3/12/15 – Lecture 16 – The Auditory and Taste/Smell Sensory Systems- Goal: to find out how sound and chemical information are sensed and processed in the brain- The Auditory Systemo (chart from power point on properties of sound waves)o Anatomy of the Ear Sound waves travel into the ear and into the ear canal -> vibrates the ear drum -> causes the 3 bones (hammer, anvil, and stirrup) to vibrate -> causes vibrations in the cochlea -> hair cells in the cochlea bend and move with the fluid- Hair Cells normally release neurotransmitter and produce action potentials on sensory neurons they synapse too Motor gated K+ Ion channels (bending one way opens the K+ channels, bending the other way closes the K+ channels) Increases then decreases the release of neurotransmitters and so the action potential firing rate of the sensory neuron is also affected- The pattern of neuronal firing that tells the nervous system how LOUD and what PITCH the noise haso The bending of hair cells one way opens K+ channels on the hair cells Opens K+ channels and depolarizes the hair cells (IN THESE CELLS, the K+ concentration is higher outside of the cell!!)o Depolarization of hair cells opens voltage-gated Ca2+ channels and lets them INTO THE CELL Causes more neurotransmitters to be released Rate of the action potentials increases- Hearing Volume and Pitcho Volume: more action potentials or more neurons with action potentials 1 – a greater number of action potentials, the hair cells bending very far back and forth 2 – a greater number of neurons producing action potentialso Pitch: a more rapid cycle of action potentials- Pathways to the Auditory Cortexo Sensory neurons in the cochlea (motor sensory) send messages down axons to neurons in nuclei in the brainstem (messages from the left ear go to the right brain and vise versa) Brainstem neurons synapse with neurons in the mid brain- Neurons in the mid brain sends the messages to the neurons in the thalamuso Thalamic neurons send messages to the auditory cortex in the temporal lobeo Temporal Lobe processes pitch, loudness, location, and patterns of sound Also receives input from other sensory cortical areas, memory areas, and frontal cortex that helps us identify sources of sounds Lateralization of sound: speech and language are processed in the left temporal lobe and music is processed in the right temporal lobe - The Chemical Senses (Taste and Smell)o Gustation/ Taste Chemicals that are able to dissolve in the saliva get to reach the taste receptors in the taste buds (mainly found in the tongue)- Chemicals bind to the receptors or enter a channel on the taste bud receptor cellso Binding to receptors or movement through channel opens Na+ channels or closes K+ channels The opening of Na+ channels or closing of K+ channels depolarizes receptor cells- Depolarization results in the release of neurotransmitter onto sensory neurons- Neurotransmitter release induces action potentials on sensory neurons What are the 5 different tastes?- Sour, bitter, sweet, salty, and umami (savory like miso soup and Asian foods)o Sweet – surface receptors bind to glucose and similar sugarso Salty – ion channel lets Na+ enter the cellso Sour – ion channels lets H+ ions into cell (acidic foods have a lot of H+ ions)o Bitter – binds to a wide range of aromatic compounds (poison detector)o Umami – binds to amino acid of glutamate (protein and savory tastes) Spicy is NOT a taste area but rather a temperature sensation Fat? – may be a 6th taste, may bind to fatty acids (mouth feel for sure, but is it a taste?) Metal? Taste sensation? Pathways to Gustatory Cortex- Neurons from taste buds send axons via the cranial nerves to the brain stemo Brainstem neurons send messages directly to the amygdala and hypothalamus that provide direct emotional and memory connections Process the quality of the food quickly so that we can keep functioningo Neurons also send messages to the thalamus which then project to the primary gustatory cortex, the insular cortex located between the frontal and temporal lobes Giving reason to the reason for us eating or not eating something What are some factors influencing taste- Smell (the other senses to create flavor), texture, sight, expectations/memories/ emotionso Emotional State – when we’re sad or anxious, food tastes less good, that’s why we look for comfort foodso Past experiences – foods that have sickened us before taste less good, new or strange foods taste less good than familiar oneso Genetics – some people have certain taste proclivities and aversions, especially for bitter tasteso Other sensory inputs – smell, texture, color (flavor vs. taste and OFC) OFC orbital frontal cortex combines all of them to create the experience Ageusia – the loss of the sense of taste- Causes – genetics, some medications, endocrine diseases, neurodegenerative diseases, damage to lingual nerve or taste buds, strokes or tumors that affect the cortical taste center- Outcomes – lose their appetite, loss of the enjoyment of eating, depression- Olfaction/ Smello Chemical odorants enter the nasal cavity and dissolves in the olfactory mucosa (mucus – generally thin, gets thinker when sick and that’s why it’s so hard to smell) Odorants bind to the receptors on the surface of the receptor cells- Binding to receptors causes opening of Ca2+ channels and depolarizationo Depolarization produces action potentials on sensory neurons There are about 400 different types of olfactory receptors found ondifferent types of olfactory receptor neurons in the human nose that probably responds to MANY different smellso Pathways to the olfactory cortex Olfactory receptor cells send messages to the olfactory bulb and synapse on mitral cells- Mitral cells send messages to several areas of the braino Amygdala, the thalamus and the hypothalamus, and even to the hippocampus and the primary olfactory cortex (piriform cortex)o Neurons in these areas are involved in emotional behaviors, memories, eating and scent identification Mitral cells synapse directly onto amygdala and to the hippocampus via piriform neurons (WITHOUT going through the thalamus) which may be why it has the strongest effect on memoryand emotiono What are some Behavioral Aspects of Olfaction (what is it important for?) Eating behaviors – good or bad smelling food may encourage or discourage us from eating- 80% of