Can understanding how nociceptors function and their role in processing pain signals help individuals who are managing injuries and/or living with chronic pain conditions?
Nociceptors
Nociceptors are nerve endings that detect harmful stimuli, such as extreme temperatures, pressure, and chemicals, and signal pain. They are the body’s first defense against potentially damaging environmental inputs.
Nociceptors are in the skin, muscles, joints, bones, internal organs, deep tissues, and cornea.
They detect harmful stimuli and convert them into electrical signals.
These signals are sent to the brain’s higher centers.
The brain interprets the signals as pain, which prompts the body to avoid the harmful stimulus.
Nociceptors, often called pain receptors, are free nerve endings all over the body. They play a pivotal role in how the body feels and reacts to pain. The main purpose of a nociceptor is to respond to damage to the body by transmitting signals to the spinal cord and brain. (Purves D, Augustine GJ, Fitzpatrick D, et al., editors. 2001) If you bang your foot, the nociceptors on the skin are activated, sending a signal to the brain via the peripheral nerves to the spinal cord. Pain resulting from any cause is transmitted this way. Pain signals are complex, carrying information about the stimuli’s location and intensity. This causes the brain to fully process the pain and send communication back to block further pain signals.
Thermal nociceptors respond to extreme hot or cold temperatures.
For instance, when touching a hot stove, the nociceptors, which signal pain, are activated immediately, sometimes before you know what you’ve done.
Mechanical
Mechanical nociceptors respond to intense stretching or strain, such as pulling a hamstring or straining a tendon.
The muscles or tendons are stretched beyond their ability, stimulating nociceptors and sending pain signals to the brain.
Chemical
Chemical nociceptors respond to chemicals released from tissue damage.
For example, prostaglandins and substance P or external chemicals like topical capsaicin pain creams.
Silent
Silent nociceptors must be first activated by tissue inflammation before responding to a mechanical, thermal, or chemical stimulus.
Most visceral nociceptors are located on organs in the body.
Polymodal
Polymodal nociceptors respond to mechanical, thermal, and chemical stimuli.
Mechano-thermal
Mechano-thermal nociceptors respond to mechanical and thermal stimuli.
Pain Transmission
Nociceptors are also classified by how fast they transmit pain signals. Transmission speed is determined by the type of nerve fiber known as an axon a nociceptor has. There are two main types.
The first type is A fiber axon, fibers surrounded by a fatty, protective sheath called myelin.
Myelin allows nerve signals/action potentials to travel rapidly.
Because of the difference in transmission speed, the pain signals from the A fibers reach the spinal cord first. As a result, after an acute injury, an individual experiences pain in two phases, one from the A fibers and one from the C fibers. (Ngassapa D. N. 1996)
Pain Perception Phases
When an injury occurs, the stimulated nociceptors activate the A fibers, causing a person to experience sharp, prickling pain.
This is the first phase of pain, known as fast pain, because it is not especially intense but comes right after the stimulus.
During the second phase of pain, the C fibers are activated, causing an intense, burning pain that persists even after the stimulus has stopped.
The fact that the C fibers carry burning pain explains why there is a short delay before feeling the sensation.
The C fibers also carry aching, sore pain caused by organs within the body, such as a sore muscle or stomachache. (Ngassapa D. N. 1996)
Injury Medical Chiropractic and Functional Medicine Clinic
Injury Medical Chiropractic and Functional Medicine Clinic works with primary healthcare providers and specialists to build optimal health and wellness solutions. We focus on what works for you to relieve pain, restore function, prevent injury, and help mitigate issues through adjustments that help the body realign itself. They can also work with other medical professionals to integrate a treatment plan to resolve musculoskeletal problems.
From Injury To Recovery With Chiropractic Care
References
Purves D, A. G., Fitzpatrick D, et al., editors. (2001). Nociceptors. In Neuroscience. 2nd edition. (2nd ed.). Sunderland (MA): Sinauer Associates. https://www.ncbi.nlm.nih.gov/books/NBK10965/
University of Texas McGovern Medical School. (2020). Chapter 6: Pain Principles. https://nba.uth.tmc.edu/neuroscience/m/s2/chapter06.html
Ngassapa D. N. (1996). Comparison of functional characteristics of intradental A- and C-nerve fibres in dental pain. East African medical journal, 73(3), 207–209.
