Somatosensory Pathways: Dorsal Column and Medial Lemniscal Pathway

Overview of Somatosensory Pathways

• The video discusses the somatosensory pathways, particularly focusing on the dorsal column, also known as the medial lemniscal pathway, which transmits touch, vibratory sense, and proprioception sensations to the cerebral cortex.

Anatomy of the Spinal Cord

• A brief overview of spinal cord anatomy is provided; sensory neurons enter through the dorsal root while motor neurons exit via the ventral roots. The dorsal column tract is located at the back of the spinal cord.

• The dorsal column can be divided into two parts:

• Fasciculus cuneatus (lateral) for upper body sensory information.

• Fasciculus gracilis (medial) for lower body sensory information.

Sensory Information Transmission

• The dorsal column tracts carry sensory information related to touch, pressure, vibration, and proprioception to the somatosensory cortex in the brain. The thalamus acts as a relay station in this ascending pathway.

• Mechanoreceptors in skin detect various sensations:

• Merkel cells: Detect touch and pressure.

• Ruffini endings: Respond to sustained pressure.

• Meissner corpuscles: Sensitive to tap and flutter sensations.

• Pacinian corpuscles: Detect deep pressure and vibration.

Neuronal Pathways

• First-order neurons transmit sensory information from mechanoreceptors to the dorsal column tract; they synapse with second-order neurons at specific nuclei in the medulla:

• Upper body signals travel via fasciculus cuneatus.

• Lower body signals travel via fasciculus gracilis.

• Second-order neurons cross over at midline of medulla and ascend through medial lemniscal tract to contralateral thalamic nucleus before synapsing with third-order neurons that project to primary somatosensory cortex in parietal lobe.

Somatotopic Organization

• The somatosensory cortex has regions corresponding to different body areas (e.g., face, hands, legs). Sensations from one side of the body are processed by the opposite side of the brain due to crossing over at medulla level.

Proprioception Explained

Understanding Proprioception and Neural Pathways

Anatomy of the Somatosensory System

• The somatosensory cortex, midbrain, pons, medial meniscal tracts, and medulla (including nucleus gracilis and nucleus cuneatus) are key components in processing sensory information.

• The spinal cord is referenced as the cervical spinal cord for context in understanding proprioceptive pathways.

Proprioceptors and Their Functions

• Muscle spindles are specialized proprioceptors that provide critical information about changes in muscle length during movement.

• Golgi tendon organs serve as another type of proprioceptor located on tendons, detecting changes in muscle tension.

• These proprioceptors relay information regarding muscle tension and length through the dorsal column pathway to the brain.

Neural Pathway to the Brain

• In upper body proprioception, first-order neurons ascend via the fasciculus cuneatus towards the medulla where they synapse with second-order neurons at the nucleus cuneatus.