TAILIEUCHUNG - Lecture Biology 25 (Human Biology): Chapter 14 - Prof. Gonsalves

Chapter 14 provides knowledge of senses. This chapter includes contents: Sensory receptors and sensations, proprioceptors and cutaneous receptors, chemical senses, sense of vision, sense of hearing, sense of equilibrium. | Chapter 14 Biology 25: Human Biology Prof. Gonsalves Los Angeles City College Based on Mader’s Human Biology,7th edition and Fox’s 8th ed Powerpoints Sensory Receptors Perceptions of world are created by the brain from AP sent from sensory receptors. Sensory receptors respond to a particular modality of environmental stimulus. Receptors transduce (change) different forms of sensation to nerve impulses. Structural Categories of Sensory Receptors Free: Pain, temperature. Encapsulated: Pressure. Meissner’s corpuscles: Touch. Rods and cones: Sight. Modified epithelial cells: Taste. Functional Categories of Sensory Receptors Grouped according to type of stimulus energy they transduce. Chemoreceptors: Chemical stimuli in environment and blood (pH, C02). Photoreceptors: Rods and cones. Thermoreceptors: Temperature. Functional Categories of Sensory Receptors Mechanoreceptors: Touch and pressure. Nociceptors: Pain. Proprioceptors: Body position. Sensory Adaptation Tonic receptors: Produce constant rate of firing as long as stimulus is applied. Phasic receptors: Burst of activity but quickly reduce firing rate (adapt). Cutaneous Sensations Free nerve endings: Temperature: heat and cold. More receptors that respond to cold than warm. Pain: Receptors do not adapt or do slowly. Use substance P or glutamate as NT Ca++ and Na+ enter through channel, depolarizing the cell. Encapsulated nerve endings: Touch and pressure. Receptors adapt quickly. Neural Pathways Sensory information from proprioceptors and cutaneous receptors are carried by large, myelinated nerve fibers. Synapses in medulla. 2nd order neuron ascends medial lemniscus to thalamus. 3rd order neurons project to sensory cortex. Lateral spinothalamic tract: Heat, cold and pain. Anterior spinothalamic tract: Touch and pressure. Receptive Fields Area of skin whose stimulation results in changes in the firing rate of the neuron. Area of each receptor field varies inversely with the density of receptors in the region. Back .

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