Exam 2 week 8 ppt 6 Ascending Pathways of Somatic Sensory System Flashcards
what system is the spinothalamic tract part of?
anterolateral system
what does DCML stand for?
Dorsal Column–Medial Lemniscal System
what system is the dorsal column a part of?
medial lemniscal system
How many major systems are there that are invovled in carrying information from somatic receptors to cerebral cortex for conscious recognition and discrimination of environmental stimuli
two
what are the two major systems involved in carrying information from somatic receptors the the cerebral cortex for conscious recognition and discriminition of environmental stimuli?
- –Dorsal column-medial lemniscal system
- –Spinothalamic tract of the anterolateral system
name three functions of the dorsal column-medial lemniscal system
- discriminative tactile sensation
- kinesthesis
- steregnosis
name three functions of the spinothalamic tract of the anterolateral system
- pain
- temperature
- non-discriminative touch
What are the sensory end organs in the dorsal column-medial lemniscal (DCML) system? (7)
they are mechanoreceptors
Skin:
- Peritrichial, (hair)
- Meissner’s,
- Merkel cell,
- Pacinian &
- Ruffini endings
Other
- Muscle receptors
- tendon receptors
- joint receptors
What fiber types are the primary afferents from the skin and joint for the DCML?
where is the cell body?
- Group II (A-beta) primary afferents &
– cell body in dorsal root ganglion
What fiber types are the primary afferents from the muscles for the DCML?
where are the cell bodies?
•Group I (A-alpha) primary afferents from muscles
(some A-beta from muscle spindles)
cell body in dorsal root ganglion
describe the pathway of the first order neurons in the DCML system:
- from their receptors, they pass through the DRG, enter the dorsal column of spinal cord, and ascend ipsilaterally in the (Fasiculus Gracilis and Cuneatus) to medulla
- •End on second-order neurons in dorsal column nuclei (nuclei gracilis and cuneatus) in the medulla
describe the path of second order neruons in the DCML?
- start at dorsal column nuclei in the medulla,
- then decussate and ascend to thalamus as the medial lemniscus.
- They end on 3rd order neuorns in the ventral posterolateral nuclei (VPL) of the contralateral thalamus
describe the path of third order neruons in the DCML?
- •Axons of 3rd-order neurons in the ventral posterolateral (VPL) nucleus of thalamus terminate in parietal lobe - again contralateral to the side from which the receptors arose
what happens to the information in teh DCML at the thalamic and dorsal column nuclei?
There is Efferent modulation by somatosensory cortex of information as it is relayed in both the thalamic and dorsal column nuclei. In this way the cortex helps regulate the extent of the somatosensory information that reaches it.
the DCML is ___________________ organized through its entire coures
Somatotopically organized
what is the orientatio nof the LE and UE in the spinal cord for The DCML?
–LE medial (in fasiculus gracilis)
and UE lateral (in the fasciculus cuneatus)
what is the orientation of the LE and UE in the Medial lemniscus in the medulla for The DCML?
–– LE ventral & UE dorsal
what is the orientation of the LE and UE in the Medial lemniscus in the pons for The DCML?
UE medial & LE lateral.
what happens at the pons to the DCML?
the addition of the trigeminothalamic tract just medial to the Medial lemniscus with somatosensory information from the head and face
what does the trigeminal tract join at the level of the pons?
the DCML
(just medial to the medial lemniscus)
what is the orientation of the LE and UE in the midbrain for The DCML?
LE dorsal & UE ventral
what is the orientation of the LE and UE in the thalamus for The DCML?
–- LE dorsal lateral & UE ventral medial
DCML: where are the trigeminothalamic fibers in the midbrain?
–Just ventral to the medial lemniscus in the midbrain
DCML: where are the trigeminothalamic fibers in the thalamus?
Just medial to the body representation in the Thalamus
in the ventroposteromedial nucleus of the thalamus
DCML system: How is the LE, UE, and head region represented in the cortex?
–LE medial & UE lateral
–Also in the cortex the head region is represented even more ventrolateral along the primary somatosensory cortex of the post-central gyrus
Anterolateral system: describe the path of the primary neurons
- •Primary afferent fibers Class III (Ad) & IV (C) come from deep cutaneous & nociceptive free nerve endings along with the Class II (A-beta) deep pressure receptors).
- they enter spinal cord and synapse in dorsal horn
- nociceptive fibes synapse in the substantia gelatinosa
- non-nociceptive neurons synapse in the nucleus proprius
Anterolateral system: describe the path of the 2nd order neurons
Axons from 2nd order neurons in the dorsal horn of the spinal cord
- decussates promptly &
- ascends contralaterally in the
- anterior part of the lateral funciculus and
- as the lateral sponothalamic tract and
- carries the nociceptive and thermal afferents
- as the lateral sponothalamic tract and
- anterior funciculus
- as the anterior spino-thalamic tracts.
- transmits the non-discriminative touch and pressure sensations
- as the anterior spino-thalamic tracts.
- anterior part of the lateral funciculus and
- The 2nd order axons end in ventral posterolateral (VPL) nucleus of thalamus
- 2nd order axons are also jointed by the nociceptive fibers from the face of the trigeminothalamic tract.
Anterolateral system/spinothalamic tract: describe the path of the 3rd order neurons
- Axons of 3rd order neurons from the body relay in the VPL thalamus project to post-central gyrus of parietal lobe (somatosensory cortex)
- those from the head (Trigeminothalamic tract) relay in the ventral posterior medial nucleus (VPM) of thalamus
Anterolateral tract/anterolateral asystem: what is the somatotopic organization of LE and UE in the cerebral cortex?
–– LE medial & UE lateral
(follows the pattern of the somatosensory homunculus)
