Cns 5


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  • Algogenic substances include seretonin, histamine, and bradykinin – promote immune function activity, cause inflammation at the injured site.
  • Myelination increases the speed of transmission and so sudden, sharp pain gets transmitted to the cerebral cortex faster than dull or aching pain. This may be important for survival. The motivational and affective elements of pain appear to be influenced strongly by the C-fibers. They project onto the thalamus, hypothalamus, and amygdala. The A-delta fibers project onto particular areas of the thalamus and sensory areas of the cerebral cortex. Neurotransmitters are also involved, in particular, substance P.
  • Episodes of neuralgia occur suddenly and without apparent cause. Someone with causalgia may report that it feels like my arm is pressed against a hot stove. Typically follows a traumatic injury like a gun shot wound or stabbing and occurs at the site of injury. Is experienced well after the wound has healed. Phantom limb pain – example might be burning sensation in your toes after the limb and foot has been amputated. Person can experience a sense of their limb moving. Can persist for months and years. Pain can be felt as shooting, burning, or cramping (e.g., feel like hand is clenched with finger nails digging into the hand).
  • Pain signals arrive from the pain fibers (A-delta and C) at the spinal cord, along with signals from other peripheral fibers (A-beta) and the brain. The solid arrows depict stimulation conditions that tend to open the gate and send pain signals through. The dotted arrows indicate inhibition conditions. Pain signals enter the spinal cord and pass through a gating mechanism before activating transmission cells, which send impulses to the brain (from text by Sarafino EP. Health Psychology, Biopsychosocical Interactions, Third Edition. John Wiley & Sons, Inc. New York: 1998.)
  • Cns 5

    1. 1. The Sensory system <ul><li>Specific sensation depends upon brain region being stimulated. </li></ul><ul><li>Receptor or nerve ending is stimulated. </li></ul><ul><li>Sensory neuron transmits signal. </li></ul><ul><li>Brain interprets signal. </li></ul><ul><li>Sensory adaptation </li></ul><ul><ul><li>Sensory receptors send signal at decreasing rate due to continuous stimulation. </li></ul></ul>
    2. 2. From Sensation to Perception <ul><li>Survival depends upon sensation and perception </li></ul><ul><li>Sensation is the awareness of changes in the internal and external environment </li></ul><ul><li>Perception is the conscious interpretation of those stimuli </li></ul>
    3. 3. Organization of the Somatosensory System <ul><li>Input comes from exteroceptors, proprioceptors, and interoceptors </li></ul><ul><li>The three main levels of neural integration in the somatosensory system are: </li></ul><ul><ul><li>Receptor level – the sensor receptors </li></ul></ul><ul><ul><li>Circuit level – ascending pathways </li></ul></ul><ul><ul><li>Perceptual level – neuronal circuits in the cerebral cortex </li></ul></ul>
    4. 4. Processing at the Receptor Lever <ul><li>The receptor must have specificity for the stimulus energy </li></ul><ul><li>The receptor’s receptive field must be stimulated </li></ul><ul><li>Stimulus energy must be converted into a graded potential </li></ul><ul><li>A generator potential in the associated sensory neuron must reach threshold </li></ul>
    5. 5. Adaptation of Sensory Receptors <ul><li>Adaptation occurs when sensory receptors are subjected to an unchanging stimulus </li></ul><ul><ul><li>Receptor membranes become less responsive </li></ul></ul><ul><ul><li>Receptor potentials decline in frequency or stop </li></ul></ul>
