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Afferent Signaling

Afferent signaling is understood to be the ‘bottom-up’ nervous pathways that send important ‘sense-signals’ to the cortex via the spinothalamic ascending pathways. Sense is registered at a tissue, passes through a peripheral nerve to its DRG, then up the spinal cord within a dedicated tract, then to a thalamus GG, then through a cortical nerve that arrives in an area of the brain for cognitive interpretation. True story.

Afferent signals include:

(1) Skin touch sense-signals: deep, light, 2-point discrimination, broad contact, and determination of rough vs. smooth (slip). The skin can relay the sensation of losing grip with a greased watermelon. The skin can relay information about intimate ‘point-contact’ at the fingertips, but does a poor job of this at the shoulders, back and thigh. The skin can relay information about deeper pressure; for some it feels like a good sports massage, and for others painful. The skin can also identify palpable things (dice, jacks, coins) and can read Braille. Touch sense-signals travel together up the spinal cord separated from the other sense signals.

(2) Organic muscles sense-signals: constriction sense of: bronchial muscles, pharyngeal muscles, rectal muscles, ciliary muscles, and stretch sense of: bladder muscles, stomach muscles, and gut tube muscles.

(3) Skin temperature sense-signals: hot and cold (dry and moist.) The skin can relay the sensation of heat using thermoreceptors; however, it is the cortex that determines whether the heat is tissue-damaging, or just a good hot shower, even when both may be the exact same temperature. Hot and cold is determined in part due to the sense-signal of evaporation. Whole body temperature is determined in part by the skin and hair follicles, and by baroreceptors (blood pressure.) Temperature sense-signals travel together up the spinal cord separated from the other sense-signals.

(4) Spatial-self sense-signals: limb position, muscle tone, joint angles, and performing work. The ‘mechanical’ features of the body relay information that determines whether a load is too heavy to carry, or if there is enough strength to hold on. Proprioceptors like Golgi Tendon Organs (GTO) or Muscle Spindles (MS) report to the brain regarding muscle lengthening-shortening, strain on tendons, speed of the lift (fast or slow) so that the brain can decide what to do about the load… hold it, or let it go. These same features help you ‘feel’ if you are smiling or frowning.

The spatial-self gets help from vision and the inner ear (balance, etc.) Spatial-self sense-signals travel together up the spinal cord separated from the other sense signals. Or, do they?

(5) Nociception (‘pain’) is a generic sense-signal that arrives at the brain for interpretation. These signals follow a nerve path called a C-Fiber, or slow fiber. These signals relay: (1) evident tissue damage/discomfort, (2) expectant tissue damage/discomfort, and (3) no tissue damage/discomfort cause whatsoever. Herein lies the conundrum; How can the body sense a ‘pain’ signal when there is no cause? Pain is an experience reaction to the idea of tissue damage/discomfort… an idea…a story. When the eyes see skin tissue damage (knife wound), the brain assigns the origin of pain to that site because it makes sense. Pain occurs with traumatic injury. Pain can be described in many ways. There is no research to support why pain can feel shooting, or sharp, or pinchy, or dull, or achy, etc. The ‘pain’ nerve pathway can become intimately entangled with other experiences in the brain, “It hurts when I think about it.” Phantom limb pain… is associated with neither a damaged tissue area nor an inflamed part of the body.” (Salto, et al., 2016) “34,000 people per year experience ongoing PLP.” (Ameet et al., 2018) “The pain system shows degeneracy, [this] means that an outcome [of pain] can have several causes… whether the pain is caused by tissue injury, deafferentation, or hypnosis,” (Brodal, 2017.)

Not all obvious origins of ‘pain’ are causing pain. This is a huge problem in a clinician’s practice. “Despite the prevalence, no specific cause can be found for almost 85% of the chronic low back pain cases.” (Steele et al., 2014)

LBP Non-afferent signals (Emotionality) include:

(1) The patient’s feelings about their LBP complaint; relentless pain, how the pain makes them feel, worry, fear, optimism, catastrophizing.

(2) The patient’s feelings about access to LBP care: geography, economics, and socially supported care.

(3) The patient’s feelings about their LBP care system: swiftness of diagnosis and care plan, degree of satisfaction with course of care results, expectations being met, stuck in the system, unheard, abandoned.

All afferent signals synapse together at ganglia; in a perfect world afferent signaling is preserved. The clinician might wonder if the LBP patient’s pain experience is attributed to only the nociceptive sense signal, or if other sense signals are involved. It is reasonable to wonder if the nociceptive signal accurately reports tissue damage, or if ‘sense-signals get crossed.’ Can other sense signals ‘jump’ the nociceptive pathway causing sense-signal confusion? Advocate for your LBP patients by studying their emotionality first, then looking for possible ‘mixed’ messaging since ‘pain is not the only problem.’

LBP Blog General information

Series Description

These articles intend to (1) re-evaluate the prevailing clinical practices thought to manage low back ‘pain’, (2) submit and debate novel low back ‘pain’ contributors and mechanisms, (3) meet patient expectations & satisfaction and clinically meaningful results, (4) recommend a conservative non-surgical course of care to over-ride ‘pain’ instantly, and (5) restore ADLs and patient confidence on the first visit at low cost. This article has a companion podcast.

Dr. Dean Bio

Forester Dean is a chiropractic and physiotherapy sports medicine doctor practicing in Los Angeles, California. Dr. Dean is a lifetime athlete, and currently teaches tennis, track, boxing, yoga. The Core X System™ Campus flagship location was opened by Dr. Dean in 2020.

© Copyright 2021 SpineSync, Forester Dean, DC
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