Ch 6: Pain & Temperature Flashcards
what are the 3 general types of sensory receptors?
1- exteroceptive receptors
2-proprioceptive receptors
3- interoceptive receptors
what do exteroceptive receptors respond to?
respond to stimuli from the external environment
including visual, auditory and tactile stimuli
what do proprioceptive captors do?
receive information about the relative positions of the body segments and of the body in space
what to interoceptive receptors detect?
internal events such as changes in BP
where does the somatic system primarily receive information from?
exteroceptive and proprioceptive receptors
what are the 4 major subclasses of somatic sensation?
1- pain sensation
2-thermal sensation
3-position sense
4-touch-pressure sensation
pain sensation results from:
noxious stimulation of the body surface
thermal sensation consists of:
the separate senses of cold and warmth and occurs with exposure to temperatures colder or warmed than the body surface
position sense results from:
mechanical changes in the muscles and joints, but it includes the sensations of static limb position and limb movement (kinesthesia)
touch-pressure sensation occurs with:
mechanical stimulation of the body surface
the anterolateral system mediates the:
sensations of pain, itching, temperature and simple touch
itching sensation is related to ____?
pain
simple touch is a form of ?
touch pressure sensation that includes a feeling of light contact with the skin associated with light pressure and crude sense of tactile localization.
the anterolateral system originates from?
neurons located in several layers of the dorsal horn of the SC
most of the axons projecting from these neurons cross the midline through the ventral white commissure and ascend the SC, to give rise to a diffuse bundle of fibers projecting through the anterior and lateral funiculi
the cells of anterolateral system origin are activated by:
small-diameter, lightly myelinated and unmyelinated dorsal root afferents
including Adelta (III) and C (IV) fibers as well as larger myelinated cutaneous afferents
the anterolateral system includes the:
spinothalamic tracts and the spinoreticular tracts (which do not reach the thalamus and thus can’t be termed spinothalamic)
dorsal roots convey __________ to the SC
essentially all sensation from receptors below the face
what is a dermatome?
area of skin supplied by one dorsal root
cutaneous branches of each peripheral nerve carries fibers from more than one spinal nerve, and the skin territory of each of these peripheral nerves covers portions of several dermatomes
a few sensory fibers have been discovered in the ventral roots. many of these ventral root afferents respond to ____?
painful stimuli from superficial or deep tissues
the cell bodies of the dorsal root fibers are located _____?
in the spinal or dorsal root, ganglia
there are no synapses in a dorsal root ganglion
dorsal root fibers enter the spinal cord through the ___?
dorsal root entry zone- a region of the dorsolateral sulcus
the largest and most heavily myelinated fibers (Aalpha and Abeta) generally occupy the most ____ position in the dorsal root entry
medial
small myelinated and unmyelinated fibers (Adelta and C) occupy the most ____ position of the dorsal root entry.
lateral
what makes up a spinal nerve?
the convergence of dorsal and ventral roots
what makes up a peripheral nerve?
peripheral to the convergence of a spinal nerve, a mixture of sensory and motor fibers from the individual spinal nerves separates into bundles or fascicles that join those of adjacent spinal nerves
what are the peripheral receptors for pain?
the naked terminals of small (Adelta and C) nerve fibers
many of these may be specialized chemoreceptors that are excited by tissue substances released in response to noxious and inflammatory stimuli.
many substances have been implicated, including histamine, bradykinin, serotonin, acetylcholine, substance P high concentrations of K, and substances involved in the arachidonic acid cascade
the concentration of hydrogen ion in these substances is critical in the activation of pain receptors
the cell bodies of Adelta and C axons mediating noxious stimuli are in the ____ and enter the SC through the ____ part of the dorsal root zone and immediately divide into _____ and ______ that run longitudinally in the _________?
dorsal root ganglia
enter the SC through the lateral part
divide into short ascending and descending branches
posterolateral fasciculus
these fibers leave to connect synaptically with neurons in the dorsal horn. At their connections with these neurons, Adealtha and C fibers release glutamate and substance P, etc.
Interneurons in laminae I-IV project to neurons in laminae V and there make synaptic connection on the cells of origin of the anterolateral system (including spinothalamic and spinoreticular tracts/projectoions. Neurons in lamina I give rise to fibers that contribute directly to spinothalamic tracts
the posterolateral faciculus is also known as:
Lissauer’s tract
what is the leminscal system?
one of the major sensory pathways ascending the spinal cord and into consciousness; conducts sensitive impulses relating to touch, pressure, vibration and joint proprioception via the dorsal funiculus and the medial lemniscus and thalamus before reaching the cortex.
what is the limbic system?
a group of brain structures (including the hippocampus, gyrus fornicatus, and amygdala) common to all mammals; it is associated with olfaction, autonomic functions, and certain aspects of emotion and behavior.
