Receptors

cell function

1. SENSORY RECEPTORS

2. Student should be able to u nderstand the types of sensory receptors e numerate and understand the properties of receptors

3. Sensory Receptors Information about the internal and external environment activates the CNS via a variety of sensory receptors. These receptors are transducers that convert various forms of energy in the environment into action potentials in neurons . Stimulus is an event or particular form of energy that evokes a specific functional reaction in an organ or receptor. (mechanical, chemical, EMG, temp)

4. SENSE ORGANS Receptors are dendritic endings of afferent neurons that are associated with non-neuronal cells forming sense organs.

5. The term Sensory unit means sensory axon and all its peripheral branches. The  receptive field  of a sensory neuron is the particular part of the body surface in which a stimulus will trigger the firing of that neuron.

6. Classification of Sensory Receptors Type of sensation Mechanoreceptors Thermoreceptors Nociceptors Electromagnetic Chemoreceptors Distance of perception Teleceptors Exteroceptors Interoceptors Proprioceptors

7. Classification of receptors Mechanoreceptors E pidermis & dermis Joints, tendons, ligaments & muscles Cochlea Vestibular apparatus Baroreceptors in vessels Thermoreceptors Warmth & cold Nociceptors Pain Electromagnetic Rods & cones Chemoreceptors Taste & smell Carotid &aortic bodies Hypothalamus Osmo receptors

8. TACTILE MECHANORECEPTORS Encapsulated Meissner’s corpuscles in dermal papilla Pacinian corpuscles in dermis, ligaments, joint capaules Ruffni’s end organs in dermis and in deeper tissues Non-Encapsulated Free nerve endings in dermis, ligaments, cornea, bones Hair end organs in hairy skin Merkel’s discs in non hairy and hairy skin

9. Mechanoreceptors Skin (epidermis, dermis) Deeper tissues

10. SENSORY CODING Receptors encode four elements of stimuli Modality Location Intensity Duration

11. SENSORY CODING Receptors encode four elements of stimuli Modality Location (texture & precise localization by meissners and merkel cells { Ganong }; discrimination by meissner {Snell}) Intensity (by frequency of action potentials and no. of fibers) Duration

12. Modality of sensation Differential Sensitivity of Receptors for particular stimulus or specific energy for which it is designed When nerve fiber from the receptors is stimulated the perception is that for which the receptor is specialized, no matter where and how that nerve is stimulated. This is Muller’s law of specific energy. The specificity of nerve fibers for transmitting only one modality of sensation is called the labeled line principle .

13. EXPLANNATION E ach nerve tract terminates at a specific point in the central nervous system, and the type of sensation felt when a nerve fiber is stimulated is determined by the point in the nervous system to which the fiber leads. For instance if a pain fiber is stimulated, the person perceives pain regardless of what type of stimulus excites the fiber. Likewise, if a touch fiber is stimulated by electrical excitation of a touch receptor or in any other way, the person perceives touch .

14. LAW OF PROJECTION No matter which part of a pathway you stimulate between the receptor and the brain center, your brain will locate the stimulus where receptors are (e.g. phantom limb) reorganization of brain map in somatosensory cortex Some believe it can be blocked by local anesthetics in spinal cord.

15. A  phantom limb  is the sensation that an amputated or missing limb is still attached to the body.  Approximately 60 to 80% of individuals with an amputation experience phantom sensations in their amputated limb, and the majority of the sensations are painful. Phantom sensations may also occur after the removal of body parts e.g. after amputation of the breast, extraction of a tooth (phantom tooth pain) or removal of an eye (phantom eye syndrome)

16. Dale’s Law At one type of synapse only one type of neurotransmitter is released

17. Transduction of Sensory Stimuli into receptor potential and Nerve Impulses Receptor Potentials When pressure is applied to pacinian corpuscle , a small non- propogated depolarizing potential develops called receptor potential.

18. Properties of receptor potential It is graded potential It is non- propagated It doesn't obey all or none law

19. Mechanisms of Receptor Potentials. Different receptors can be excited in one of several ways to cause receptor potentials: (1) by mechanical deformation of the receptor, which stretches the receptor membrane and opens ion channels; (2) by application of a chemical to the membrane, which also opens ion channels; (3) by change of the temperature of the membrane, which alters the permeability of the membrane; or (4) by the effects of electromagnetic radiation,

20. Relation of the Receptor Potential to Action Potentials When the receptor potential rises above the threshold for eliciting action potentials in the nerve fiber attached to the receptor, then action potentials occur. More the receptor potential rises above the threshold level, the greater becomes the action potential frequency.