For individuals dealing with chronic pain, can undergoing a nerve block procedure help alleviate and manage symptoms?
Nerve Blocks
A nerve block is a procedure done to interrupt/block pain signals due to nerve dysfunction or injury. They can be used for diagnostic or treatment purposes, and their effects can be short or long-term, depending on the type being used.
A temporary nerve block may involve the application or injection that stops pain signals from transmitting for a short time.
For example, in pregnancy, an epidural injection can be used during labor and delivery.
Permanent nerve blocks involve cutting/severing or removing certain parts of a nerve to stop pain signals.
These are used in cases with severe injuries or other chronic pain conditions that have not improved with other treatment approaches.
Treatment Usage
When healthcare providers diagnose a chronic pain condition caused by nerve injury or dysfunction, they may use a nerve block to locate the area generating pain signals. They may perform electromyography and/or a nerve conduction velocity/NCV test to pinpoint the cause of chronic nerve pain. Nerve blocks can also treat chronic neuropathic pain, such as pain caused by nerve damage or compression. Nerve blocks are regularly used to treat back and neck pain caused by herniated discs or spinal stenosis. (Johns Hopkins Medicine. 2024)
Types
Three types include:
Local
Neurolytic
Surgical
All three can be used for conditions that cause chronic pain. However, neurolytic and surgical blocks are permanent and are only used for severe pain that has worsened with other treatments unable to provide relief.
Temporary Blocks
A local block is done by injecting or applying local anesthetics, like lidocaine, to a certain area.
An epidural is a local nerve block that injects steroids or analgesics into an area around the spinal cord.
These are common during pregnancy, labor, and delivery.
Epidurals can also be used to treat chronic neck or back pain due to a compressed spinal nerve.
Local blocks are usually temporary, but in a treatment plan, they can be repeated over time to manage chronic pain from conditions like arthritis, sciatica, and migraines. (NYU Langone Health. 2023)
Permanent Blocks
A neurolytic block uses alcohol, phenol, or thermal agents to treat chronic nerve pain. (National Institute of Neurological Disorders and Stroke. 2023) These procedures damage certain areas of the nerve pathway on purpose so that pain signals cannot be transmitted. A neurolytic block is mainly used for severe chronic pain cases, like pain from cancer or complex regional pain syndrome/CRPS. They are sometimes used to treat ongoing pain from chronic pancreatitis and pain in the chest wall after surgery. (Johns Hopkins Medicine. 2024) (Alberto M. Cappellari et al., 2018)
The neurosurgeon performs a surgical nerve block that involves surgically removing or damaging specific areas of the nerve. (National Institute of Neurological Disorders and Stroke. 2023) A surgical nerve block is only used for severe pain cases, such as cancer pain or trigeminal neuralgia.
Although neurolytic and surgical nerve blocks are permanent procedures, pain symptoms, and sensations can come back if the nerves are able to regrow and repair themselves. (Eun Ji Choi et al., 2016) However, symptoms and sensations may not return months or years after the procedure.
These procedures can have the potential risk of permanent nerve damage. (Anthem BlueCross. 2023) Nerves are sensitive and regenerate slowly, so a tiny error can cause side effects. (D O’Flaherty et al., 2018) Common side effects include:
Muscle paralysis
Weakness
Frequent numbness
In rare cases, the block could irritate the nerve and cause added pain.
Skilled and licensed health practitioners like surgeons, pain management physicians, anesthesiologists, and dentists are trained to perform these procedures carefully.
There is always a risk of nerve damage or injury, but the majority of nerve blocks safely and successfully decrease and help manage chronic pain. (Anthem BlueCross. 2023)
What to Expect
Individuals may feel numbness or soreness and/or notice redness or irritation near or around the area that is temporary.
There can also be swelling, which compresses the nerve and requires time to improve. (Stanford Medicine. 2024)
Individuals may be asked to rest for a certain amount of time after the procedure.
Depending on the type of procedure, individuals may have to spend a few days in a hospital.
Some pain may still be present, but that does not mean the procedure did not work.
Individuals should consult with a healthcare provider about the risks and benefits to ensure it is the right treatment.
