Psych 210 Review for Exam Number 2 Main Types of Receptors Merkel s disc touch Meissner s corpuscle touch Pacinian corpuscle vibration Ruffini s ending stretch Free nerve ending pain temperature Adaptation and Receptors Tonic receptors little or no decrease in the frequency of action potentials as stimulation is maintained Phasic receptors display adaptation rapidly decreasing the frequency of action potentials when the stimulus is maintained Levels of Sensory Processing Spinal cord Brainstem Midbrain Thalamus Primary sensory cortical areas Nonprimary sensory cortical areas True for all sensory systems except for smell Receptor Fields in Cerebral Cortex Primary sensory cortex for a given sensory modality ex vision somatosensory etc the region of cortex that receives most of the info about that modality from the thalamus Secondary sensory cortex nonprimary sensory cortex the cortical regions receiving direct projections from primary sensory cortex for that modality Information is sent back and forth between these cortexes through subcortical loops Somatosensory Cortex Primary somatosensory cortex S1 receives touch information from opposite side of the body Secondary somatosensory cortex S2 maps both sides of the body in registered overlay The more sensitive the organ is to touch the larger the portion of the somatosensory cortex is devoted to respond to it Attention Some visual cells also respond to auditory or touch stimuli association areas Polymodal cells several sensory modalities Frontal eye field attentive visual exploration of space Cingulate gyrus cortex motivational aspects of attention Posterior parietal lobe responsive in expecting the appearance of a stimulus auditory or visual Lesions in this region lead to inattention on the opposite side Dorsal Column System A somatosensory system that delivers most touch stimuli via the dorsal columns of spinal white matter to the brain dorsal column nuclei in the medulla Dermatomes Strip of skin innervated by a particular spinal nerve Based on quadrupedal posture Cervical face arms and hands Thoracic chest abs Lumbar lower back top of legs top of feet Sacral butt back of legs bottom of feet Plasticity in Cortical Maps Cortical maps change with experience Expanded cortical representations for areas that are stimulated more often Changes may arise from production of new synapses and dendrites or loss of others Nociceptors Nociceptor a receptor that responds to stimuli that produce tissue damage or pose the threat of damage sense pain Free nerve ending axon that ends in the skin w o any specialized cell associated with it and that detects pain and or changes in temperature Pain Temperature Receptors TRPV1 receptor that binds capsaicin to transmit burning sensation from chili peppers normally detects sudden increase in temperature TRPV2 detects even higher temps than TRPV1 doesn t respond to capsaicin and are found on larger nerve fibers A fiber large myelinated axon that transmits pain info very quickly and adapts quickly TRPV2 C fiber small unmyelinated axon that conducts pain info slowly and adapts slowly TRPV1 CMR1 opens an ion channel in response to a mild temperature drop exposure to menthol found on C fibers GRP stimulate neurons in dorsal horn to provide sensation of itch Na channel relates to pain CNS Pathways and Pain Cingulate cortex located in medial cerebral cortex activated when experiencing pain Neuropathic pain pain caused by damage to peripheral nerves difficult to treat EX phantom limb pain Glutamate most common excitatory transmitter Anterolateral spinothalamic system system that carries most of the pain info from body to brain Pain info crosses midline in spinal cord before ascending to the brain sensory info from one side of the body ends up in the opposite side of the brain Hearing Ear and its Parts Inner ear contains cochlea and vestibular apparatus External ear pinna the part of the ear that we readily see including the ear canal Middle ear cavity between tympanic membrane and cochlea Ossicles 3 small bones incus malleus stapes that transmit sound across middle ear from tympanic membrane to the oval window Tympanic membrane malleus incus stapes oval window External Ear Pinna modifies character of sound that reaches middle ear Helps identify the direction and distance of the source of a sound Captures focuses and filters sound Middle Ear Tympanic membrane also called eardrum Ossicles focus the pressures from the tympanic membrane onto the smaller oval window amplify sound pressure to produce movement in fluid of inner ear Two muscles that protect inner ear stiffen the linkages of middle ear bones reducing effectiveness of sounds help us ignore self made sounds Tensor tympani attached to malleus Stapedius attached to stapes Inner Ear Cochlea coiled fluid filled structure that is embedded in the temporal bone of the skull The cochlea is a coil of three parallel canals all filled with non compressible fluid Scala vestibuli vestibular canal Scala media middle canal Scala tympani tympanic canal Round window separates cochlea scala tympani from middle ear Organ of Corti components that convert sounds into neural activity Hair cells stereocilia Supporting cells Terminations of auditory fibers Base of organ of Corti basilar membrane separates scala tympani from scala media and vibrates in response to sound Different areas of basilar membrane are affected by different frequencies of sound High frequency base of basilar membrane Low frequency apex of basilar membrane Auditory System Pathways Input from auditory nerve is distributed to both sides of the brain dorsal and ventral cochlear nuclei Auditory pathways display tonotopic organization Neurons are arranged as an orderly map of stimulus frequency with cells responsive to high frequencies located at a distance from those responsive to low frequencies Theories of Discriminating Pitch Place theory pitch is encoded in the physical location of activated receptors in basilar membrane Activation near base high frequencies treble Activation near apex low frequencies bass Volley theory frequency of auditory stimuli is directly encoded in firing pattern of auditory neurons Contemporary view incorporates both perspectives Deafness Conduction deafness disorders of outer or middle ear keep vibrations from reaching cochlea doesn t usually involve nervous system Sensorineural deafness auditory nerve fibers are unable to become excited in a normal manner usually permanent