Sensory physiology Brain interprets what sensory receptors deliver
Sensory physiology Brain interprets what sensory receptors deliver to it Chemoreceptors- smell and taste, also blood chemistry Photoreceptors- rods and cones in retina Thermoreceptors- heat and cold Mechanoreceptors- touch and pressure; hearing (hair cells in inner ear)
Pain receptors (nocireceptors) harder to stimulate, thankfully Types of pain receptors proprioreceptors- body position and movement cutaneous receptors (aka generalized) touch, pressure, pain, heat, cold special senses- sight, hearing, taste, smell
Sensory adaptation Phasic receptors- slow down after initial stimulus adaptation- e. g. , odor, touch, temperature fast-adapting Tonic receptors- fire at constant rate slow-adapting Receptors deliver specific stimulus; brain filters out a lot of the stimuli Produce action potential in response to stimulus
Cutaneous sensations Different neurons perceive different sensations Free nerve endings- light touch, temperature, pain Merkel’s discs-sustained touch and pressure (superficial) Ruffini’s corpuscles sustained pressure (deep) Meissner’s corpuscles- texture, slow vibration Pacinian corpuscles- deep pressure, fast vibration
Cold receptors are more numerous and closer to surface than heat receptors Cold receptors are inhibited by warming Sharp pain- conducted by myelinated axons dull pain by unmyelinated axons Capsaicin receptor- ion channel; produces sensation of pain in response to high heat
Neural pathways to postcentral gyrus Ascending fibers in dorsal columns of spinal cord Synapse in medulla oblongata Ascends to thalamus Sensory neurons project to postcentral gyrus
Receptive fields in skin large if receptors are few, small if receptors are dense measured by two-point touch threshold Lateral inhibition- sensory neurons most strongly affected by a stimulus inhibit others in nearby receptive fields
Taste and smell (chemical receptors) tend to influence each other Taste (gustation) Taste buds- epithelial cells that act like neurotransmitters Innervated by cranial nerves
Four major sensations of taste Sweet- G-protein activates second messenger system Bitter- also G-protein activated specific receptor Sour- proton channel (acids taste sour) Salty- sodium channels Tastes seem to be enhanced in different parts of the tongue
Smell (olfaction) receptor cells in olfactory epithelium sense of smell transmitted directly to cerebral cortex (all others go through thalamus) receptors in medial temporal lobes and in limbic system (emotional response to odors) Molecular basis for smell is complexhumans can distinguish up to 10, 000 different odors
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