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)