    6. 6. Adaptation of Sensory Receptors <ul><li>Receptors responding to pressure, touch, and smell adapt quickly </li></ul><ul><li>Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood </li></ul><ul><li>Pain receptors and proprioceptors do not exhibit adaptation </li></ul>
    7. 7. Processing at the Circuit Level <ul><li>Chains of three neurons (first-, second-, and third-order) conduct sensory impulses upward to the brain </li></ul><ul><li>First-order neurons – soma reside in dorsal root or cranial ganglia, and conduct impulses from the skin to the spinal cord or brain stem </li></ul><ul><li>Second-order neurons – soma reside in the dorsal horn of the spinal cord or medullary nuclei and transmit impulses to the thalamus or cerebellum </li></ul><ul><li>Third-order neurons – located in the thalamus and conduct impulses to the somatosensory cortex of the cerebrum </li></ul>
    8. 8. Receptive Fields <ul><li>Area of skin whose stimulation results in changes in the firing rate of the neuron. </li></ul><ul><ul><li>Area of each receptor field varies inversely with the density of receptors in the region. </li></ul></ul><ul><li>Back and legs have few sensory endings. </li></ul><ul><ul><li>Receptive field is large. </li></ul></ul><ul><li>Fingertips have large # of cutaneous receptors. </li></ul><ul><ul><li>Receptive field is small. </li></ul></ul>
    9. 9. Two-Point Touch Threshold <ul><li>Minimum distance at which 2 points of touch can be perceived as separate. </li></ul><ul><ul><li>Measures of distance between receptive fields. </li></ul></ul><ul><li>Indication of tactile acuity. </li></ul><ul><ul><li>If distance between 2 points is less than minimum distance, only 1 point will be felt. </li></ul></ul>
    10. 10. Lateral Inhibition <ul><li>Sharpening of sensation. </li></ul><ul><ul><li>When a blunt object touches the skin, sensory neurons in the center areas are stimulated more than neighboring fields. </li></ul></ul><ul><ul><li>No clear, sharp boundary. </li></ul></ul><ul><ul><ul><li>Will be perceived as a single touch with well defined borders. </li></ul></ul></ul><ul><ul><li>Occurs within CNS. </li></ul></ul>Figure 10-6
    11. 11. Sensory Areas <ul><li>Cortical areas involved in conscious awareness of sensation </li></ul><ul><li>Distinct area for each of the major senses </li></ul>
    12. 12. Sensory Areas – Primary Somatosensory Cortex <ul><li>Located along the postcentral gyrus </li></ul><ul><li>Involved with conscious awareness of general somatic senses </li></ul>
    13. 13. Sensory Areas – Primary Somatosensory Cortex <ul><li>Projection is contralateral </li></ul><ul><ul><li>Cerebral hemispheres </li></ul></ul><ul><ul><ul><li>Receive sensory input from the opposite side of the body </li></ul></ul></ul><ul><li>Sensory homunculus – a body map of the sensory cortex </li></ul>
    14. 14. Sensory Areas – Sensory Homunculus
    15. 15. Sensory Areas – Somatosensory Association Area <ul><li>Lies posterior to the primary somatosensory cortex </li></ul><ul><li>Integrates different sensory inputs </li></ul><ul><ul><li>Touch, pressure, and others </li></ul></ul><ul><li>Draws upon stored memories of past sensory experiences </li></ul>
    16. 16. White Matter Anterior Funiculus (Anterior White Column) Posterior Funiculus (Posterior White Column) Fasciculus Gracilis & Fasciculus Cuneatus Lateral Funiculus (Lateral White Column) Gray Matter Anterior Horn ------------ --- motor Posterior Horn -------------- sensory Lateral Horn ----------------- autonomic (sympathetic) Gray Commissure -------- anterior and posterior Spinal Cord Internal Structure
    17. 17. Lamina I Posteromarginal Nucleus Lamina II Substantia Gelatinosa of Rolando Lamina III Lamina IV, V, VI ----- Nucleus Proprius Lamina VII - Intermediate Gray - I ntermediolateral cell column (ILM) - Clarke’s column (Nucleus dorsalis) - I ntermediomedial cell column (IMM) Lamina VIII Lamina IX ---------- Anterior Horn (Motor) Cell Lamina X ----------- Gray Commissure Lamina of Rexed