21. Relation of the Receptor Potential to Action Potentials More the receptor potential rises above the threshold level, the greater becomes the action potential frequency.

22. Relation Between Stimulus Intensity and the Receptor Potential. Amplitude increases rapidly and then less rapid rise at high stimulus strength the frequency of repetitive action potentials transmitted from sensory receptors also increase But very strong stimulation decrease action potentials as well

23. Adaptation of Receptors Another characteristic of all sensory receptors is that they adapt either partially or completely to any constant stimulus after a period of time. That is, when a continuous sensory stimulus is applied, the receptor responds at a high impulse rate at first and then at a progressively slower rate until finally the rate of action potentials decreases to very few or often to none at all.

24. Mechanisms by Which Receptors Adapt part of the adaptation results from readjustments in the structure of the receptor itself, and part from an electrical type of accommodation in the terminal nerve fibril

25. Slowly and rapidly adapting receptors Slowly Adapting Receptors Detect Continuous Stimulus Strength—The “Tonic” Receptors. impulses from the muscle spindles and Golgi tendon apparatuses allow the nervous system to know the status of muscle contraction Receptors of the macula in the vestibular apparatuses pain receptors baroreceptors of the arterial tree chemoreceptors of the carotid and aortic bodies. Rapidly Adapting Receptors Detect Change in Stimulus Strength—The “Rate Receptors,” “Movement Receptors,” or “Phasic Receptors .” Pacinian and meissner’s Importance of the Rate Receptors—Their Predictive Function.

26. TYPES OF NERVE FIBERS

27. To classify nerve fibers To understand the properties and differences of nerve fibers

28. Nerve Fibers That Transmit Different Types of Signals, and Their Physiologic Classification nerve fibers come in all sizes between 0.5 and 20 micrometers in diameter— the larger the diameter, the greater the conducting velocity The range of conducting velocities is between 0.5 and 120 m/sec

29. General Classification of Nerve Fibers In the general classification, the fibers are divided into types A, B and C, A&B are myelinated . C fibers are not the type A fibers are further subdivided into A α ( annulospiral endings) A β (touch and pressure) A ɣ (motor to muscle spindles) A δ (Pain and temp) B fibers are pre-ganglionic fibers C fibers are post ganglionic and also transmit slow pain

30. Alternative Classification Used by Sensory Physiologists Group Ia Muscle spindle Group Ib Golgi tendon organs Group II Cutaneous tactile receptors Group III Fibers carrying temperature, crude touch, and pricking pain sensations Group IV Un- myelinated fibers carrying pain, itch, temperature, and crude touch sensations

31. Diameter in micrometers Conduction velocity in m/sec Motor Fiber Type A α 0.12-20 0.72-120 Extrafusal skeletal muscle fibers A γ 0.12-8.2 0.12-48 Intrafusal muscle fibers B 0.21-33 0.86-18 Preganglionic autonomic fibers C 0.2-2 0.5-2 Postganglionic autonomic fibers

32. Peripheral nerve fibers Afferents Diameter of nerve fibers in mm Conduction velocity in m/sec Receptors Sensory Fiber Type A α Ia and Ib 0.13-20 0.80-120 m/sec Primary muscle spindles, Golgi tendon organ A β II 0.16-12 0.35-75 Secondary muscle spindles, skin mechanoreceptors A δ III 0.11-5 0.15-30 Skin mechanoreceptors, thermal receptors, fast pain C IV 0.2-1.5 0.5-2 Slow pain and temp

33. Transmission of Signals of Different Intensity in Nerve Tracts- Spatial and Temporal Summation

34. Temporal summation A mean for transmitting signals of increasing strength is by increasing the frequency of nerve impulses in each fiber, which is called temporal summation . Spatial summation

35. Relaying of signals in neuronal pool

36. DIVERGING PATHWAYS

37. Two types of divergence Amplifying type in same direction Divergence into multiple tracts to enter multiple areas of brain

38. CONVERGING PATHWAYS

39. Convergence of Signals Convergence means signals from multiple inputs uniting to excite a single neuron. C onvergence from a single source. That is, multiple terminals from a single incoming fiber tract terminate on the same neuron. Convergence can also result from input signals (excitatory or inhibitory) from multiple sources

