Exam 2 material Flashcards
Forms of sensation
- Touch (edges/superficial touch, pressure/deep, texture/sliding)
- Vibration
- Pain (sharp, burning)
- Temp (hot, cold)
- Proprioception
- Itch
Sensory pathways
- dorsal root ganglion
- posterior columns
- anterolateral pathways
- Trigeminothalamic tract
- Spinocerebellar tracts
Dorsal root ganglion
- pseudounipolar sensory neurons
- cell bodies in ganglion dorsal to spinal cord
Posterior columns sense what?
- vibration
- proprioception
- fine touch
Posterior columns pathway *
1) primary sensory neuron enters dorsal root entry zone
2) ascends posterior columns (fasciculus gracilis: medial/legs) (fasciculus cuneatus: lateral/arms)
3) synapses on nucleus gracilis/cuneatus in medulla
4) decussates in LOWER MEDULLA
5) ascends medial lemniscus
6) synapses in ventral posterior lateral nucleus of thalamus
7) ascends in posterior internal capsule to primary somatosensory cortex
Anterolateral pathways sense what?
- pain
- temp-
- crude touch
Anterolateral pathways (path!)
1) primary sensory neuron enters dorsal root entry zone
2) synapses on secondary neuron within spinal cord gray matter
3) decussates within a few levels in the spinal cord
4) travels up anterolateral tract
5) TRACKS (spinoreticular, spinomesencephalic, spinothalamic tract)
6) ascends in posterior internal capsule to primary somatosensory cortex
Spinoreticular tract
(part of anterolateral pathway)
- synapses in medullary reticular formation
- involved in alertness
spinomesencephalic tract
(part of anterolateral pathway)
- synapses in midbrain periaquductal gray
- involved in pain modulation
spinothalamic tract *
(part of anterolateral pathway)
-synapses in ventral posterior lateral nucleus of thalamus
Trigeminothalamic tract
- similar to posterior columns / anterolateral pathways
- originates in trigeminal brainstem nuclei
- travels up trigeminal lemniscus (parallel to medial lemniscus)
- synapses in ventral posterior medial nucleus of the thalamus
Spinocerebellar tracts
- dorsal/ventral spinocerebellar = leg proprioception
- rostral spinoverebellar/cuneocerebellar = arm proprioception
Dorsal spinocerebellar tract
- information on limb position to cerebellum
- type 1a and II fibers enter with dorsal fibers
- some form spinal reflexes (stretch reflex)
- Lower body
- fibers ascend fasiculus gracilis
- synapse on Clarke’s nucleus, ipsilaterally
- column of cells in posterior horn
- runs through lumbar/thoracic spinal cord, but most concentrated at thoracolumbar junction
- ascends in dorsal spinocerebellar tract
- Enters cerebellum through inferior cerebellar peduncles
-upper body
- fibers ascend fasciculus cuneatus
- synapses on external cuneate nucleus (just lateral to cuneate nucleus)
- ascends through the inferior cerevellar peduncle (cuneocerebellar tract)
Ventral spinocerebellar tract
- information from spinal interneurons in lower limbs
- starts in spinal cord intermediate cells (near Clarke’s nucleus)
- decussates immediatelly
- travels up ventral spinoverebellar tract
- enters cerebellum through superior cerebellar peduncle (decussates again)
Rostral spinocerebellar tract
- information from spinal interneurons in upper limbs
- poorly characterized pathway
- some fibers ascend ipsilaterally entering the inferior cerebellar peduncle, some double-cross and enter the superior cerebellar peduncle
Spain cord vascularization (major components)
- anterior spinal artery
- posterior spinal arteries
- spinal artery plexus
Spain cord vascularization (major supplies)
- vertebral arteries form rostral end
- aorta supplies thoracic and lumbar cord through radicular arteries, largest is the great radicular artery of Adamkiewicz
- watershed zone (T4-T8)
watershed zone
T4-T8
-area that gets the least blood because it is between the two sources
Spain cord vascularization (Distribution - anterior and posterior)
Anterior spinal artery
- anterior and lateral columns
- anterior and lateral horns
Posterior spinal artery
- posterior columns
- posterior horns
sensory receptors: adaptation
(rapidly vs slowly adapting)
- Rapidly adapting: only responds to changes
- slow adapting: contiunues to respond
sensory receptors: receptive field
- related to sensory neuron branching
- inversely related to receptor density
- tested with 2-point discrimination (feel one or two touches?)