    18. 18. Spinal Nerves <ul><li>A series of connective tissue layer surrounds each spinal nerve. </li></ul><ul><li>Epineurium- outermost layer, consists of a dense network of collagen fibers. </li></ul><ul><li>Perineurium -extend inward from the epineurium, dividing the nerve into a series of compartments. </li></ul><ul><li>Endoneurium -delicate connective tissue fibers. </li></ul>
    19. 19. Ventral and Dorsal Roots <ul><li>In the vicinity of the cord, each spinal nerve divides into a ventral (anterior, motor) root and a dorsal (posterior, sensory) root. </li></ul><ul><li>Ventral roots contain mostly efferent nerve fibers and convey motor information. </li></ul><ul><li>Dorsal roots contain afferent nerve fibers and convey sensory information. </li></ul><ul><li>The axons of motor neurons whose cell bodies are located within the CNS in the ant. Horn emerge from the spinal cord to form ventral roots (motor). </li></ul><ul><li>Groups of sensory neurons , whose axons make up the dorsal roots lie outside the cord in the dorsal root ganglia or spinal ganglia of the PNS. </li></ul>
    20. 20. Peripheral distribution of Spinal Nerves <ul><li>A typical spinal nerve has a white ramus(this contains myelinated axons), and a gray ramus (unmyelinated fibers that innervate glands and smooth muscles in the body wall or limbs) </li></ul><ul><li>A dorsal ramus(providing sensory and motor innervation to the skin and muscles of the back), and a ventral ramus (supplying the ventrolateral body surface, structures in the body wall and the limbs). </li></ul><ul><li>Each pair of nerves monitors a region of the body surface called a dermatome. </li></ul>
    21. 21. Nerve Plexuses <ul><li>A complex, interwoven network of nerves is a nerve plexus. </li></ul><ul><li>The three large plexuses are the cervical plexus, the brachial plexus and the lumbosacral plexus. The latter can be further divided into the lumbar plexus and the sacral plexus. </li></ul>
    22. 22. White Matter of the Spinal Cord
    23. 23. Sensory and Motor Pathways <ul><li>Most motor pathways: </li></ul><ul><ul><li>Decussate at some point along their course </li></ul></ul><ul><ul><li>Consist of a chain of two or three neurons </li></ul></ul><ul><ul><li>Exhibit somatotopy </li></ul></ul><ul><ul><ul><li>Tracts arranged according to the body region they supply </li></ul></ul></ul><ul><li>All pathways are paired </li></ul><ul><ul><li>One of each on each side of the body </li></ul></ul>
    24. 24. Fasciculus cuneatus and Fasciculus gracilis Figure 12.33a
    25. 26. Posterior White Column-Medial Lemniscal Pathway (Tract of gall and burdach) Modality: Discriminative Touch Sensation (include Vibration) and Conscious Proprioception (Position Sensation, Kinesthesia) Receptor: Most receptors except free nerve endings Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion) Posterior Root - Posterior White Column 2nd Neuron: Dorsal Column Nuclei (Nucleus Gracilis and Cuneatus) Internal Arcuate Fiber - Lemniscal Decussation - Medial Lemniscus 3rd Neuron: Thalamus (VPLc) Internal Capsule ----- Corona Radiata Termination: Primary Somesthetic Area (S I) Spinal Cord Ascending Tracts
    26. 27. Lateral spinothalamic tract
    27. 28. Spinothalamic Tract Modality: Pain & Temperature Sensation, Light Touch Receptor: Free Nerve Ending Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion) Posterior Root 2nd Neuron: Dorsal Horn (Lamina IV, V, VI) Spinothalamic Tract - (Spinal Lemniscus) 3rd Neuron: Thalamus (VPLc, CL & POm) Internal Capsule ----- Corona Radiata Termination: Primary Somesthetic Area (S I) & Diffuse Widespread Cortical Region Spinal Cord Ascending Tracts
