Neuroanatomy/Pain Review

Anatomy Cell body (in ganglion) nucleus Dendrites Dendrite Body axon Synapse

Anatomy Cont. Axons (actual nerve fibers) peripheral nervous system: may be covered by myelin sheath (schwann cell) which allows for regrowth CNS: oligodendrocytes are the “myelin” but it doesn't allow for regrowth

Anatomy Cont. Nodes of Ranier: breaks in myelin. Action potentials jump from node to node (salutatory condition) myelin acts as resistance and insulation and thus needs nodes for function.

Nerve Types Afferent; sensory nerves (ascending tracts) AA Beta): sensory, large diameter with myelin (Fastest) A delta: pain fibers, smaller with less myelin (4-30m/s) C: pain, smallest, non myelinated (.5-2m/s) dull slow pain See Prentice Table 1-2 for Classes of Afferent Neurons Note: First pain is from Adelts (faster), second pain is C

Nerve Types Cont. Efferent Nerves: motor nerves (descending tracts) Gamma: motor neuron Ascending and descending tracts: myelination increases conduction velocity Diameter increases conduction velocity (less resistance)

Nerve Types: Afferent Nerves CNS A Beta Adelta C

Physiology Excitable Tissue: only nerves and muscles are excitable tissue due to the fact only they have a resting membrane potential

Physiology Cont. Resting membrane Potential: a chemical and electrical balance with a pump to aid in return to homeostasis. at rest membrane in -70 mV to -90 mV semipermeable membrane which is impermeable to Sodium at rest

Physiology Cont. Sodium Potassium pump keeps the potential by pump in K+ in and Na+ out Na+ want in the cell but if it gets in an action potential is formed to +30 mV (a 100 mV difference) hormone , chemical, electrical, thermal or mechanical factors may create action potentials As athletic trainers we try and change this status and create an action potential

Threshold The minimum amount of stimulus necessary to create an action potential Polar: refers to negative depolarize: less negative repolarize: becoming negative hyperpolarize: more negative

Physiology Cont. All or none theory: If stimulus meets the threshold, action potential will always go to +30mV, even if supra-threshold stimulus is given

Physiology Cont. Refractory period: membrane potential goes below the resting potential of -70mV and may not be stimulated for a given period of time. This limits how many action potentials may be produced Absolute refractory period: NO stimulus will create a response no matter how strong Relative refractory period: resting potential is much lower, therefore a higher stimulus is needed

How is this class affecting your pain receptors?

Pain The purpose of pain is as a protective mechanism. Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage: The types of pain are Acute Chronic Referred

Acute Pain First pain: carried in A-delta fires: larger diameter fibers contain myelin, reflex to get off source, goes to cognitive level (more discrete - very localized) Second Pain: carried in C fibers. Smaller diameter, non myelinated, slower. (less discrete - more diffuse)

Acute Pain Treatment Goal block the pain through: inhibition blocking A fibers (Gate Control)

Chronic Pain: Any pain which lasts for six months or more (in athletes we may consider chronic pain to be pain which is continue from months but is not in proportion to tissue injury or activity... i.e... chronic tendinitis may be long lasting but have organic root) No real purpose (?) numerous by-passes. Also goes to limbic system (emotional control)- learned response

Chronic Pain Goals in treating unlearn the Pain Acute pain control techniques are usually ineffective Exercise my affect pain by distraction Important to have guidance under a physician

Referred Pain (projected pain) Felt at other site than injured area Dermatome (skin represented by nerve root) Myotome (muscle innovated by nerve root) Sclerotome (bones innovated by nerve root)

Pain Transmission A-Beta C-Delta Doral Horn Acute Pain Acute Pain Noxious Stimulus travel Via A-Delta and C-delta Fibers to Dorsal Horn (spinal Cord) STT (Spinal thalamic Tract) Limbic System & Cortex Thalamus and Cortex location and discrimination Pain Transmitted to Higher Brain Centers Descending Control Mech. Activated here once noxious stimuli reaches higher centers of brain. Incoming stimuli can be inhibited at various levels and endoginous opiates released Retinacular Formation & Periaquductal Gray (PAG) Motor, sensory and autonomic Response Discrimination and Location of pain occurs during this sequence

Pain theories Specificity Theory Pattern Theory Gate Control Theory

Specificity theory: specific stimulus has a specific receptor which goes to a location in the brain The specific location identifies the pain’s quality. Thus any noxious stimulus applied to the surface of the skin results in a pain sensation. The evaluation of the type of pain occurs in the brain.

