Pain & Thermoregulation PDF

pain & Thermoregulation Tobi Ajayi Lesson Objectives: 1. Review of somatosensory transmission. 2. Physiology of pain: transmission, perception & modulation 3. Types of Pain 4. Pain Assessment 5. Management of Pain 6. Nursing considerations  SOMATOSENSORY FUNCTION The somatosensory syste...

pain & Thermoregulation Tobi Ajayi Lesson Objectives: 1. Review of somatosensory transmission. 2. Physiology of pain: transmission, perception & modulation 3. Types of Pain 4. Pain Assessment 5. Management of Pain 6. Nursing considerations  SOMATOSENSORY FUNCTION The somatosensory system is designed to provide the central nervous system (CNS) with information on: Touch, temperature, body position, and pain. 1st order neurons: transmit sensory information from the periphery to the CNS. 2nd order neurons: communicate with various reflex networks and sensory pathways in the spinal cord and transmit information to the thalamus. 3rd order neurons: relay information from the thalamus to the cerebral cortex  levels of somatosensory system 1. Sensory Units: are made up of sensory receptors (like those in the skin) and the neurons that carry signals from those receptors. Nerve fibers are like different types of wires that carry signals in the nervous system. Type A nerve fiber – fast Myelinated: protective covering (myelin) that helps them send messages quickly. Carry information about sharp pain, touch, and pressure. They help us react quickly to things like touching something hot. (Can trigger ‘reflexes’). Type B nerve fiber – myelinated but regular speed Transmit signals related to things like sensations from internal organs and autonomic functions (like heart rate). Type C nerve fiber -unmyelinated (slow) Carry dull, aching, burning pain and sensations like warmth. Responsible for the longer-lasting, more diffuse pain after the initial sharp pain. Dorsal root ganglion (DRG) = cluster of nerve cell bodies located near the dorsal (back) of spinal cord, containing the cell bodies of sensory neurons. When you feel something (e.g. touch or pain), the sensory nerve endings in the skin send that signal to the DRG, where the axon continues into the spinal cord to connect with second-order neurons.  levels of somatosensory system 2. The Ascending pathways: are the neural pathways that carry sensory information from the spinal cord up to the brain Discriminative pathway (medial lemniscus): helps to detect exactly where and what kind of sensation is felt. responsible for transmitting detail sensation such as fine touch, 2-point discrimination, pressure, vibration, and proprioception (awareness of body position). Signals travel from the sensory receptors in the skin through first-order neurons to the spinal cord, then up to the brain without crossing over until they reach the brainstem. Anterolateral pathway: mainly carries information about pain, temperature, and crude (less precise) touch. Signals from the sensory receptors travel through first-order neurons to the spinal cord, where they immediately cross over to the opposite side and then ascend to the brain. Both pathways work together to provide a complete picture of sensory experiences. For example, if you touch something hot, the discriminative pathway helps you identify the exact spot and texture, while the anterolateral pathway alerts you to the pain and temperature. Neuron crossover (decussation) helps in coordinating complex movements, allowing for smoother and more integrated actions between both sides of the body. It also affects how information is processed. For example, in the discriminative pathway, signals cross over in the brainstem, allowing the brain to pinpoint exact locations of stimuli. Whereas, in the anterolateral pathway, signals cross over at the spinal cord, enabling a quicker response to potential harm. levels of somatosensory system  levels of somatosensory system 3. Central processing unit: are the specific areas in the brain that process and interpret sensory information coming from the ascending pathway Thalamus and the somatosensory cortex. Help recognize what is being felt (e.g. hot, cold, sharp, or dull) and where it’s coming from on the body. The afferent pathway relays sensory information from PNS to CNS The sensory impulse must be strong enough to reach threshold and general action potential (no message sent if stimuli is not strong enough).  Sensory Receptprs Mechanoreceptors: detect changes in the environment caused by mechanical forces, such as pressure on the skin, stretching muscles, or feeling vibrations. Tactile Receptors: Found in the skin, help us feel light touch, pressure, and texture. Free nerve endings, Meissner corpuscles, Merkel disks, Pacinian corpuscles, Hair follicle end organs, and Ruffini end organs. Proprioceptors: Located in muscles and joints. They help sense body position and movement, letting us know where the limbs are without looking. Baroreceptors: Found in blood vessels, they detect changes in blood pressure.  