40. Neuronal Circuit with both Excitatory and Inhibitory Output Signals RECIPROCAL INHIBITION CIRCUIT (Flexors & extensors of legs)

41. Prolongation of a Signal by a Neuronal Pool-" Afterdischarge ” A signal entering a pool causes a prolonged output discharge, called after-discharge , after the incoming signal is over. The input stimulus may last only 1 millisecond or so, and yet the output can last for many milliseconds or even minutes. The most important mechanisms by which after-discharge occurs are the following. Synaptic after-discharge due to long acting neurotransmitter Reverberatory circuits

42. Reverberatory , or Oscillatory Circuit The output neuron simply sends a collateral nerve fiber back to its own dendrites or soma to re-stimulate itself. Once the neuron discharges, the feedback stimuli could keep the neuron discharging for a protracted time.

43. Continuous Signal Output from Some Neuronal Circuits without input continuous intrinsic neuronal discharge (inter-neurons of spinal cord & cerebellum) (2) continuous reverberatory circuits that do not fatigue

44. Rhythmical Signal Output

45. Mechanisms of stabilizing Nervous system function Inhibitory circuits Synaptic fatigue Short term by synaptic fatigue Long term by affecting no. of synaptic receptors

46. Somatic sensations and mechanical receptors Dr. Sadia Nazir Assistant Professor Physiology LMDC

47. Classify somatic sensations Classify mechanical receptors

48. Classification of Sensations The somatic senses are the nervous mechanisms that collect sensory information from all over the body. Special senses , which mean specifically vision, hearing, smell, taste and equilibrium.

49. CLASSIFICATION OF SOMATIC SENSES The mechanoreceptive somatic senses, which include both tactile and position sensations. The thermoreceptive senses, which detect heat and cold The pain sense, which is activated by any factor that damages the tissues.

50. M echanoreceptive somatic senses The tactile senses include touch, pressure, vibration, and tickle the position senses include static position and rate of movement

51. Detection and Transmission of Tactile Sensations T ouch, pressure, and vibration are all detected by the same types of receptors called tactile receptors. There are at least six entirely different types of tactile receptors

52. Free nerve endings F ree nerve endings, which are found everywhere in the skin and in many other tissues, can detect touch and pressure

53. Meissner’s corpuscle Elongated encapsulated nerve ending of a large (type A B) myelinated nerve fiber. Inside the capsulation are many branching terminal nerve filaments. These corpuscles are present in the non hairy parts of the skin . Meissner’s corpuscles adapt in a fraction of a second after they are stimulated, Detect low frequency vibration.

54. Merkel’s discs The hairy parts and non hairy part of the skin also contain moderate numbers of expanded tip receptors they transmit an initially strong but partially adapting signal and then a continuing weaker signal adapts only slowly. Therefore, they are responsible for giving steady-state signals

55. Iggo dome receptor Merkel’s discs are often grouped together in a receptor organ called the Iggo dome receptor, which projects upward against the underside of the epithelium of the skin

56. Hair end-organ This receptor adapts readily and, like Meissner’s corpuscles, detects mainly (a) movement of objects on the surface of the body or (b) initial contact with the body.

57. Ruffini’s end-organs Multibranched , encapsulated endings, These endings adapt very slowly They are also found in joint capsules and help to signal the degree of joint rotation Found in skin and deeper tissues

58. Pacinian corpuscles Lie both immediately beneath the skin and deep in the fascial tissues of the body. They are stimulated only by rapid local compression of the tissues because they adapt in a few hundredths of a second. Important for detecting tissue vibration or other rapid changes in the mechanical state of the tissues.

59. Position sense Static Rate of movement called kinesthesia Receptors M uscle spindles Golgi tendon organs Ruffni’s endings P acinian

60. Texture meissner & merkel Localization meissner & merkel Discrimination meissner Vibration meissner & pacinian Prolonged touch merkel’s Prolonged deep touch & pressure ruffni’s

61. Transmission of Tactile Signals in Peripheral Nerve Fibers Transmit their signals in type A-beta nerve fibers that have transmission velocities ranging from 30 to 70 m/sec. free nerve ending tactile receptors transmit signals mainly by way of the small type A-delta myelinated fibers that conduct at velocities of only 5 to 30 m/sec. Some tactile free nerve endings transmit by way of type C unmyelinated fibers (up to 2 m/sec ;) these send signals into the spinal cord and lower brain stem, mainly the sensation of tickle.

