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Neuroanatomy & Audition June 14, 2011 Zooming In Perspective What is a Neuron? http://www.nikonsmallworld.com/gallery/year/2005/37/true Neurons Neurons control brain function on a cellular level. There are 100 billion neurons in human brain! Neurons come in many shapes and sizes. Each neuron communicates with many others to coordinate various functions of the nervous system. Image courtesy of Dr. Joshua Sanes, Harvard University, 2005 “Typical” Neuron Soma (nucleus) Myelin Sheath Adapted from http://www.mhhe.com/socscience/intro/ibank/ibank/0002.jpg The Soma Cell body Contains A nucleus with genetic information Ribosomes for processing genetic information into proteins Endoplasmic reticulum for transport of materials Mitochondria for energy Several other important organelles http://faculty.washington.edu/chudler/cells.html The Axon Carries information AWAY from the Soma (Axons Away!) Typically only 1 Axon per Neuron Can be covered in a fatty conductive substance called Myelin Speeds the transfer of information http://faculty.washington.edu/chudler/cells.html Dendrites Bring information from other neurons to the soma Rough surface covered with spines Unmyelinated Most neurons have MANY dendrites with extensive branching http://www.usc.edu/programs/neuroscience/faculty/profile.php?fid=12 And Let’s Not Forget…Glia Glia are non-neuronal supporting cells in the brain Although there are many more glia than neurons in the brain, they cannot generate action potentials, and also don’t communicate with neurotransmitters. So what DO they do? Glial Types & Functions Astrocytes Microglia Create myelin for insulated axons Schwann Cells Digest parts of dead neurons Oligodendrocytes Clean up brain debris & “eat” dead neurons Bring nutrients to neurons Hold neurons in place Also create myelin for insulating axons Satellite Cells Provide structural support for neurons located in the periphery http://www.psych.ndsu.nodak.edu/mccourt/Psy460/Neurophysiology%20of%20vision/ Neuronal Modeling http://www.enchantedlearning.com/subjects/anatomy/brain/Neuron.shtml Brief Overview of Neuroanatomy Parietal Lobe Frontal Lobe Occipital Lobe Corpus Callosum Temporal Lobe Brain Stem Cerebellum Frontal Lobe Found behind your forehead Involved in: Reasoning & Planning Some parts of speech Movement Emotions Problem solving Contains Motor Cortex Return to brain parts Frontal Lobe Parietal Lobe Found on the top of your head Contains Sensory Cortex Involved in: Touch Pressure Temperature Pain Spatial Orientation Parietal Lobe Temporal Lobe Found on the sides of head above your ears Contains Limbic Cortex Involved in: Speech perception Hearing Some types of memory Emotion Return to brain parts Temporal Lobe Occipital Lobe Found at the back of your head Receives input from the eyes Often referred to as the visual cortex Occipital Lobe Return to brain parts Cerebellum Found at the at the back of your head under the cerebrum. Means “little brain” Involved in: Unconscious coordination Movement Balance Posture Often takes over learned activities Cerebellum Brainstem Most basic part of your brain Controls essential functions automatically Contains 2 parts: Medulla controls breathing, heart & blood vessel activity, digesting, eliminating waste, sleeping, maintaining body temperature… Pons regulates breathing Also responsible for movement Return to brain parts Brainstem Cerebral Cortex Corpus Callosum Located centrally between the left and right hemispheres of your brain. Thick bundle of nerve fibers that connects the left and right hemispheres. Involved in: Creativity Problem solving Allows hemispheres to process information together Corpus Callosum Create a Brain! How Do Neurons Communicate? The Normal, At Rest, Condition When the neuron is at rest, there are several important ions (+ or – charged chemicals) that are carefully balanced. Important ions K+ (Potassium) Na+ (Sodium) Cl- (Chloride) Ca2+ (Calcium) These ions enter and leave the neuron through ion channels and pumps. The Neuron At Rest The balance of these ions inside and outside of the cell membrane creates a membrane potential. For the neuron at rest, this is -70 mV. How does the neuron achieve this? Electrical & Chemical Gradients Na+ K+ Cl- Outside Inside -70mV Na+ K+ Concentration Gradient Electrical Gradient Cl- At Rest So at rest, the inside of the