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Epilepsy & Membrane Potentials EEG WAVEFORM Ca2+ Neural Recording Excessive Calcium influx leads to a depolarized Resting Membrane Neurophysiology Anatomy of the Neuron Dendrites Axon Hillock = Trigger Zone Cell Body (organelles) Direction of Action Potential Axon Terminals Schwann cells and Nodes of Ranvier Schwann cells make MYELIN MYELIN is an electrical insulator Action Potential “jump” down myelinated axons by SALTATORY CONDUCTION Peripheral Nervous System: Support Cells CNS Support Cells = Neuroglia Action potential propagation along neurons How does the action potential move from the terminal of neuron 1 to the dendrites of neuron 2? Direction of Action Potential SYNAPSE 2 main types: electrical and chemical Electrical SYNAPSE Gap Junction Action potential moves DIRECTLY between neurons EXAMPLES: Smooth Muscle Cardiac Muscle Gap junction between adjacent cardiac cells Chemical SYNAPSE Presynaptic Terminal Synaptic CLEFT Postsynaptic membrane Chemical SYNAPSE: Function 1) Action potential down axon to terminal 2) Ca2+ Channel open; Ca2+ influx 3) Vesicles of Neurotransmitters release into synaptic cleft - 4) Neurotransmitter diffuse into synaptic cleft - Bind to LIGAND-gated ion channels on post-synaptic membrane Chemical SYNAPSE: Signal types on post-synaptic membrane 1) EPSP: Excitatory post-synaptic potential Mechanism Ligand-gated Na+ channels OPEN Importance Increases likelihood of AP in postsynaptic cell If ENOUGH neurotransmitters are released….AP Local Anesthetics: Novacain, Lidocaine, etc. Lidocaine Painful stimulus Action potential Sensory Neuron Blocks LIGAND-gated NA+ channels NO EPSP……no Action potential on post-synaptic cell……no perception of PAIN Chemical SYNAPSE: Signal types on post-synaptic membrane 2) IPSP: Inhibitory post-synaptic potential Mechanism Ligand-gated K+ or CL- channels OPEN on post-synaptic membrane Importance Decreases likelihood of AP in postsynaptic cell Presynaptic INHIBITION and FACILITATION: Neuromodulators Can modulate the ability of a neuron to release neurotransmitter Neuron Collateral Neuron INHIBITION of neurotransmitter release at POST-SYNAPTIC membrane Clinically important neurotransmitters & neuromodulators Cocaine Alcohol Caffeine Nicotine Heroin Morphine Viagara Marijuana Anti-depressants: Prozac Crystal Meth Strychnine LSD We will cover how some of these drugs work Neural Summation Spatial Axon hillock Temporal Spatial & Temporal SUMS EPSP & IPSP Functional Organization of Nervous System Central Nervous System Brain & Spinal Cord Peripheral Nervous System Spinal Nerves & all other nerves Sensory Motor Sensory Physiology Sensory Physiology • Perception of sensation involves 1) External physical signals 2) Converted by physiological process 3) To neural signals (graded & action potentials) Light Eye Phototransduction 1 Action Potential in Optic Nerve 3 General senses Perceive touch, pressure, pain, heat, cold, stretch, vibration, changes in position Located on skin and in joints/muscles Cutaneous Somatic Receptors Muscle spindle: stretch receptor Golgi Tendon Organ: Tendon stretch receptor Sensory Neurons Collagen Fibers within Tendon Physiology of Cutaneous Receptors 1. Stimulus (Vibration, Pressure, Temperature, Stretch, etc) 2. Mechanical and/or biomolecules cause opening/closing of ion channels (K+, Ca2+, Na+) on receptor membrane = Graded Receptor Potential 3. If receptor membrane depolarizes to threshold = ACTION POTENTIAL Functional classifications of sensory receptors Sustained Pressure Pain Vibration General sensory neural pathways Dorsal Column thalamus Tertiary Neuron Proprioreception, Vibration, Pressure Secondary Neuron Primary Neuron Anterolateral System Tertiary Neuron Touch, Itch, Pain, Temperature Secondary Neuron Primary Neuron Blocking Pain Perception Pressure, Vibration Dorsal Column Pain Anterolateral system 2) Triggered by BRAIN (endorphins) Via Blood Heroin & Morphine can trigger 1) Triggered by Massage, Exercise : Presynaptic inhibition of 2nd Neuron in Anterolateral System Sensory Perception in Brain Somatosensory Cortex (Postcentral Gyrus) Area on cortex = sensitivity of body part = # of sensory receptors on that part of body Special senses (located in the head region) 1) 2) 3) 4) Vision Hearing and equilibrium Olfaction Taste We will ONLY cover Vision as an example of a Special Sense! Eye: Basic Anatomy Lens Pupil Optic Nerve Retina Rod & Cones Bipolar Cells Ganglion Cells Retina Pupil Lens Disk Rhodopsin Rhodopsin Transducin (G-protien) cGMP cGMP-gated Na+/Ca2+ Channel K+ channel Glutamate DARK Bipolar Cells -Rhodopsin: inactive -Transducin: inactive -Intracellular cGMP levels HIGH -Ion channels are OPEN -Membrane potential = -40 mV -Glutamate release high onto Bipolar cells! Retinal Activated Transducin (G-protien) decreases Intracellular cGMP 1 Rhodopsin BLEACHES 2 cGMP-gated Na+/Ca2+ Channels CLOSE cGMP 3 K+ channel LIGHT 5 Glutamate decreases Photoreceptor Membrane potential (mV) Opsin -40 -70 4 HYPERPOLARIZATION Time Bipolar Cell 6 Cones: Color & Day Vision Rod: Night Vision Optic Nerve Neural pathway to optic nerve & brain Rod & Cones Bipolar Cells Ganglion Cells Neural Layer of Retina Neural Pathway in Brain Optic Chiasm Optic Cortex Optic Nerve Neural Processing in Brain V4 V3 V2 V1 Layers of signal processing V1 sends projections Dorsal & Ventral Dorsal Stream: “Where” & “How” Pathway Ventral Stream: “What” Pathway Color Vision: 3 cone types Retina Distribution of Rod vs. Cones # of photoreceptors Position on Retina Processing Visual Stimuli Retinal Processing: Convergent Neural Network! 125 million photoreceptors! Amount of convergence 1 million ganglion cells! 200:1 1:1 Position on Retina Neural Networks Brain Commands to Muscle (Motor Output) Vision Circadian Rhythms: Why you get tired when its dark! Melanopsin Rhodopsin Suprachiasmatic Nucleus (SCN)