Week 5 Learning Issues Part 2 Flashcards
3 major categories of somatosensory receptors
- Mechanoreceptors
- Proprioceptors
- Nociceptors/ Thermoceptors
Major CNS destinations for somatosensory information
- Local Reflexes
- Cerebellum
- Brainstem
- Forebrain
Local Reflexes at level of
brainstem and spinal cord
local reflexes provide mechanism for
quick, stereotyped responses, to primary afferent input
Cerebellum receives
all types of somatosensory input, particularly proprioceptive input, via spinocerebellar pathways
cerebellum processes
sensory and motor information to regulate on-going motor programs
processing in cerebellum is
subconscious
brainstem circuitry for
generating/ controlling gait depends on somatosensory information
brainstem neuromodulatory systems
- include ascending reticular activating system (ARAS)
and monoaime pathways - activity in the systems controlled in part by incoming sensory info
brainstem neuromodulatry systems influence activity in many other areas of the brain including
brainstem, hypothalamus, thalamus, limbic structures, cerebellum, and neocortex
neuromodulatory systems play a role in
general activation of the brain (arousal), affect, emotion, motivation, and modulation in pain pathway
forebrain
diencephalon (thalamus and hypothalamus), Basal Nuclei, Cerebral Cortex, and Limbic Structures
Somatosensory pathways to forebrain
- Specific pathways
2. Non specific pathways
Specific pathways
- relay information such that brain can interpret location, sub modality, intensity, and quality of stimulus
- these pathways utilize somatosensory relay nuclei in lateral thalamus to reach primary somatosensory area of neocortex in parietal lobe
what are the specific somatosensory pathways to forebrain
- DC-ML
- Spinocervicothalmic
- Direct Spinothalamic Pathways
Non-specific pathways
- relay information about the stimulus location, submodality, and quality, other than perhaps intensity, is less faithfully relayed
what is the non-specific pathway
indirect spinothalamic pathway
where does non-specific pathway synapse
- synapses in a number of nuclei in the reticular formation of cd brainstem as well as in intralaminar nuclei of medial thalamus and terminates diffusely throughout the cerebral cortex, basal nuclei, and hypothalamus
specific information is processed in
forebrain structures for conscious awareness, memory, learning, decision making, motor planning, and other complex behaviors
non-specific sensory information
plays an important role in regulating emotion, affect, motivation, and aspects of autonomic fx by influencing activity in reticular formation, intralaminar nuclei, hypothalamus, cerebral cortex, and limbic pathways
visceral afferents
- not part of somatosensory system
- sensory info from viscera utilized in CNS in many of same ways somatosensory info is used
visceral afferents regulate
spinal cord, brainstem reflexes, influence activity in neuromodulatory pathways, may be consciously perceived, and afferent complex behaviors via pathways involving hypothalamus cortex and limbic structures
signal from visceral receptors
often not consciously perceived; involved in visceral reflexes and homeostatic regulations
info from visceral receptors
relayed to CNS predominately via Vagus Nerve to the Nucleus of the Solitary Tract or to sacral spinal cord via pelvic nerves
conscious perception of pain or discomfort
can be from distention of viscera and stimulation of some visceral chemoreceptors -> conscious perception of pain
distention of bladder and rectum
can be consciously perceived; visceral afferents
referred pain
CNS less accustomed to interpreting visceral pain than somatic pain, stimulation of visceral nociceptors can be misinterpreted by CNS as somatic pain and then pain is perceived to arise in regions of muscle or skin innervated by same spinal cord segments as stimulated visceral tissue (ex pain in arm during heart attack)
DC-ML
Dorsal Column- Medial Lemniscal Pathway
DC-ML mediates
conscious perception of touch and pressure from mechanoreceptors and cortical processing of body position via proprioceptors
