Touch & Somatosensory Processing — Study Guide

What are the key receptors in the skin and their primary functions?

Merkel discs (edges, form), Meissner corpuscles (light flutter), Pacinian corpuscles (vibration), Ruffini endings (skin stretch), Hair follicle receptors (hair movement).

What does the Dorsal Column–Medial Lemniscus (DCML) pathway carry?

Discriminative touch, pressure, vibration, conscious proprioception.

Where does the DCML pathway cross?

In the medulla.

What type of fibers travel mainly in the DCML pathway?

Aβ fibers (large, myelinated).

What sensory modalities does the Anterolateral/Spinothalamic System carry?

Pain, temperature, and some crude touch.

What is the role of the thalamus in sensory processing?

Major relay station to the cortex, integrates and contributes to attention and pain perception.

What occurs during the first step of the DCML pathway?

Stimulus transduction of skin deformation opens mechanically gated channels in receptors, causing receptor potential and action potentials in Aβ fibers.

What does the cerebellum use for movement correction?

Proprioceptive input via spinocerebellar tracts.

What are dermatomes?

Skin territories corresponding to specific spinal nerves, helpful for localizing lesions.

Compare the adaptation of rapidly adapting vs slowly adapting receptors.

Rapidly adapting receptors (e.g., Pacinian, Meissner) respond quickly to changes; slowly adapting receptors (e.g., Merkel, Ruffini) provide sustained responses.

What happens with a right T10 hemisection regarding sensory loss?

Ipsilateral loss of touch/proprioception (DCML), contralateral loss of pain/temperature (spinothalamic).

What is somatotopy?

The preserved organization of sensory representation from the spinal cord to the thalamus to the cortex.

What is the purpose of the brainstem in sensory processing?

Houses relays for the medulla, medial lemniscus, and integrative networks crucial for sensorimotor control.

What is two-point discrimination and where is it best performed?

The ability to perceive two distinct points of touch, best in fingertips due to high receptor density.

What is the function of the medial lemniscus?

It carries sensory information from the medulla to the thalamus after decussation.

What are the key receptors in the skin and their primary functions?

Merkel discs (edges, form), Meissner corpuscles (light flutter), Pacinian corpuscles (vibration), Ruffini endings (skin stretch), Hair follicle receptors (hair movement).

What does the Dorsal Column–Medial Lemniscus (DCML) pathway carry?

Discriminative touch, pressure, vibration, conscious proprioception.

Where does the DCML pathway cross?

In the medulla.

What type of fibers travel mainly in the DCML pathway?

Aβ fibers (large, myelinated).

What sensory modalities does the Anterolateral/Spinothalamic System carry?

Pain, temperature, and some crude touch.

What is the role of the thalamus in sensory processing?

Major relay station to the cortex, integrates and contributes to attention and pain perception.

What occurs during the first step of the DCML pathway?

Stimulus transduction of skin deformation opens mechanically gated channels in receptors, causing receptor potential and action potentials in Aβ fibers.

What does the cerebellum use for movement correction?

Proprioceptive input via spinocerebellar tracts.

What are dermatomes?

Skin territories corresponding to specific spinal nerves, helpful for localizing lesions.

Compare the adaptation of rapidly adapting vs slowly adapting receptors.

Rapidly adapting receptors (e.g., Pacinian, Meissner) respond quickly to changes; slowly adapting receptors (e.g., Merkel, Ruffini) provide sustained responses.

What happens with a right T10 hemisection regarding sensory loss?

Ipsilateral loss of touch/proprioception (DCML), contralateral loss of pain/temperature (spinothalamic).

What is somatotopy?

The preserved organization of sensory representation from the spinal cord to the thalamus to the cortex.

What is the purpose of the brainstem in sensory processing?

Houses relays for the medulla, medial lemniscus, and integrative networks crucial for sensorimotor control.

What is two-point discrimination and where is it best performed?

The ability to perceive two distinct points of touch, best in fingertips due to high receptor density.

What is the function of the medial lemniscus?

It carries sensory information from the medulla to the thalamus after decussation.

Describe the pathway for discriminative touch and proprioception from the periphery to the cortex via the Dorsal Column-Medial Lemniscus (DCML) pathway.

1. First-order neuron: Mechanoreceptors detect stimuli, sending Aβ fiber signals via dorsal root ganglion (DRG) to the ipsilateral dorsal column of the spinal cord, ascending to the medulla (gracile/cuneate nuclei).
2. Second-order neuron: From the medulla, fibers decussate (cross) and ascend as the medial lemniscus to the thalamus (Ventral Posterior Lateral nucleus - VPL).
3. Third-order neuron: From the thalamus, fibers project to the primary somatosensory cortex (S1).

Describe the pathway for pain and temperature from the periphery to the cortex via the Anterolateral/Spinothalamic System.

1. First-order neuron: Nociceptors/thermoreceptors detect stimuli, sending Aδ or C fiber signals via DRG to the ipsilateral dorsal horn of the spinal cord.
2. Second-order neuron: From the dorsal horn, fibers decussate (cross) at the spinal cord level and ascend as the spinothalamic tract to the thalamus (VPL and intralaminar nuclei).
3. Third-order neuron: From the thalamus, fibers project to the primary somatosensory cortex (S1) and other cortical areas.

Describe the main pathway for proprioceptive input to the cerebellum via the spinocerebellar tracts.

1. First-order neuron: Proprioceptors in muscles/joints send signals via DRG to the ipsilateral spinal cord.
2. Second-order neuron: From the spinal cord (e.g., Clarke's nucleus for dorsal, laminae V-VII for ventral), fibers ascend primarily via the dorsal and ventral spinocerebellar tracts, entering the cerebellum (often ipsilaterally or decussating twice). This pathway conveys unconscious proprioception for motor coordination.