NYU Langone Health. (2023). Nerve block for migraine (Education and Research, Issue. https://nyulangone.org/conditions/migraine/treatments/nerve-block-for-migraine
National Institute of Neurological Disorders and Stroke. (2023). Pain. Retrieved from https://www.ninds.nih.gov/health-information/disorders/pain#3084_9
Cappellari, A. M., Tiberio, F., Alicandro, G., Spagnoli, D., & Grimoldi, N. (2018). Intercostal Neurolysis for The Treatment of Postsurgical Thoracic Pain: a Case Series. Muscle & nerve, 58(5), 671–675. https://doi.org/10.1002/mus.26298
Choi, E. J., Choi, Y. M., Jang, E. J., Kim, J. Y., Kim, T. K., & Kim, K. H. (2016). Neural Ablation and Regeneration in Pain Practice. The Korean journal of pain, 29(1), 3–11. https://doi.org/10.3344/kjp.2016.29.1.3
Hospital for Special Surgery. (2023). Regional anesthesia. https://www.hss.edu/condition-list_regional-anesthesia.asp
Anthem BlueCross. (2023). Peripheral nerve blocks for treatment of neuropathic pain. (Medical Policy, Issue. https://www.anthem.com/dam/medpolicies/abc/active/policies/mp_pw_c181196.html
O’Flaherty, D., McCartney, C. J. L., & Ng, S. C. (2018). Nerve injury after peripheral nerve blockade-current understanding and guidelines. BJA education, 18(12), 384–390. https://doi.org/10.1016/j.bjae.2018.09.004
Stanford Medicine. (2024). Common patient questions about nerve blocks. (For Patients, Issue. https://med.stanford.edu/ra-apm/for-patients/nerve-block-questions.html
Nerve irritation occurs when the nerves exiting the spine become irritated and sensitized. Also known as nerve gliding restriction, it is a condition whereby a nerve becomes irritated by inflamed swelling of structures close to the nerve, such as joints, ligaments, muscles, or discs, that have sustained an accumulative strain which results in swelling and inflammation. A thorough chiropractic assessment and examination can diagnose the extent of the irritation and develop a personalized treatment plan.
Nerve Irritation
When swelling and inflammation interfere with the nerve root, the nerve transmits signals to the brain to let it know there is a threat. The brain interprets these signals and creates a protective response to avoid worsening the damage to the nerve. The protective reactions vary from person to person but can include the following:
Muscle tightness and guarding
Aching sensation
Cramping
Radiating discomfort or pain
Pins and needles
Tingling
Numbness
Nerve root irritation also inhibits the body from recovering as fast as it should.
Nerve irritation is not to be confused with nerve root compression or radiculopathy. This is when the nerve becomes compressed/pinched, resulting in the loss of its functions like muscle strength and sensation. Sometimes individuals with nerve irritation can also experience increased neural tension. The nerves adapt to the mechanical loads placed on them through regular movements. Restrictions to neural mobility can cause symptoms to worsen along the pathway and distribution of the nerve.
The nervous system consists of the brain, spine, and nerve branches.
The branches, similar to electrical cables, cannot stretch.
Tension is generated when straightening out body areas, creating a pull and gliding of the nerve to the spinal cord.
When nerve irritation occurs, signals are sent to protect the body, brain, spine, and branches.
Causes
Most commonly, nerve irritation occurs when a structure adjacent to the nerve; this could be a joint, ligament, and/or muscle that accumulates strain and becomes dysfunctional, swollen, inflamed, and/or spasms resulting from protective guarding.
Mild nerve irritation can include accumulated strain from postural overload and swelling from a minor tear in an adjacent ligament.
Often nothing shows as a problem on an MRI scan.
Severe nerve irritation can include disc herniation and shows up on an MRI scan; surgery could be required in some cases.
Symptoms
Stiffness
Tightness
Aches
Pains
Persist even after days of rest, stretching, targeted exercises, avoiding movements, etc.
Stretching feels good at first, but the pain returns or worsens a few hours later or the next day.
The irritation blocks the effective recovery of muscle, joint, tendon, and ligament discomfort symptoms.