collaterals from DC-ML pathway
terminate in brainstem where provide input for motor coordination fo gait and other brainstem controlled motor function
DC-ML pathway pathway
- primary afferent axons ascend spinal cord in dorsal funiculus (Fasciculus Gracilis and Fasciculus Cuneatus)
- Synapse in cd medulla on Nucleus Gracilis or Nucleus Cuneatus
- Axons from projection neurons in Nucleus Gracilis or Nucleus Cuneatus decussate in cd medulla and ascend through brainstem in md leminiscus
- Projection neurons synapse in somatosensory thalamic relay nucleus
- Axons from thalamus project to somatosensory cortical areas in parietal lobe
fasiculus gracullis
carry axons from cd half of body
fasiculus cuneatus
carry axons from rostral half of body
Spinocerebellar pathways
carry proprioceptive and other SA information from spinal cord to ipsilateral cerebellum
cuneocerebellar pathway
spinocerebellar pathways; carries info from thoracic limb
dorsal spinocerebellar pathway
spinocerebellar pathways; carries information from pelvic limb
axons of spinocerebellar pathways travel in
dorsal lateral and dorsal funiculi of spinal cord
spinocerebellar pathways reach cerebellum via
cd cerebellar peduncle
spinocerebellar pathways may be disrupted by lesions impacting
- dorsal lateral funiclus
- cd medulla
- cd cerebellar peduncle
location of dorsal lateral funiculus, cd medulla, and cd cerebellar peduncle
superficial location of these pathways in spinal cord and brainstem makes them susceptible to damage from dorsolateral extra-axial lesions
Proprioceptive Information form DCML and spinocerebellar pathway is used by
brainstem, cerebellum, and cerebral cortex to coordinate locomotion and postural reactions
interruption of proprioceptive pathways can cause deficits on
postural reaction tests; seen in limbs ipsilateral to lesions in spinal cord, medulla oblongata, and pons and contralateral to lesions in forebrain
general proprioceptive ataxia
atixia that occurs due to interruption of ascending proprioceptive pathways; can be in spinal cord or brainstem; presents in limbs ipsilateral to lesions in medulla and pons
without proprioceptive information brainstem, cerebellum, and cerebral cotex
can’t properly coordinate locomotion
manifestation of general proprioceptive ataixa
manifests as scuffling or knuckling of digits, hooves, floating or overreaching, delayed protraction, wide swinging movements and/ or crossing over of limbs during locomotion
milder ataxia
may occur in contralateral limbs if pathway is interrupted in forebrain
spinocervicothalmic pathway
- carries information from nociceptors and mechanoreceptors to primary somatosensory cortex for conscious perception and higher level cortical processing
- well developed in carnivores likely has important role in perception of localized pain in carnivores
spinocervicothalmic pathway pathway
- Primary afferents from low threshold mechanoreptors and nociceptors synapse on projection neurons in DH
- Projection neurons from DH ascend in spinal cord in ipsilateral lateral funiculus and synapse in lateral cervical nucleus in rostral cervical spinal cord
- Projection neurons from Lateral Cervical Nucleus dcussate near junction of spinal cord and medulla and ascend to thalamus via contralateral medial lemniscus
- Neurons synapse in somatosensory thalamic relay nucleus which projects Somatosensory Cortical Areas in Parietal Lobes
somatotopic organization
specific somatosensory pathways organized somatotopically means information from adjacent areas of skin is represented in spatially corresponding pattern within tracts and nuclei or cortical areas of somatosensory pathways
Spinothalamic Pathways
- relay information from nociceptors (somatic and visceral), thermoceptors, and to a lesser extent mechanoreceptors to CNS
- subdivided into multiple tracts
- Specific (direct spinothalmic pathway)
- non-specific (indirect spinothalmic pathway)
different tracts of spinothalamic pathways