the axons of spinothalamic tract cells in laminae I-V cross ___________ and then course ________?
cross anterior to the central canal in the ventral white commissure
and then course rostrally in the anterolateral funiculus
the spinothalamic and spinoreticular tracts ascend through the _____ and supply ____?
through the SC and brain stem
supply inputs to:
- other SC segments
- the reticular formation
- superior colliculus
- several thalamic nuclei (including the intralaminar nuclei and then ventral posterolateral nucleus (VPL)
what is the VPL?
ventral posterolateral nucleus
the VPL is considered to be part of the ?
ventrobasal complex in which activity mediated by the spinothalamic projections converges with activity carred by the lemniscal system
projections of the anterolateral system to the VPL are organized ___?
somatotopically, so the fibers carrying input from the upper body are located medial to those with input from the lower body
somatosensory organization is maintained in the projections of fibers from the VPL conveying painful and thermal sensation to the ____?
primary somatosensory cortex: Brodmann’s areas, 3,1, and 2 of the postcentral gyrus
the primary somatosensory cortex is organized by __?
body parts (somatotopically), like the adjacent primary motor cortex
the fibers from the upper parts of the body project to cortical areas near the lateral fissure
the lower limb and perineum terminate on the medial surface of the hemisphere in the paracentral lobule
the postcentral gyrus is interconnected with the ____? together, these areas are responsible for _____?
posterior portions of the parietal lobe
responsible for localizing pain stimuli and for integrating the pain modality with other types of sensory stimuli
only a few fibers in the anterolateral system project directly from the SC to the thalamus; these fibers constitute the ______?
spinothalamic tracts
the spinothalamic tracts include a group of old phylogenetically old fibers _____ and the phylogenetically newer ____?
old fibers- Paleospinothalamic tract
new fibers- Neospinothalamic tract
the paleospinothalamic tract projects to the ___
medial portions of the thalamus (the intralaminar nuclei)
the neospinothalamic tract projects to the ____
ventral posterolateral region of the thalamus
the anterolateral system is predominantly a ?
slowly conducting, polysynaptic system
where do most of the anterolateral system fibers synapse?
in the reticular (net-like) formation of the brain stem
**Spinoreticular tracts
from the cells of the reticular formation, ascending fibers relay…
relay pain information to the medial and intralaminar nuclei of the thalamus and to the hypothalamus and limbic system
although most fibers of the anterolateral system cross the midline before ascending, some, particularly those _____
conveying visceral sensory information in the spinoreticular tracts, ascend ipsilaterally
pain fibers from the face, cornea of the eye, the sinuses, and the mucosa of the lips, cheeks, and tongue travel in the ____
trigeminal nerve to its sensory ganglion
trigeminal nerve sensory ganglion=
semilunar, trigeminal or gasserian ganglion
what is VPM?
ventral posteromedial nucleus
the ascending trigeminal pathway also projects to the:
reticular formation and the medial and intralaminar thalamic nuclei which receive projections from the anterolateral system of the SC
the cortical projections of the VPM are to the part of the somatosensory cortex closest to the lateral fissure
what areas of the body are most sensitive to somatosensory stimuli?
lips and fingers
these areas have disproportionately large areas of neuronal representation in the somatosensory cortex
thalamocortical fibers from neurons in the intralaminar thalamic nuclei and parts of the VPL-VPM complex relay pain information to the ____?
secondary somatic sensory area of the cerebral cortex
what are the 4 aspects of pain?
distinctive sensation
the individual’s reaction to this sensation (including accompanying emotional overtones)
activity in both somatic & autonomic systems
both reflex & volitional efforts of avoidance or escape
what are the 3 types of pain sensation?
1- fast pain
2- slow pain
3- deep/visceral pain
what is fast pain?
consists of a sharp, pricking sensation that can be localized accurately
results from activation of Adelta fibers (myelinated)
what is slow pain?
burning sensation that has a slower onset, greater persistence and a less clear location
results from the activation of C fibers (unmyelinated)
what is deep/visceral pain?
either aching, sometimes with a burning quality, or cramping
results from stimulation of visceral and deep somatic receptors such as those in joints and muscles
cramping type may signify the obstruction of a hollow viscus
innervated by both unmyelinated C fibers and Adelta myelinated fibers that pass through the sympathetic nerves
neospinothalamic pathway is essential for __?
spatial and temporal discriminateion of painful sensations
neospinothalamic pathway projects …
to the VPL of the thalamus and from there to the primary somatosensory cortex
paleospinothalamic pathway and the spinoreticular pathways connect to the __?
secondary somatosensory cortex, hypothalamus and limbic system
paleospinothalamic pathway and the spinoreticular pathways mediate ___?
