The spinal cord is a vital communication and processing center located in the vertebral column, connecting the brain to the rest of the body. A transverse cross-section of the spinal cord reveals a characteristic butterfly pattern of dark grey matter encircled by a lighter-coloured white matter. This grey matter can be organized into four distinct columns- the dorsal horn, the intermediate column, the lateral horn and the ventral horn.
The dorsal horn (also known as the posterior horn) includes neurons that receive somatosensory information from the body and then transmit these signals via ascending pathways up to the brain. The ventral horn (also known as the anterior horn) contains mainly motor neurons which exit the spinal cord to innervate skeletal muscle. The intermediate column and lateral horn contain neurons that innervate visceral and pelvic organs.
The spinal cord contains a range of prominent nuclei (groups of neuron cell bodies). These include:
In 1950s, Bror Rexed proposed an alternative system of classification than nuclei. He delineated laminae, or layers, within the spinal cord in which nerve cells were arranged according to their structure and function, rather than by their position alone. Lamina I consists of cells that respond to noxious or thermal stimuli and then transmit these messages to the brain via the contralateral spinothalamic tract. Lamina II is involved in the perception of both noxious and non-noxious stimuli, and in modulating sensory input to assist the brain in decoding incoming signals as painful or not. Lamina III is active in proprioception and sensation of light touch, and is connected to cells in laminae IV, V and VI. Lamina IV is responsible for non-noxious sensory information relay and processing and is linked to cells in lamina II, while lamina V relays sensory information, including nociceptive (potentially painful) signals, to the brain via the contralateral and spinothalamic tracts.
Therefore, the spinal cord grey matter consists of four columns of nuclei and laminae that are essential for various sensory and motor functions. These columns and laminae are responsible for receiving, relaying and processing a range of stimuli from the body and transmitting it to the brain, allowing us to understand and react to our environment.
Lamina III is associated with proprioception and sensation of light touch, and works closely with Lamina IV. Lamina IV is in charge of relaying and processing non-noxious sensory information and receives data from Lamina II. Lamina V transmits sensory signals to the brain, including potentially painful noxious stimuli, using the contralateral and spinothalamic tracts. Data is received from the brain through the corticospinal and rubrospinal tracts. Lamina VI has multiple small interneurons involved in spinal reflexes, and also receives sensory information from muscle spindles. Lamina VII is an expansive, heterogenous area that changes along the spinal cord's length, and provides both sensory and motor information to the brain and viscera. Lamina VIII is peculiar to every level of the spinal cord, and is more distinct in the cervical and lumbar enlargements. Also, Lamina IX is comprised of individual motor neurons, all responsible for innervating skeltal muscles. Lastly, Lamina X encapsulates the central canal and contains axons that travel in a crossed pattern from each side of the spinal cord.
Clinically, referred pain happens when viscera pain is felt as cutaneous pain. This is because of neurons in the dorsal horn sending signals from the viscera, that are also responsible for transmitting cutaneous pain signals, thus making it difficult to determine the original source of the pain.
