Pain Physiology

Question 1

What is pain

Answer 1

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

Question 2

What is the peripheral nervous system

Answer 2

Part of the nervous system consisting of nerves and ganglia (outside of brain and or spinal cord

Question 3

What is the central nervous system

Answer 3

Part of the nervous system consisting of brain and spinal cord

Question 4

What is noxious

Answer 4

An actually or potentially tissue damaging event. It is a prerequisite for nociception, which itself is a prerequisite for nociceptive pain

Question 5

What is nociception

Answer 5

Activation of the pns and CNS in response to noxious stimuli

Question 6

Requirements to experience pain

Answer 6

Alive
Conscious or sentience
Have the capacity to experience pain

Question 7

Pain types

Answer 7

Acute
Chronic
Somatic pain
Visceral pain
Nociceptive

Question 8

What is neuropathic

Answer 8

Neuropathic refers to a condition or symptom that arises from damage or dysfunction in the nervous system.

Question 9

What are neuromas

Answer 9

Neuromas are abnormal growths or tumors that arise from nerve cells or nerve tissue.

Question 10

What is ischemic pain

Answer 10

Ischemic pain is a type of pain that results from a lack of blood flow and oxygen to a specific part of the body. This can occur when there is a blockage or narrowing in the arteries that supply blood to that area, such as in the case of peripheral artery disease (PAD) or coronary artery disease (CAD).

Question 11

What is referred pain

Answer 11

Referred pain is a type of pain that is felt in a different part of the body than where the actual cause of the pain is located. For example, someone experiencing a heart attack may feel pain in their arm or jaw, rather than in their chest where the heart is located.

Question 12

What is psychogenic pain

Answer 12

Psychogenic pain is a type of pain that is not caused by a physical injury or disease, but rather by psychological factors such as stress, anxiety, or depression.

Question 13

What is phantom pain

Answer 13

Phantom pain is a type of pain that is perceived in a part of the body that has been amputated or lost due to injury or disease.

Question 14

What is nociception

Answer 14

Nociception is the process by which the nervous system detects and responds to potentially harmful or damaging stimuli, such as tissue damage, chemical irritants, or extreme temperatures. It is the body’s way of sensing pain and alerting us to potential harm or injury. Nociception involves specialized sensory receptors called nociceptors, which are located throughout the body in skin, muscles, and organs. When these nociceptors are activated by a noxious stimulus, they send electrical signals along nerve fibers to the spinal cord and brain, where the sensation of pain is perceived.

Question 15

What are delta fibres

Answer 15

Delta fibers are a type of nerve fiber or axon that transmit sensory information related to pain and temperature.

They are classified as A-delta fibers based on their size and speed of conduction, with a diameter of 1 to 5 micrometers and a conduction velocity of 1 to 30 meters per second.

Delta fibers are responsible for transmitting fast, sharp pain signals that are typically associated with mechanical or thermal stimuli, such as touching a hot stove or pricking a finger with a needle.

These fibers also play a role in the sensation of cold temperature, as they are activated by temperatures below 15-20 degrees Celsius.

Delta fibers are part of the peripheral nervous system and are found in the skin, muscles, and internal organs. They synapse with neurons in the spinal cord and brain, where the sensation of pain is ultimately perceived.

They’re myelinated

Question 16

What are C fibres

Answer 16

C fibers are a type of nerve fiber or axon that transmit sensory information related to pain, temperature, and touch.

They are classified as C fibers based on their size and speed of conduction, with a diameter of less than 1 micrometer and a conduction velocity of less than 2 meters per second.

C fibers are responsible for transmitting slow, dull, and persistent pain signals that are typically associated with chemical, mechanical, or thermal stimuli, such as inflammation or tissue damage.

These fibers also play a role in the sensation of warm temperature, as they are activated by temperatures above 45 degrees Celsius.

C fibers are part of the peripheral nervous system and are found in the skin, muscles, and internal organs.

They synapse with neurons in the spinal cord and brain, where the sensation of pain is ultimately perceived.

C fibers can also transmit non-painful sensory information, such as the sensation of light touch or pressure.

They’re unmyelinated

Question 17

What do primary afferent terminals release

Answer 17

In nociception, primary afferent terminals (i.e. the nerve fibers that originate in the peripheral sensory receptors and transmit signals to the spinal cord) release excitatory neurotransmitters such as substance P and glutamate at the synapse with second-order neurons in the dorsal horn of the spinal cord. These neurotransmitters bind to receptors on the second-order neurons, leading to depolarization and the generation of action potentials that transmit the pain signal to higher levels of the nervous system. This process is part of the peripheral sensitization that occurs in response to noxious stimuli and contributes to the amplification and persistence of pain signals.