62. Detection of Vibration Pacinian corpuscles can detect signal vibrations from 30 to 800 cycles per second and they also transmit their signals over type A-beta nerve fibers. Meissner’s corpuscles detect vibrations from 2 to 80 cycles per seconds

63. TICKLE AND ITCH rapidly adapting mechanoreceptive free nerve endings elicit only the tickle and itch sensations. These sensations are transmitted by very small type C, unmyelinated fibers similar to those that transmit the aching, slow type of pain.

64. Receptors afferents dorsal root ganglia gray column ascending tracts thalamus sensory cortex

65. SENSORY PATHWAYS Dorsal Column-medial lemsiscus pathway Sensations carried: Light touch pressure Tactile localisation 2 point discrimination Flutter and vibration Stereognosis Propioception Graphesthesia Large myleinated nerve fibres (fast) Spatial orientation

66. DORSAL COLUMN MEDIAL LEMNISCUS PATHWAY Nerve fibres enters through dorsal roots  divides into medial +lateral barnches Medial ascends in dorsal columns Lateral further branches and synapse with local neurons Some fibres are given off to the dorsal column Some form local reflexes Others form spinocerebellar tract

67. Ascending fibres terminate on cuneate and gracile nuclei Decussate to the opposite side immediately medial lemniscus Fibers terminate in the thalamic sensory relay area, called the ventrobasal complex. third-order nerve fibers project, mainly to the postcentral gyrus of the cerebral cortex, (called somatic sensory area I) also project to a smaller area in the lateral parietal cortex called somatic sensory area II).

68. the fibers from the lower parts of the body lie toward the center of the cord , whereas new fibres enter laterally. In the thalamus, the tail end of the body represented by the most lateral portions of the ventrobasal complex and the head and face represented by medial areas of the complex. because of the crossing of the medial lemnisci in the medulla , the left side of the body is represented in the right side of the thalamus, and the right side of the body in the left side of the thalamus. Spatial Orientation

69. Anterolateral System Transmits sensory signals that DO NOT require highly discrete localization Composed of smaller, myelinated nerve fibers (transmission speeds 40 m/sec) Less spatial orientation Sensory modalities – wide range Comprise of: Anterior spinothalamic tract Lateral spinothalamic tract

70. Anterolateral System Pain Thermal sensations (including warmth & cold) Crude touch and pressure sensations Tickle and itch sensations Sexual sensations

71. From receptors (free nerve ending  enter dorsal horn (cell bodies of these first order neurons are in the dorsal root ganglion ) Synapse with 2 nd order within 1-2 segments Second order neurons dorsal horn (at all levels). Their axons decussate in the anterior white and gray commisure Joined by trigeminothalmic fibers in medulla, send collaterals to reticular formation (alertness to pain)

72. 3rd order neurons VPL nucleus of thalamus. Their fibres ascend through the posterior limb of internal capsule corona radiate 4th order neurons of the cerebral cortex ( Broadmans areas 3,1.2 Somatosensory cortex) Some fibers from the second order neuron decussate and ascend as anterior spinothalmic tract Both anterior & lateral spinothalamic tracts unite in MO forming spinal lemniscus

73. The spinal cord anterolateral fibers originate mainly in dorsal horn laminae I, IV, V, and VI

74. Anterior and lateral spinothalmic tracts Some fibers carrying crude touch, tickle may ascend 8-10 spinal cord segments before synapsing with secondary neurons.  Ascend more anteriorly as the anterior spinothalmic tract Secondary fibers decussate in anterior gray or white commissures . Acend to the medulla  together spinal lemniscus

75. Head and neck? Ist order neurons for touch, pressure, pain, and temperature in the head  trigeminal ( semilunar ) CN V ( blue and red lines) 1 st order Neurons for proprioception  mesencephalic nucleus of CN V (purple fibers ). 1 st order neurons  VPM nucleus of the thalamus (2 nd order) SS1 Basically second order fibers from spinothalmic tract are are joined in brainstem by fibers of the trigeminothalamic tract: ( Pain and temperature from face and teeth.)