    28. 29. Spinocerebellar Tract Modality: Unconscious Proprioception Receptor: Muscle spindle, Golgi tendon organ Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion) Posterior Root , [Posterior Column] 2nd Neuron: 1. Clarke’s column (Lamina VII) Posterior Spinocerebellar Tract 2 . Posterior Horn Anterior Spinocerebellar Tract Termination: Cerebellar Cortex Spinal Cord Ascending Tracts
    29. 31. Spinocerebellar Tract Inferior cerebellar peduncle posterior spinocerebellar tract Clarke’s column posterior white column posterior root Posterior SCbllT Inferior cerebellar peduncle cuneocerebellar tract (upper body) posterior white column posterior root Anterior SCbllT superior cerebellar peduncle anterior spinocerebellar tract anterior white commissure posterior root
    30. 32. Spinocerebellar Tract
    31. 35. What is pain? <ul><li>A sensory and emotional experience of discomfort. </li></ul><ul><li>Single most common medical complaint. </li></ul>
    32. 36. Perceiving Pain <ul><li>Algogenic substances – chemicals released at the site of the injury </li></ul><ul><li>Nociceptors – afferent neurons that carry pain messages </li></ul><ul><li>Referred pain – pain that is perceived as if it were coming from somewhere else in the body </li></ul>
    33. 37. Peripheral Nerve Fibers Involved in Pain Perception <ul><li>A-delta fibers – small, myelinated fibers that transmit sharp pain </li></ul><ul><li>C-fibers – small unmyelinated nerve fibers that transmit dull or aching pain. </li></ul>
    34. 38. Three Chronic Pain Conditions <ul><li>Neuralgia – an extremely painful condition consisting of recurrent episodes of intense shooting or stabbing pain along the course of the nerve. </li></ul><ul><li>Causalgia – recurrent episodes of severe burning pain. </li></ul><ul><li>Phantom limb pain – feelings of pain in a limb that is no longer there and has no functioning nerves. </li></ul>
    35. 39. Pain Transmission Acute Pain Noxious Stimulus travel Via A-Delta and C-delta Fibers to Dorsal Horn (spinal Cord) Doral Horn A-Beta C-Delta Pain Transmitted to Higher Brain Centers Acute Pain STT (Spinal thalamic Tract) Thalamus and Cortex location and discrimination Retinacular Formation & Periaquductal Gray (PAG) Motor, sensory and autonomic Response Discrimination and Location of pain occurs during this sequence Limbic System & Cortex Descending Control Mech. Activated here once noxious stimuli reaches higher centers of brain. Incoming stimuli can be inhibited at various levels and endogenous opiates released
    36. 40. Pain Nerve Fibers <ul><li>Acute Pain Fibers : conduct impulses rapidly. Sharp pain. Restricted area of skin. Seldom continues after stimulation stops. </li></ul><ul><li>Chronic Pain Fibers : slower, dull, aching pain. Diffuse and difficult to pinpoint. May continue after stimulus ceases. May be felt in deeper tissues. </li></ul><ul><li>An event usually triggers both acute and chronic pain fibers (dual sensation) </li></ul>
    37. 41. Acute Pain <ul><li>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) </li></ul><ul><li>Second Pain: carried in C fibers. Smaller diameter, non myelinated, slower. (less discrete - more diffuse) </li></ul>
    38. 42. Acute Pain Treatment <ul><li>Goal </li></ul><ul><ul><li>block the pain through: </li></ul></ul><ul><ul><ul><li>inhibition </li></ul></ul></ul><ul><ul><ul><li>blocking A fibers (Gate Control) </li></ul></ul></ul>
    39. 43. Chronic Pain: <ul><li>Any pain which lasts for six months or more – </li></ul><ul><li>numerous by-passes. Also goes to limbic system (emotional control)- learned response </li></ul>
    40. 44. Referred Pain (projected pain) <ul><li>Felt at other site than injured area </li></ul><ul><ul><li>Dermatome (skin represented by nerve root) </li></ul></ul>
    41. 45. Pain theories <ul><li>Specificity Theory </li></ul><ul><li>Pattern Theory </li></ul><ul><li>Gate Control Theory </li></ul>
    42. 46. 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.
    43. 47. 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.