Question 18

What are inflammatory mediators of pain

Answer 18

Inflammatory mediators are substances released by the immune system during the inflammatory response, which is a normal protective response to tissue injury, infection, or other types of tissue damage. Some of these mediators can also contribute to the sensation of pain by sensitizing the peripheral sensory nerves or enhancing the transmission of pain signals to the central nervous system. Examples of inflammatory mediators that can cause pain include:

Prostaglandins - These are lipid molecules that are synthesized from arachidonic acid and are involved in many physiological processes, including inflammation and pain. They sensitize nociceptors and lower their activation threshold, making them more responsive to painful stimuli.

Bradykinin - This is a peptide that is generated during inflammation and tissue injury. It activates nociceptors directly and also sensitizes them to other stimuli, leading to the amplification of pain signals.

Histamine - This is a biogenic amine that is released from mast cells during inflammation and allergic reactions. It can directly activate nociceptors and also increase their sensitivity to other stimuli.

Cytokines - These are signaling molecules that are released by immune cells during inflammation. Some cytokines, such as interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α), can enhance the sensitivity of nociceptors to painful stimuli and also contribute to the development of chronic pain.

These inflammatory mediators can act synergistically to produce pain and contribute to the development of chronic pain conditions, such as neuropathic pain and inflammatory pain.

Question 19

Sensitisation can have persistant effect, causing what

Answer 19

Sensitization can have a persistent effect on the nervous system, leading to chronic pain conditions. When nociceptors are repeatedly exposed to noxious stimuli, they can become sensitized, meaning they become more responsive to subsequent stimuli and can lower their activation threshold. This sensitization can be caused by peripheral sensitization, which involves changes in the excitability and responsiveness of nociceptors and other sensory neurons in the peripheral nervous system, or by central sensitization, which involves changes in the processing of sensory information in the central nervous system.

Chronic pain conditions that are thought to be related to sensitization include neuropathic pain, inflammatory pain, and fibromyalgia. These conditions are characterized by persistent pain that is often accompanied by other symptoms such as fatigue, sleep disturbances, and mood changes. Sensitization can also contribute to the development of hyperalgesia, which is an increased sensitivity to painful stimuli, and allodynia, which is pain caused by non-noxious stimuli.

The mechanisms underlying sensitization are complex and involve multiple factors, including the release of inflammatory mediators, changes in gene expression, and alterations in the function of ion channels and receptors in sensory neurons. The persistent effects of sensitization on the nervous system can make it difficult to manage chronic pain conditions and can require a multidisciplinary approach that addresses both the physical and psychological aspects of pain.

Question 20

What is hyperalgesia

Answer 20

Hyperalgesia is a condition in which a person experiences an increased sensitivity to pain, which can be caused by a variety of factors such as tissue injury, inflammation, or nerve damage.

Question 21

What are the two types of hyperaglesia

Answer 21

There are two main types of hyperalgesia: primary and secondary. Primary hyperalgesia occurs at the site of tissue damage or injury and is characterized by an increased sensitivity to noxious stimuli. Secondary hyperalgesia occurs in areas surrounding the site of injury and is thought to be caused by the sensitization of the central nervous system.

Question 22

What is allodynia

Answer 22

Allodynia is a condition in which a person experiences pain in response to a normally non-painful stimulus. In other words, the stimulus that would not normally be perceived as painful, such as a light touch or gentle pressure, can cause pain in someone with allodynia.

Question 23

Pain pathways in the dorsal horn can be suppressed via three mechanisms

Answer 23

Interneurones acting presynaptically on afferent neurones

Midbrain descending pathways, which synapse afferent neurone terminals

Segmental projections synapsing with afferent neurone terminal (gate control theory)

Question 24

Pain pathways in the dorsal horn can be modulated via three mechanisms

Answer 24

Descending inhibition: This mechanism involves the brain sending signals down the spinal cord to reduce the activity of pain pathways in the dorsal horn. This process can be stimulated by various factors, such as endogenous opioids, and is the basis for the analgesic effects of some medications.
Segmental inhibition: This mechanism involves inhibitory interneurons in the spinal cord that can inhibit pain pathways in the same or adjacent spinal segments. This process can reduce the spread of pain signals to other parts of the body and help limit the overall amount of pain being experienced.
Central modulation: This mechanism involves the brain actively modulating the activity of neurons in the dorsal horn to reduce pain transmission. This process is thought to be involved in the placebo effect, where the belief in a treatment’s effectiveness can lead to a reduction in pain perception.

Question 25

What is oxytocin

Answer 25

Oxytocin is a hormone produced in the hypothalamus and released into the bloodstream by the posterior pituitary gland.

It is often referred to as the “love hormone” or “cuddle hormone” because it is released during intimate social and physical interactions such as hugging, kissing, and sexual activity.

Oxytocin has a number of physiological and psychological effects, including promoting uterine contractions during childbirth and stimulating milk ejection during breastfeeding.

It is also believed to play a role in social bonding, trust, and emotional attachment.

Research has suggested that oxytocin may have potential therapeutic applications in areas such as autism, anxiety disorders, and depression, although more research is needed to fully understand its effects on human behavior and health.

