Topic 7 - Sensory Systems (1).pptx

Topic 5 Sensory Systems • Sensory Transduction • Functional Processing in Sensory Pathways • The Pain System • Pain Control Methods Quiz 1 Answers Quiz 2 Answers Quiz 3 Answers Sensing your environment Sensory transduction Conversion of energy from an environmental stimulus into a change in...

Topic 5 Sensory Systems • Sensory Transduction • Functional Processing in Sensory Pathways • The Pain System • Pain Control Methods Quiz 1 Answers Quiz 2 Answers Quiz 3 Answers Sensing your environment Sensory transduction Conversion of energy from an environmental stimulus into a change in membrane potential Sensory receptor organs are organs specialized to detect a certain stimulus. Sensing your envionment Animals evolve sensory organs that are specialized to help them survive • Example: eyes Sensing your environment Horizontal pupils allow animal to enhance light received from front and rear • Animals with landbased predators – especially grazers • Eyes on side of head Sensing your environment Vertical slit pupils help animals to accurately judge distance without having to move their head • Small ambush predators that hunt on ground • Eyes on front of head Sensing your environment Circular pupils allow for high detail, precise vision – handy for tracking and following moving prey • Foragers, pack hunters, pursuit predators • eyes on front of head Sensory Transduction Receptor cells – specialized cells that perform sensory transduction Sensory Transduction Labeled lines – senses kept distinct because their APs travel along separate nerve tracts. Our example: the somatosensory system Somatosensory system (“body sense”) - neural processes responsible conscious perception of: • • • • • • • Touch Pressure Pain Temperature Position Movement Vibration Organizing sensory information Labeled lines tell the somatosensory system: • where a sensation is occurring. • the specific type of touch being experienced Sensory transduction in the somatosensory system Receptor potential – local, graded change in Vm that is proportional in size to the stimulus that caused it. Receptor potentials = EPSPs caused by a sensory stimulus Sensory transduction in the somatosensory system Pacinian corpuscle - skin receptor cell that responds to vibration and pressure. Sensory transduction in the somatosensory system 1. Stimulus stretches corpuscle’s membrane 2. Opening of stretchsensitive Na+ channels (mechanoreceptors) 3. Na+ entry  graded receptor potential 4. If receptor potential reaches threshold  AP Six aspects of sensory processing • Frequency Coding • Adaptation • Suppression • Pathways • Receptive fields • Attention Aspects of sensory processing A single neuron can convey stimulus intensity by changing the frequency of its action potentials. Aspects of sensory processing Multiple neurons can act in parallel; as the stimulus strengthens, more neurons are recruited. Range fractionation takes place when different cells have different thresholds for firing, over a range of stimulus intensities. Aspects of sensory processing Two strategies used by sensory systems to detect varied stimuli: 1. Use multiple versions of same receptor cell • Visual system: Cones (S-,M-,L-) • Auditory system: hair cells arranged in cochlea according to frequency sensitivity Aspects of sensory processing Two strategies used by sensory systems to detect varied stimuli: 2. Use different receptor cells to respond to different types of stimuli • Pacinian corpuscle – vibration and pressure • Meissner’s corpuscles - changes in touch stimuli • Merkel’s discs - edges and isolated points • Ruffini corpuscles - skin stretch • Free nerve endings - pain, heat, itch, and cold. Aspects of sensory processing Senses prioritize changes in information about the environment Sensory adaptation— progressive decrease in a receptor’s response to sustained stimulation • Phasic receptors display adaptation. • Tonic receptors show little or no adaptation. Aspects of sensory processing Suppress a constant stimulus by: • Removing stimulus • Top-down processing • Higher brain centers suppress some sensory inputs, amplify others Aspects of sensory processing Each sense has an associated pathway containing: 1. a specialized thalamic nucleus 2. primary sensory cortex, 3. nonprimary/ secondary sensory cortex The somatosensory pathway Sensory receptor cells in skin Dorsal column system Ventral posterior thalamus (VPL) Medial lemniscus Primary somatosensory cortex (S1) The somatosensory pathway Primary somatosensory cortex (S1) is located in the postcentral gyrus The somatosensory pathway Some body parts (hands, face) have higher density of receptors than others Sensory homunculus – representation of body surface with each area drawn in proportion to the size of its representation in S1 Sensory homunculi in other animals Images courtesy of Alex