Somatosensory Pathways Flashcards
Afferent sensory info travels on the…
1st order neurons from somatic segments of body
Afferent sensory info enters…
spinal cord through dorsal roots
All sensory info that travels to higher centers in the CNS proceed through the…
white fiber tracts
2nd order neurons travel to…
thalamus to be relayed to appropriate area of cortex
Conscious perception of somatic sensation occurs in the…
somatosensory cortex
Most important ascending somatosensory pathways (2):
- dorsal column medial leminscal tract
- spinothalamic tracts
Most important facial somatosensory pathway:
trigemnothalamic tract
First order neurons carry signals from…
receptors into the spinal cord through the dorsal root
Cell body of first order neurons are in the…
dorsal root ganglion
Dermatomes determine where…
nerves carry information
Second order neurons carry signals from…
spinal cord/brain stem to thalamus
Axons of second order neurons…
decussate (crossover) in the spinal cord/brain stem
Second order neurons end in _____ thalamus where they _______
contralateral, synapse w/ third order neuron
Ventroposterolateral (VPL) nucleus of thalamus is associated w/…
body
- 2nd order neuron
Ventroposteromedial nucleus (VPM) is associated w/…
face
- 2nd order neuron
3rd order neuron transmits info from…
thalamus to primary somatosensory area
3rd order neuron travels to which side of the cortex
ipsilateral (same side)
DCML is made up of…
large myelinated fibers (A beta or type II)
- rapidly transmits info
DCML carries info about…
- fine discriminative touch
- pressure and stretch
- proprioception
- visceral sensations
Precise touch comes from…
cutaneous receptors
Examples of cutaneous receptors:
- Meissner’s corpuscles
- Pacinian corpuscles
- Ruffini endings
- Merkel cells
Precise touch provides:
- high degrees of localization
- differentiation between two stimuli
- vibration
- stereogenesis
Stereogenesis is the identification…
of objects based on size, shape, texture
Pressure and stretch allows…
judgement of weight of an object/differences in weights
Proprioception comes from receptors in…
- skeletal muscles (muscle spindle)
- ligaments
- tendons (Golgi tendon organ)
- joint capsules
T/F: proprioception senses both phasic and tonic conditions
T
Examples of phasic conditions:
- vibrations
- movement against skin
- position sensations
Phasic information goes to…
cerebral cortex and cerebellum
Example of tonic conditions:
conscious orientation of body/body parts relative to one another
Tonic conditions are unconsciously monitored by…
cerebellum
DCML has precise somatotopic arrangement of…
neurons and axons at all levels
Damage to the DCML tract will impair…
tactile recognition of objects placed in hands
DCML: 1st order neurons travels along the..
same side that it entered on up to medulla
DCML: medulla is the site of…
1st synapse of 1st order neurons and 2nd order neurons in dorsal column nuclei
DCML: 1st order neurons collaterals from _____ synapse w/ ______ in the dorsal horn
primary afferents, interneurons
- mediates reflexes
DCML: thalamus is the site of synapse between…
2nd and 3rd order neurons
DCML: _____ info from the thalamus is relayed to _____
contralateral, VPL and ventrobasal complex
Thalamus:
- highly mapped regions
- relays info to specific areas of somatosensory cortex
Thalamic neuron excitability depends on…
stage of the sleep/wake cycle
DCML: most 3rd order neurons project to the…
somatosensory cortex
Somatosensory cortex is located in the…
cortical gray matter of parietal lobes of cerebrum
Somatosensory cortex is organized…
contralaterally
Somatosensory cortex is the main area posterior to…
central sulcus on post central gyrus
- somatic sensory area I (SSI)
- somatic secondary area 2 (SSII): behind SSI
Sensory homunculus:
- distorted representation of body on surface of brain
- proportionate area of cortex to # of receptors from area
Large area of the sensory homunculus is dedicated to…
- lips
- face
- fingers
Small area of sensory homunculus is dedicated to…
- trunk
- eyes
- nose
Anteriolateral pathway is made of…
A delta and C fibers
- slower than DCML
Anteriolateral pathway carries _____ info
less precise b/c degree of spatial localization is poor
In the anteriolateral pathway, 1st order neurons enter the…
dorsal root
In the anteriolateral pathway, 1st order neurons will immediately synapses w/ _____ in lateral part of _____
interneurons and 2nd order neurons, dorsal horn of spinal cord
Two types of anteriolateral pathways:
- anterior spinothalamic tract (AST)
- lateral spinothalamic tract (LST)
- both differ in type of info carried
AST transmits what type of info…
crude touch (non-discriminating) w/ 2nd order neurons
Crude touch includes…
- sexual sensations
- pressure
- tickle
- itch
AST is mainly made up of what type of fibers?
