Learning Outcomes BIOL1082 -- 3/27

Using acetylcholine as an example, describe how neurotransmitters transmit the action potential signal.

-action potential flows down through pre-synaptic terminal causing Ca2+ channels to open; Ca2+ diffuses into cell causing the release of ACh into the synaptic cleft; at the cleft ACh binds to receptor proteins on the ligand-gated sodium channel, this binding cause channel to open and sodium flows into the cell across membrane; if depolarization of membrane reaches threshold, action potential would occur. this action potential would cause muscle contraction

Describe how action potentials are propagated, and sometimes accelerated along axons. Explain why action potentials are unidirectional and always travel without loss of signal.

-action potentials are propagated down an axon when one region of the axon produces an action potential which triggers the depolarization of regions next to the earlier one, these regions then reach threshold and fire another potential. action potentials are accelerated along axons when axons are myelinated; action potentials are only produced at Nodes of Ranvier so the depolarization at one node spreads quickly to the next node, like it is jumping

Define action potentials, distinguishing between action potentials and graded potentials.

-action potentials: short term disruptions of the potential triggered by the threshold change in potential; action potentials are the actual signals that move along the axon. -action potentials always lead to the depolarization of a membrane, usually have the same size and duration and conduct across entire axon, action potentials are all-or-none events; graded potentials can lead to the depolarization (less negative, moves closer to threshold) or hyperpolarization (more negative, move farther from threshold), size and duration of graded potentials is determined by size of inhibitory and excitatory inputs, do not pass into axons of most types of neurons, decay with time

Distinguish between excitatory and inhibitory postsynaptic potentials, and between spatial and temporal summation.

-both excitatory and inhibitory postsynaptic potentials interact with each other; excitatory postsynaptic potentials are produced from depolarization of the membrane and work to bring membrane potential closer to threshold, whereas inhibitory postsynaptic potentials are produced from hyperpolarziation of the membrane and work against or subtract from excitatory postsynaptic potentials to keep the membrane potential from reaching the threshold -spatial summation and temporal summation constitute the two ways that a membrane can reach threshold voltage. 1. spatial summation: many dendrites produce excitatory postsynaptic potentials at the same time that sum to threshold voltage 2. temporal summation: one dendrite produces many excitatory postsynaptic potentials at a fast enough rate where the membrane reaches threshold voltage

Explain the effects of nicotine on the nervous system.

-nicotine binds directly to specific receptors originally designed for ACh on postsynaptic neurons of the brain; in smokers, this has caused the brain to make fewer receptor proteins for nicotine to bind to and has altered the sensitivity to stimulation by neurotransmitters

Distinguish between electrical and chemical synapses and describe how signals cross synapses.

-synapses: found at the end of the axon, synapses are junctions used by motor neurons to communicate with other neurons (muscle cells or gland cells) -two types of synapses: pre-synapse-- transmits action potential to cell; post-synapse-- cell receiving signal on other side of the synapse -electrical synapses: conductive link formed between neurons where membrane potentials pass through gap junctions formed between the pre-synaptic cell and the post-synaptic cell -chemical synapses: junction through which neurons and non-neural cells communicate through -crossing synapses: ends of presynaptic axons contain many synaptic vesicles, these vesicles contain neurotransmitters. when the action potential arrives, Ca2+ channels are opened and Ca2+ flows in, this causes the fusion of the plasma membranes and the release of neurotransmitters. neurotransmitters move to the other side of the cleft and bind to receptors in the membrane. these transmitters must be removed quickly in order for new signals to be transmitted (done so through enzymes or re-uptake by other cells

Draw an action potential, identifying the phases of the action potential and the causes of the voltage changes at the membrane level.

on paper