Unit 2 Flashcards
(30 cards)
What are the four modalities of somatic sensibility?
1) discriminative touch: recognizing size, shape, and texture of objects
2) Proprioception: sense of static position and movement of limbs/body
3) Temperature Sense
4) Nociception: pain/itch, signals tissue damage or chemical irritation
Describe the classes of Somatic Sensation
1) epicritic sensations: fine aspects of touch
- highly localizable/discriminative
- encapsulated receptors
2) Protopathic sensations: involve pain, temperature, tickle, itch sensations
- poorly localizable/discriminatory
- nonencapsulated receptors
Exteroceptors
-deals with sensation from external stimuli
Proprioceptors
- deals with kinesthetics
- conscious proprioception relayed to cerebral cortex, unconscious to cerebellum
Interoceptors
-processing of visceral information
Meissner’s corpuscle
- for discriminative touch
- encapsulated
Pacinian corpuscle
- perceives vibration
- encapsulated
Ruffini ending
- for perception of grasped objects/pressure
- deep encapsulated receptors
Nonencapsulated Receptors
- ex: Merkel Cells
- mostly deals with touch in a nonspecific sense
Describe different receptive fields
- small field have many neurons for fine touch (merkels, meissner)
- large fields have fewer neurons with crude touch (pacinian, ruffini)
All somatosensory receptors are ____ neurons
pseudounipolar
Dorsal Root Entry Zones
1) small unmyelinated axons enter through substantia gelatinosa: pain, temp, crude touch, and visceral
2) Large myelinated axons enter through posterior funiculus: discriminative touch and proprioception
Brown Sequard Syndrome
- spinal cord hemisection
- loss of both sensory and motor function
Syringomelia
-loss of pain and temp sensation
Explain the general significance of the DC-ML
- dorsal column medial lemniscus
- for fine touch, conscious proprioception and vibration sensation excluding the head
- highly localizable/discriminative
Go through and describe the DC-ML 3 neuron pathway.
1) primary neuron: in dorsal root ganglion
- pseudounipolar with peripheral and central axons
- fibers enter spinal cord through the medial dorsal root entry zone (large myelinated fibers)
- small branches here for spinal reflexes
- main axon enters dorsal funiculus, and forms either fasciculus gracilis or fasciculus cuneatus: together called dorsal columns
- tracts are arranged from medial to lateral as you go up
2) second neuron: beings in nucleus gracilis and nucleus cuneatus in caudal medulla
- axons head ventromedially, though medullary tegmentum
- cross over the midline and terminate just dorsal to the pyramids as medial lemniscus (crossing fibers termed Internal arcuate fibers)
3) third neuron: medial lemniscus heads up into ventral posterolateral (VPL) thalamus and terminates in the primary somatosensory area
Unconscious proprioception
1) ipsilateral: dorso-spino-cerebellar tract (lower C8) and cuneo-cerebellar tract (upper C8) goes through inferior cerebellar peduncle
2) contralateral: ventro-spino-cerebellar tract, goes through superior cerebellar peduncle
What are the three tract of the anterolateral system? The main differences.
- spinothalamic: sharp, fast pain sensation, epicritic
- spinoreticulothalamic: slow, crude pain, crude touch sensation: protopathic
- spinotectal: both and reflex sensations
Describe the pathway for the spinothalamic tract.
1) first neuron: starts in dorsal root ganglion, associated receptors: nociceptors, thermal
- fibers enter spinal cord through lateral dorsal root entry zone and into lissauers tract
- main axon stays in gray matter of dorsal horn
2) second neuron: located either in substantia gelatinosa (lamina 2) or lamina 5 of dorsal horn
- axons decussate in anterior white commissure and move ventrolaterally (note not directly across, but up the cord a bit and across)
- continues up laterally through medulla/pons/midbrain, terminates in ventral posterolateral nucleus of thalamus
3) third neuron: from VPL terminates in primary and association sensory cortex
Describe the pathway for the spinoreticulothalamic tract.
1) first neuron: in dorsal root ganglion
2) second neuron: either in substantia gelatinosa (lamina 2) or lamina 5 in dorsal horn
- like STT, fibers decussate in anterior white commissure, and move ventrolaterally, but then heads up towards reticular formation
3) third neuron: in reticular formation and project to intralaminar nuclei of thalamus
4) fourth neuron: in intralaminar nuclei and ultimately projects to many areas of cerebral cortex
Describe the pathway for the spinotectal tract.
1) first neuron: in dorsal root ganglion, nociceptors, thermal, tactile receptors
2) second neuron: either in substantia gelatinosa (lamina 2) or lamina 5 in dorsal horn of spinal cord
- fibers decussate in anterior white commissure and move ventrolaterally joining with STT and SRTT
- fibers head up similar to STT but once they hit the midbrain, go to superior colliculus and periaqueductal gray
3) third neuron: in superior colliculus: DESCENDS to upper cervical spinal cord, involved in reflex control for head, neck and eyes
- in periaqueductal gray: descends, enkephalin/substance P pathway meant to inhibit the other two pathways when needed
- THIS TRACT DOES NOT REACH CONSCIOUSNESS
General trigeminal pathway components
1) spinal trigeminal nucleus
2) chief sensory nucleus
3) mesencephalic nucleus
first three sensory plus the motor nucleus
Spinal trigeminal nucleus and tract
concerned with pain, temp, and crude touch info from head
-analogous to anterolateral system
Chief nucleus
- main sensory nucleus
- concerned with fine touch, vibrations, and conscious proprioception from head
- analogous to medical lemniscal system