Cates The somatosensory pathway S1 projects largely to secondary somatosensory cortex (S2)  more advanced processing Aspects of sensory processing Receptive field - area in which the presence of a stimulus will alter a receptor cell’s firing rate. Receptive fields differ in size, shape, and response to types of stimulation. Aspects of sensory processing Attention - process by which we select or focus on specific stimuli for enhanced processing and analysis. Two brain regions important in attention ( activated when expecting a stimulus): • Posterior parietal lobe • Cingulate cortex Aspects of sensory processing Association areas process inputs from different modalities. • Polymodal neurons process several different sensory modalities at the same time. Aspects of sensory processing Synesthesia is a condition in which a stimulus in one modality also creates a sensation in another. • May perceive colors when looking at letters, or a taste when hearing a tone. Pain Pain—discomfort associated with tissue damage • Causes us to withdraw from its source, to engage in recuperative actions, and to warn others. Pain Nociceptors – pain receptors found on free nerve endings in the skin Pain Some nociceptors contain TRPV1 channels • cation channels • open at high, dangerous temperatures • also bind capsaicin – “hot” chemical in chili peppers Found on nociceptor sensory neurons with thin, unmyelinated C fibers • Slow-traveling, long-lasting Pain TRPM3 channels: • detect even higher temperatures than TRPV1 • do not bind to capsaicin Found on nociceptor sensory neurons with large, myelinated A delta (Aδ) fibers Pain Fast pain (first pain) – sharp, quick pain that triggers protective reflexes • Carried by Aδ fibers Slow pain (second pain) – slow, throbbing, longlasting pain that encourages protecting site of damage • Carried by C fibers The pain pathway Pain signals reach brain via anterolateral or spinothalamic pathway (different from touch/vibration sense) Receptor  thalamus  S1 The pain pathway Key structure in the natural pain control system: periaqueductal gray (PAG) PAG neurons project onto inhibitory interneurons in spinal cord Pain control PAG activated by strong pain signals  releases endogenous opioids (like endorphins) into spinal cord Opioid actions in spinal cord inhibit ascending pain signals – act as pain “gates” (gate control theory) Opioids Opioid drugs are extremely effective analgesics! Exogenous opioids: • • • • • Morphine Codeine Heroin Fentanyl Many, many more! Opium poppy with opium sap Opioid painkiller Opium poppy after flowering Pain control Opioid drugs bind to opioid receptors in the spinal cord, gate pain signals directly Epidural injections during childbirthing process place opioids and/or Na+ channel blocking anesthetics directly into the spinal cord to block pain signals at or below that level Pain control Opioids in reward system highly involved in generation of pleasurable sensation • Low dose = pain-killing effects • High dose = pleasureproducing Functional tolerance  steady need to increase dose for analgesic effects Psychogenic Pain Control Methods Methods used to control pain typically do so via either central modification of sensory information or gate control theory Type Mechanism Placebo May activate endorphin-mediated pain control system Hypnosis Alters brain’s perception of pain Stress Uses both opioid and non-opioid mechanisms Cognitive (learning, May activate endorphin-mediated pain control system coping strategies) Pharmacological Pain Control Methods Methods used to control pain typically do so via either central modification of sensory information or gate control theory Type Mechanism Opiates Bind to opioid receptors in periaqueductal gray and spinal cord Spinal block Blocks pain signals in spinal cord Anti-inflammatory drugs (NSAIDs) Block chemical inflammatory signals at the site of injury Cannabinoids Act in nociceptor endings, spinal cord, and brain Stimulation-based Pain Control Methods Methods used to control pain typically do so via either central modification of sensory information or gate control theory Type Mechanism TENS/mechanical On large fibers, blocks or alters pain signal to brain Acupuncture Activates endogenous opioids and/or placebo-like effect, possibly modulating effect on activity of peripheral pain pathways Central gray Electrically activates endorphin-mediated pain control systems, blocking pain signal in spinal cord Your action items (9/26) Exam 1 on Thursday No lab this week! (Get some rest and prepare) • For next week (Neuroplasticity week): • Read Doidge, Chapters 1 & 7 • Neuroplasticity group presents • For week of October 10: • Listen to Radiolab: Born This Way and complete PRA3 • Reward Processing group presents Coming Up: • Tuesday 10/3: T8: The Motor Hierarchy • Thursday 10/5: T9: Reproductive Behavior and Sexual Development