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Lecture 20

01:119:116 Lecture 20: Lecture 20 - Synapses & Sensory Receptors

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Rutgers University
Biological Sciences
Dr.Christy Beal

Lecture 20 - Synapses & Sensory Receptors I. Synapses A. Introduction ➢ Junction between a synapse term and another neuron or effector ○ Some are electrical (no Neurotransmitters) ○ Most are chemical B. Types ➢ Synaptic cleft - gap ~20nm ➢ Presynaptic neuron ○ Synthesizes neurotransmitter & stores vesicles 1. AP depolarizes membrane 2. Voltage gated Ca2+open 3. Vesicles fuse with terminal membrane & release neurotransmitter 4. Neurotransmitter diffuses across cleft Postsynaptic potentials 1. Graded potential in postsynaptic cells 2. Receptor protein, binds & responds to neurotransmitters a. Directly opposite synaptic terminal b. Opens channel & allows specific ions to diffuse across postsynaptic membrane c. This generates a postsynaptic potential C. Neurotransmitters ➢ Examples of neurotransmitters 1. Acetylcholine ■ Muscle stimulation, memory, & learning 2. Glutamate ■ Amino acid ■ Brain excitatory neurotransmitter 3. Dopamine ■ Mood 4. Endorphins ■ Pain regulation D. Synapses ➢ Excitatory postsynaptic potential (EPSP) ○ Membrane depolarizes when channels open ➢ Inhibitory postsynaptic potentials (IPSP) ○ Membrane hyperpolarizes when channels open Summary of Postsynaptic Potentials ➢ Postsynaptic neuron receives many signals (EPSP & IPSP) ➢ If EPSP is too small by axon hillock - no signal ➢ How does the signal reach threshold? ➢ Temporal summation - rapid stimuli - additive effect ➢ Spatial summation - many different dendrites receive ➢ Axon hillock - neurons integrating system EPSP - IPSP ○ If membrane reaches threshold → AP! II. Memory and Learning A. Nervous System Development ➢ Embryonic development ➢ Structure of nervous system established ○ Gene expression ○ Signal transduction ➢ Brain continue to develop & remodel ○ Competition for growth-supporting factors ○ Synapse elimination - keep only required ■ Fig 49.11 After Birth ➢ Most reshaping occurs at synapses ○ Synaptic connections reinforced ■ If synapse does not work with others - weakens ■ If synapses often work together - strengthens ● Use it or lose it! B. Neuronal plasticity ➢ Long term memory ○ Also stored in cerebral cortex but.. ○ Links to hippocampus replaced by permanent connections in cerebral cortex ○ Memories are consolidated during SLEEP ➢ Hippocampus damage impairs formation of new memories C. Memory & Learning ➢ Short-term memory ○ Held for short time ○ Stored in cerebral cortex ○ Accessed via temporary links formed in hippocampus ➢ Hippocampus ○ Acquiring memories, not maintaining them D. Long-Term Potentiation (LTP) ➢ Long la
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