1.5.1 Somatic Sensation

Question 1

The Dorsal Column-Medial Lemniscus (DC-ML) system conveys what and crosses the midline where?

Answer 1

• Conveys: fine touch, proprioception, pressure, and vibration
• Crosses Midline At: In the medial lemniscus after the Gracile & Cuneate Nuclei in Medulla

Question 2

The AL pathway conveys pain, temperature, and crude touch via?

Answer 2

small diameter peripheral neurons clustered in the lateral root of the DRG

Question 3

What is the location of the third order neuron?

Answer 3

Thalamus

Question 4

How is somatotopic representation maintained in the spinal cord in the AL pathway?

Answer 4

• Lateral: sacral inputs
• Medial: cervical inputs

Question 5

How does the medial spinal cord compare to the lateral spinal cord in the DC-ML pathway?

Answer 5

• Medial Spinal Cord: large fibers, lower body
• Lateral Spinal Cord: small fibers, upper body

Question 6

A delta and group C fibers are used for?

Answer 6

-A delta and Group C fibers are used for nociceptors and thermal receptors

Question 7

Describe the termination of the second order neurons and where the third order neurons extend to within the DC-ML pathway.

Answer 7

-Medial lemniscus neurons terminate at the VPL of the thalamus and synapse with third order neurons, which extend to sensory cortex

Question 8

What is the pathway of second order neurons in the AL system?

Answer 8

Originates in the dorsal horn decussates at anterior white commissure and will ascend contralaterally

Question 9

Mechanoreceptors display properties of adaptation. What does this mean?

Answer 9

-decrease in neural response to a maintained stimulation

Question 10

Where does a first order neuron exist?

Answer 10

Within the dorsal roots

Question 11

Where is the location of the second order neuron?

Answer 11

-where the pathway crosses the midline

Question 12

In the AL system primary neurons will then do what once entering the spinal cord?

Answer 12

• 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

Question 13

Where does the decussation occur in the DC-ML system vs the AL system?

Answer 13

DC-ML: 2° neuron crosses midline at the lemniscus in the medulla

AL: anterior white commissure, local segment

Question 14

What is convergence?

Answer 14

hierarchical processing, information collected in the cortex to interpret the whole sensation

Question 15

What is the labeled line theory?

Answer 15

DC-ML system, specialized neuron is the same through the whole tract (periphery to brain) like a telephone line

Question 16

Somatotropy is ____ in the spinal cord.

Answer 16

Maintained

Question 17

What is the pattern theory?

Answer 17

pain processing, peripheral receptors are unspecialized but brain discriminates different quality of pain (burn, dull, sharp, local/wide-spread)

Question 18

How do the first order neurons in the DC-ML pathway terminate?

Answer 18

-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

Question 19

The Anterolateral System (AL and also known as spinothalamic tract) conveys what and crosses the midline where?

Answer 19

• Conveys: Temperature, Pain, & Crude Touch
• Crosses Midline At: Segmental Level of Spinal Cord (w/in 1-2 vertebral levels)

Question 20

Describe the pathways of the second order neurons in the DC-ML pathway.

Answer 20

• Second order neurons ascend to the thalamus through the medial lemniscus pathway
• Information is now on the contralateral side

Question 21

What are the characteristics of Group A mechanoreceptor nerve fibers?

Answer 21

• Mechanoreceptors transmit information via myelinated nerve fibers
• Group A: alpha, beta, delta
• Alpha (fastest) → Delta (slowest)

Question 22

The DC-ML and AL pathways both terminate in the?

Answer 22

Somatosensory cortex

Question 23

What is the role of third order neurons in the AL system?

Answer 23

Receive synapse from the second order neurons in the thalamus and then project to the somatosensory cortex

Question 24

Describe the ascent of the DC-ML pathway in the spinal cord.

Answer 24

-Will immediately enter dorsal column white matter and ascend on ipsilateral side of the cord to the brainstem

Question 25

What is the pathway of the primary neurons in the AL pathway?

Answer 25

-Primary neurons will terminate almost immediately, in the dorsal grey matter of the spinal cord

Question 26

What are receptive fields?

Answer 26

dense innervation = better two point discrimination = larger representation in the cortex

Question 27

Describe the somatopotic representation of the DC-ML system.

Answer 27

Question 28

What is plasticity?

Answer 28

neurons can adapt and change if an area loses neuron sensation → cortex rearrangement

Question 29

The DC-ML system conveys discriminative touch and proprioception via?

Answer 29

large diameter peripheral neurons that course through DRG and into spinal cord via dorsal root