originate from different laminae in spinal cord, carry different aspects of sensory information, and end in different targets within brain to influence many aspects of behavior and phylsiological fx
direct spinothalmic pathway
mediates conscious perception of noxious stimuli and temperature; info relayed so brain can interpret location, submodailty, intensity, and quality of the stimulus
direction spinothalmic pathway info used for
conscious perception and sensory-motor processing that requires specific information such as stimulus localization
direct spinothalmic pathway is primary pathway for
conscious perception of sharp, well localized noxious stimuli in primates; less well developed in domestic animals
direct spinothalmic pathway pathway
- Proximal afferents (mostly AS) fibers synapse on projection neuron in DH
- Axons from projection neurons decussate in spinal cord (w/ in a few segments) and ascend in contralateral ventrolateral white matter then in ventrolateral brainstem tegmentum (D to medial lemniscus)
- Projection neurons synapse in somatosensory thalamic relay nucleus which projects to somatosensory cortical areas
indirect spinothalmic pathway
- includes several pathways that relay non-specific somatosensory and visceral sensory information to variety of nuclei in brainstem reticular formation, PAG, hypothalamus, and intralaminar thalamic nuclei
Indirect spinothalmic pathway fx
mediates arousal, general CNS activation, affective aspects of pain and modulation of activity in pain pathway
spinothalmic pathways in domestic animals more consistent with
indirect pathways
indirect spinothalmic pathways utilize
- projection neurons that may ascend spinal cord ipsilaterally or contralaterally
- projection neurons synapse on neurons in spinal cord or brainstem before pathway reaches thalamus (polysynaptic)
when intense or painful stimuli detected indirect spinothalmic pathways relay information that something potentially threatening is occurring for purposes of
- activating or suppressing regions CNS via neuromodulatory pathways so that income info can be processed more effectively
- eliciting autonomic and emotional responses via cortical and limbic-hypothalamic circuits
- enhancing motor processing and learning via cerebellar and basal ganglia circuits
- modulating activitiy in pain pathway to facilitate acquisition of sensory info or allow animal to push through pain
big difference between indirect and direct pathways
indirect do not require specific stimulus information
slow pain
indirect spinothalmic pathway plays role in processing and conscious perception of slow pain which = clinically important likely involving pathways of hypothalamus and limbic structures
Trigeminothalmic pathway
somatosensory afferents from trigenimal nerve carry info from proprioceptors, mechanoreceptors, nociceptors, and thermoreceptors that innervate face and regions of head
trigeminothalmic pathway synapses
afferents synapse in one of three subcomponent nuclei of trigeminal sensory nuclear complex
- mechanoreceptors -> sensory nucleus of trigeminal nerve (pons)
- nociceptors and thermoceptors -> nucleus of spinal trigeminal tract (medulla)
trigeminothalmic pathway pathway
- Afferents from face and regions of head synapse in Trigeminal Sensory Nuclear Complex
- axons arcing from projection neurons in trigeminal sensory nuclei decussate and ascend in brainstem near medial lemniscus to synapse in thalamic somatosensory relay nucleus
- nuclei also project to somatosensory cortex in parietal lobe via internal capsule
behavior response to sensory stimulation of the face
requires integrity of trigeminal nerve branches and trigeminothalmic pathway to cerebral cortex
ipsilateral facial hypalgesia or analgesia can be caused by
trigemical nerve lesions or lesions of pons or medulla oblongata
contralateral facial hypalgesia or analgesia causes
forebrain lesions (thalamus or cerebral cortex)
hypalgesia
reduced sensation fo pain
analgesia
lack of pain sensation
what regulates extent to which information from nociceptors is relayed to CNS for conscious awareness, arousal, emotional manifestation, and autonomic activation?
