17.17: Spinal Cord: Information Processing
The spinal cord is an integral hub for motor and sensory information that enables the brain to communicate with the peripheral nervous system (PNS). This communication consists of relaying sensory data and transmission of motor commands.
Sensory Information Processing
Sensory information processing begins at the sensory receptors located in the skin and other tissues, which detect somatic sensory stimuli such as touch, temperature, or pain. These receptors function as catalysts, initiating nerve impulses that are transmitted towards the spinal cord via sensory neurons. Upon reaching the spinal cord, these impulses enter through the dorsal root, which serves as the entry point for all sensory information from the peripheral body into the spinal cord. The impulses then proceed to the dorsal gray horn of the spinal cord, which acts as a processing and relay center for incoming sensory data. From the dorsal gray horn, the sensory impulse can follow one of several paths.
- • Direct Ascension to the Brain: Impulses from stimuli such as fine touch or vibration enter the white matter of the spinal cord almost immediately upon arrival and ascend directly to the brain. This pathway allows the rapid relay of sensory information to the brain for processing and response.
- • Interneuron Relay: Impulses from other stimuli, such as pain and temperature, may be transferred to interneurons located within the dorsal gray horn. The axons of these interneurons then project into the white matter, where they ascend to the brain. This path allows for the integration and modulation of sensory signals before they reach higher processing centers.
- • Spinal Reflex Pathways: Another possible route for an impulse entering the dorsal gray horn is to engage the somatic motor neurons involved in spinal reflex pathways. This mechanism enables reflex actions, such as the withdrawal reflex from a painful stimulus, without direct brain intervention and providing an immediate response to certain sensory inputs.
Motor Information Processing
Motor output from the brain, which directs voluntary movements and reflex responses, descends into the spinal cord through white matter tracts. These descending motor signals convey instructions from the brain to various body parts.
The motor impulse travels down the spinal cord and enters the ventral gray horn, which houses motor neurons for transmitting signals to the muscles. From the ventral gray horn, the impulse moves into the ventral root, which serves as the exit point from the spinal cord to the spinal nerve. Finally, the impulse is carried through the spinal nerve to the target muscles, culminating in the intended response, whether it be muscle contraction, movement, or modulation of muscle tone.
