1.5.1 Somatic Sensation Flashcards
The Dorsal Column-Medial Lemniscus (DC-ML) system conveys what and crosses the midline where?
- Conveys: fine touch, proprioception, pressure, and vibration
- Crosses Midline At: In the medial lemniscus after the Gracile & Cuneate Nuclei in Medulla
The AL pathway conveys pain, temperature, and crude touch via?
small diameter peripheral neurons clustered in the lateral root of the DRG
What is the location of the third order neuron?
Thalamus
How is somatotopic representation maintained in the spinal cord in the AL pathway?
- Lateral: sacral inputs
- Medial: cervical inputs
How does the medial spinal cord compare to the lateral spinal cord in the DC-ML pathway?
- Medial Spinal Cord: large fibers, lower body
- Lateral Spinal Cord: small fibers, upper body
A delta and group C fibers are used for?
-A delta and Group C fibers are used for nociceptors and thermal receptors
Describe the termination of the second order neurons and where the third order neurons extend to within the DC-ML pathway.
-Medial lemniscus neurons terminate at the VPL of the thalamus and synapse with third order neurons, which extend to sensory cortex
What is the pathway of second order neurons in the AL system?
Originates in the dorsal horn decussates at anterior white commissure and will ascend contralaterally
Mechanoreceptors display properties of adaptation. What does this mean?
-decrease in neural response to a maintained stimulation
Where does a first order neuron exist?
Within the dorsal roots
Where is the location of the second order neuron?
-where the pathway crosses the midline
In the AL system primary neurons will then do what once entering the spinal cord?
- Primary neurons synapse with the secondary neurons of the spinothalamic tract in the ipsilateral dorsal horn, the second order neuron will send a projection through the anterior white commisure to the contralateral side
- Projection is ascending in the anterolateral quadrant of the white matter of spinal cord
Where does the decussation occur in the DC-ML system vs the AL system?
DC-ML: 2° neuron crosses midline at the lemniscus in the medulla
AL: anterior white commissure, local segment
What is convergence?
hierarchical processing, information collected in the cortex to interpret the whole sensation
What is the labeled line theory?
DC-ML system, specialized neuron is the same through the whole tract (periphery to brain) like a telephone line
Somatotropy is ____ in the spinal cord.
Maintained
What is the pattern theory?
pain processing, peripheral receptors are unspecialized but brain discriminates different quality of pain (burn, dull, sharp, local/wide-spread)
How do the first order neurons in the DC-ML pathway terminate?
-Termination of first order neurons lies in the cuneate and gracilie nuclei of the medulla, where they synapse with the second order neurons and cross the midline
The Anterolateral System (AL and also known as spinothalamic tract) conveys what and crosses the midline where?
- Conveys: Temperature, Pain, & Crude Touch
- Crosses Midline At: Segmental Level of Spinal Cord (w/in 1-2 vertebral levels)
Describe the pathways of the second order neurons in the DC-ML pathway.
- Second order neurons ascend to the thalamus through the medial lemniscus pathway
- Information is now on the contralateral side
What are the characteristics of Group A mechanoreceptor nerve fibers?
- Mechanoreceptors transmit information via myelinated nerve fibers
- Group A: alpha, beta, delta
- Alpha (fastest) → Delta (slowest)
The DC-ML and AL pathways both terminate in the?
Somatosensory cortex
What is the role of third order neurons in the AL system?
Receive synapse from the second order neurons in the thalamus and then project to the somatosensory cortex
Describe the ascent of the DC-ML pathway in the spinal cord.
-Will immediately enter dorsal column white matter and ascend on ipsilateral side of the cord to the brainstem
What is the pathway of the primary neurons in the AL pathway?
-Primary neurons will terminate almost immediately, in the dorsal grey matter of the spinal cord
What are receptive fields?
dense innervation = better two point discrimination = larger representation in the cortex
Describe the somatopotic representation of the DC-ML system.
What is plasticity?
neurons can adapt and change if an area loses neuron sensation → cortex rearrangement
The DC-ML system conveys discriminative touch and proprioception via?
large diameter peripheral neurons that course through DRG and into spinal cord via dorsal root
