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 parts 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.