Chapter 17- Sensory Coding

9 classes of receptor cells
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9 classes of receptor cells
1. Vision - mediated by receptors in the eye
2. Smell - mediated by receptors in the nose
3. Taste - mediated by receptors in the mouth
4. Touch - mediated by receptors in the skin
5. Thermal Senses - mediated by receptors throughout the body
6. Pain - mediated by receptors throughout the body
7. Hearing - mediated by receptors throughout the body
8. Balance - mediated by receptors in the inner ear
9. Proprioception - mediated by receptors throughout the body
Visual System
Vision
Stimulus: light (photons)
Class: photoreceptor
Receptor cells: rods and cones
Auditory System
Hearing
Stimulus: sound (pressure waves)
Class: mechanoreceptor
Cells: hair cells in cochlea
Vestibular System
Head Motion
Stimulus: gravity, acceleration, and head motion
Class: mechanoreceptor
Cells: hair cells in vestibular labyrinths
Somatosensory System- Touch
Stimulus: skin deformation and motion
Class: mechanoreceptor
Cells: skin
Somatosensory System- Proprioception
Stimulus: muscle length, muscle force, and joint angle
Class: mechanoreceptor
Cells: muscle spindles, Golgi tendon organs, and joint capsules
Somatosensory System- Pain
Stimulus: noxious stimuli (thermal, mechanical, and chemical stimuli)
Class: thermoreceptor, mechanoreceptor, and chemoreceptor
Cells: all tissue except central nervous system
Somatosensory System- Itch
Stimulus: histamine, pruritogens
Class: chemoreceptor
Cells: skin
Somatosensory System- Visceral (Not Pain)
Stimulus: wide range...(thermal, mechanical, and chemical stimuli)
Class: thermoreceptor, mechanoreceptor, and chemoreceptor
Cells: cardiovascular, gastrointestinal tract, urinary bladder, and lungs
Gustatory System
Taste
Stimulus: chemicals
Class: chemoreceptor
Cells: taste buds, intraoral thermal, and chemoreceptors
OIfactory SystemSmell Stimulus: odorants Class: chemoreceptor Cells: olfactory sensory neuronsTypical Neural Circuit for sensory processingSensory information is transmitted in the central nervous system through hierarchical processing networks. Neural signaling initiated by a stimulus to the skin reaches a large group of postsynaptic neurons in relay nuclei in the brain stem and thalamus and is most strong in neurons in the center of the array of postsynaptic cells (red neuron).Spatial distribution of excitation and inhibition among relay neuronsInhibition (gray areas) mediated by local interneurons (gray) confines excitation (orange area) to the central zone in the array of relay neurons where stimulation is strongest. This pattern of inhibition within the relay nucleus enhances the contrast between strongly and weakly stimulated relay neurons.Types of inhibition in relay nucleiInhibitory interneurons in a relay nucleus are activated by three distinct excitatory pathways. 1. Feed-forward inhibition is initiated by the afferent fibers of sensory neurons that terminate on the inhibitory interneurons. 2. Feedback inhibition is initiated by recurrent collateral axons of neurons in the output pathway from the nucleus that project back to interneurons in the source nucleus. The interneurons in turn inhibit nearby output neurons, creating sharply defined zones of excitatory and inhibitory activity in the relay nucleus. In this way, the most active relay neurons reduce the output of adjacent, less active neurons, thus ensuring that only one of two or more active neurons will send out signals. 3. Descending inhibition is initiated by neurons in other brain regions such as the cerebral cortex. The descending commands allow cortical neurons to control the afferent relay of sensory information, providingDescribe the flow of visual stimuli processed by serial and parallel networks in the cerebral cortexSpatial pattern of the letters is sent to the cerebral cortex through successive synaptic links comprising photoreceptors, bipolar cells of the retina, retinal ganglion cells, cells in the lateral geniculate nucleus (LGN) of the thalamus, and neurons of the primary visual cortex (V1). Within the cortex, there is a gradual divergence to successive processing areas called ventral and dorsal streams that are neither wholly serial nor parallel. The ventral stream in the temporal lobe (red shading) analyzes and encodes information about the form and structure of the visual scene and objects within it, delivering this information to the parahippocampal cortex (not shown) and prefrontal cortex (PF). The dorsal stream in the parietal lobe (blue shading) analyzes and represents information about stimulus location and motion and delivers this information to motor areas of the frontal cortex that control movements of the eyes, hand, and arm. The anatomical connections between these areas are reciprocal, involving both feedforward and feedback circuits. The zone of overlap (purple) shows that both pathways originate from the same source in V1. Connections to subcortical structures in the thalamus and midbrain are defined in Figure 21-7B. (Abbreviations: V1, V2, V3, and V4, occipital visual areas; MT, middle temporal; MST, medial superior temporal; AIP, VIP, LIP, and MIP, anterior, ventral, lateral, and medial intraparietal; TEO, temporal-occipital; IT, inferior temporal; PMd and PMv, dorsal and ventral premotor; FEF, frontal eye fields.)