76. Unconscious Ascending Pathway Posterior Spinocerebellar Fibers enter SC at dorsal horn Ascend ipsilaterally to cerebellum Carries: muscle joint info from muscle spindles, tendon organs & joint receptors of trunk & lower limbs Anterior Spinocerebellar Fibers enter SC at dorsal horn Ascend contralaterally to cerebellum Carries: muscle joint info from muscle spindles, tendon organs & joint receptors of trunk , upper & lower limbs

77. Dorsal Column–Medial Lemniscal System 1. Touch sensations requiring a high degree of localization of the stimulus 2. Touch sensations requiring transmission of fine gradations of intensity 3. Phasic sensations, such as vibratory sensations 4. Sensations that signal movement against the skin 5. Position sensations from the joints 6. Pressure sensations having to do with fine degrees of judgment of pressure intensity Anterolateral System 1. Pain 2. Thermal sensations, including both warmth and cold sensations 3. Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body 4. Tickle and itch sensations 5. Sexual sensations

78. OBJECTIVES: Understand Structure of spinal cord and thalamus Understand the structure of sensory cortex and clinical application when sensory cortex is not working

79. Functional anatomy of spinal cord

80. Comparison of Structural Details in Different Regions of the Spinal Cord

81. OBJECTIVES Understand the structure of sensory cortex and clinical application when sensory cortex is not working Understand the pathway of two main Ascending pathways

82. Cortex: Broadmann’s areas (50) Central fissure: anterior to it  motor cortex Posterior sensory cortex Occipital lobe visual Tempral Lobe Auditory SS1 and SS2 Located  aneterior part of parietal lobe SS1-high degree of localization

83. Molecular layer External granular layer External pyramidal layer Internal granular layer Internal pyramidal layer Polymorphic layer

84. Functions of Somatosensory Area I Localize and discriminate discretely the different sensations in the different parts of the body judge critical degrees of pressure against the body judge the texture, weights, shapes or forms of objects by touch. This is called stereognosis . Judge the shape by drawing. graphaesthesia Bilateral excision of somatosensory area Pt is unable to Localize and discriminate discretely the different sensations in the different parts of the body judge critical degrees of pressure against the body judge the texture, weights, shapes or forms of objects. This is called astereognosis . Judge the shape by drawing. Agraphaesthesia

85. Effect of Removing the Somatosensory Association Area—(5,7) Amorphosynthesis The person loses ability to recognize complex objects and complex forms felt on the opposite side of the body. He or she loses most of the sense of form of his or her own body parts on the opposite side and forgets that it is there . When feeling objects, the person tends to recognize only one side of the object and forgets that the other side even exists.

86. Ascending tracts Dorsal column medial- leminiscal system Anterolateral tract 3. Anterior and posterior spinocerebellar 4. Cuneocerebellar 5. Olivocerebellar 6. Spinotectal 7. Spinoreticular 8. Visceral afferents

87. Dorsal Column–Medial Lemniscal System Touch sensations requiring a high degree of localization and discrimination of the stimulus Phasic sensations, such as vibratory sensations Sensations that signal movement against the skin Position sensations from the joints Pressure sensations having to do with fine degrees of judgment of pressure intensity Anterolateral System Pain Thermal sensations, including both warmth and cold sensations Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body Tickle and itch sensations Sexual sensations

88. Transmission in the Dorsal Column–Medial Lemniscal System Anatomy of the Dorsal Column–Medial Lemniscal System nerve fibers entering the dorsal columns pass uninterrupted up to the dorsal medulla, where they synapse in the dorsal column nuclei (the cuneate and gracile nuclei).

89. SPINOTHALAMIC TRACT

90. Lesions of Dorsal Column Tract Sensory ataxia Loss of vibration Loss of tactile discrimination Loss of tactile localization

91. Dorsal Column–Medial Lemniscal System Touch sensations requiring a high degree of localization of the stimulus Touch sensations requiring transmission of fine gradations of intensity Phasic sensations, such as vibratory sensations Sensations that signal movement against the skin Position sensations from the joints Pressure sensations having to do with fine degrees of judgment of pressure intensity Anterolateral System Pain Thermal sensations, including both warmth and cold sensations Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body Tickle and itch sensations Sexual sensations

92. Organization in dorsal column and anterolateral pathways Dorsal column system Composed of large,myelinated nerve fibers that transmit signals to the brain at velocities of 30 to 110 m/sec, high degree of spatial orientation of the nerve fibers with respect to their origin Fine gradation of intensity Termination VPL & SC Anterolateral Pathway The velocities of transmission are only one third to one half those in the dorsal column–medial lemniscal system , ranging between 8 and 40 m/sec; The degree of spatial localization of signals is poor; The gradations of intensities are also far less accurate Termination in RN, ILN, VPL, SC

