The dorsal column is a part of the spinal cord, located in the posterior section of its white matter. Its primary function involves transmitting specific types of sensory information from the body up to the brain for processing. This pathway carries signals related to touch, body position, and vibration, allowing the brain to understand the physical environment and the body’s interaction with it.
Role in Sensation
The dorsal column system relays several distinct types of sensations. One is proprioception, the body’s ability to sense its own position and movement in space without needing to look. For example, proprioception allows someone to touch their nose with their eyes closed or know if their feet are on grass or concrete even with shoes on. This sense relies on continuous feedback from sensory receptors in the skin, joints, and muscles.
Another sensation transmitted by the dorsal column is discriminative touch. This refers to the ability to perceive fine details of touch, such as an object’s texture or shape. It also allows for two-point discrimination, the ability to distinguish between two closely spaced points touching the skin. For instance, discriminative touch enables a person to identify a coin by feel in their pocket without looking at it.
The dorsal column also carries vibration sense, known as pallesthesia. This is the ability to feel vibrations, which are rapid and regular changes in pressure. Mechanoreceptors, such as Pacinian corpuscles found deep in the skin, muscles, and joints, detect these vibrations. A common example is feeling a vibrating cell phone in a pocket.
Direct Sensory Losses from Injury
An injury to the dorsal column directly impairs the specific sensory functions it transmits. A common manifestation is the loss or impairment of proprioception, making it difficult to know where one’s limbs are without visual input. Individuals might feel disconnected from their own body or struggle to perform actions like walking in a straight line or balancing on one foot without looking. This can lead to clumsiness, such as dropping objects or bumping into things.
Damage to the dorsal column also results in a loss or impairment of discriminative touch. This makes it challenging to identify objects by touch alone, a condition known as astereognosis. A person might struggle to perceive fine textures, such as the grain of wood, or differentiate between the shapes of objects when handled. The ability to distinguish two closely spaced points on the skin, known as two-point discrimination, is also impaired.
An injury to the dorsal column can lead to a reduced or absent ability to feel vibrations. This diminished sense of vibration is called pallhypesthesia. For example, a person might not feel the subtle hum of a running engine or the vibrations of a phone. Testing for this often involves placing a vibrating tuning fork on the skin over a bone, as bones are good resonators of vibrations.
Impact on Movement and Daily Life
The direct sensory losses from a dorsal column injury have functional consequences for movement and daily activities. One is sensory ataxia, which describes uncoordinated movements resulting from a lack of sensory feedback, particularly concerning body position. This unsteadiness often worsens when visual input is removed, such as when walking in the dark or closing the eyes in the shower. Patients with sensory ataxia may compensate by keeping their eyes on the ground to gather visual cues, as sensory cues are diminished.
Impaired balance is another issue, as the loss of proprioception directly affects stability while standing and walking. This can lead to frequent falls, especially in low-light conditions or when the eyes are closed. The body’s ability to make unconscious adjustments to maintain upright posture is compromised, increasing the risk of instability.
Difficulty with fine motor skills often arises due to impaired discriminative touch. Tasks requiring precision and dexterity, such as buttoning clothes, writing, or picking up small objects, become challenging. Manipulating tools or performing intricate tasks that rely on detailed tactile feedback also becomes harder.
Gait disturbances are common, with individuals often developing characteristic walking patterns. These can include a high-stepping gait, where the legs are lifted higher than usual to prevent tripping, or a wide-based gait, where the feet are placed widely apart to enhance stability. A “foot slap” may also occur, where the foot hits the ground heavily due to the lack of proprioceptive feedback. These impairments collectively affect various activities of daily living, including dressing, eating, and personal care, impacting independence and overall quality of life.