1. SOMATOSENSORY SYSTEM
1.1. Sensation
1.1.1. Adequate stimuli are detected by sensory receptors with differential sensitivities.
1.1.1.1. Stretching/compression
1.1.1.1.1. Mechanoreceptors
1.1.1.2. Temperature changes
1.1.1.2.1. Thermoreceptors
1.1.1.3. Physical/chemical damage
1.1.1.3.1. Nociceptors
1.1.1.4. Light
1.1.1.4.1. Photoreceptors
1.1.1.5. Taste; smell; arterial oxygen; osmolality; blood carbon dioxide, glucose, amino acids, fatty acids
1.1.1.5.1. Chemoreceptors
1.1.2. Signal Transduction
1.1.2.1. Activated receptors generate receptor potential by increasing ion flow through channels or by increasing membrane permeability.
1.1.2.1.1. Receptor/Generator Potential
1.1.3. Action Potential
1.1.3.1. Occurs when receptor potential reaches treshold
1.1.4. Parameters of Effective Receptor Activation
1.1.4.1. Stimulus intensity
1.1.4.1.1. Proportional to amplitude and frequency of generated receptor potentials
1.1.4.2. Localization
1.1.4.2.1. Receptive Field
1.1.5. Adaptation
1.1.5.1. Phasic/Fast-Adapting Receptors
1.1.5.1.1. Active during onset and offset
1.1.5.2. Tonic/Slow-Adapting Receptors
1.1.5.2.1. Active during maintenance
1.2. Perception
1.2.1. Adequate stimuli are selected, organized, and interpreted.
2. SOMATOSENSORY AREAS
2.1. Primary Somatosensory Cortex
2.1.1. Somatosensory Area I
2.1.1.1. High degree of localization
2.1.2. Somatosensory Area II
2.1.2.1. Receives projections from somatosensory area I; poor localization
2.2. Somatosensory Association Area
2.2.1. Input from primary somatosensory cortex, thalamus, visual and auditory cortex
2.2.2. Refine sensation
2.2.3. Poor localization
3. CLINICAL CORRELATES
3.1. Sensory Alterations
3.1.1. Paresthesia
3.1.1.1. "Pins and needles"
3.1.2. Dysesthesia
3.1.2.1. Abnormal, unpleasant sensations
3.1.3. Anesthesia
3.1.3.1. Numbness to touch
3.1.4. Pallanesthesia
3.1.4.1. Vibration unperceived
3.1.5. Hyperalgesia
3.1.5.1. Exaggerated pain response
3.1.6. Hypoalgesia
3.1.6.1. Decreased pain sensation
3.1.7. Analgesia
3.1.7.1. Loss of pain sensation
3.1.8. Hyperapathia
3.1.8.1. Exaggerated pain response
3.1.9. Allodynia
3.1.9.1. Pain from non-painful stimulus
3.1.10. Causalgia
3.1.10.1. Burning pain
3.2. Herpes Zoster Virus
3.2.1. Dorsal root ganglion infected will manifest through severe pain in the subserved dermatomal segment.
4. SOMATIC SENSATIONS
4.1. Mechanoreceptive Senses
4.1.1. Tactile
4.1.1.1. Free nerve endings
4.1.1.1.1. A-delta and C nerve fibers
4.1.1.2. Meissner's corpuscle
4.1.1.2.1. A-beta nerve fibers
4.1.1.3. Merkel's receptor
4.1.1.3.1. A-beta nerve fibers
4.1.1.4. Hair follicle/tactile hair receptor
4.1.1.4.1. A-beta nerve fibers
4.1.1.5. Ruffini's corpuscle/endings
4.1.1.5.1. A-beta nerve fibers
4.1.2. Position
4.1.2.1. Muscle spindle
4.1.2.1.1. Relays info on muscle length
4.1.2.2. Golgi tendon
4.1.2.2.1. Relays info on muscle tension
4.2. Thermoreceptive Senses
4.2.1. Cold Receptor
4.2.1.1. A-delta and C nerve fibers
4.2.2. Warm Receptor
4.2.2.1. C nerve fibers
4.3. Nociceptive Senses
4.3.1. Nociceptors
4.3.1.1. Mechanical/thermal
4.3.1.1.1. For sharp, pricking pain
4.3.1.2. Polymodal/chemical
4.3.1.2.1. For high-intensity mechanical, chemical or thermal stimuli
4.3.2. Pain
4.3.2.1. Pathways
4.3.2.1.1. Neospinothalamic Tract
4.3.2.1.2. Paleospinothalamic Tract
4.3.2.2. Suppression
4.3.2.2.1. Analgesia System
4.3.2.2.2. Gate Control Theory
4.3.2.3. Types
4.3.2.3.1. Visceral Pain
4.3.2.3.2. Somatic Pain
4.3.2.3.3. Acute Pain
4.3.2.3.4. Chronic Pain
4.3.2.3.5. Fast Pain
4.3.2.3.6. Slow Pain
4.4. Exteroceptive
4.4.1. For the external world
4.5. Proprioceptive
4.5.1. For body and limb position
4.6. Enteroceptive
4.6.1. For the internal state of the body
5. SENSORY PATHWAYS
5.1. Ascending Pathways
5.1.1. Dorsal Column-Medial Lemniscal Pathway
5.1.1.1. For fine touch and pressure, phasic sensations, proprioception; groups I and II nerve fibers
5.1.1.2. 1st order neurons: Dorsal root ganglion
5.1.1.3. 2nd order neurons: Nucleus gracilis (lower body)/Nucleus cuneatus (upper body)
5.1.1.4. 3rd order neurons: ventroposterolateral pathway of thalamus
5.1.1.5. 4th order neurons: Postcentral gyrus/primary somatosensory cortex
5.1.2. Anterolateral Spinothalamic Tract
5.1.2.1. For pain, thermal sensations, crude touch and pressure, tickle and itch, sexual sensations; groups III and IV nerve fibers
5.1.2.2. 1st order neurons: Dorsal root ganglion
5.1.2.3. 2nd order neurons: Dorsal horn laminae
5.1.2.4. 3rd order neurons: ventroposterolateral pathway of thalamus
5.1.2.5. 4th order neurons: Postcentral gyrus/primary somatosensory cortex