In general the actions of the sympathetic and the

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In general, the actions of the sympathetic and the parasympathetic nervous systems are antagonistic, meaning that when one stimulates something, the other inhibits it and
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vice versa. The organs, with few exceptions, receive efferences from these two systems and the antagonism between them serves to balance their effects. For example, the parasympathetic system stimulates salivation while the sympathetic system inhibits it; the parasympathetic system constricts pupils while the sympathetic system dilates them; the parasympathetic system contracts the bronchi while the sympathetic system relaxes them; and the parasympathetic system excites the genital organs while the parasympathetic system inhibits the excitation. Cephalization and the Evolution of the Nervous System 36. Using examples of invertebrate nervous systems, how can the process of evolutionary cephalization be described? Considering invertebrates, it is possible to observe that evolution accompanies the increasing complexity of organisms with the convergence of nervous cells at special structures for controlling and commanding: the ganglia and the brain. In simple invertebrates, such as cnidarians, nervous cells are not concentrated rather they are found dispersed in the body. In platyhelminthes, the beginning of cephalization with an anterior ganglion concentrating neurons is already verified. In annelids and arthropods the existence of a cerebral ganglion is evident. In cephalopod molluscs, the cephalization is even greater and the brain controls the nervous system.
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37. What are some of the main differences between vertebrate and invertebrate nervous systems? In vertebrates, the nervous system is well-defined, with a brain and dorsal neural cord protected by rigid skeletal structures. In most invertebrates, the nervous system is predominantly ganglial, with ventral neural cords. 38. What are the protective structures of the central nervous system present in vertebrates? In vertebrates, the brain and the spinal cord are protected by membranes, the meninges, and by osseous structures, the skull and the spine, respectively. These protective structures are fundamental in maintaining the integrity of these important organs, which control the functioning of the body. Neurophysiology 39. What is the nature of the stimuli received and transmitted by neurons? Neurons receive and transmit chemical stimuli through neurotransmitters released in the synapses. However, the impulse transmission is electrical along the neuron body. Therefore, neurons conduct electrical and chemical stimuli.
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40. What are the two main ions that participate in electrical impulse transmission in neurons? The two main ions that participate in electrical impulse transmission in neurons are the sodium cation (Na ) and the potassium cation (K ). 41. Is the electric charge between the two sides of the neuron plasma membrane positive or negative? What is the potential difference (voltage) generated between these two sides?
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