Chapter 38 The Nervous System Lecture Outlines by Gregory Ahearn University of North Florida Copyright 2011 Pearson Education Inc Chapter 38 At a Glance 38 1 What Are the Structures and Functions of 38 2 How Do Neurons Produce and Transmit 38 3 How Do Nervous Systems Process Nerve Cells Information Information 38 5 What Are the Structures and Functions of the Human Nervous System Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells The nervous system has two principal cell types Neurons often called nerve cells which receive process and transmit information Glia which assist neuronal function by Providing nutrients Regulating the composition of the extracellular fluid in the brain and spinal cord Modulating communication between neurons Speeding up the movement of electrical signals within neurons Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells The functions of a neuron are localized in separate parts of the cell A neuron must perform four functions Receive info from the environment Process the info and produce electrical signals Conduct electrical signals over distances to a junction where it meets another cell Transmit info to other neurons muscles or glands Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells The functions of a neuron are localized in separate parts of the cell continued Typical neurons have four distinct parts that carry out these four functions Dendrites A cell body An axon Synaptic terminals Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells Dendrites respond to stimuli Dendrites are branched tendrils protruding from the cell body that perform the receive information function Their branches provide a large surface area for receiving signals either from the environment or from other neurons Dendrites of sensory neurons respond to specific stimuli such as pressure odor light body temperature blood pH or the position of a joint Dendrites of neurons in the brain and spinal cord usually respond to chemicals called neurotransmitters that are released by other neurons Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells The cell body processes signals from the dendrites Electrical signals travel down the dendrites and converge on the neuron s cell body which integrates incoming information performing the process information function If incoming signals are positive enough a large rapid electrical signal called an action potential is produced The cell body also contains other organelles such as the nucleus endoplasmic reticulum and Golgi apparatus that are typical of other cells synthesizing complex molecules and coordinating the cell s metabolism Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells The axon conducts action potentials along long distances In a typical neuron a long thin strand called an axon extends outward from the cell body and conducts action potentials from the cell body to synaptic terminals at the axon s end Single axons may stretch from our spinal cord to our toes a distance of about 3 feet Axons are typically bundled together into nerves much like wires are bundled within an electrical cable Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells At synapses signals are transmitted from one cell to another The site where a neuron communicates with another cell is called a synapse A typical synapse consists of The synaptic terminal which is a swelling at the end of an axon of the sending neuron A dendrite or cell body of a receiving neuron muscle or gland cell A small gap separating the two cells Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 1 What Are the Structures and Functions of Nerve Cells At synapses signals are transmitted from one cell to another continued Most synaptic terminals contain neurotransmitters that are released in response to an action potential reaching the terminal The plasma membrane of the receiving neuron bears receptors that bind the neurotransmitters and stimulate a response in this cell Therefore at a synapse the output of the first cell becomes the input to the second cell Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 2 How Do Neurons Produce and Transmit Information Neurons use chemicals to communicate with one another at synapses Although there are electrical synapses where electrical activity can pass directly from neuron to neuron through gap junctions connecting the insides of the cells as occurs in heart tissue most synapses use chemicals to transmit information from one neuron to another A synapse is where the synaptic terminal of one neuron meets the dendrite of another Biology Life on Earth 9e Copyright 2011 Pearson Education Inc Figure 38 1 Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 2 How Do Neurons Produce and Transmit Information Neurons use chemicals to communicate with one another at synapses continued The two neurons do not actually touch at a synapse A tiny gap the synaptic cleft separates the first or presynaptic neuron from the second or postsynaptic neuron The presynaptic neuron sends neurotransmitter chemicals across the gap to the postsynaptic neuron There are many types of neurotransmitters A synaptic terminal contains scores of vesicles each full of neurotransmitter molecules When an action potential is initiated it travels down an axon until it reaches its synaptic terminal Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 2 How Do Neurons Produce and Transmit Information Neurons use chemicals to communicate with one another at synapses continued The inside of the terminal becomes positively charged and triggers a cascade of changes that cause some of the vesicles to release neurotransmitters into the synapatic cleft The outer surface of the plasma membrane of the postsynaptic neuron is packed with receptor proteins that are specialized to bind the neurotransmitter released by the presynaptic neuron The neurotransmitter molecules diffuse across the gap and bind to these receptors Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 38 2 How
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