A delta
LST receptors are…
tonic (slow/no adaptation)
LST transmits info about…
- fast/acute pain
- slow/chronic pain
- temp
- does this through 2nd order neurons
Fast/acute pain:
- through mechanical nociceptors and A delta fibers
- activated by intense mechanical stimulation
Fast/acute pain is perceived as…
- sharp
- intense
- pricking
- electric
Slow/chronic pain:
- through polymodal nociceptors and C fibers
- responds to several types of noxious stimuli
- thermal (extremes of cold/heat)
Slow/chronic pain is perceived as…
- dull
- burning
- aching
- throbbing
Temperature is sensed by…
primary sensory thermoreceptors for response to cold/warm sensations
A delta fibers for temperature carries…
cold temp info
C fibers for temperature carries…
warm temp info
Info can take a few tracts to get the thalamus:
- 2nd order neurons/collateral branches
- thalamic nuclei
- fast-pain pathway
- slow-pain pathway
Collateral branches activate…
motor neuron pools in the spinal cord that participates in reflex actions
Collateral branches have inputs to the…
reticular formation in the brain stem
- most pain fibers synapse here
Most of the synapses of the thalamic nuclei occurs in the…
- intralaminar (IL) nucleus
- ventrobasal (VB) nuclei
Intralaminar nucleus transmits…
slow pain signals
VB nuclei transmits…
- tactile signals
- fast pain signals
Thalamic nuclei:
- nonspecific
- poorly mapped relay area
Thalamic nuclei has 3rd order neurons from intralaminar and VB nucleui that projects to…
nonspecific regions of the brain including SSI, limbic system, and basal ganglia
Small portion of thalamic nuclei synapses in the…
ventral posterior lateral (VPL) nucleus
- some nondiscriminating tactile responses and some fast pain is here
Thalamic nuclei has 3rd order neurons from VPL nucleus that projects to…
- somatosensory cortex
- frontal cortex
Fast pain pathway is located in:
- reticular areas
- VB
- basal areas of brain
- somatosensory cortex
Slow pain pathway is located in:
- thalamus (IL and VB)
- reticular areas
- tectal area in mesencephalon
- periaqueductal gray
- hypothalamus
- basal areas of brain
Pain includes:
- sensory discrimination and motivational-affective components
T/F: sensory experience involves emotional response
T
Nociceptors:
- tonic
- sensitization can result in hyperalgesia
Primary nociceptive neurons release…
neurotransmitters (substance P and calcitonin-gene related peptide (CGRP)
SSI and SSII interpret pain info:
- determination of quality of pain
- location
- intensity
- duration
Other areas provide motivational-affective responses:
- level of attention and arousal
- somatic and autonomic reflexes
- endocrine responses
- emotional changes
Neurogenic pain is the…
perception of pain in the absence of nociceptive stimulation
Neurogenic pain can occur after damage to…
- peripheral nerves
- parts of CNS
Visceral pain is the…
pain relayed from organs
Viscera do not have ____ receptors
- proprioceptors
- temp
- touch
Nociceptors are usually inactive, but activated when…
sensitized by injury or inflammation
Sensors for visceral pain are associated w/ the _____ system
autonomic
- usually involved in reflexes
Sensors for visceral pain include…
- mechanoreceptors (creates sensation of distension)
- nociceptive information that travels same pathways as somatic sensations
Referred pain:
pain originating from deep structures (muscle/viscera) that is perceived as if from superficial somatic structures
Referred pain occurs b/c of…
convergence of somatic and visceral pain fibers in spinal cord
Referred pain is generally referred to…
an area that is remote from the actual origin of pain
Heart attacks that can feel like pain in the chest wall and left arm are an example of…
referred pain
Pain suppression mechanisms:
- group of interneurons w/ inhibitory receptive fields associated w/ binding of GABA, glycine and endogenous opioids to membrane receptors
- gating of pain
- endogenous analgesia system
Inhibitory fields of interneurons can be activated by…
- weak mechanical stimuli
- other noxious stimuli
Examples of noxious stimuli:
- transcutaneous electric nerve stimulation (TENS)
- acupuncture
- physical manipulation
Gating of pain is the process of…
interfering w/ the pain pathway
- closes the gate passage for pain
Gating of pain can occur w/in the…
brainstem/spinal cord
Gating of pain will inhibit the release of…
subtance P from pain neurons
Gating of pain involves the _____ system
enkephalin
Enkephalin system is activated by…
pain signals relayed from reticular formation
Gating of pain will stimulate
neurons in periaqueductal gray matter
- releases enkephalin
Serotonergic nerves descend to…
the level of the incoming signal in the spinal cord
Serotonergic nerves synapse on the…
pain suppression complex (interneuron pool) in the dorsal horn
Gating of pain will stimulate GABAminergic/enkephalin neurons which release…
GABA onto the synapse between primary and secondary sensory neurons
When gating of pain releases GABA onto synapse between primary and secondary sensory neurons, the prevention of ____ and _____ occurs
- release of substance P (presyn inhibition)
- stimulation of substance P (postsyn inhibition)
Spinal cord pain gating system works by…
stimulating pain suppression complex
Endogenous analgesia system:
CNS suppression of incoming info at the level of the brain
Endogenous analgesia system is activated by…
stressful/intensely painful situation
Pain signals relayed from reticular formation activates…
sympathetic division of autonomic nervous system (fight or flight)
Hypothalamic (periventricular nuclei) neurons release…
beta endorphins into cerebral spinal fluid (bathes neurons in higher centers and suppresses pain)
Gating of pain signals will descend to
raphe magnus nucleus in reticular formation and activate serotonergic nerves
- releases serotonin
Components of gating pain signals:
- enkephalin system
- periaqueductal gray matter (releases enkephalin)
- raphe magnus nucleus in reticular formation (releases serotonin)
- serotonergic nerves