93. Anterior and posterior spinocerebellar Cuneocerebellar Olivocerebellar Spinotectal Spinoreticular Visceral afferents

94. Judgment of Stimulus Intensity Spatial & temporal summation Lateral inhibition increases contrast

95. Judgment of Stimulus Intensity by sensory cortex Weber-Fechner Principle Interpreted signal strength = Log (stimulus) + constant Power Law Interpreted signal strength = K ( stimulus-k)y

96. Dermatome Segment of skin supplied by the spinal nerve

97. Pain and analgesia system Dr. Sadia Nazir Assistant Professor Physiology LMDC

98. By the end of this lecture you should be able to Define and classify pain Differentiate between fast and slow pain Identify the role of thalamus, cortex and reticular formation in pain perception Describe the brain analgesia system Explain visceral pain and its types Discuss the mechanisms of referred pain

99. Pain Is a Protective Mechanism Pain occurs whenever any tissues are being damaged, and it causes the individual to react to remove the pain stimulus.

100. Types of Pain Fast Pain Slow Pain Fast pain is felt within about 0.1 second after a pain stimulus is applied S low pain begins after 1 second or more and then increases slowly over many seconds and sometimes even minutes.

101. QUALITIES OF PAIN Fast pain is also described by many alternative names, such as sharp pain, pricking pain, acute pain, and electric pain Slow pain also goes by many names, such as slow burning pain, aching pain, throbbing pain, nauseous pain, and chronic pain

102. Pain Receptors Are Free Nerve Endings They are widespread in the superficial layers of the skin as well as in certain internal tissues, such as the periosteum , the arterial walls, the joint surfaces, and the falx and tentorium in the cranial vault . Non-adapting Nature of Pain Receptors

103. Three Types of Stimuli Excite Pain Receptors— Mechanical Thermal Chemical

104. Some of the chemicals that excite the chemical type of pain are bradykinin , serotonin, histamine, potassium ions, acids, acetylcholine, and proteolytic enzymes In addition, prostaglandins and substance P enhance the sensitivity of pain endings but do not directly excite them

105. Dual Pathways for Transmission of Pain Signals into the Central Nervous System Peripheral Pain Fibers— “Fast ” (A delta) and “Slow” Fibers (C fibers) The two pathways mainly correspond to the two types of pain— a fast-sharp pain pathway and a slow-chronic pain pathway.

106. Dual Pathways for Transmission of Pain Signals into the Central Nervous System Fast Pain ( Neospinothalamic Pathway) Mechanical or thermal pain stimuli A delta fibers at velocities between 6 and 30 m/sec. They terminate mainly in lamina I (lamina marginalis ) Slow Pain ( Paleospinothalamic Pathway) Mostly by chemical types of pain stimuli but sometimes by persisting mechanical or thermal stimuli. C fibers at velocities between 0.5 and 2 m/sec. laminae II and III of the dorsal horns, which together are called the substantia gelatinosa ,

107. Fast pain most pass all the way to the thalamus ( Ventrobasal ) Project to somatosensory cortex. can be localized much more exactly in the different parts of the body than can slow-chronic pain. Glutamate, the Probable Neurotransmitter of the Fast Pain Fibers Slow Pain most terminate in one of three areas: (a) reticular nuclei (b) tectal area of the mesencephalon (c) periaqueductal gray region (d) Intralaminar nuclei and hypothalamus Poorly localized. Type C pain fiber terminals entering the spinal cord secrete both glutamate transmitter and substance P transmitter.

108. Pain Suppression (“Analgesia”) System in the Brain and Spinal Cord Inhibition of pain signals at spinal cord by descending brain fibers Encephalin secreting neurons in cord and brain stem Inhibition of pain fibers by tactile incoming fibers

109. Acupuncture analgesia (AA) technique of relieving pain by inserting and manipulating threadlike needles at key points acupuncture endorphin hypothesis Acupuncture needles activate specific afferent nerve fi b ers  CNS  blocking pain transmission at both the spinal-cord and brain levels through use of endorphins and closely related endogenous opiates .

