Unit 4 Lecture 4 Notes I Synapses A Remember neuron threshold is 55 to 50 mv B Sum of the EPSPs facilitate firing and IPSPs block firing determine if this is reached C Action potential is propagated IF graded potential reaching axon hillock depolarizes to threshold level II Summations A Temporal Summation 2 or more synapses close in time only one stimulation continues i EPSPs summate and produce 1 depolarization B Spatial Summation 2 or more synapses spaced very close together on dendrite or cell body all form one postsynaptic stimulus i EPSPs summate and produce 1 large depolarization III Synaptic Potentiation A Similar effect in synapse repeated stimulation Synaptic Potentiation Ca2 remains and causes more NT released during next stimulation larger EPSPs B Learning process increases efficiency of neurotransmission i Linked to memory and learning ex questions trigger responses IV Synapse Transmission Speeds A Much slower than speeds along axon about 2 million times slower B NT diffuses across synaptic cleft I millionth inch i Axon propagation speeds 150 meters per second C Functional influence more neurons in chain slower information passage i Reflexes are fast because 1 3 synapses D Fatigue in Synapse i Synapse transmission oxygen intensive lack of oxygen so fatigue ii Nerve Propagation requires little oxygen will go on forever easy Chemical electrical V Neural Coding Nervous system able to interpret and communicate information A Complex info is reduced to simple neural code depending on i Specific neuron stimulation ii Firing rate frequency B Action potential is the same regardless of information C QUALitative information encoded by firing specific neurons i Ex seeing the color blue only some receptors in eye stimulated by ii AP travel along fibers of that specific neuron to the brain where blue wave length interpreted D QUANtitative information information about intensity of stimulus loud soft bright light i Encoded 2 ways 1 Threshold excitation of neuron a Weak stimulus excited only low threshold neurons b Strong stimulus excites less sensitive high threshold c Brain judges strength based on which neurons and how they fire 2 Frequency stronger stimuli increases firing frequency a Weak 10 AP per second b Strong 500 AP per second VI Neural Integration and Organization A Neurons function in group each group contributes to total function B Large numbers require integration for efficient function C So Neurons organized into Neuronal Pools i Functional groups receptors or from other neuronal pools of neurons integrate incoming information from 1 Ex pools for breathing control body temp hunger ect ii Single presynaptic fiber synapses with many other neurons in pool enter neuronal pool many branches and iii Some postsynaptic neurons have enough synapses to fire in discharge zones iv Few synapses fire in Facilitated Zone D Information then forwarded to other destinations VII Neural Circuits complicated A Diverging circuits amplifies signal patterns of synaptic connection in neuronal pools very one incoming fiber transmits to many neurons and i Increases number of neurons carrying information B Converging Circuits several inputs from one neuron one neuron receives input from several neurons or i Concentrates information from many sources C Reverberating Circuits incoming signal through chain of neurons i Each neurons has a collateral synapses with pervious part of the circuit In pulses reverberate echo sent over the same path ii iii Probably involved in rhythmic activities ex arm swimming during walking D Parallel After Discharge Circuit parallel neurons and eventually stimulate a one common output cell incoming signal stimulates several i Different number of synapses in each parallel path ii Impulse reach output cell at different times creating BURSTS of impulses after discharge Lasts 15 ms iii Involved in complex mental processes that require keeping one thought while dealing with others VIII Patterns of Neural Processing A Serial Processing 1st reflexes cause withdraw from pain i System works in predictable all or none manner ii Reflexes rapid automatic response to stimuli always causes some motor response iii Neurons fire in succession chain reaction Ex Patellar Tendon Reflex Arc steps 1 Extensor muscle stretched stimulates muscle spindle 2 Primary afferent neuron excited stimulates a motor neuron to extensor muscle 3 Primary afferent neuron stimulates inhibitory interneuron interneuron inhibits a motor neuron to flexor muscle 4 A motor neuron stimulates extensor muscle to contract 5 Flexor muscle antagonist relaxes iv 5 Components of Serial Processing r site of stimulus 1 Recepto 2 Sensory Neuron 3 Integration Center CNS afferent impulse to CNS a Single synapses monosynaptic between sensory and motor neurons b Multiple synapses polysynaptic with association neurons 4 Motor neuron 5 Effector muscle or gland cell efferent impulses from CNS to effector B Parallel Processing 2nd then you remember other accidents and seek first aid i ii Inputs segregated into many pathways Information dealt with simultaneously by different parts of neural circuitry same information sent to different places iii Evokes different responses in each place IX Receptors about external and internal events dendritic end of sensory neurons that are specialized to gather info A B Transducer Information transmitted to CNS convers one form of energy to another i Heat to be electrical or Sound to be electrical C Classification based on Location of Stimulus stimuli outside body receptors in skin touch i Exteroreceptors light pressure pain temperature 1 Teloreceptors distant stimuli light sound odors special class of exteroreceptors activated by ii Interoreceptors primary part of ANS visceral pain hunger thirst stimuli inside body signal changes in viscera iii Proprioceptors change in muscle tendon and ligament tension and joints info about kinesthetic sense or movement location of limb or total body in a space Stimuli D Classification based on Types of sensitive to chemical concentration smell and i Chemorecpetors ii Nociceptors iii Thermoreceptors iv Mechanoreceptors pain receptors sensitive to tissue damage taste changes in mechanical energy pressure movement of fluids changes in tension proprioceptors are mechanoreceptors sensitive to temperature heat or cold light intensity only in eyes v Photoreceptors E Types of Receptors encapsulates and unencapsulated i Unencapsulated 1 Free Nerve Endings widely