    44. 48. Gate Control Theory (1965) <ul><li>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. </li></ul>
    45. 49. Gate Control Theory <ul><li>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). </li></ul><ul><li>A nonpainful stimulus can block the transmission of a noxious stimulus </li></ul>Brain/Pain centers C delta noxious stimulus A-beta non-painful stimulus Blocking entry of c-delta Fibers
    46. 50. Gate Control Theory Cont. <ul><li>The second order neuron, the T-cell and the substantia gelatinosa can exert affects on the primary afferent </li></ul><ul><li>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 </li></ul>
    47. 51. Gate Control <ul><li>In Dorsal Horn of Spinal Cord </li></ul>T Brain . A-Beta Sensory, Proprioception, Etc A-Delta, C Fibers Pain Transmission SG Facilitator Synapse Inhibitory Synapse
    48. 52. The second order neuron <ul><li>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 </li></ul><ul><li>If the S.G. is relatively inactive the “gate” is open </li></ul><ul><li>the balance of activity in the large and small diameter sensory neurons determines the position of the “gate” </li></ul>
    49. 53. Gate Control Theory <ul><li>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 </li></ul>
    50. 54. Gate Control Theory Cont. <ul><li>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 </li></ul>
    51. 55. Gate Control Theory <ul><li>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. </li></ul>
    52. 56. Gate Control Theory <ul><li>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. </li></ul><ul><li>PAIN is an excellent “bible” for those working clinically with pain control </li></ul>
    53. 57. Pain modulation: Levels Theory of Pain Control <ul><li>Spinal Levels of Pain Control </li></ul><ul><ul><li>Gate Control Theory </li></ul></ul><ul><ul><li>Central Biasing (hyperstimulation analgesia) </li></ul></ul><ul><ul><li>Endogenous Opiate (Pituitary level) </li></ul></ul>
    54. 58. Level I: Presynaptic inhibition Gate Control Theory <ul><li>The concept that when several sensory stimuli reach the spinal cord at the same location and time. one of them becomes dominant. </li></ul><ul><li>As long as the stimulation is causing firing of the sensory nerve, the gate to pain should be closed </li></ul><ul><li>If accommodation occurs (electrical stimulus) the gate is then open and pain returns </li></ul>
    57. 61. Level 2: Descending inhibition <ul><ul><li>A theory of pain modulation where higher centers such as the cerebral cortex influence the perception of and response to pain </li></ul></ul><ul><ul><ul><li>Impulses from higher centers act to close the gate and block transmission of the pain message at the dorsal horn synapse </li></ul></ul></ul>Transmission of sensory input to higher brain centers Transmission Cell Substantia gelitinosa A-beta fiber Afferents A-Delta & C fiber afferents Central Control + - + - + -
    58. 63. Level 3:  -Endorphin modulation Endogenous Opiate <ul><li>Opiate like substance made by the body </li></ul><ul><ul><ul><li>Norepinephrine </li></ul></ul></ul><ul><ul><ul><li>Seratonin </li></ul></ul></ul><ul><li>These opiates inhibit the depolarization of second order nociceptive nerve fibers (thus no pain) </li></ul><ul><ul><li>Found in substantia gelatinosa - activated in tract </li></ul></ul><ul><ul><li>Causes degeneration of prostaglandin and dorsal horn inhibition </li></ul></ul>
    59. 64. Gate-Control Theory Gate is open Gate is closed Brain Spinal Cord Gating Mechanism Transmission Cells From pain fibers From other Peripheral fibers To brain Brain Spinal Cord Gating Mechanism Transmission Cells From pain fibers From other Peripheral fibers To brain
    60. 65. Three Factors Involved in Opening and Closing the Gate <ul><li>The amount of activity in the pain fibers. </li></ul><ul><li>The amount of activity in other peripheral fibers </li></ul><ul><li>Messages that descend from the brain. </li></ul>
    61. 66. Conditions that Open the Gate <ul><li>Physical conditions </li></ul><ul><ul><li>Extent of injury </li></ul></ul><ul><ul><li>Inappropriate activity level </li></ul></ul><ul><li>Emotional conditions </li></ul><ul><ul><li>Anxiety or worry </li></ul></ul><ul><ul><li>Tension </li></ul></ul><ul><ul><li>Depression </li></ul></ul><ul><li>Mental Conditions </li></ul><ul><ul><li>Focusing on pain </li></ul></ul><ul><ul><li>Boredom </li></ul></ul>