Chiropractic Care
Treatment involves various therapies and strengthening the supporting structures while relaxing and releasing tight structures to avoid recurring injuries. Chiropractic care realigns the spine, corrects joints that have shifted out of place, helps to regulate the nervous system’s function, and relieves irritation and inflammation. Whether in the form of an adjustment, traction, or guided exercise, all systems in the body are moved closer to a balanced state. This includes the:
Nervous system
Immune system
Respiratory system
Circulatory system
Endocrine system
Skeletal system
All help support the body’s self-healing process and increase the nervous system’s function.
The chiropractic team will guide the patient through the rehabilitation process to get back to full strength.
Peroneal Nerve Irritation
References
Ellis, Richard F, and Wayne A Hing. “Neural mobilization: a systematic review of randomized controlled trials with an analysis of therapeutic efficacy.” The Journal of manual & manipulative therapy vol. 16,1 (2008): 8-22. doi:10.1179/106698108790818594
Gibson, William, et al. “Transcutaneous electrical nerve stimulation (TENS) for neuropathic pain in adults.” The Cochrane database of systematic reviews vol. 9,9 CD011976. 14 Sep. 2017, doi:10.1002/14651858.CD011976.pub2
O’Shea, Simone D et al. “Peripheral muscle strength training in COPD: a systematic review.” Chest vol. 126,3 (2004): 903-14. doi:10.1378/chest.126.3.903
Rozmaryn, L M et al. “Nerve and tendon gliding exercises and the conservative management of carpal tunnel syndrome.” Journal of hand therapy: official Journal of the American Society of Hand Therapists vol. 11,3 (1998): 171-9. doi:10.1016/s0894-1130(98)80035-5
Sipko, Tomasz, et al. “Mobility of cervical spine and postural equilibrium in patients with spinal overload syndrome.” Ortopedia, traumatologia, rehabilitacja vol. 9,2 (2007): 141-8.
Low back and mid-back pain could be caused by abdominal or pelvic organ distress/irritation or infection that an individual doesn’t know about. This could be a viscerosomatic reflex. This can be the case when there is no back injury, muscle strain, or sprain that would coincide with back aching and soreness. Identifying the symptoms and diagnosing the underlying cause is the first step in getting ultimate pain relief.
The Organs
Inflammation and other issues with any internal organs in the central, abdominal, or pelvic region can produce low back pain. These include the following:
Heart
Lungs
Stomach
Intestines
Liver
Gallbladder
Viscerosomatic reflex pain can also be felt in a completely different body part than where the organ is located. This can cause an individual to think something is wrong in that body region when there is not.
Kidneys
The kidneys help remove liquid waste from the body.
Urine that contains more chemical substances than what can be diluted can cause kidney stones to form and sharp pain in the side and the lower back.
Kidney stones can also cause difficulty urinating and blood to show up in the urine.
Inflammation of the large intestine/colon and/or ulcerative colitis can also cause:
Low back pain.
Abdominal cramps
Rectal pain.
Visceral Pain
Visceral pain is different as it can be harder to pinpoint a source and feels like a dull aching or tightening pressure. The pain originates in the organs of the respiratory system, stomach, or pelvis that is often described as a dull ache but is also described as:
It can accompany other symptoms like nausea, vomiting, sweating, or heart palpitations.
Psychological symptoms like depression can begin to present.
Chiropractic Care
Chiropractic focuses on healing the musculoskeletal system of aches and pain, muscle stiffness, and/or chronic conditions that complement traditional medical care. Adjustments can correct the body’s alignment and how the body physically functions. A chiropractor will use manual or mechanical decompression techniques to realign the spine. This will release the muscle, tendon, ligament, and nerve tension, bringing pain relief, and improving nervous system function, and viscerosomatic reflex. Treatments include:
Adjustments
Will gently realign the joints to decrease pain and increase range of motion.
Soft-tissue therapy
Will relax tight muscles, relieve spasms, and release tension in the surrounding connective tissues.
Exercises and stretches
Will restore and maintain joint stability and mobility.
Joint bracing and Kinesio taping
Will support sprained joints or muscles as the healing process continues.
Integrative medicine expert referrals
Experts will guide individuals on diet and nutrition to reduce inflammation and promote healthy eating for overall health.
DRX9000 Low Back Pain, Sciatica, Herniated Disc
References
Bath M, Owens J. Physiology, Viscerosomatic Reflexes. [Updated 2022 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559218/
Beal, M C. “Viscerosomatic reflexes: a review.” The Journal of the American Osteopathic Association vol. 85,12 (1985): 786-801.
