BISC 307L 2nd Edition Lecture 10 Current Lecture Sound Localization How good is this mechanism In a carefully conducted trial where the only sound is coming from a specific sound source if you play a tone at varied locations in your azimuth plane of hearing you would be able to detect a 1 2 degree change in sound half of the time This corresponds to a very short difference in arrival time of the inputs about 1 microsecond for a 90 degree difference Are these axons perfectly symmetrical and precisely regulated No neither the conduction velocity path length nor trajectory of the inputs are standardized But due to synaptic plasticity during development the system learns this degree of precision and is self correcting for its own sloppiness Sound Localization in the Medial Superior Olive To the right is a model of a circuit in the MSO of a cat There are thousands of arrays of place encoding neurons see above and across the one dimension of the nucleus of this MSO these different arrays map out the frequencies of the sounds Each array is maximally sensitive to a particular frequency and they are systematically arranged such that with distance in this dimension it maps out along the log of this frequency There are not five neurons in each array like in the simplified schematic above but something like 10 000 Cat s can still move their ears The funnel shaped pin of the external ear can collect sound and amplify the intensity To tune in the most sensitive part of the ear because the ear is not perfectly symmetrical and some positions are better for hearing people adjust themselves to focus their attention on sound Owls have two ears but unlike most mammals the ears are not on the same plane they are displaced They are in front of the face under the eyes and are vertically displaced which gives them the ability to place sound in the vertical plane as well The Autonomic Nervous System General properties Provides critical homeostatic mechanisms Reflexes are mediated by local circuits in spinal cord and brainstem and don t involve the brain Reflexes like regulation of blood pressure and respiration rate are all mediated by the ANS For example sensors carrying information about blood pressure and distention in stretch sensitive nerves in aortic bodies would cause blood vessels to be dilated contraction strength to be weakened or beating to be slowed if blood pressure was too high The brain would not even be aware of these processes An effector and sensory system Effector system Efferent carrying commands away from CNS Commands are called effectors because they bring about an effect Ex motor commands Sensory system Afferent carrying towards CNS typically sensory information This has two subdivisions somatosensory which gives information about things like touch pressure and position of body parts and the visceral afferents that bring sensory information from the viscera organs in the body cavities information like blood pressure contents of the duodenum and any other information necessary to maintain homeostasis basically In the efferent part of the ANS there are 2 or 3 Divisions 1 Sympathetic 2 Parasympathetic 3 Enteric made up of sensory and effector nerves embedded in the walls of the digestive tract Most of the ANS is in the digestive tract Responses to Recovery from Emergencies The responses on the left are for the sympathetic nervous system prepare the body for fighting or fleeing Increased respiratory and heart rate oxygenation of blood and blood pressure and profusion of organs Vasodilation of limb muscles which would be needed to get more blood flow to the muscles to run or fight and blood vessels in the brain would dilate Vasoconstriction in visceral organs that are not necessary to deal with emergencies like intestines digestive organs the skin and reproductive organs Dilation of lung airway there are springy cartilage y rings around some parts of the small airways in the lungs In addition the elasticity of the lungs tends to pull things apart If you are not restricting the bronchiole muscles then the cartilaginous skeleton of the larger airways and the general pull of the surrounding lung tissue which will open up the airway and cause bronchodilation more air into lungs increased respiratory rate which will increase blood oxygenation Decrease in secretion of saliva is part of digestive shutdown Increase in general alertness goes along with increased blood flow to the brain Those are just some of the other responses Relaxation of the muscles in the iris so eyes open up to get more light When danger is passed we have rest and digest response on the right Parasympathetic activity is not just the cessation of sympathetic activity Digestive secretion returns to normal and alertness may either return to normal or even go down These shifting from one to the other is not one being active and the other not but is a balance between the two One doesn t have to shut off for the other to have an effect CNS Centers regulating the ANS These ANS reflexes are extremely important There are many things that can go wrong acid reflux high blood pressure asthma and other diseases conditions that involve malfunction at one or more of these systems Therefore drugs which target the autonomic synaptic transmission mechanisms by blocking receptors increasing and decreasing transmitter release affecting secondary messenger systems downstream from the transmitters are all heavily researched for therapeutic intervention There are small clusters of nerve cells and nuclei in the CNS that control the ANS These control centers are mostly in the brainstem at an important area called the hypothalamus which is jam packed with small nuclei that are not well defined in that organ is packed the control of a whole bunch of important things like eating water balance in the body thirst kidney function control of temperature all the appetitive behaviors things we have an appetite for food drinking sex It contains a shockingly small number of neurons only a few thousand are responsible for all these bodily functions The pons and medulla are also important parts of the brainstem a lot of these ANS control nuclei are located there as well So these centers all tend to be vital you can get derangement in behavior with damage to the hypothalamus for example And damage to cardiovascular or respiratory centers would be fatal Pre and Postganglionic Neurons Activity originates in the brainstem or hypothalamic nuclei as a result of