neuron is negatively charged because of the balance of ions inside and outside the cell. What happens when a signal comes along?? Ions move!! Action Potential: Na+ Na+ Outside Inside -55 -70 mV Na+ When a stimulus occurs, Na+ channels open and Na+ rushes into the neuron, making it more positively charged. This also passes a negative (depolarizing) current along to the next section of axon. Action Potentials: All or None If Na+ outflow causes the potential to reach -55 mV, an action potential will occur and the signal will be sent. This is known as the threshold potential. If the potential does not reach the threshold, no action potential will occur…thus it is an “All or None” phenomenon. Action Potential: K+ K+ Outside Inside +55mV -75 mV K+ Once the action potential is generated, Na+ channels close and K+ channels open. K+ moves slowly outward to bring the potential back to -75 mV (repolarization). Action Potential: Overshoot So much K+ flows out of the neuron that the membrane potential returns to a value lower than that of its resting state. This is called hyperpolarization. What effect do you think this might have on the neuron’s ability to fire again and send a second message? Refractory Period While the neuron is hyperpolarized, it cannot fire again. This also prevents a signal from traveling backwards. Once the neuron regains its resting membrane potential, it will be able to send a second message. Propagation Action potential in one region of axon depolarizes the next region to pass along, or propagate, the action potential. This process can be sped up by myelin coating on the axons. Nodes of Ranvier: Small segments of unmyelinated axon Action potential “jumps” from Node to Node: much speedier! This is called saltatory conduction. Putting it All Together At Rest: -70 mV (membrane potential) Na+ enters the cell K+ leaves the cell If -55 mV threshold potential is reached, action potential begins Cell becomes hyperpolarized (-75 mV) and is temporarily refractory. Action potential is passed in one direction down the axon. Whew! We finally made it down the axon! Now What?? http://fleetfeetsportswinston-salem.blogspot.com/2010/05/moving-from-competitor-to-spectator.html We still need to get the message to the next neuron. http://www.georgiapainphysicians.com/l2_edu_pharma_mod1_slides.htm Neurons Communicate at Synapses Neurons talk to each other all the time, but never actually touch. Two neurons meet at a place called the synapse. Special chemicals called neurotransmitters carry the message across the synapse. Neurons Talk at Synapses Photo by T. Due, Harvard University, 7/2005 These C. elegan worms contain a transgene encoding unc-49 gene (GABA receptor) fused to its own promoter and GFP (Harvard Medical School) From Dr.Venkatesh N. Murthy, Harvard University, 7/2005 Neurons Talk Through Neurotransmitters & Receptors Neurotransmitters: Chemicals that carry messages from one neuron to another across the synapse (messages travel really fast!) Receptors: Protein molecules that receive and translate the chemical message Neurotransmitters Neurotransmitters are how the brain passes messages from one neuron to the next. Neurotransmitters can be either: Inhibitory (they prevent other neurons from firing) Excitatory (they increase firing in other neurons) http://www.besttreatments.co.uk/btuk/images/epilepsy_ne urotransmitter.gif Neurotransmitters: GABA & Glu GABA Primary inhibitory neurotransmitter Involved in: Epilepsy Depression & Anxiety Anesthesia Glutamate Primary excitatory neurotransmitter Involved in: Epilepsy Learning & Memory Schizophrenia http://www.cnsforum.com/imagebank/item/Neuro_path_GABA/default.aspxhttp://www.cnsforum.com/imagebank/item/Neuro_path_GLUT/default.aspx Neurotransmitters: 5-HT & NE Serotonin Involved in: Depression & Mood Eating Sleep & Wake Pain Norepinephrine Implicated in Mood & Depression Sleep & Wake Drug Abuse Parkinson’s Disease http://www.deplin.com/LifeWithDepression,Causes Neurotransmitters: DA & ACh Dopamine Involved in: Drug Abuse Parkinson’s Disease Schizophrenia http://www.3dchem.com/molecules.asp?ID=289 Acetylcholine Involved in: Muscular movement Nicotine Addiction Alzheimer’s Disease http://www.worldofmolecules.com/emotions/acetylcholine.htm Illustrate a Neurotransmitter Brain Beliefs June 14, 2011 True or False? The brain is static, unchanging, and set before you start school. True