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neural integration.docx

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Biological Sciences
Kenneth Welch

Neural Integration : Sensory Pathways and the Somatic Nervous System An Overview of Sensory Pathways and the Somatic Nervous System Neural pathways • Afferent pathways • Sensory information coming from the sensory receptors through peripheral nerves to the spinal cord and on to the brain • Efferent pathways • Motor commands coming from the brain and spinal cord, through peripheral nerves to effecter organs Sensory Receptors and their Classification Sensory receptor • Specialized cell or cell process that monitors specific conditions • Arriving information is a sensation • Awareness of a sensation is a perception Senses • General senses • Pain • Temperature • Physical distortion • Chemical detection • Receptors for general senses scattered throughout the body • Special senses • Located in specific sense organs • Structurally complex Sensory receptors • Each receptor cell monitors a specific receptive field • Transduction • A large enough stimulus changes the receptor potential, reaching generator potential Receptors • Tonic receptors • Always active • Slow acting receptors • Phasic receptors • Provide information about the intensity and rate of change of a stimulus • Fast acting receptors • Adaptation • Reduction in sensitivity in the presence of a constant stimulus The general senses • Three types of nociceptor • Provide information on pain as related to extremes of temperature • Provide information on pain as related to extremes of mechanical damage • Provide information on pain as related to extremes of dissolved chemicals • Myelinated type A fibers carry fast pain • Slower type C fibers carry slow pain Thermoceptors and mechaniceptors • Found in the dermis • Mechaniceptors • Sensitive to distortion of their membrane • Tactile receptors (six types) • Baroreceptors • Proprioceptors (three groups) Chemoreceptors • Chemoreceptors • Carotid bodies • Aortic bodies Neural Integration I: Sensory Pathways and the Somatic Nervous System The Organization of Sensory Pathways First, second, and third order neurons • First order neurons • Sensory neurons that deliver sensory information to the CNS • Second order neurons • First order neurons synapse on these in the brain or spinal cord • Third order neurons • Found in the thalamus • Second order neurons synapse on these Somatic sensory pathways • Three major pathways carry sensory information • Posterior column pathway • Anterolateral pathway • Spinocerebellar pathway Posterior column pathway • Carries fine touch, pressure and proprioceptive sensations • Axons ascend within the fasciculus gracilis
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