[USEMAP] PAIN q pain is a protective modality q International Association for the Study of Pain (IASP): „Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage“. q pain threshold: the minimum intensity of a stimulus that is perceived as painful, the intensity at which a stimulus begins to evoke pain varies [USEMAP] Nociceptors/nocisensors q nocere – to injure or to hurt in Latin q are activated by noxious mechanical, thermal or chemical stimuli q detect signals from damaged tissue or the threat of damage q free nerve endings found in the skin, muscles, joints, bones and viscera [USEMAP] Nociceptors q nociceptors of Aδ fibres (5-30 meters/sec) §Aδ mechanical nociceptors §Aδ thermal nociceptors q nociceptors of C fibres (0.5-2.0 meters/sec) §C polymodal nociceptors – react to thermal, mechanical and chemical stimuli qsilent nociceptors (MIA = mechanically insensitive afferents) - responsive after inflammation and tissue injury q [USEMAP] Factors that activate nociceptors [USEMAP] q Peripheral sensitization q Central sensitization = activity- or use-dependent neuronal plasticity in the spinal cord § hyperalgesia - exaggerated or prolonged response to noxious inputs § allodynia - pain induced by normally innocuous inputs [USEMAP] q Aδ fibres – thin myelinated fibres § sharp, localized pain q C non-myelinated fibres §dull, non-localized pain Nociceptive afferents Spinoreticular tract http://fce-study.netdna-ssl.com/images/upload-flashcards/931975/636704_m.png [USEMAP] The noxious information from visceral organs is mostly carried to the CNS in different pathways than that from the skin. Pain pathways from the trunk and limbs PALEOSPINOTHALAMIC PATHWAY q tr. spino-reticulo-thalamicus §diffuse, non-localized pain §autonomic and reflexive responses to pain stimuli §emotional and affective reactions to pain §intralaminar nuclei of the thalamus, hypothalamus §postcentral gyrus, insula and cingulate gyrus NEOSPINOTHALAMIC PATHWAY q tr. spino-thalamicus lat. §sharp, well localized pain §somatotopic representation §ventral posterolateral (VPL) and posterior nucleus of the thalamus §postcentral gyrus Cortex Thalamus Spinal cord Paleospino- thalamic pathway Neospino- thalamic pathway [USEMAP] Pain pathways from the TRACTUS TRIGEMINO-RETICULO- THALAMICUS q diffuse, non-localized pain TRACTUS TRIGEMINO- THALAMICUS ANTERIOR q sharp, well localized pain Cortex Thalamus Medulla [USEMAP] The phylogenetically old, paleospinothalamic and trigemino- reticulothalamic, pathways through the RF are concerned with the arousal and affective (emotional) aspects of somatic sensory stimuli. In contrast, the direct, neospinothalamic and anterior trigeminothalamic, pathways are analytic, encoding information about modality, intensity, and location. Primary somatosensory (somesthetic) cortex (SI) http://www.ufrgs.br/imunovet/molecular_immunology/sensoryhomunculus.jpg https://classconnection.s3.amazonaws.com/632/flashcards/117632/png/screen_shot_2011-05-02_at_1.48.2 6_am.png [USEMAP] [USEMAP] Referred pain Common dermatome hypothesis Convergence theory Facilitation or irritable focus Learned phenomenon [USEMAP] Dental Pain qAβ + Aδ fibres – tingling, vibration, touch, sharp pain qC fibres – dull ache qpulp + dentin – enormous number of free nerve endings qperiodontal ligament – Ruffini mechanoreceptors and proprioreceptors qinflammed pulp or periapex – peripheral and central sensitization – hyperalgesia, allodynia and spontaneous pain qreferred orofacial pain – both source and referral site qwide area of pain – difficulty to locate the pathology q [USEMAP] MODULATING SYSTEMS OF NOCICEPTIVE PATHWAYS q level of modulation of nociceptive pathways §spinal cord (“gate control theory”) §RF of brain stem §periaquaeductal gray matter (PAG) [USEMAP] “Gate control theory” [USEMAP] http://accessphysiotherapy.mhmedical.com/data/Multimedia/grandRounds/somatosensorypathways/media/sl ideImages/Somatosensory%20Pathways%2010.png [USEMAP] Stress-induced analgesia (both opiate and non-opiate forms) [USEMAP] Necessary components of proper motor control qVolition qCoordination of signals to many muscle groups qProprioception qPostural adjustments qSensory feedback qCompensation for the physical characteristics of the body and muscles qUnconscious processing qAdaptability [USEMAP] Levels of movement regulation q spinal cord q brain stem q cortex q cerebellum q basal ganglia [USEMAP] Lower motor neurons – spinal cord q α motoneurons q γ motoneurons q q Somatotopic organization §medial column – axial muscles §lateral column – limb muscles §anteriorly – extensors §posteriorly - flexors [USEMAP] q Motor neurons have highly branched, elaborate dendritic trees, enabling them to integrate the inputs from large numbers of other neurons and to calculate proper outputs. q The combination of an individual motor neuron and all of the muscle fibers that it innervates is called a motor unit. q size of motor unit § small motor unit – 1 motoneuron innervates several muscle fibers (extraocular muscles, muscles of hand) §large motor unit – 1 motoneuron innervates 500 – 1000 muscle fibers (back muscles) Lower motor neurons – brain stem q Somatomotor nuclei CN III, IV, VI, XII q Branchiomotor nuclei CN V, VII, IX, X, XI Supraspinal system of movement control q Medial system § bilateral §terminates on the interneurons or the medial column of lower motor neurons §controls maintenance of balance and postural movements § qLateral system §mostly cross the midline and descend contralaterally §terminates on the interneurons or the lateral column of lower motor neurons § controls fine manipulative movements of the hand and fingers qThe “third” motor system § aminergic pathways of the brain stem § [USEMAP] [USEMAP] Medial system q Subcortical pathways § Medial (MLF) and lateral vestibulospinal tracts - control of balance and postural movements, head movements §Tectospinal tract (sup. colliculus, MLF) – coordination of movements of the head and eyes during watching §Medial (pontine) and lateral (medullary) reticulospinal tracts - control of postural movements q Cortical pathways §Anterior corticospinal tract - medial column of lower motor neurons [USEMAP] Lateral system qSubcortical pathways § Rubrospinal tract - contralaterally descends to the lateral column q Cortical pathways §Lateral corticospinal tract [USEMAP] Corticospinal and corticonuclear tracts [USEMAP] [USEMAP] DIRECT MOTOR PATHWAYS (PYRAMIDAL): §corticospinal tract §corticonuclear tract § INDIRECT MOTOR PATHWAYS (EXTRAPYRAMIDAL): §corticorubrospinal tract §cerebellorubrospinal tract §corticoreticulospinal tracts §cerebelloreticulospinal tracts §corticotectospinal tract §cerbellovestibulospinal tracts § [USEMAP] The third system q the oldest one q nuclei of RF – raphespinal and coeruleospinal tracts q control of involuntary emotional movements q [USEMAP] Motor cortex [USEMAP] Planning of movements Illustrations were copied from: Neuroscience Online, the Open-Access Neuroscience Electronic Textbook Department of Neurobiology and Anatomy University of Texas Medical School at Houston