lecture_notes_10_(ta)

lecture_notes_10_(ta) - Sensory Systems II Receptor...

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Sensory Systems II – Receptor Physiology Receptor Physiology - Stimulation of a receptor cell causes a change in the permeability of the cell's plasma membrane to a particular ion(s), which leads to either depolarization or hyperpolarization at the site of stimulation. This change in membrane potential is called the receptor potential , and it can have one or more actions (Figure 6-4) . It can directly influence the release of neurotransmitter by the receptor cell, or cause the receptor axon to fire action potentials by depolarizing it above threshold. The magnitude of the receptor potential is influenced by the intensity of the stimulus. Each type of receptor cell is sensitive to a particular category of stimulus energy, which defines its modality specificity (Figure 6-6) . The location on the receptor surface within which a stimulus (of the appropriate modality) can influence the activity of a sensory neuron is referred to as the receptive field of that neuron (Figure 6-7,6-8) . Within each sensory modality, such as vision, hearing and somatosensation, receptor surfaces are organized into a map of the sensory modality ( FOR EXAMPLE , VISUOTOPIC , TONITOPIC , OR SOMATOTOPIC ) . Sensory acuity is determined by the density of receptors in the sensory map, the size of the receptive fields, and by a process that occurs in the central nervous system called lateral inhibition (Figure 6-8) . ( THE RECEPTOR POTENTIAL IS THE CHANGE IN THE SENSORY RECEPTOR S MEMBRANE VOLTAGE FOLLOWING A STIMULUS . M OST SENSORY RECEPTORS ( PHOTORECEPTORS AND HAIR CELLS , FOR EXAMPLE ) RESPOND TO A STIMULUS WITH A GRADED RECEPTOR POTENTIAL . T HIS MEANS THEY DO NOT FIRE AN ACTION POTENTIAL . T HE GRADED POTENTIAL CAN CAUSE THE RELEASE OF NEUROTRANSMITTER , HOWEVER . O THER RECEPTORS FIRE ACTION POTENTIALS ( SO THEY MUST POSSESS VOLTAGE GATED PROTEIN ION CHANNELS IN THEIR MEMBRANES , YEAH ?) ) (‘ MODALITY SPECIFICITY JUST MEANS THAT A GIVEN RECEPTOR ONLY RESPONDS TO ONE TYPE OF STIMULUS ENERGY . W E THEREFORE WOULDN T EXPECT AN AUDITORY HAIR CELL TO RESPOND TO LIGHT , OR A PHOTORECEPTOR TO RESPOND TO SOUND ) (‘L ATERAL INHIBITION IS AN INTERESTING , AND ALTHOUGH SIMPLE , PROFOUNDLY USEFUL COMPUTATION PERFORMED EARLY IN THE PROCESSING OF MANY SENSORY STIMULI . T HE GIST IS THAT A GIVEN RECEPTOR S RESPONSE IS MODULATED BY THAT
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This note was uploaded on 05/02/2008 for the course NPB 101 taught by Professor Fuller,charles/goldberg,jack during the Winter '08 term at UC Davis.

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lecture_notes_10_(ta) - Sensory Systems II Receptor...

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