2. Transduction a process by which an environmental stimulus becomes encoded as a sequence of nerve impulses in an afferent nerve fiber Transduce sensory energy into neural (bioelectrical) energy Receptor potentials: Changes in the transmembrane potential of a receptor caused by the stimulus Generator Potential: A receptor potentia that is strong enough(reaches threshold to generate an action potential The stronger the sitmulus above threshold) the more APs are fired over a given time period translated by the cns as a strong sensation
2. Transduction – A process by which an environmental stimulus becomes encoded as a sequence of nerve impulses in an afferent nerve fiber • Transduce sensory energy into neural (bioelectrical) energy – Receptor potentials: Changes in the transmembrane potential of a receptor caused by the stimulus. – Generator Potential: A receptor potential that is strong enough (reaches threshold) to generate an action potential • The stronger the sitmulus (above threshold) the more APs are fired over a given time period; • translated by the CNS as a strong sensation
Receptor potential and generator Potential Action potentials +30 三 0 30 Receptor potential E-60Threshold 与 90 Resting membrane potential 0102030406080100120140 Milliseconds
Receptor Potential and Generator Potential
3. Adaptation The sensory receptor adapt to any constant stimulus after a period of mulus Stimulus time Phasic receptors quickly adapt Most exteroceptors Tonic receptors adap p slowly or not at all potentials Most visceroceptors
3. Adaptation The sensory receptor adapt to any constant stimulus after a period of time Phasic receptors quickly adapt. Most exteroceptors Tonic receptors adapt slowly or not at all. Most visceroceptors
Phasic and Tonic Receptors Phasic Receptor alert us to changes in sensory stimuli Joint capsule receptors 250 Muscle spindle cease paying Hair receptor Pacinian corpuscle attention to constant 200 =o- stimuli 150 Tonic receptor useful in situations requiring maintained Seconds information about a stimulus
Phasic and Tonic Receptors • Phasic Receptor – alert us to changes in sensory stimuli – cease paying attention to constant stimuli • Tonic Receptor – useful in situations requiring maintained information about a stimulus
4. Encoding The quality of the stimulus is encoded in the frequency of the action potentials
4. Encoding • The quality of the stimulus is encoded in the frequency of the action potentials