2-Minute Neuroscience: Touch and the Dorsal Columns-Medial Lemniscus

In my 2-Minute Neuroscience videos I explain neuroscience topics in 2 minutes or less. In this video, I discuss touch and the dorsal columns-medial lemniscus pathway. I describe the pathway somatosensory information takes from cutaneous receptors in the skin to the spinal cord and into either the fasciculus gracilis or fasciculus cuneatus. Then I follow the pathway through the medulla, to the ventral posterolateral nucles of the thalamus, and on to the somatosensory cortex. I also briefly describe the somatotopic arrangment of the somatosensory cortex.

TRANSCRIPT:

Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics in 2 minutes or less. In this installment I will discuss touch and the dorsal columns-medial lemniscus pathway.

Somatosensation involves sensations from the body. When these sensations come from the external environment, they are picked up by receptors in the skin called cutaneous receptors. There are several different types of cutaneous receptors, each designed to respond to specific types of touch sensations like pressure, pain, or vibration. In this video I’ll discuss signals that involve information about fine touch and vibration. I’ll cover pain in a separate video.

The main pathway that carries information about touch to the brain is the dorsal columns-medial lemniscus (also called the posterior columns-medial lemniscus). This pathway also carries information about proprioception, or the position of the body in space; these signals come from proprioceptors in muscles and joints. Fibers in the dorsal columns-medial lemniscus leave cutaneous receptors or proprioceptors and enter the spinal cord via the dorsal roots. They travel up the spinal cord to the medulla in one of two fiber bundles within the dorsal columns: the fasciculus gracilis, which carries information from the lower half of the body, or the fasciculus cuneatus, which carries information from the upper limbs and torso. In the medulla, the fasciculus gracilis and fasciculus cuneatus synapse on the next neurons in the pathway in areas called the nucleus gracilis and the nucleus cuneatus, respectively. It is from these nuclei that the second part of the pathway arises: a fiber bundle called the medial lemniscus. The medial lemniscus leaves the dorsal column nuclei and quickly decussates, or crosses over to the other side of the brain, before traveling up to the thalamus, where it synapses in a part of the thalamus called the ventral posterolateral nucleus, or VPL.

A third part of the pathway arises from the thalamus and travels up to an area of the cortex called the postcentral gyrus, which contains the main sensory area for touch in the brain: the somatosensory cortex. Specific parts of the somatosensory cortex receive signals from specific areas of the body, an arrangement that is known somatotopic. Information about the nature and location of the sensation are integrated in the somatosensory cortex, where the conscious perception of the sensation begins.

REFERENCE:

Nolte J. The Human Brain: An Introduction to its Functional Anatomy. 6th ed. Philadelphia, PA. Elsevier; 2009.