Lefebvre R, Peterson D, Haas M. Evidence-Based Practice and Chiropractic Care. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3716373/) J Evid Based Complementary Altern Med. 2012;18(1):75-79. Accessed 4/25/2022.
Sikandar, Shafaq, and Anthony H Dickenson. “Visceral pain: the ins and outs, the ups and downs.” Current opinion in supportive and palliative care vol. 6,1 (2012): 17-26. doi:10.1097/SPC.0b013e32834f6ec9
Zhou, QiQi, and G Nicholas Verne. “New insights into visceral hypersensitivity–clinical implications in IBS.” Nature reviews. Gastroenterology & hepatology vol. 8,6 (2011): 349-55. doi:10.1038/nrgastro.2011.83
Neurophysiology: There are two ways that nociceptive information reaches the central nervous system. One is the neospinothalamic tract for quick pain and two is the paleospinothalamic tract for slow pain that increases.
Neurophysiology Of Pain Part II
Intensity, Location & Quality of Pain…
… involve Spinothalamic and Trigeminal Pathways
The trigeminal pathway brings information from the face area.
The spinothalamic pathway brings information from the rest of the body.
Both these pathways project to the sensory cortex, which also receives information on innocuous stimuli such as touch, pressure and warmth via a separate pathway.
2 Pain Transmission Pathways For Location Intensity Quality
There is difference between the objective and subjective aspects of injury and pain.
Despite similar injury, people can differ in how much pain they feel.
Depending on the context, pain may not be felt despite injury, e.g. battlefield injury, during intense sports.
This suggests that there is a physiological mechanism that controls the transmission of nociceptive signals to the brain or modifies the interpretation of pain.
The pain control system can also explain the placebo effect.
Pain Modulation Pathway
Nerve signals are sent form the somatic sensory cortex and hypothalamus to the periaqueductal gray matter (PAG).
PAG sends signals to the parabrachial nucleus, medullary reticular formation, locus coeruleus, and Raphe neulei.
These in turn can control the in the transmission of nociceptive signals from the spinal cord to the brain.
This involves different involves different neurotransmitters.
Endogenous Opioids
Internally produced molecules with opioid-like action which regulate transmission of nociceptive signals.
Three classes of these molecules have been identified. All are peptide molecules
Enkephalins
Endorphins
Dynorphins
Despite these being powerful, endogenous modifiers of nociceptive signals, it has been difficult to produce and administer them in a way than can used in clinical practice.
Location Of Nerve Cells With Endogenous Opioid Receptors
In the spinal cord, endogenous opioids can prevent transmission between 1st order nerve cells (bringing signals from the periphery) and 2nd order spinal nerve cells that transmit the signals to the brain.
Also can prevent the increased synaptic efficiency, which plays a role in hyperalgesia.
Knowing the molecules involved in the �inflammatory soup� and how they are synthesized provides possible targets for pain reduction.
e.g. prostaglandins are produced by the COX enzyme. The activity of this enzyme is blocked by non-steroidal anti- inflammatory drugs (NSAIDs) such as ibuprofen, diclofenac.
Allodynia
A condition when normally non- painful stimuli cause pain, e.g., touch, light pressure, cold.
Involves changes in the synaptic sensitivity of the nociceptive neurons in the spinal cord (central sensitization).
Drugs such as ketamine, block NMDA receptors and so reduce transmisison of the nociceptive stimuli.
Gate Control Theory of Pain
Mother says to child, �Come I will rub the area which is painful and this will make it feel better.�
After stubbing a toe, we instinctively rub the area; this reduces the sensation of pain.
Ronald Melzack and Patrick Wall in 1962 provided an possible explanation for this effect.
Ascending Tracts | Pain Modulation: Gate Control Theory
Gate Theory
Rubbing the area that hurts stimulates receptors of innocuous stimuli like touch, pressure and vibration.
These mechano-receptors send signals along the A? nerve fibers that:
(1) stimulate spinal nerves (inhibitory inter-neurons) that in turn inhibit signaling in the 2nd order neurons (projection neuron) and (2) directly inhibit the 2nd order neuron to reduce or stop pain signal from being sent to the brain
Transcutaneous Nerve Stimulation (TENS) is based on the Gate Control Theory. Nerves of the innocuous sensory system are stimulated and they in turn, inhibit transmission of nociceptive stimuli in the spinal cord.