    62. 67. Conditions That Close the Gate <ul><li>Physical conditions </li></ul><ul><ul><li>Medications </li></ul></ul><ul><ul><li>Counter stimulation (e.g., heat, message) </li></ul></ul><ul><li>Emotional conditions </li></ul><ul><ul><li>Positive emotions </li></ul></ul><ul><ul><li>Relaxation, Rest </li></ul></ul><ul><li>Mental conditions </li></ul><ul><ul><li>Intense concentration or distraction </li></ul></ul><ul><ul><li>Involvement and interest in life activities </li></ul></ul>
    63. 68. Types of Pain Medications <ul><li>Peripherally active analgesics – work at the periphery (e.g., aspirin). </li></ul><ul><li>Centrally active analgesics – narcotics that bind to the opiate receptors in the brain (e.g., codeine, morphine, heroin). </li></ul><ul><li>Local analgesics – can be injected into the site of injury or applied topically (e.g., novocaine). </li></ul><ul><li>Indirectly acting drugs – affect non-pain conditions such as emotions that can exacerbate pain experience. </li></ul>
    64. 69. Psychological Pain Control Methods <ul><li>Biofeedback – provides biophysiological feedback to patient about some bodily process the patient is unaware of (e.g., forehead muscle tension). </li></ul><ul><li>Relaxation – systematic relaxation of the large muscle groups. </li></ul><ul><li>Hypnosis – relaxation + suggestion + distraction + altering the meaning of pain. </li></ul>
    65. 70. Psychological Pain Methods <ul><li>Acupuncture – </li></ul><ul><ul><li>Counter-irritation – may close the spinal gating mechanism in pain perception. </li></ul></ul>
    66. 71. Referred pain <ul><li>Visceral pain may feel as if it is coming from some part of the body other than the part being stimulated. May arise from common nerve pathways. </li></ul><ul><ul><li>Example: Pain originating in the heart may be referred to the left shoulder and left upper limb. </li></ul></ul>
    67. 72. Pain originating in the heart may feel as if it is coming from the skin because sensory impulses from those two regions follow common nerve pathways to the brain.
    68. 73. Surface regions to which visceral pain may be referred
    69. 74. Theories <ul><li>A. Convergence theory </li></ul><ul><li>B. Facilitation theory </li></ul>
    70. 75. Other sensations <ul><li>Hyperalgesia </li></ul><ul><li>Itch (pruritus) </li></ul><ul><li>Vibration sense </li></ul><ul><li>Two point discrimination </li></ul><ul><li>Stereognosis </li></ul>
    71. 76. Headaches <ul><li>Nervous tissue of the brain lacks pain receptors but nearly all other tissues of the head including meninges and blood vessels are richly innervated </li></ul><ul><li>Many headaches are associated with stressful life situations that cause fatigue, emotional tension, anxiety, or frustration </li></ul>
    72. 77. Tension Headache <ul><li>Triggered by various physiological changes such as prolonged contraction of skeletal muscles in forehead, sides of head, back of neck. </li></ul><ul><li>Contractions stimulate pain receptors </li></ul>
    73. 78. Vascular Headache <ul><li>Accompanies constriction or dilation of cranial blood vessels. </li></ul><ul><li>Ex. Throbbing headache of “hang-over” from drinking too much alcohol may be due to blood pulsating through dilated cranial vessels </li></ul>
    74. 79. Migraine <ul><li>Form of vascular headache </li></ul><ul><li>Certain cranial vessels constrict producing a localized cerebral blood deficiency </li></ul><ul><li>Variety of symptoms: seeing patterns of bright light that obstruct vision, numbness in limbs or face </li></ul><ul><li>Vasoconstriction subsequently leads to vasodilation of affected vessels causing severe headache usually on one side of the head. </li></ul><ul><li>Can last several hours or more </li></ul>
    75. 80. Other Causes of Headaches <ul><li>Sensitivity to food additives </li></ul><ul><li>High blood pressure </li></ul><ul><li>Increased intracranial pressure due to tumor or hematoma </li></ul><ul><li>Decreased cerebrospinal fluid pressure following lumbar puncture </li></ul><ul><li>Sensitivity to or withdrawal from certain drugs </li></ul>