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Senses

Senses. Sensory modalities in human. Sensory processing. Levels of organization uderlying sensory processing: Receptors Sensory circuits and pathways Sensory perception. Receptors. transduction of the sensory stimuli. impulse initiation. stimulus. Receptor potential.

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Senses

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  1. Senses

  2. Sensory modalities in human

  3. Sensory processing • Levels of organization uderlying sensory processing: • Receptors • Sensory circuits and pathways • Sensory perception

  4. Receptors transduction of the sensory stimuli impulse initiation stimulus

  5. Receptor potential Receptor potential in a muscle stretch receptor (mechanoreceptor). A. These receptors signal muscle length and the speed at which the muscle is stretched. The receptor consists of a bundle of specialized muscle fibers enclosed by a capsule. The sensory nerve endings respond to stretch of the muscle fibers. Mechanical deformation of the membrane opens the stretch-sensitive ion channels. The influx of Na+ and Ca2+ depolarizes the nerve ending, producing the receptor potential. B. Upper records: depolarizing receptor potentials recorded from the sensory axon (APs have been blocked with TTX) when the muscle spindle is stretched to different lengths. Lower records: amplitude and rate of stretch. The initial depolarization of the receptor in response to change in muscle length (dynamic response) is proportional to both the rate and amplitude of stretch. When stretch is maintained, the receptor potential decays to a lower value proportional only to the amount of stretch (static response). C. Patch clamp records of a single stretch-sensitive channel. As the pressure on the membrane is increased, the channel opens more often and remains in the open state for longer time intervals.

  6. Stimulus intensity Firing rate Stimulus encoding Intensity coding in skin touch receptors. Left: in slowly adapting mechanoreceptors the firing rate is higher at the beginning of skin contact than during steady pressure. Right: rapidly adapting mechanoreceptors respond only at the beginning and end of the stimulus, signaling the rate at which the stimulus is applied or removed. The receptor is silent when the indentation is maintained at a fixed amplitude. Receptor potential and impulse frequency exhibit close correlation.

  7. Hierarchical information processing • Basic rules: • Divergence • Converrgence • Parallel processing • Feedback

  8. Connections • Connection patterns between neurons: • Converrgence • Divergence • Serial processing • Parallel processing • Self-feedback • Excitatory positive feedback • Inhibitory positive feedback • Negative feedback

  9. Synaptic triad Synaptic triad: input elements, relay neurons, intrinsic neurons,

  10. Microcircuits Examples of synaptic triads in senosory systems. There are input elements (the receptors) and output neurons (A; ganglion cells, B: mitral cells). There are interneurons for straight-through transmission and there are interneurons for horizontal interactions. The horizontal connections are organized at two levels. In both cases there is provision for straight-through transfer of signals to the output neuron and local processing of signals through the interneurons.

  11. Limulus (skrzypłocz) Limulus - Atlantic horseshoe crab The blood of horseshoe crabs contains one type of blood cell, the amebocytes. These produce visible reaction when exposed to some bacteria. It is used to detect bacteria and fungi and to test for several bacterial diseases, e.g., by astronauts in the International Space Station. The blood of horseshoe crabs contains the copper-containing protein hemocyanin, which is dark blue when oxygenated.

  12. Lateral inhibition Limulus has been extensively used in research into the physiology of vision. The Nobel prize in Medicine was awarded in 1967 in part for research performed on the horseshoe eye. A.The compound eye of Limulus consists of some 800 receptor units, called ommatidia. Each ommatidium has 10-15 receptor cells (retinula) arranged in a circle around eccentric cell, which is the main output cell. Eccentric cells are connected by dendrodendritic synapses mediating lateral inhibitory interactions. B. Pattern of activity in population of of eccentric cells in response to light – dark edge stimulus. The enhancement of response on the light side of the edge and depression on the dark side are due to inhibitory interactions.

  13. Lateral inhibition • Surface of the Limulus eye with rectangular stimulus pattern. B. Recordings of spike frequency in ommatidia. Lower curve: responses to rectangular pattern, upper curve: responses to small spot of light. The differences between the two curves illustrate that lateral inhibition enhances the response on the light side of an edge and depresses the response on the dark side of an edge. Mutual inhibition plays a role in contrast enhancement and feature extraction.

  14. The Cafe Wall illusion

  15. The Cafe Wall illusion The original of the Café Wall, St Michael's Hill, Bristol.

  16. The Cafe Wall illusion The part of the line indicated by an violet circle is surrounded by a large white region. These areas will be dimmed in the retina. The part of the line indicated by a orange circle is surrounded by dark regions, and will be slightly brightened in the retina. The result is that each line acquires a faint diagonal striping, which develops into converging slopes. http://www.positscience.com/brain-resources/brain-teasers/cafe-wall-illusion

  17. Perception 1. Detection (receptor threshold, behavior threshold) P – pupil FP – fixation point M - monochromators S – shutter L - lamp Setup for measuring minimal energy to induce visual response. The eye at the pupil P fixates the red point FP and observes the test field formed by the lens FL and the diaphragm D. The light for this field comes from the lamp L through the neutral filter F and wedge W, through the double monochromator M1,M2 and is controlled by the shutter S. From: Selig Hecht, Simon Shaleri Maurice Henri Pirenne. Energy, Quanta and Vision. The Journal of General Physiology, Vol 25, 819-840 (1942) Conclusions: - Single photon is adequate for stimulating a single photoreceptor in human retina (it was known before). - Simultaneous activation of 7 (5 - 14) receptors is necessary to perceive that stimulation has occured.

  18. Perception 2. Magnitude estimation Weber – Fechner law p – perception k – constant to be determined experimentally S – stimulus S0- threshold stimulus Stevens’ power law a - exponent

  19. Weber – Fechner law vs. Stevens’ law

  20. Perception 3. Spatial discrimination Two – point discrimination in various body parts. The best discrimination occurs at the finger tips, lips and tongue.

  21. 4. Quality discrimination Perception Analytic Synthetic

  22. 5. Pattern recognition Perception Gestalt psychology is a theory of mind and brain. Its operational principle is that the brain is holistic, parallel, and analog, with self-organizing tendencies. The principle maintains that the human eye sees objects in their entirety before perceiving their individual parts, suggesting the whole is greater than the sum of its parts.

  23. The silence of the lambs - poster detail Salvador Dali In Voluptas Mors, 1951 Perception – dependence on past experience The silence of the lambs - poster

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