Nervous System Neurons nerve cells Generate and conduct electric impulses Aps Can be very long or very short Basic Structure Cell body Dendrites Axon Synaptic Knobs also called terminals or pre synaptic terminals Form connections with other neurons called synapses Presynaptic neuron Postsynaptic neuron Nervous System Can form large complex circuits especially in the brain About 100 billion neurons in brain 5000 synapses per neuron 500 trillion synapses in brain Circuits make function of brain possible Pre synaptic neuron communicates with post synaptic neuron by releasing neurotransmitter into the synapse Nervous System So how do chemical messengers electric impulses and all that work First we need to cover a little physics Voltage separation of charge Another word for voltage is potential know this Current flow of charged particles Resistance anything that makes it harder for charged particles to flow i e anything that messes up current Nervous System The concepts of voltage current and resistance all apply to cell membranes Nervous System Where is there more positive charge inside or outside the cell Where is there more negative charge inside or outside the cell What is a separation of charge called When all the ions are at equilibrium the cell is at its resting membrane potential 70 mV Nervous System Where is there more positive charge inside or outside the cell Where is there more negative charge inside or outside the cell What is a separation of charge called When all the ions are at equilibrium the cell is at its resting membrane potential 70 mV see diagram Nervous System Where are there more sodium ions inside or outside the cell Where are there more potassium ions inside or outside the cell Nervous System Assume that the membrane protein channel labeled A has a shape that only allows sodium ions to pass through when it is open If membrane protein channel A is open will sodium ions flow into the cell or out of the cell Will the inside of the cell become more postive or negative Depolarization is when the charges become less separated loss of voltage Nervous System Assume that the membrane protein channel labeled B has a shape that only allows potassium ions to pass through when it is open If membrane protein channel B is open will potassium ions flow into the cell or out of the cell Will the inside of the cell become more postive or negative Hyperpolarization is when charges become more separated gain of voltage Nervous System What is the flow of a charged particle called What makes it easy for ions to flow into the cell What makes it easy for ions to flow out of the cell What determines the electrical resistance of a membrane Nervous System Let s get the party started Presynaptic neuron not pictured releases a nt labeled ligand below nt binds to ligand gated Na channel on postsynaptic neuron Na enters postsynaptic neuron If enough Na enters then postsynaptic neuron will be depolarized to its threshold voltage Threshold voltage is the critical voltage necessary to get another set of ion channels to open Voltage gated channels Nervous System Voltage gated channels Two types Na and K V gated Na and K very numerous from axon hillock also called trigger zone down the axon and to the axon terminals They only open when a critical membrane voltage has been reached see diagram V gated channels are responsible for creating the action potentials Where do APs begin Nervous System Note we are looking at one tiny region of membrane Action potentials axon Begin at the axon hillock and spread down the Nervous System Note we are looking at the same tiny region of membrane 1 Neuron is at resting membrane potential voltage What are all the channels doing Nervous System Note we are still looking at the same tiny region of membrane 2 Ligand gated channels on dendrites cell body open cause neuron to depolarize What will happen if threshold V not reached Nervous System Note we are still looking at the same tiny region of membrane 3 V gated Na channels open fast V gated K channels open slow What ion is flowing the most Nervous System Note we are still looking at the same tiny region of membrane 4 V gated Na channels close V gated K channels wide open What ion is flowing the most now Nervous System Note we are still looking at the same tiny region of membrane 5 V gated Na channels still closed V gated K channels almost closed What ion is flowing the most now Nervous System Note we are still looking at the same tiny region of membrane Membrane returns to resting membrane potential As soon as V gated Na channels reset this region could undergo another AP
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