Pattern Theory: a pattern or coding of sensory information is created by different sensations. This theory is faulty due to the number of different types of receptors proven to exist.

Gate Control Theory (1965) Melzack and Wall originally described a neurophsiologic mechanism which involved the concept of peripheral and central “gating”. The gate theory utilizes the specificity theory and the pattern theory and added the interaction of peripheral afferents with a modulation system in the spinal cord gray matter. Additionally Melzack and Wall believed there also exists a descending modulation system.

Blocking entry of c-delta Fibers Gate Control Theory First Order neurons: the theory focuses on the first order neurons (primary afferents): the A-beta (large diameter sensory neurons) and A-delta and C neurons (both small diameter sensory neurons). A non-painful stimulus can block the transmission of a noxious stimulus Brain/Pain centers A-beta non-painful stimulus Blocking entry of c-delta Fibers C delta noxious stimulus

Gate Control Theory Cont. The second order neuron, the T-cell and the substantia gelatinosa (Rexed’s laminae II and II of the dorsal horn of the spinal gray matter) can exert affects on the primary afferent Works on the premise that the SG (located in dorsal horn) modulates afferent nerve impulses and influence transmission of T cells. This activates a central controlling mechanism

Gate Control In Dorsal Horn of Spinal Cord Brain . A-Beta Sensory, Proprioception, Etc T SG Inhibitory Synapse A-Delta, C Fibers Pain Transmission Facilitator Synapse

The second order neuron When the substantia gelatinosa is active the “gate” is closed and there is a decrease in the amount of sensory input to the T-cell If the S.G. is relatively inactive the “gate” is open the balance of activity in the large and small diameter sensory neurons determines the position of the “gate”

Gate Control Theory Large diameter afferents cause an initial increase in the T-cells followed by a reduction of activity. The initial increase is due to direct activation of the second-order neuron by primary afferents. The reduction is an indirect result due to large-diameter afferents also activating the s.g. cells which causes the gate to close

Gate Control Theory Cont. Small diameter afferents increase T-cell activity by these primary afferents also activate inhibitory interneurons that reduce activity in the s.g which open the gate

Gate Control Theory When the balance of small to large diameter sensory neuronal input is no longer maintained and reaches a critical value the second-order neurons are activated. This activation is of the ascending system and leads to the perception of pain and the subsequent behavioral responses.

Gate Control Theory The Descending control system in which emotion and past experience evoke descending input, impinging upon the gating mechanism to block pain sensation at the spinal level. PAIN is an excellent “bible” for those working clinically with pain control

Pain modulation: Levels Theory of Pain Control Spinal Levels of Pain Control Gate Control Theory Central Biasing (hyperstimulation analgesia) Endogenous Opiate (Pituitary level)

Level I: Presynaptic inhibition Gate Control Theory The concept that when several sensory stimuli reach the spinal cord at the same location and time. one of them becomes dominant. As long as the stimulation is causing firing of the sensory nerve, the gate to pain should be closed If accommodation occurs (electrical stimulus) the gate is then open and pain returns

Level 2: Descending inhibition Central Biasing A theory of pain modulation where higher centers such as the cerebral cortex influence the perception of and response to pain Impulses from higher centers act to close the gate and block transmission of the pain message at the dorsal horn synapse Transmission of sensory input ot higher brain centers Transmission Cell Central Control + - + - Substantia gelitinosa + - A-beta fiber Afferents A-Delta & C fiber afferents

Level 3: -Endorphin modulation Endogenous Opiate Opiate like substance made by the body Norepinephrine Seratonin These opiates inhibit the depolarization of second order nociceptive nerve fibers (thus no pain) Found in substantia gelatinosa - activated in tract Causes degeneration of prostaglandin and dorsal horn inhibition

The purpose of knowing all the pain control theories is to use modalities to assess these pain theories and decrease the athlete/patient’s pain