Lesson 4 Somatosensory PDF

- Peripheral nervous system divided into Somatic nervous system and autonomic nervous system - Decussation = crossing - Transduction = converting a sensory stimulus into an electrical signal that is transmitted to the CNS - Transmission = conduction of a sensory impulse from PNS t...

- Peripheral nervous system divided into Somatic nervous system and autonomic nervous system - Decussation = crossing - Transduction = converting a sensory stimulus into an electrical signal that is transmitted to the CNS - Transmission = conduction of a sensory impulse from PNS to CNS - Types of receptors - Mechanoreceptor detect mechanical compression or stretching - Free nerve endings - Meissner's corpuscles - Tactile receptors - Raffini's endings = prolonged touch and pressure - Pascinian corpuscles = vibration and deep pressure - Thermoreceptor detect changes in temperature - Nociceptor detect tissue damage - Electromagnetic receptors - Chemoreceptors - Exteroreceptor = from surface of body (exterior) - Proprioceptor - Visceral from internal organs - Deep receptors are from deep tissue - All sensation involves activation of receptor activation of neurons impulse transmission to the CNS - How the brain differentiates certain stimuli - Differential sensitivity = different receptors are specifically designed for specific sensations - Labeled line principle = certain nerve fibers will only transmit certain sensations - Stimuli changes the electrical membrane potential (i.e. receptor potential) causing ions channels to open - Action potentials - All or none - The more the receptor potential rises above threshold, the greater the frequency - Very intense stimulation causes progressively less and less additional action potentials - Amplitude increases rapidly with increased stimulus strength but less rapidly at high stimulus strength - Pacinian corpuscle - Structurally has central nerve fiber extending through core surrounded by multiple concentric layers - How you can sense light and deep pressure with the same mechanoreceptor - Receptor adaptation = initial response is high but diminishes with continued/frequent stimulation - Different receptor adapt at different rates - Rapid receptors e.g. rate receptors, phasic receptors, hair receptors, Pacinian receptors - Slow receptors e.g. baroreceptors, chemoreceptors - Nerve fibers are categorized by size, function, and myelination - Nerve diameter range = 0.5-20 micrometers - Nerve conduction velocity = 0.5-120 m/s - General classification - Type A myelinated and large i.e. faster conduction - Type B myelinated and small. Found in pre-ganglionic (ANS) - Type C unmyelinated and small i.e. slower conduction - Sensory nerve classification (1-4) - 1-3 myelinated - 4 unmyelinated - Type 1 fibers = large, myelinated, and fast - Fibers from muscle spindles, Golgi tendon organs - Know nerve fiber classification chart - Differential blockade - Sympathetic fibers blocked first followed by sensory followed by motor - Sympathetic at highest level, sensory at middle level, motor at lowest level - It may take longer for motor neurons to be blocked i.e. motor blockade will take the longest to occur - Spatial summation = increasing signal strength is transmitted by using progressively greater numbers of fibers - Temporal summation = increasing signal is transmitted by increased frequency of nerve impulses in each fiber - Neuronal pools - Divergence - Convergence - Reciprocal inhibition - Incoming signal causes output excitatory signal and inhibitory signal in other direction - Characteristic for control of opposing muscle groups e.g. biceps flex and triceps relax - Signal prolongation - Afterdischarge = prolonged output discharge - Sensory pathways - Most sensory input enters spinal cord through the dorsal roots of spinal nerves - Sensory information travels to the brain via either the - Dorsal column medial leminiscal system -- ascend then cross at medulla - Anterolateral system -- cross then ascend - Anterior spinothalamic tract -- crude touch - Lateral spinothalamic tract -- pain and temperature - Know first, second, third and know where they cross over - Dorsal column medial leminiscal system - Sensory stimuli travel via type A-B or type C fibers - Sensations that require discrete localization - Anterolateral system - Sensations that do not require discrete localization e.g. temperature, crude touch, tickle, sexual sensations - Dermatome landmarks - Clavicles = C4 - Nipples = T4 - Xiphoid = T6 - Umbilicus = T10 - Tibia = L4-L5 - Perineum = S2-S5 - Peripheral nerve injuries - Pain - Acute pain is protective because it allows us to withdraw from painful stimuli - Pain receptors are free nerve endings - Pain is divided into 2 types = fast pain and slow pain - Fast pain = neospinothalamic tract via A-d fibers - Slow pain = paleospinothalamic tract via C fibers - Neospinothalamic tract - Glutamate is excitatory NT - Fast A-d fibers transmit mainly mechanical and acute thermal pain - Paleospinothalamic tract - Glutamate and substance P excitatory NT - Slow C fibers - Endorphins and enkaphalins - Eye anatomy - Sclera - Retina - Cornea - Iris - Lens - Glaucoma = increase in intraocular pressure - Retrobulbar block - Complication = retrobulbar apnea syndrome - Agents that increase IOP = succinylcholine, ketamine, intubation - Agents that decrease IOP = inhalation anesthetics, propofol, opioids, benzodiazepines - N2O should not be used in eye surgery - 5 and dime/ oculocardiac nerve reflex - Common in pediatrics receiving striabmus repair - Interventions = treat symptoms, atropine, deepen anesthetic - Visual evoked potentials - Corneal abrasion - Hearing and balance - External and middle ears are only involved in hearing - Inner ear is involved in hearing and balance - Gustation - Function of taste buds - 5 primary taste sensations - Smell