Exam Two - DCML Flashcards
DCML
dorsal column medial lemniscus
What is the overall purpose of the DCML system?
discriminative touch and conscious proprioception
What are the 5 general structural components of the somatosensory system?
- in the PNS
1 - peripheral receptory
2 - primary afferent fibers and their ganglia - in the CNS
3 - a decussation
4 - a thalamic relay nucleus
5 - a cortical projection target
What are the key steps in sensory transduction?
- sensory receptor (adequate specific stimulus)
- membrane conductance changes
- generator potentials
- action potentials
- primary afferent signals
4 ways to code sensory information?
modality
intensity
duration
location
receptive field
the space where the receptor is located and transduce the stimuli
small receptive fields increase the likelihood of discrimination
GSA
general somatic afferents
receptors are mainly located in body/soma wall (skin, muscle, joints, periosteum, and associated structures)
GVA
general visceral afferent
located within or near visceral organs
SSA
special somatic afferents
vision and hearing
SVA
special visceral afferents
smell and taste
What are the 3 classifications of somatosensory receptors?
mechanoreceptors
thermoreceptors
nociceptors
proprioception
- awareness of the body position and movement
- dynamic 3D mental construct of the body generated by integrative activity occurring the the parietal lobe
What 3 systems provide integrate to form proprioception
- vestibular
- visual
- somatosensory
What are the 4 main somatosensory proprioceptors
- cutaneous mechanoreceptors
- muscle spindles
- golgi tendon length
- mechanoreceptors in joints
What are the 4 main functions of peripheral receptors functions?
1 - general arousing and alerting (consciousness)
2 - conscious discrimination of environmental events by acting on neurons of the cerebral cortex via ascending systems
3 - to elicit reflexes
4 - enabling coordinated movements by acting on neurons belonging to the motor control system
What systems are included in GSA conscious classification?
-DCML
-ALS
- cranial nerves 5, 7, 9, 10
What systems are included in GSA unconscious classification
- spinal cord and brains tem reflex connections
- dorsal spinocerebellar tract
- ventral spinocerebellar tract
- cuneocerebellar tract
How many neurons are involved in the DCML pathway?
3 projection neurons, 1st, 2nd, 3rd order neruons
Where is the 1st order neurons’s soma for DCML?
DRG
How does the 1st order neuron for DCML enter the CNS?
via the dorsal root without synapsing!
Do first order or second order neurons cross in the DCML system?
second order, 1st order neurons project ipsilaterally to the second order neurons
Where are the second order neurons located in the DCML system?
nucleus gracilis(Lower Extremity) and nucleus cuneatus(Upper Extremity) in the medulla
Where do second order neurons terminate in the DCML system?
2nd order neurons cross the midline (forming the medial lemniscus) and ascend to the thalamus to terminate of 3rd order neurons
How do 3rd order neurons of the DCML project to the cerebral cortex?
the posterior limb of the internal capsule
Where specifically do 3rd order neurons of the DCML terminate in on the cerebral cortex?
the primary somatosensory cortex (areas 3, 1,2) of the post-central gyrus
What specific part of the thalamus do 2nd order neurons synapse with?
VPL
What is the orientation of the ML at the medulla
A
T
L
What is the orientation of the ML at the middle to rostral pontine level?
L T A
What is the somatotopic organization of the thalamus?
foot = lateral
hand = medial
What is the somatotopic organization of the priamry somatosensory cortex (SI)
foot = medial
hand (and face) = lateral
site 3 of SI receives:
most thalamic input, site of initial processing
site 3b receives?
touch (cutaneous, SA)
site 3a receives?
proprioception (deep, muscle)
sites 1 and 2 of SI receive?
they are connected to 3b, sites of complex processing
1 = cutaneous RA
2 = deep, joint
sensory homunculus
- not body proportional
- not a “single” map
- FOOT MEDIAL AND FACE LATERAL
Role of SII?
- performs higher order functions
- association area for sensory input
- ROLE IN EPISODIC MEMORY, VISUOSPATIAL PROCESSING, CONSCIOUSNESS AND HIGH ORDER FUNCTIONS, SUCH AS SELF-REFLECTION
- connected to the limbic system
Where is SII located?
parietal operculum
What is the parietal operculum?
the part of the parietal lobe that overlies the caudal portion of the insula in primates. It is defined by dissection
Purpose of brodmann areas 5 and 7?
- association cortex for somesthesis
- INTERPRET MEANING OF INPUT
somesthesis
body sensibility including the cutaneous and kinesthetic senses
What can damage of brodmann areas 5 and 7 produce?
hemi-neglet syndrome (amorphosynthesis) - the patient is unaware of somatic sensations from one side of the body
functional properties of the DCML
- receives input via large diameter myelinated axons
- highly topographic at all levels
- RF size small
- submodality purity at all levels
- secure relays (a single AP can prudce a perception)
describe organization of DCML at the SC, thalamus, and SI cortex
SC: food medial, hand lat
thalamus: foot lateral, hand/face medial
SI cortex: foot medial, hand/face lateral
lesions at the DCML
- increase in the two point threshold
- decrease in vibratory sensitivity
- decrease in position sense and kinesthesia
- agraphesthesia
- astereognosis
- increase in spontaneous pain
kinesthesia
awareness of movement of the parts of the body
agraphesthesia
impaired ability to recognize letters or numbers drawn by an examiners fingertip on the patients skin (with patients eyes closed)
astereognosis
inability to identify a common object by active touch without other sensory input such as visual information