- more density = smaller 2-point discrimination
touch receptors
- Merkel cells
- Meissner Corpuscles
- Pacinian corpuscles
- Ruffini corpuscles
Merkel cells
- Touch
- fine touch, edges (static pressure)
- slow adapting, small receptive field
Meissner corpuscles
- Skin motion, sliding, texture (dynamic)
- rapid adaptation, small receptive field (3mm)
Pacinian corpuscles
touch
- vibration
- rapid adapting (dynamic pressure), large receptive fields
Ruffini corpuscles
- Stretch
- slow adapting, large receptive field
- Joint capsules stuff
Proprioception (receptors)
- Muscle spindles
- Golgi tendon organs
- joint receptors (ruffini)
Pain/temp receptors
- Free nerve endings (peripheral)
- TRP membrane channels (sensitive to hot and cold)
Sense receptor fiber types
- 1a, II fibers
- A-beta fibers
- A-delta fibers
- C fibers
1a and II fibers
- proprioception
- muscle spindle
- large, fast myelinated fibers (~100 m/s)
A-beta fibers
- touch
- merkel, meissner, pacinian, and ruffini cells
- large, fast myelinated fibers (~50m/s)
A-delta fibers
- sharp pain, temperature
- free nerve endings
- small, slower myelinated fibers (~5-30 m/s)
C-fibers
- Dull pain, temp, itch
- free nerve endings (unmyelinated)
- small, slow unmyelinated fibers (~1 m/s)
Pain vs suffering
- pain can be helpful (protective)
- suffering is not always productive (response to pain?)
Nociception vs normal sensation
- Different systems (pain is not just increased normal sensation)
- nociceptor pathways don’t fire for non-painful stimulation
- stimulation of normal pathways maximally don’t produce sensation of pain
Fast vs slow pain
- A-delta
- myelinated, fast(-er) fibers
- initial sharp painful response
- C fibers
- unmyelinated, slow
- dull, slow response
Visceral pain (transmitted through…)
- Anterolateral system
- vagus nerve
dorsal columns
Visceral pain (referred pain)
- uncommon sensation is perceived as coming from a more common location
- heart
- chest, arm, face regions
Peripheral sensitization (Mediators)
Hyperalgesia = up sensitivity to pain
- substance P
- ATP
- Prostaglandins
- Bradykinin
- Cytokines
Substance P
peripheral mediator
- pain substance, kind of line pain neurotransmitter. Up regulates pain
ATP (peripheral mediator)
- With pain… should not be in tissue floating around so it means that something is wrong
Prostaglandins
peripheral mediator
- cause pain, as well as up-regulate pain sensitivity
Bradykinin
peripheral mediator
- cause pain, as well as up-regulate pain sensitivity
Cytokines
peripheral mediator
- inflammatory modulators
- cause pain, and as well as up-regulate pain sensitivity
Gate theory of pain
- (Central sensitization)
- touch receptors inhibit pain sensation.
- Compete for pathways
- smash hand and press on it to make it hurt less
TENS
Transcutaneous electrical nerve stimulation
- stim theoretically inhibits pain transmission
Allodynia
- Experience normal stimuli as painful
Endogenous pain modulation
- enkenphalins
- endorphins
- dynorphins
Neuropathic pain
- damage to neurons
- causes burning, tingling sensation
- difficult to treat
- better treated with neural-modulators relative to analgesics
Chronic pain
- short-term sensitization: (pull your back and it starts to hurt. you dont rest it so the pathway is strengthed and the pain gets worse)
- long-term potentiation: pathway is strengthened?
- psychologic mechanisms:
COX-inhibitors for pain treatment
- inhibits synthesis of prostaglandins
- NSAIDs
- ASA
- Acetaminophen
Opiates as treatment for pain
- replicate endorphins
- ***work on spinal gating