Question 26

Concept of pain in animals

Answer 26

The concept of pain in animals is a topic of ongoing research and debate in the scientific and ethical communities. While it is widely accepted that many animals, particularly mammals, experience pain, the extent and nature of their pain experiences can be difficult to measure and interpret.

Studies have shown that animals have similar nervous systems and neurochemical pathways involved in pain processing as humans, suggesting that they can experience pain in a similar way. Animals have been observed exhibiting behaviors such as vocalization, avoidance, and self-protective responses that suggest they are experiencing pain. For example, animals may limp or favor a certain area of their body that is injured or painful, they may lick or chew at a wound, or they may vocalize in response to noxious stimuli.

However, the subjective experience of pain is difficult to measure in animals. Unlike humans, animals cannot self-report their pain experiences, so researchers must rely on behavioral and physiological indicators of pain. This can be complicated by the fact that animals may exhibit different pain behaviors depending on their species, individual temperament, and social context.

The concept of pain in animals also raises ethical questions about the treatment of animals in research, agriculture, and other settings. Many animal welfare organizations advocate for the recognition and alleviation of animal pain, and guidelines for the ethical treatment of animals in research and other settings often include provisions for the management of animal pain.

Overall, the concept of pain in animals is a complex and multifaceted issue that requires ongoing research and discussion in order to better understand and address animal pain experiences.

Question 27

Physiology of pain in animals

Answer 27

The physiology of pain in animals is similar to that in humans. Like humans, animals have specialized nerve cells called nociceptors that detect and respond to noxious stimuli such as heat, pressure, or chemicals. These nociceptors send signals to the spinal cord and brain, where they are processed and interpreted as pain.

In animals, as in humans, there are two main types of nerve fibers involved in pain transmission: A-delta fibers and C fibers. A-delta fibers are myelinated and transmit sharp, fast pain signals, while C fibers are unmyelinated and transmit slower, duller pain signals. Both types of fibers activate the release of neurotransmitters and neuropeptides that transmit and modulate pain signals in the spinal cord and brain.

In addition to these basic mechanisms, the physiology of pain in animals can be influenced by a variety of factors such as species, age, and sex. For example, some animal species may have specialized nerve endings that respond to specific types of noxious stimuli, while others may have different pain thresholds or sensitivity to pain. Age can also affect pain sensitivity, with younger animals often being more sensitive to pain than adults.

The physiology of pain in animals also has important implications for pain management and treatment. Many of the same drugs and therapies used to manage pain in humans, such as opioids and nonsteroidal anti-inflammatory drugs (NSAIDs), can also be used in animals. However, the dosages and treatment regimens must be carefully calibrated to account for species differences and potential side effects.

Overall, the physiology of pain in animals is complex and multifaceted, and requires ongoing research and understanding in order to effectively manage and treat pain in animals.

Question 28

Nociceptors

Answer 28

Nociceptors: Nociceptors are specialized nerve cells that detect and respond to noxious stimuli. They are found in the skin, muscles, bones, and internal organs of animals. Nociceptors have specialized receptors on their cell membranes that respond to different types of stimuli such as mechanical pressure, temperature changes, or chemical irritants. When a nociceptor is activated, it sends an electrical signal along its nerve fiber to the spinal cord.

Question 29

Transmission of pain signals

Answer 29

Transmission of pain signals: Once a nociceptor sends a signal to the spinal cord, the pain signal is transmitted to the brain via a network of nerves. There are two main types of nerve fibers involved in pain transmission: A-delta fibers and C fibers. A-delta fibers are myelinated, which means they have a fatty coating that allows for faster transmission of electrical signals. They are responsible for transmitting sharp, fast pain signals such as a pinprick. C fibers are unmyelinated, which means they transmit electrical signals more slowly. They are responsible for transmitting dull, aching pain signals such as a toothache.

Question 30

Processing of pain signals

Answer 30

Processing of pain signals: Once pain signals reach the spinal cord, they are processed and transmitted to the brain via a series of specialized nerve cells called interneurons. These interneurons can amplify or dampen pain signals, and can also release neurotransmitters and neuropeptides that can affect the perception of pain.

Question 31

Modulation of pain signals

Answer 31

Modulation of pain signals: The perception of pain can also be modulated by a variety of factors such as emotions, expectations, and past experiences. For example, anxiety or depression can amplify the perception of pain, while distraction or relaxation techniques can reduce the perception of pain. Additionally, the brain can release its own pain-relieving chemicals, such as endorphins, in response to certain stimuli.

Question 32

Species differences to pain

Answer 32

Species differences: The physiology of pain can vary between different animal species. For example, some animals have specialized nerve endings called free nerve endings that respond to specific types of noxious stimuli such as extreme cold or pressure. Additionally, some animals may have different pain thresholds or sensitivity to pain due to genetic or evolutionary differences. These species differences can affect the way animals experience and respond to pain, and must be taken into account when managing and treating pain in animals.