Abnormalities Of Pain System
Phantom Pain
Patients with amputation often have burning or tingling pain in the body part removed.
One possible cause is that nerve fibers at the stump are stimulated and the brain interprets the signals as originating in the amputated portion.
The other is the rearrangement within the cortical areas so that area say for the hand now responds to signals from other parts of the body but still interprets them as coming for the amputated hand.
Peripheral Sensitization
Peripheral sensitization represents a reduction in the threshold and/or an increase in magnitude of responsiveness at the peripheral ends of sensory nerve fibers.
This occurs in response to chemical mediators released by nociceptors and non-neuronal cells (e.g. mast cells, basophils, platelets, macrophages, neutrophils, endothelial cells, keratinocytes and fibroblasts) at the site of tissue injury or inflammation.
Basically, it is an increased sensitivity to an afferent nerve stimuli.
Central Sensitization
Peripheral & Central Sensitisation
A condition of the nervous sytem that is associated with the development and maintenance of chronic pain.
Known as �wind-up� or persistent high reactivity.
�Plastiticity in pain pathways� or the persistence of pain even after an injury has healed.
Is this negative or positive plasticity?
Central Sensitization & C Fibers
Two Main Characteristics Of Central Sensitization:
� Allodynia � occurs when a person experiences pain with things that are normally not painful, ie, soft touch causes pain.
� Hyperalgesia � occurs when a stimulus that is typically painful is perceived as more painful that it should be, ie, a simple bump.
Both are due to hyperreactivity of the nervous system.
Neurophysiology of pain: Pain�defined is the unpleasant sensation that accompanies injury or near injury to tissues, though it can also occur in the absence of such damage if the nociception system is not functioning. Nociception means the system that carries pain signals of injury from the tissues. This is the physiological incident that comes with pain.
Neurophysiology Of Pain
Objectives
Basics of the nervous system
Synaptic function
Nerve impulses
Transduction of peripheral painful stimuli
Central pathways
Central Sensitization
PeripheralSensitization
Control or modulation of pain signals
Pathophysiology of pain signaling pathway
Definition Of Pain
“Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”.
It is important to know the basic structure of the nervous system.
This will help in:
� Understanding the mechanism by which nociceptive signals are produced.
� Know the different regions of the nervous system involved in processing these signals.
� Learn how the different medications and treatment for pain management work.
Nervous System
Central nervous system (CNS)
Brain and Spinal Cord
Peripheral Nervous System (PNS)
Nerve fibers go to all parts of the body.
Send signals to the different tissues and send signals back to the CNS.
Nerve Cells
The nervous system is made up of nerve cells which send long processes (axons) to make contact with other cells.
Nerve Cell-To-Nerve Cell Communication
Nerve cells communicate with other cells by releasing a chemical from the nerve endings � Neurotransmitters
Basic Steps In Synaptic Transmission
Synaptic Transmission
Steps in the passage of signal from one nerve cell to other.
Drugs are used to block the transmission of signals from one nerve cell to other.
These drugs can effect:
Ca2+ ion channel to prevent Ca2+ inflow which is essential for neurotransmitter (NT) release, e.g., the action of gabapentin.
Release of NT.
Prevent NT from binding to its receptor so stop further transmission of the signal.
Electrical Impulse
Signals move along a nerve process (axon) as a wave of membrane depolarization called the Action Potential.
The inside of all nerve cells has a negative electrical potential of around � 60 mV.
When stimulated this negative electrical potential becomes positive and then negative again in milliseconds.
The action potential moves along the nerve process (axon) to the nerve ending where it cause release of NT.
Action Potential
When there is no stimulation the membrane potential is at its Resting Potential.
When stimulated, channels in the nerve membrane open allowing the flow of sodium ions (Na+) or calcium ions (Ca2+) into the nerve or cell. This makes the inside less negative and in fact positive -the peak of the action potential (+40 mV).
These channels than close and by the opening of K+ channels the membrane potential returns to its resting level.
