NervousSystem-four

NervousSystem-four - 44 Local hormones Slow diffusion Short...

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44 Neurons and Nervous Systems Brain Legs Eat giraffe ! Run ! The problem: how to communicate over long distances . ..fast ? Local hormones? • Slow diffusion • Short distance Circulating hormones? • Long distance • Relatively slow • Specificity limited by receptors on target cells Blood vessel The problem: how to communicate over long distances . ..fast ? The solution: stretch the endocrine cell !!
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The simplest “neuronal network” consists of three cells Sensory neuron Motor neuron Muscle 44 Nervous Systems: Cells and Functions • The simplest neural network consists of three cells: a sensory neuron connected to a motor neuron connected to a muscle cell. • Most neuronal networks are more complex. The human brain has an estimated 10 11 neurons and 10 14 synapses . • World population: 6.5 x 10 9 (Human brain has 150x more neurons) • The neurons and synapses in the human brain are divided into thousands of distinct but interacting networks that function in parallel . 44 Nervous Systems: Cells and Functions Neurons are specialized cells of the nervous system that receive, encode, and transmit information. • Neurons with their support cells ( glial cells ) make up nervous systems . • Information is received by sensory cells and converted or transduced into electrical signals that are transmitted and processed by neurons. • To cause behavioral or physiological responses, a nervous system communicates these signals to effectors , such as muscles and glands. 44 Nervous Systems: Cells and Functions • Simple animals process information with a simple network of neurons ( nerve net ) that does little more than provide direct lines of communication from sensory cells to effectors. • The next level of nervous system complexity includes clusters of neurons called ganglia . • Frequently one pair of ganglia is larger and more central and is given the designation brain .
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Nervous Systems Vary in Size and Complexity 44 CNS - PNS • In vertebrates, most of the cells of the nervous system are found in the brain and the spinal cord, which together are called the central nervous system ( CNS ). • Information is transmitted from sensory cells to the CNS and from the CNS to effectors via neurons, which extend or reside outside of the brain and spinal cord. • Neurons and supporting cells found outside the CNS are called the peripheral nervous system (PNS) . Figure 44.1 Nervous Systems Vary in Size and Complexity Figure 44.2 Neurons (Part 1) Cell body Axon Denrites Axon terminals (synapses)
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44 Neurons • Most neurons have four regions: a cell body, dendrites, an axon, and axon terminals. ! The cell body contains the nucleus and most of the cell’s organelles. ! Many projections sprout from the cell body;
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NervousSystem-four - 44 Local hormones Slow diffusion Short...

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