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Sensory Receptors (Beginning of Neural Arc )

Sensory Receptors (Beginning of Neural Arc ). many different types free nerve [cell] endings e.g., in skin complex multicellular structures e.g., retina of the eye. The Neural Arc. Transduction. Physical stimuli are detected and communicated via nerve signals;

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Sensory Receptors (Beginning of Neural Arc )

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  1. Sensory Receptors (Beginning of Neural Arc) • many different types • free nerve [cell] endings • e.g., in skin • complex multicellular structures • e.g., retina of the eye The Neural Arc

  2. Transduction • Physical stimuli are detected and communicated via nerve signals; the physical stimulus is converted (transduced) into a nerve signal. • Types of sensory receptors • mechanoreceptors • thermoreceptors • chemoreceptors • nociceptors • electromagnetic radiation receptors

  3. Generator Potential • graded potential produced by the physical stimulus (cf. EPSP, IPSP) • e.g., stretch receptor (a mechanoreceptor) stretch  activation of mechanically-gated channels  depolarization (graded)  action potential (“downstream”)

  4. Somatic Sensation • Modalities • proprioception: position and movement • position of joints / position of the body in space • movement of joints / movement of the body in space • “skin senses” • tactile sensations • touch • pressure / vibration • itch • tickle • temperature • pain

  5. Sensory Receptors of the Skin Fig. 6.1

  6. Lamellated (Pacinian) Corpuscle connective tissue capsule first node of Ranvier – action potentials start here nerve [cell] ending – generator potentials produced here Fig, 5-1 Ganong

  7. Frequency Modulation of Stimulus Strength Fig. 5-4 Ganong

  8. Adaptation • adaptation • decreasing response to a stimulus over time • time to adaptation • seconds to days • phasic receptors • adapt rapidly • give the CNS information about changes in stimulus strength • tonic receptors • adapt slowly (or not at all) • give the CNS information about stimulus strength • information about how things are

  9. Phasic Responses • especially important in producing and detecting movement • movement over rough terrain or up stairs • vision

  10. The spindle is tonic, giving the CNS information about muscle length. Adaptation • spindle - tonic receptor • pressure - mixed • phasic: vibration • tonic: pressure • touch - phasic • hairs - phasic The Pacinian Corpuscle (Pressure) is more phasic than tonic. The nerve ending itself gives a tonic response. However, the capsule changes shape over time, and transmits less pressure to the nerve ending. Fig. 5-3 Ganong

  11. Somatic Sensation Summary • Proprioception (Types I and II) • movement information: phasic • position information: tonic • Tactile Reception (Types II and III) • different sensations based on • different rates of adaptation • different sensitivities • mild stimulus: touch • strong stimulus: pressure • changing stimulus: vibration

  12. Somatic Sensation Summary • Thermoreception (Types III and IV) • cold • warm • Extreme heat and cold also stimulate pain receptors. • Pain reception • acute = type III • dull = type IV

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