Stopping Action Potentials To Stop Nociceptive Stimuli
Nociceptive stimuli are those that will create a sensation of pain after they are processed in the CNS.
Nociceptive signals can be prevented from reaching the CNS by blocking the action of the channels that control the movement of ions across the nerve membrane.
A number of anesthetic agents stop Na+ channel from working and hence stop the generation of actions potentials and transmission of signals to the CNS.
Sensory Systems
The sensory system that can be divided into two divisions:
A Sensory System that transmits innocuous stimuli such as touch, pressure, warmth.
A System that transmits stimuli that indicate that tissues have been damaged = nociceptive .
These two systems have different receptors and pathways in the PNS & CNS
Nociceptors are free nerve endings that respond to stimuli that can cause tissue damage or when tissue damage has taken place.
Present in membrane of free nerve endings are receptors (protein molecules) whose activity changes in the presence of painful stimuli.
(Note the use of the same term receptor is used for cell or organs or molecules that involved in transduction of a stimuli.)
Transduction
Transduction is the process of converting the stimuli into a nerve impulse.
For this to occur the flow of ions across the nerve membrane has to change to allow entry of either Na+ or Ca2+ ions to cause depolarization of the membrane potential.
This involves a receptor molecule that either directly or indirectly opens the ion channels.
Chemical Agents…
… which can cause the membrane potential at the free nerve ending (nociceptor) to produce an action potential.
Many stimuli � mechanical, chemical and thermal � give rise to painful sensation making transduction a complex process.
Recently receptor molecules have been identified�� Transient Receptor Potential (TRP) channels � that respond to a number of strong stimuli.
TRP receptors are also involved in transmitting the burning sensation of chili pepper.
In time, drugs that act on these receptors will be developed to control pain.
Different TRP Channels
Capsasin, the active ingredient in chili pepper, is used in patches for relief of pain.
Menthol and peppermint gels are used to relieve muscle pain.
Motor Output & Sensory Input To Spinal Cord
Sensory nerves have their cell body outside the spinal cord in the dorsal root ganglia ( = 1st order neurons).
One process goes to the periphery, the other goes to the spinal cord where it makes synaptic contact with nerve cells in the spinal cord ( = 2nd order neurons).
The 2nd order neuron sends processes to other nerve cells in the spinal cord and to the brain.
2nd Order Nerve Cells Send Nerve Fibers In The Spinal Cord White Matter
Transmission Of Nociceptive Signals From The Periphery To The Brain
Silverthorn
A Delta (?) & C Nerve Fibers
Nerve fibers are classified according to the:
� (1) diameter of the nerve fiber and
� (2) whether myelinated or not.
A? and C nerve fiber endings respond to strong stimuli.
A? are myelinated and C are not.
Action potentials are transmitted 10 times faster in the A?
(20 m/sec) fibers than in C fibers (2 m/sec).
A? & C fibers
A? fibers respond mainly to mechanical and mechno-thermal stimuli.
C fibers are polymodal, i.e. the nerve ending responds to several modalities � thermal, mechanical and chemical
This polymodal ability is due to the presence of different receptor molecules in a single nerve ending.
Fast & Slow Pain
Most people when they are hit by an object or scrape their skin, feel a sharp first pain (epicritic) followed by a second dull, aching, longer lasting pain (protopathic).
The first fast pain is transmitted by the myelinated A? fibers and the second pain by the unmyelinated C fibers.
Central Pain Pathways
Nociceptive signals are sent to the spinal cord and then to different parts of the brain where sensation of pain is processed.
There are a pathways/regions for assessing the:
Location, intensity, and quality of the noxious stimuli
Unpleasantness and autonomic activation (fight-or-flight response, depression, anxiety).
Dr. Sletten Discussing Central Sensitization Syndrome (CSS)
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Brain Areas Involved In Processing Of Nociceptive Signals
The Anterior Cingulate & Insula Cortex Are Activated In Human Subjects
Inflammatory Soup – Hyperalgesia
Gate Control Theory of Pain
Abnormalities Of Pain System
Peripheral Sensitization
Somatosensory Cortex Organization
Cortical Reorganization
Nerve Cell-To-Nerve Cell Communication
Nerve cells communicate with other cells by releasing a chemical from the nerve endings � Neurotransmitters
TRP Channels
