There are three sub-types of A fibers, each even more specialized for certain types of physical sensation: they are called alpha, beta, and delta. Of course, like everything in the human nervous system, we have to make things more complicated. They are ordered from the least to the most myelinated: A being the least, C being the most. The differences between the three lies in the degree of myelination of the axons, which influences the speed at which thy transmit signals. In the medial lemniscal pathway, there are three different types of nerve fibers: A, B, and C. Nuclear bag fibers: Detect the progressive stretch, or entire act of the stretch, of the muscle.Nuclear chain fibers: Detects the onset of the stretching – it is important to note that it is the “onset” specifically that is detected by these fibers! This is because they work in tandem with the second type of intrafusal fiber….Intrafusal fibers break further down into two sub-types of proprioceptive fibers (also called “1A” fibers)… Intrafusal fibers: fibers that function as proprioceptors, detecting the stretching of muscles (this detection is assisted by structures known as the Golgi tendon organs). They are the main ones responsible for the contraction of the muscle. Proprioception (specifically as it relates to skeletal muscles) that is regulated by the medial lemniscal pathway is transmitted by two distinct types of fibers (that, of course, divide even further into more types of fibers!):Įxtrafusal fibers: fibers that surround the majority of muscle spindles. They do this by detecting tension deep in the skin and fascia (the fibrous membrane that envelops muscles, internal organs, and many other bodily tissues). These mechanoreceptors are also called bulbous corpuscles or Ruffini endings and respond to the stretching of the skin. These nerve fibers are found in the hair follicles and respond to the bending of the hair and are partially receptive to fine touch. Their location enables them to respond to deep pressure. These receptors are just a bit deeper than the Meisner’s corpuscles and Merkel’s discs and can be found in more than one layer – in the dermis, hypodermis, and more. Merkel’s discs are receptors of fine touch and superficial pressure. These are in the stratum basale (also known as the stratum germinativum) of the skin – which is the deepest of the five layers of the epidermis. (Discriminative touch is also known as “fine touch,” wherein receptors provide highly detailed information on what is being touched, and assisted by its position in the skin, it informs the dorsal column on very gentle, or “fine” touch, such as a spider web or strand of hair on the skin.) These are in the dermal papillae of the skin (structures located between the epidermis and dermis layers of the skin) and take in information related to discriminative touch. The receptors that work with the medial lemniscal pathway are the… Proprioception: awareness of the position of joints and muscles in space (anatomical spatial awareness).Discriminative touch: picking up fine touch, and touch that occurs at more than one point of contact.It is responsible for transmitting sensory information related to The dorsal column, also known as the medial lemniscal pathway, is an ascending pathway of the spinal cord (meaning it is responsible only for sending information from receptors and elsewhere in the peripheral nervous system up toward the brain) and is located on the posterior portion of the spinal cord. Let’s look a bit closer at the structure and functionality of the dorsal column. Just like all other sensory, motor, and cognitive pathways in the body, however, the dorsal column is continuously sending an incredible amount of neuronal information from the receptors in the skin, muscles, and more, straight to the brain, through the brainstem, and other structures such as the thalamus. In fact, because of the nerve connections that are regulated by the dorsal column, along with its wide variety of functions, the stimulation of the dorsal column is used as a form of treatment for chronic pain like complex regional pain syndrome (CRPS). The nerve signals that travel through the dorsal column also travel a bit differently than most others, in that they decussate at a different point in their transmission pathway, and the stages of transmission and points of synapsing are different from other spinal tracts. It relays information related to many different types of touch, motor functionality, and more. The dorsal column sustains an immense amount of connections with the peripheral nervous system. Pathway of Action Impulses Through the Dorsal Column.
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