110. The periaqueductal gray and periventricular areas of the mesencephalon and upper pons surround the aqueduct of Sylvius and portions of the third and fourth ventricles. Neurons from these areas send signals to T he raphe magnus nucleus, a thin midline nucleus located in the lower pons and upper medulla, and the nucleus reticularis paragigantocellularis , located laterally in the medulla. From these nuclei, second-order signals are transmitted down the dorsolateral columns in the spinal cord to P ain inhibitory complex located in the dorsal horns of the spinal cord.

111. Inhibition of Pain Transmission by Simultaneous Tactile Sensory Signals Stimulation of large type A beta sensory fibers from peripheral tactile receptors can depress transmission of pain signals from the same body area. This presumably results from local lateral inhibition in the spinal cord. It explains why such simple maneuvers as rubbing the skin near painful areas is often effective in relieving pain. It also explains why liniments are often useful for pain relief.

112. Allodynia Non painful stimulus causes pain (Lesion of VPL of thalamus) Hyperalgesia Hypersensitivity to pain A pain nervous pathway sometimes becomes excessively excitable ;. Possible causes of hyperalgesia are Excessive sensitivity of the pain receptors themselves, which is called primary hyperalgesia (Burns) Facilitation of sensory transmission, which is called secondary hyperalgesia Analgesia Loss of pain

113. Referred Pain Often a person feels pain in a part of the body that is fairly remote from the tissue causing the pain. This is called referred pain. For instance, pain in one of the visceral organs often is referred to an area on the body surface.

114. Referred Pain

115. Mechanism of Referred Pain.

116. Visceral Pain and Surface Pain Visceral Pain Highly localized types of damage to the viscera seldom cause severe pain. True visceral pain is transmitted via pain sensory fibers within the autonomic nerve bundles, and the sensations are referred to surface areas of the body often far from the painful organ. Surface Pain/Parietal Pain Parietal sensations are conducted directly into local spinal nerves from the parietal peritoneum, pleura, or pericardium, and these sensations are usually localized over painful area.

117. Visceral” and the “Parietal” Pain Transmission Pathways

118. Causes of True Visceral Pain Any stimulus that excites pain nerve endings in diffuse areas of the viscera can cause visceral pain. Such stimuli include ischemia of visceral tissue, chemical damage to the surfaces of the viscera, spasm of the smooth muscle of a hollow viscus , excess distention of a hollow viscus , and stretching of the connective tissue surrounding or within the viscus . Essentially all visceral pain that originates in the thoracic and abdominal cavities is transmitted through small type C pain fibers and, therefore, can transmit only the chronic-aching-suffering type of pain.

119. Hyperalgesia A pain nervous pathway sometimes becomes excessively excitable; this gives rise to hyperalgesia , which means hypersensitivity to pain. Possible causes of hyperalgesia are (1) excessive sensitivity of the pain receptors themselves, which is called primary hyperalgesia (2) facilitation of sensory transmission, which is called secondary hyperalgesia .

120. Herpes Zoster (Shingles) Herpesvirus infects a dorsal root ganglion. This causes severe pain in the dermatomal segment served by the ganglion, thus eliciting a segmental type of pain that circles halfway around the body. The disease is called herpes zoster, or “shingles,” because of a skin eruption that often ensues.

121. Tic Douloureux Lancinating pain occasionally occurs in some people over one side of the face in the sensory distribution area (or part of the area) of the fifth or ninth nerves; This phenomenon is called tic douloureux (trigeminal neuralgia or glossopharyngeal neuralgia). The pain feels like sudden electrical shocks, and it may appear for only a few seconds at a time or may be almost continuous.

122. Headache Headaches are a type of pain referred to the surface of the head from deep head structures. Pain-Sensitive Areas in Cranial Vault. Tugging on the venous sinuses around the brain, Damaging the tentorium , Stretching the dura at the base of the brain can cause intense pain that is recognized as headache Middle meningeal artery is a pain sensitive structure

123. Types of Intracranial Headache Brain tumors Headache of Meningitis. Headache Caused by Low Cerebrospinal Fluid Pressure. Migraine Headache Alcoholic Headache Types of Extracranial Headache Headache Resulting from Muscle Spasm. Headache Caused by Irritation of Nasal and Accessory Nasal Structures. Headache Caused by Eye Disorders

124. Thermal Sensations The human being can perceive different gradations of cold and heat, from freezing cold cold cool Indifferent to warm hot burning hot.

125. Thermal gradations are discriminated by at least three types of sensory receptors: cold receptors, warmth receptors, and pain receptors.