Lecture 10 Functional identification of neurons: afferent neurons, interneurons and efferent neurons Info into the CNS Info out of the CNS Long projections Homeostasis via negative feedback regulation Set of processes that maintain a stable extracellular fluid. It involves one or more organ systems Value is optimized for survival Change in a variable will trigger a response to oppose it Action potential frequency in afferent axons is directly correlated with the amplitude of receptor potential Perception The process by which receptor potentials and action potentials are interpreted by the CNS General principles of coding sensory information Stimulus modality Stimulus location Stimulus intensity Stimulus modality is determined by: The type of receptor activated The neural pathway involved in transmitting the info to the cortex Modality is determined by a unique pathway from the receptor to a specific region in the CNS. The labeled line General principles of coding sensory information Stimulus modality Stimulus location Stimulus intensity Stimulus location is determined by the site of the activated receptor field and the area in the somatosensory cortex Sharpening location with lateral inhibition Spatial resolution increases as the size of receptive field decreases Location is determined by a unique pathway from the receptor to a specific region in the CNS. The labeled line General principles of coding sensory information Stimulus modality Stimulus location Stimulus intensity Receptor density Action potential frequency depends on the amplitude of receptor potential Somatotopy Neighboring cells in the somatosensory cortex respond to neighboring areas in the periphery The amount of space allocated to a given body part depends on its importance to the organism Pain Pain is a highly subjective sensation Pain sensation can be divided into several quantities based on: site of origin and characteristic of pain Site of origin characteristics where Nociceptors - free nerve endings Nerve endings contain transient receptor potential (TRP) channels that transduce a variety of noxious (tissue-damaging) stimuli into receptor potentials There are 4 major types of nociceptors: Mechano nociceptors: Respond to mechanical stimulus such as pinching and cutting Thermal nociceptors: Respond to thermal stimulus (hot and cold) Chemical nociceptors: Respond to chemicals such as histamine, bradykanin, prostaglandins Polymodal nociceptors: Respond to high intensity mechanical/thermal/chemical stimuli Somatic superficial pain sensation Fast pain: Sharp and localized. Generated by mechanical, thermal or chemical nociceptors. Conducted by myelinated axons (A delta afferents) Delayed pain: Dull and poorly localized. Generated by polymodal nociceptors. Last longer and more unpleasant. Conducted by unmyelinated axons (C afferents) Nociceptors in internal organs Mechanical nociceptors in smooth muscles (viscera) Mechanical and polymodal nociceptors in the lungs Nociceptors in the heart muscle responding to lower levels of oxygen (angina pectoris) Pain sensation Fast and slow pain in response to damaged tissue Pain that is not directly related to damaged tissue Projected pain Referred pain Projected pain- generated without activating nociceptors Phantom pain: pain from a body part that is no longer there amputation Referred pain results from convergence of somatic and visceral nociceptive inputs onto same neurons in the CNS Neural pathways modulating pain sensation CNS endorphins Spinal cord codeine endorphins Pain and stress are the most common factors leading to the release of endorphins. Secretion of endorphins causes feelings of euphoria, modulation of appetite, release of sex hormones ?Endorphins have been suggested as modulators of the so-called "runner's high" that athletes achieve with prolonged exercise.?
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