Sensory Receptprs Thermoreceptors: detect changes in temperature (heat and cold). These receptors respond rapidly to sudden changes in temperature and then adapt over the next few minutes although they do not adapt completely E.g. Walking out to the cold.  pain PHYSIOLOGY AND PHARMACOLOGY OF PAIN  pain Pain is an “unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. Pain receptors (Nociceptors) are free nerve endings that are activated in response to actual or impending tissue injury. They respond to mechanical, thermal and chemical stimuli. Stimulation of nociceptors Mechanical: can arise from intense pressure applied to skin form from extreme stretch or contraction of muscles. Thermal: Extreme heat or cold stimuli nociceptors. Chemical: arise from tissue trauma, ischemia, and inflammation that cause the release of chemical mediators from injured or inflamed tissue Bradykinin, Histamine, Serotonin & Potassium activate and also sensitize nociceptors. Prostaglandins sensitizes nociceptors by lowering mechanical and thermal activation thresholds in nociceptive nerve endings, thus reducing the stimulus intensity required to elicit action potential firing.  Nociceptors Nociceptive action potential are transmitted to the spinal cord through: A-delta fibers: Myelinated - transmit sharp, localized, fast pain” at a rate of 6-20 m/s. Typically elicited by mechanical or thermal stimuli. Often triggers ‘reflexes’. C-fibers: Unmyelinated - transmit “slow-wave pain” impulses at a rate of 0.5-2 m/s. Incited by chemical stimuli or persistent mechanical or thermal stimuli. Responsible for aching, burning, dull, diffuse pain.  PNS to CNS When nociceptors are stimulated, A or C fibers (1st order) of the PNS contacts second-order pain-transmission neurons (interneurons) in the spinal cord. The second-order neurons ascend the spinal cord to the thalamus (relay center). From there thalamus, 2nd order neurons synapse with 3rd order neuron, leading to the somatosensory cortex in the brain where perception and localization of pain takes place = awareness. The cortex has a body part map called the sensory homunculus.  pain mediators Transmission of impulses between the nociceptive neurons(1st order) and dorsal horn neurons (2nd order) in the spinal cord is mediated by chemical neurotransmitters released from nociceptive neurons. Glutamate: main excitatory neurotransmitter for pain. (Binds NMDA receptor) Substance P: elicit slow, excitatory action potentials. Also prolongs and enhances the action of glutamate. (Mostly on C-fibers) Endorphins: inhibitory neurotransmitters aka ‘neuromodulators’.  Pain pathways From the spinal cord, signal ascend through different pathways: Neospinothalamic tract: fast-conducting fibers (sharp, fast pain) transmit information to the thalamus, which relays to the somatosensory area to provide precise location of the pain. Paleospinothalamic tract: slow-conducting fibers terminate in several thalamic regions, including parts that project to the limbic system. (Limbic system regulates emotions and behaviors). This pathway is associated with the emotional- motivational aspects of pain). This pathway also projects into the reticular nuclei of the brain stem, contributing to alertness which indirectly influences the hypothalamus to increase blood pressure, heart rate, and other responses.  Flexor Reflex: Withdrawal reflex Stimulus – sharp pain => reflex withdrawal without cerebral control Activation of a sensory neuron (afferent)– interneuron (at level of stimulus in CNS) – automatic activation of a motor neuron (efferent) - Response by the effector  pain gate theory Gate control theory: postulates the presence of neural gating mechanisms at the segmental spinal cord level to account for interactions between pain and other sensory modalities. Nociceptors inhibit inhibitory neurons, but when other receptors are activated they block this The simultaneous firing of the large-diameter touch fibers (A-beta) can block the transmission of impulses from the small-diameter myelinated and unmyelinated pain fibers. Pain intensity can be reduced during active tactile stimulation Rubbing a wound, ice, transcutaneous nerve stimulation. Brain also send descending signals to spinal cord to reduce pain, through Endorphins  summary of pain transmission 1. Pain begins a s a message received by nerve endings (e.g. burnt finger). 2. The release of substance P, bradykinin, and prostaglandins sensitize nerve endings, helping to transmit the pain from site of injury towards the brain. 3. The pain signal travels as an electrochemical impulse along the nerve to the dorsal horn of the spinal cord. 4. The spinal cord sends the message to the thalamus, and then the cortex. 5. Pain relief starts with signals from the brain that descend to the spinal cord, where: 6. Chemicals such as endorphin S are released in the dorsal horn to diminish pain message Endogenous Analgesic Mechanism - Efferent ‘Endogenous opioid peptides’ – inhibitory neurotransmitters aka ‘neuromodulators’: endorphins, enkephalins, dynorphins. Act on mu, delta, and kappa receptors. Released from hypothalamus, limbic system, reticular formation. DESCENDING (efferent) pathway. inhibit substance P. induced secretion of: Serotonin: enhances mood and reduce pain perception. Norepinephrine: dampens pain signals at the spinal level, and enhances alertness/stress responses.  Types of Pain Acute pain: Elicited by nociceptive stimuli at the site of local tissue damage. Serves as a warning system. Short duration (Seconds to