m/s (slow)
Skin mechanoreceptors, thermal receptors, and nociceptors
Motor Aα
What receptors does it supply?
Extrafusal skeletal muscle fibers
Motor Aβ
What receptors does it supply?
Intrafusal skeletal muscle fibers
Motor B
What receptors does it supply?
Preganglionic autonomic fibers
Motor C
What receptors does it supply?
Postganglionic autonomic fibers
What does Meissner corpuscle sense?
Touch and vibration; flutter and tapping
<100 Hz
Where is Meissner corpuscle located?
Glaborous skin
What does Pacinian corpuscle sense?
High frequency vibration
Where is Pacinian corpuscle located?
Both hairy and glaborous skin
What does Ruffini corpuscle sense?
Magnitude and direction of stretch
Touch, pressure, and proprioception
Where is Ruffini corpuscle located?
Both hairy and glaborous skin
What does a Merkel cell sense?
Pressure
Where is a Merkel cell corpuscle located?
Glaborous skin
What does a hair follicle receptor sense?
Motion across skin and directionality of that motion
What does a tactile free-nerve ending sense?
Pain and temperature
What is two point discrimination?
Ability to distinguish between two stimuli applied at a close distance is determined by measuring the minimum distance between the two stimuli
Where is tactile acuity the highest?
Are receptive fields small or large?
Fingertips and lips
Small
Where is tactile acuity the lowest?
Are receptive fields small or large?
Calf, back, thigh
Large
Where is Somatosensory area 1 located?
Post central gyus
What is the function of Somatosensory area 1?
Integration of information for position sense, size, and shape discrimination
Where is Somatosensory area 2 located?
Wall of Sylvian Fissure
Receives input from S1
What is the function of Somatosensory area 2?
Responsible for comparisons between objects, different tactile sensation, and deciding what becomes a memory
What is the function of parieto-temporal-occipital association area?
High level interpretation of sensory inputs
What is the law of projection?
Regardless of the place along an afferent pathway that is stimulated, the sensation is perceived to come from the place that the innervation arises.
What phenomenon can the law of projection explain?
Phantom limb
What is pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
What is nociception?
The neural process of encoding noxious stimuli
What is hypersensitivity?
Increased responsiveness of nociceptive neurons to their normal input, and/or recruitment of a response to normally subthreshold inputs
What is hyperaesthesia?
Increased sensitivity to stimulation, excluding the special senses
What is hyperalgesia?
Increased pain from a stimulus that normally provokes pain
What is allodynia?
Pain due to a stimulus that does not normally provoke pain.
Classic example is the lay of sheets on skin that has been sunburned.
What fibers provide precise localization of pain?
Aδ
What fibers provide pain information?
Aδ (sharp localized) and C fibers (dull, throbbing)
What are mechanical nociceptors?
Response to mechanical forces ranging from moderate pressure with a blunt object to overtly tissue-damaging stimuli
What are chemical nociceptors?
Response to endogenous or exogenous chemical compounds, such as pro-inflammatory mediators, acids, or capsaicin
What are thermal nociceptors?
Response to noxious heat and cold will directly activate thermal receptors expressed by nociceptors
What is the function of the transient receptor potential (TRP) family of receptor ion channels?
Sense a broad range of changing environments in the body tissue: pH, inflammatory mediators, heat, cold, and exogenous chemicals.
What does TRPV1 sense?
Sensitive to vanilloid compounds, most notably, capsaicin
What pain conditions is TRPV1 involved with?
Migraine Dental pain Cancer pain Inflammatory pain Neuropathic pain Visceral pain Osteoarthritis
What pain conditions is TRPA1 involved with?
Dermatitis Chronic itch Painful bladder syndrome Migraine Irritable bowel syndrome Pancreatitis
What activates TRMP8
Cold temperatures and agents
What happens where there are no pain inputs to the C fibers?
Inhibitory interneurons suppress pain pathway
What happens when there are pain inputs to the C fiber?
C fibers stop the inhibitory interneurons and send a strong signal to brain
How can pain be modulated?
- Aβ fiber is activated and travels to dorsal horn and synapses on an inhibitory neuron, releasing an EAA.
- Released glycine inhibits secondary sensory neuron on nociceptive pathway.
How are pain signals reduced?
- Activation of PAG leads to fibers going to Locus Coeruleus (NE) and Raphe nucleus (serotonin)
- NE and serotonin released into dorsal horn and activate inhibitory interneurons
- Opiates released and activates mu receptors on terminals of C-fibers, reducing nociception
What does the theory of central sensitization say?
- Level of spinal cord, higher brain areas, or both
- Reduces threshold of involved neurons to noxious stimuli
- Synaptic Plasticity: Persistent stimulation of NMDA receptors and intracellular signaling cascades
- Central Inflammation
What does the theory of peripheral sensitization say?
- Inflammation can make nociceptors in injured tissues more sensitive (e.g. Prostaglandins and bradykinin)
- Body more sensitive to thermal changes, activating TRPV1
What role does the primary sensory cortex play when it comes to the sensory system?
Recognizes crude senses
What role does the secondary sensory cortex play when it comes to the sensory system?
Cognitive interpretation of crude senses
What role does the PTO play when it comes to the sensory system?
High level integration of many senses
What role do the primary and secondary sensory cortices play when it comes to pain?
Crude localization
What role does the insular cortex play when it comes to pain?
Interpretation fo pain
What role does the amygdala play when it comes to pain?
Emotional component
What role does the hypothalamus/medulla play when it comes to pain?
Physiologic integration
What neuropeptides do peptidergic nociceptors express?
Substance P and CGRP
What up-regulates neuropeptides?
Chronic inflammation
What are non-peptidergic nociceptors involved in?
Somatic chronic pain (e.g. diabetic neuropathy)