descending pathways from cortex and brainstem
neurocircuitry within spinal cord;
these pathways provide adaptive mechanisms to suppress pain when animal needs to push trough
there are also pathways that can enhance pain where central sensitization of nociceptive pathways and hyperalgesic states -> lower threshold for experiencing pain
neuromodulation
nociceptive projection neurons in DH revive modulatory input form local interneurons as well as from descending pathways from brain; these interneurons and descending neurons can release neuromodulatory substances on presynaptic terminals of afferent neurons or projection neurons that give rise to ascending nociceptive pathways effects can diminish or enhance neurotransmission in nociceptive pathways
Afferent neurons provide local input to
DH neuromodulatory interneurons
- Mechanoreceptors (rub site of injury to feel better)
- Nociceptors (stimulate As fibers -> analgesic affects accupuncture by activating neuromodulatory interneurons)
Descending input from brainstem
- can activate DH interneurons or inhibit release of neurotransmitter from As and C fibers
Descending pathways rise from
Raphe Nuclei
Locus Coeruleus
Periaqueductal Gray In Midbrain (PAG) receives input from
cortex, limbic structures, hypothalamus, reticular formation, spinal cord
perioaquductal gray in Midbrain
Raphe Nuclei and Locus Coeruleus in cd brainstem which then projects to spinal cord to inhibit pain transmission
Periaquductal gray can be activated by
stress, fear, exercise, pain, opiates, and other drugs
estrogen sensitive pathway from periaqueductal gray
females have this to inhibit pain transmission when estrogen levels are high like during parturition
enhance nociceptive transmission via PAG
separate population of neurons in PAG -> Raphe pathway exists that can selectivity enhance nociceptive transmission when such information is behaviorally relevant
Cerebral cortex controls flow of
somatosensory information in thalamus, dorsal column nuclei, trigeminal sensory nuclei and DH projection neurons via descending pathways
limbic system includes
a number of brain regions involved in emotional experience and expression, learning, motivational drives, and many other behaviors
limbic associated brain regions project to
hypothalamus, PAG, and other nuclei in reticular foramen
limbic associated brain regions can
influence descending pathways that modulate the transmission of information in nociceptive pathways
what are involved with spinal cord withdrawal reflexes
As and C fibers
Input from As fibers carried to
neocortex via direct spinothalmic and spinocerticothalmic pathways for conscious perception of sharp well localized pain (“fast pain”)
why does complete loss of pain perception due to spinal cord damage require severe lesion
bc As fibers carry nociceptive information at different levels of CNS bc the decussate at diff levels of CNS and carry nociceptive information bilaterally in spinal cord via direct spinothalmic and spinocervicothalmic pathways; additionally indirect spinothalmic tract has diffuse nature so all these things combined means lots of different tracts in different places on both sides of spinal cord carrying nociception making it very hard to knock out
- indirect spinothalmic pathway is bilateral using projection neurons that may ascend spinal cord ipsilaterally or contralaterally; projection neurons synapse on neurons in spinal cord or brainstem before reaching thalamus (polysynaptic pathway)
- Spinothalmic pathway axons from projection neurons ascend spinal cord in contralateral ventrolateral whit matter then in ventrolateral brainstem tegmentum
- spinocervicothalmic pathway axons from second order neurons ascend spinal cord in ipsilateral lateral funiculus
Input from As and C fibers is carried
bilaterally in indirect spinothalmic pathway
Indirect As and C fibers carried to
reticular formation, PAG, hypothalamus, and intralaminar nuclei of thalamus
fx of input carried by As and C fibers
to mediate arousal, affective, and autonomic responses associated with pain; these neuromodulatory pathways are also associated with limbic structures and cortical areas to facilitate sensory processing and the formation of memories regrind behavior and situations that elicit pain
input from C fibers carried
through reticular formation and intralaminar nuclei of thalamus likely also to areas of hypothalamus, cerebral cortex, and limbic structures for conscious perception of “slow” pain
nociceptor
receptor activated by stimuli that either produce tissue damage or would do so if stimulus continued and/or indicate presence of tissue damage
nociception typically triggers
reflexes and may or may not produce the experience of pain
pain
subjective physiological, emotional, and typically unpleasant experience; can occur without nociception; it is unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
experience of pain involves activity in
many parts of the brain especially structures associated with limbic function
fast pain
physiologic experience associated with conscious perception of sharp, well localized pain carried by As fibers occurs with short latency and ceases when stimulus terminates; depends on information carried by specific sensory pathways
slow pain
psychological experience associated with conscious perception of dull throbbing, poorly localized pain carried by C fibers; experience often outlives duration of noxious stimulus by considerable length of time can have profound effect on mood, behavior, and autonomic output
neuropathic pain
pain caused by nervous system damage resulting in aberrant activity in somatosensory pathways
- damage may be in nerves or in CNS
