Week 6 Neuro

Okay, here are the updated study notes:

• There are three groups of neurons involved in sensory pathways of the body to the cerebral cortex: first, second, and third-order neurons.
• Light touch, vibration, and conscious proprioception from the body are relayed to the cerebral cortex via the dorsal column-medial lemniscus (DCML) pathway, which is a three-neuron pathway.
• Fast nociception (pain), temperature, and crude touch, are relayed via the spinothalamic tract, also a three-neuron pathway.
• The anterolateral system also consists of two tracts, the anterior and lateral spinothalamic tracts.

Dorsal Column-Medial Lemniscus (DCML) Pathway

• DCML carries the sensory modalities of fine touch (tactile sensation), vibration, and proprioception.
• Sensory information travels through first-order neurons to the medulla oblongata, then transmitted through the medial lemniscus in the brainstem.
• Clinically assessed through light touch, vibration, and proprioception tests.
• Light touch is assessed using a cotton wisp, vibration is assessed using a tuning fork, and proprioception is assessed by moving a joint.
• Proprioception is the ability to detect where a joint or the body is in space
• Its name comes from the dorsal (posterior) columns in the spinal cord and the medial lemniscus of the brainstem.
• Runs similarly to the corticospinal pathway

DCML: First-Order Neurons

• First-order neurons carry sensory information regarding touch, proprioception, or vibration, from peripheral receptors to the medulla.
• First-order neurons carry sensory information from peripheral receptors to the medulla, entering the spinal cord ipsilaterally in the dorsal aspect.
• Cell bodies are located in the dorsal root ganglion, entering the spinal cord ipsilaterally in the dorsal aspect.
• Signals from the upper limb (above T6) travel in the fasciculus cuneatus (lateral part of the dorsal column) and synapse in the nucleus cuneatus of the medulla oblongata.
• Signals from the lower limb (below T6) travel in the fasciculus gracilis (medial part of the dorsal column) and synapse in the nucleus gracilis of the medulla oblongata.

DCML: Second-Order Neurons

• Second-order neurons begin in the cuneate nucleus or gracilis, receiving information from the preceding neurons.
• Fibers decussate (cross the midline) within the medulla oblongata and travel in the contralateral medial lemniscus to reach the thalamus.

DCML: Third-Order Neurons

• Third-order neurons transmit sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain.
• Ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule, and terminate at the sensory cortex.
• Location is in the postcentral gyrus.
• Information is processed contralaterally in the cortex; lateral aspects process information from the head, neck, and upper extremities, while medial aspects process information from the trunk and lower extremities.

Spinothalamic Tract

• Transmits signals more slowly because pain and temperature information is transmitted by A-delta and C fibers, which are poorly myelinated or not myelinated.
• Some pain and temperature information also goes to the amygdala, which is involved in processing emotions and pain.
• A-beta fibers are more heavily myelinated and transmit signals faster for light touch, vibration, and stretch.
• Assessed clinically with pinprick tests using sharp and dull objects and by using probes that are either heated or cooled to assess temperature sensitivity.

Spinothalamic Tract Neurons

• First-order neurons carry sensory information from peripheral receptors to the dorsal horn of the spinal cord, where they synapse.
• Cell bodies are located in the dorsal root ganglion.
• Second-order neurons immediately decussate (cross the midline) and ascend contralaterally to the thalamus.
• Third-order neurons project from the thalamus to the somatosensory cortex.
• Pain and temperature uses 𝛅, C fibers and are noxious and thermal.

Anterolateral System

• Two separate tracts here are the anterior and lateral spinothalamic tracts.
• The tracts run alongside each other and can be considered as a single pathway, traveling superiorly within the spinal cord and synapsing in the thalamus.
• The anterolateral system has three groups of neurons, similar to the DCML
• First-order neurons arise from the sensory receptors in the periphery, enter the spinal cord, ascend 1-2 vertebral levels, and synapse at the substantia gelatinosa at the tip of the dorsal horn.
• Second-order neurons carry sensory information from the substantia gelatinosa to the thalamus, with fibers decussating within the spinal cord.

Anterolateral Tract Fibers

• Crude touch and pressure fibers enter the anterior spinothalamic tract
• Pain and temperature fibers enter the lateral spinothalamic tract
• Third-order neurons carry sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain.
• Fibers ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule, and terminate at the sensory cortex.
• ATP is Anterior Spinothalamic Tract and it carries Crude Touch and Pressure
• LPT is Lateral Spinothalamic Tract and it carries Pain and Temperature

Spinal Cord & Cerebellum

• Spinal cord serves as location of the first-order neurons synapse with second-order neurons.
• Cerebellum serves as the destination of the second-order neurons of the spinocerebellar tracts

DCML & Spinothalamic Tract Crossing

• DCML tract crosses (decussates) in the medulla, specifically when the first-order neurons synapse with the second-order neurons.
• Spinothalamic tract crosses (decussates) immediately in the spinal cord, when the first-order neurons synapse with the second-order neurons.

Functions of Sensory Tracts

• DCML pathway is responsible for light touch, vibration, and conscious proprioception.
• Spinothalamic tract is responsible for pain and temperature sensations.
• Spinocerebellar tracts are responsible for unconscious proprioception and kinesthesia.

Dorsal Root Ganglion

• Location of the cell bodies of the first-order neurons for both the DCML pathway and the spinothalamic tract.
• Dorsal part of the spine

Spinal Cord Lesions & Sensory Impairments

• A lesion affecting either the right or left half of the spinal cord results in a condition called Brown-Sequard syndrome, with sensory impairments predicted based on the location of the lesion and the pathways of the ascending tracts

Ipsilateral Sensory Loss

• Occurs on the same side of the lesion.
• Loss of light touch, proprioception, and vibration due to damage to the DCML pathway, which ascends ipsilaterally in the spinal cord.

Contralateral Sensory Loss

• Occurs on the opposite side of the lesion.
• Loss of pain and temperature sensation due to damage to the spinothalamic tract, which decussates immediately in the spinal cord.

Lesion Side Sensory & Motor Impairment Predictions

• A lesion on the right side of the spinal cord will cause a loss of light touch, proprioception, and vibration on the right side of the body, as well as a loss of pain and temperature sensation on the left side of the body.
• A lesion on the left side of the spinal cord will cause a loss of light touch, proprioception, and vibration on the left side of the body, as well as a loss of pain and temperature sensation on the right side of the body.
• Distal is the last to remedy

Incomplete Spinal Cord Injury Syndromes

• Brown-Sequard Syndrome impacts half of the spinal cord to cause ipsilateral motor and DC loss with contralateral pain and temperature
• Central Cord Syndrome is typically caused by hyperextension or whiplash, with motor issues in upper extremities than in lower extremities, with sensory deficits
• Anterior Cord Syndrome, Loss of motor function, pain and temperature below the level of the injury, light touch, proprioception and vibration are preserved
• Cauda Equina Syndrome below C1, vary based on injury with bowel and bladder dysfunction
• Hypotonia can present