Anatomy & Physiology I and II

Anatomy & Physiology Study Guide • A synapse is either electrical (with direct physical contact between cells) or chemical (involving a neurotransmitter). • Electrical synapses occur in the CNS and PNS, but they are rare. At an electrical synapse, the presynaptic and postsynaptic plasma membranes are bound by interlocking membrane proteins at a gap junction. Pores within these proteins permit the passage of local currents, and the two neurons act as if they share a common plasma membrane. • Chemical synapses are far more common than electrical synapses. Excitatory neurotransmitters cause depolarization and promote the generation of action potentials, whereas inhibitory neurotransmitters cause hyperpolarization and suppress the generation of action potentials. • The effect of a neurotransmitter on the postsynaptic membrane depends on the properties of the receptor, not on the nature of the neurotransmitter. • Cholinergic synapses release the neurotransmitter acetylcholine (ACh). Communication moves from the presynaptic neuron to the postsynaptic neuron across a synaptic cleft. A synaptic delay occurs because calcium influx and the release of the neurotransmitter takes an appreciable length of time. Neurotransmitters and neuromodulators have various functions: • Adrenergic synapses release norepinephrine (NE), also called noradrenaline. Other important neurotransmitters include dopamine, serotonin, and gamma aminobutyric acid (GABA). • Neuromodulators influence the postsynaptic cell's response to neurotransmitters. • Neurotransmitters can have a direct or indirect effect on membrane potential, or they can exert their effects via lipid-soluble gases that diffuse across the plasma membrane. Information processing by individual neurons involves integrating excitatory and inhibitory stimuli: • Excitatory and inhibitory stimuli are integrated through interactions between postsynaptic potentials. This interaction is the simplest level of information processing in the nervous system. • A depolarization caused by a neurotransmitter is an excitatory postsynaptic potential (EPSP). Individual EPSPs can combine through summation, which can be either temporal (occurring at a single synapse when a second EPSP arrives before the effects of the first have disappeared) or spatial (resulting from the cumulative effects of multiple synapses at various locations). • Hyperpolarization of the postsynaptic membrane is an inhibitory postsynaptic potential (IPSP). • The most important determinants of neural activity are EPSP–IPSP interactions. ©2018 Achieve Test Prep Page 158 of 367