systemic autonomic responses to pain and probably the emotional and affective responses as well
In patients with complete destruction of the somatosensory areas of cerebral cortex on one side of the brain..
painful stimuli can be detected on the contralateral side of the body (provided the thalamus and lower structures remain intact)
destruction of the posterior and intralaminar nucleu of the thalamus can ?
relieve intractable pain
such lesions may be effective only briefly, however, and pain may return
lesions of the dorsomedial and anterior nuclei of the thalamus or transection of the fibers linking these nuclei to the frontal lobe and anterior cingulate cortex (prefrontal leukotomy) can..
diminish the anguish of constant pain by changing the psychologic response to painful stimu
unfortunately, marked negative changes in personality and intellectual capacities occur after creation of these lesions
bilateral section of the cingulum bundle has proved to be effective in relieving patients’ reaction to pain without causing the drastic personality changes that occur with prefrontal leukotomy
the receptors in the skin for the sensations of cold and warmth consist of ___?
naked nerve endings
the peripheral nerve fibers mediating temperature sensations are..
thinly myelinated Adelta and some C fibers
other types of C fibers mediate only the painful components of the extremes of hot and cold stimuli
the CNS pathway for thermal sensation appears to follow the same course as what pathway?
Pain
the 2 systems are so closely associated in the CNS that they cannot be distinguished anatomically, and injury to one usually affects the other to a similar degree
the parenchyma of internal organs, including the brain itself, doesn’t contain:
pain receptors
visceral pain pathways are located:
- within the walls of arteries
- all peritoneal surfaces
- pleural membranes
- dura mater covering the brain
these structures can be sources of severe pain, especially with inflammation or mechanical deformation
abnormal contraction or dilation of the walls of hollow viscera, including blood vessels, also causes pain
pain fibers from viscera project to:
to the SC as components of the sympathetic nerves
in contrast, fibers conveying primarily nonpainful visceral sensations project to the CNS as components of parasympathetic nerves
what is referred pain?
pain of visceral orgigin is apt to be vaguely localized. it may be perceived in a surface area of the body far removed from its actual source
a theory- visceraly sensory fibers discharge into the same pool of neurons in the SC as fibers from the skin and an “overflow” of impulses results in misinterpretation of the true origin of pain
what is tractotomy?
sectioning of the lateral spinothalamic tract in the SC to relieve intractable pain
cut in the anterior part of the lateral funinculus
usually some damage to the ventral spinocerebellar tract but no permanent symptoms develop except for a loss of pain sensibility on the contralateral side beginning 1 or 2 segments below the cut
in some patients, pain relief occurs only temporally- suggesting that other routes may be available or that both crossed and uncrossed tracts mediate nociceptive sensations in the SC
mechanical compression or local inflammation of dorsal nerve roots irritates …
pain fibers and commonly produces pain along the distribution of the affected roots
what is radicular pain?
pain distributed over an area that is consistent with the boundaries of 1 dermatome or more than one adjacent dermatome
sensory changes other than pain associated with dorsal root irritation
-paresthesias, hyperesthesia, hypethesia, anesthesia
what are paresthesias?
localized areas
spontaneous sensations of prickling, tingling, or numbness
what is hyperesthesia?
zones in which tactile stimuli appear to be grossly exaggerated
What is hypesthesia?
diminshed sensitivity
pathologic process progresses and gradually destroys fibers, the dorsal roots will eventually lose their ability conduct sensory impulses
what is anesthesia?
=complete absence of all forms of sensibility in the affected dermatomes.
essentially all areas of skin receive fibers from more than a single dorsal root; consequently:
damage to a single dorsal root may cause little or no sensory loss
what natural substances mediate analgesia?
opioid peptides, serotonin, dopamine, norepinenphrine
interneurons are activated that inhibit the transmission of painful sensations at the first synaptic connection in the pain pathway- pain may be suppressed through intrinsic, endogenous CNS mechanisms
what is central pain?
injury of the CNS, usually affecting the spinothalamic or trigeminothalamic tracts, can result in severe, spontaneous pain in portions of the body represented in the damaged tracts.
often cutaneous stimulation of the affected region triggers or worsens central pain, although the pain can also occur without provocation.
lesions of many portions of the CNS can lead to central pain, including the cerebral cortex, thalamus, brain stem and SC
what is a frequently encountered form of central pain?
after injury to the thalamus (often from stroke)
the VPL and VPM are usually involved and the patient develops a marked decrease of all modalities of sensation on the contralateral side of the body. usually the affected limbs are also paralyzed bc of damage to the corticospinal tract which is located in the internal capsule adjacent to the thalamus. generally several weeks later the patient develops an agonizing burning pain in the affected parts of the body, worsened by any sort of sensory stimulation of the painful areas.
what is thalamic syndrome?
the comination of hemianesthesia with spontaneous pain and hemiparesis