or False The brain contains more supporting cells (glia) than it does neurons (cells that send signals throughout the brain). True or False? Prior to birth, a baby gains 250,000 neurons per minute. True or False? Some people are left-brained and some are right-brained. True or False? We use only 10 percent of our brains. True or False? Rats have a broader hearing range than humans. True or False? Male and female brains are extremely different. True or False? Your brain is made up primarily of water and fat. Review & View a Neuron Review Parts of a Neuron Lobes of the Brain Action Potentials & Neurotransmission Neurotransmitters http://students.cis.uab.edu/nkm188/project_back2.html Neurons Galore! Spinal Cord Purkinje Neuron in Cerebellum Pyramidal Cortical Neuron Hippocampal Neuron http://faculty.washington.edu/chudler/gall1.html Auditory System Anatomy of the Auditory System http://www.hearingcarecenter.com/hearing_neural.htm Hear Ye, Hear Ye Sounds waves enter the outer ear (pinna), where they are amplified and localized. The sound wave then vibrates the tympanic membrane (eardrum) and passes to the ossicles. http://sciencewithmorton.phoenix.wikispaces.net/Sound+and+Light, http://health.allrefer.com/health/ruptured-or-perforated-eardrum-eardrum-repair-series.html Middle Ear Ossicles 3 small bones Malleus (hammer) Incus (anvil) Stapes (stirrup) Continue to pass along the vibration from the sound waves to the cochlea http://health.allrefer.com/health/fusion-of-the-ear-bones-earanatomy.html The Inner Ear The cochlea is filled with fluid & converts air sounds into liquid sounds Organ of Corti Contains hair cells on the basilar membrane Sound waves move the hair cells on the basilar membrane against the tectorial membrane Bending these hair cells causes depolarization and neurotransmitter release Onward to the Brain! Organ of Corti transmits signals to the cochlear nerve Medulla Cochlear Nucleus to Superior Olivary Complex Lateral Lemniscus fiber bundle carries information to the inferior colliculus Proceeds to the Medial Geniculate Nucleus of the thalamus and on to the auditory cortex http://www.neuroreille.com/promenade/english/ptw/zoom1.htm Auditory Cortex Tonotopic Organization Different frequencies of sound are mapped to different regions of the auditory cortex Extends to the level of the cochlea Zhou, X. and M. M. Merzenich (2007). "Intensive training in adults refines A1 representations degraded in an early postnatal critical period." Proceedings of the National Academy of Sciences 104(40): 15935-15940. Sound Localization Experiment Auditory Acuity Brainstorming What factors might affect hearing? What are some possible causes of hearing disorders? Factors in Hearing One ear vs. Two ears Frequency of Sound Humans can hear sounds btw 20 to 20,000 Hz Age Particularly important for localization Frequency range narrows with age Competing sounds Wax or fluid build up Why Are 2 Ears Better Than 1? Sound arrives at different times to each ear (unless its directly ahead of us). This phase difference is translated to the brain, where some neurons respond to sounds 90° out of phase; others respond to 180° out of phase, etc. McAlpine, D. (2005). "Creating a sense of auditory space." The Journal of Physiology 566(1): 21-28. Hearing Disorders Otosclerosis Tinnitus Presbycusis Auditory Processing Disorder Ménière's Disease Otosclerosis Abnormal growth of the ossicles Usually affects the stapes http://www.marshfieldclinic.org/patients/?page=ent_ear_otosclerosis Causes conductive hearing loss Sometimes can cause a sensorineural hearing loss that damages sensory cells or nerve fibers Tinnitus Persistent ringing in the ears May result from the brain’s attempt to adapt to inner ear damage by “turning up” the auditory system Increase in unilateral brain activity on PET http://www.newyorker.com/reporting/2009/02/09/090209fa_fact_groopman Presbycusis Age-related hearing loss Particularly sensitive to high-pitch Sensorineural hearing disorder Damage to the sensory hair cells or cochlear nerve May be due to decreased blood flow to these regions Auditory Processing Disorder Difficulty paying attention to and understanding speech Unknown cause Ménière's Disease Excess buildup of fluid on cochlea Interferes with ability to transmit sound from cochlea to auditory cortex Auditory Acuity Experiment http://faculty.washington.edu/chudler/hearing.html