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; most of them are dendrites , which bring information from other neurons or sensory cells to the cell body.
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