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Human Biology Sylvia S. Mader Michael Windelspecht Chapter 13 Nervous System Lecture Outline Part 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 13.1 Overview of the Nervous System The nerve impulse: Stimulus causes the axon to reach its threshold Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. − + − + + + + + + + + + + + + direction of signal + − + − + + + + + open Na+ channel Figure 13.3b Generation of an action potential. b. Stimulus causes the axon to reach its threshold; the axon potential increases from −70 to −55. The action potential has begun. 2 13.1 Overview of the Nervous System The nerve impulse: Action potential Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + + + + + + + + + + + + + direction of signal + + + + + + + open Na+ channel c. Depolarization continues as Na+ gates open and Na+ moves inside the axon. Figure 13.3c Generation of an action potential. 3 13.1 Overview of the Nervous System The synapse • The synapse is a small gap between the _________ neuron (presynaptic membrane) and the________ neuron (postsynaptic membrane). • Transmission is accomplished across this gap by a _______________ (e.g., ACh, dopamine, or serotonin). • Neurotransmitters are stored in synaptic vesicles in the axon terminals. 4 13.1 Overview of the Nervous System How does transmission across the synapse occur? • Nerve impulse reaches the axon terminal. • Calcium ions enter the axon terminal and stimulate the synaptic vesicles to fuse with the presynaptic membrane. • Neurotransmitters are released and diffuse across the synapse, where they bind with the postsynaptic membrane to inhibit or excite the neuron. 5 13.1 Overview of the Nervous System A synapse and how it functions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. arriving action potential 1. After an action potential arrives at an axon terminal (arrow), Ca2+ enters, and synaptic vesicles fuse with the plasma membrane of the sending neuron. Sending neuron Ca2+ axon of sending neuron axon terminal Synaptic vesicles enclose neurotransmitter. Synapse receiving neuron Receiving neuron Synaptic cleft 2. Neurotransmitter molecules are released and bind to receptors on the membrane of the receiving neuron. Receiving neuron neurotransmitter neurotransmitter receptor Na+ Figure 13.4 Signal transmission at the synapse. Receiving neuron ion channel 3. When an excitatory neurotransmitter binds to a receptor, Na+ diffuses into the receiving neuron, and an action potential begins. 6 13.1 Overview of the Nervous System Synaptic integration • Integration is the _____________ of the inhibitory and excitatory signals received by a postsynaptic neuron. • This occurs because a neuron receives many signals. 7 13.1 Overview of the Nervous System Synaptic integration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. +20 0 excitatory signal integration inhibitory signal 20 Cell body of the receiving neuron axon branches of sending neurons 40 threshold 70 resting potential axon terminals 80 dendrite Time (milliseconds) b. inhibitory synapse excitatory synapse a. a: © Science VU/Lewis-Everhart-Zeevi/Visuals Unlimited Figure 13.5 Integration of excitatory and inhibitory signals at the synapse. 8 13.2 The Central Nervous System The central nervous system • The CNS consists of the brain and spinal cord. • Both are protected by • ________ – skull and vertebral column • ___________ – 3 protective membranes that wrap around CNS • _______________ (CSF) – space between meninges is filled with this fluid that cushions and protects the CNS 9 13.2 The Central Nervous System The central nervous system • Both the brain and spinal cord are made up of 2 types of nervous tissue. • Gray matter – contains cell bodies and _______________ fibers • White matter – contains _____________ axons 10 13.2 The Central Nervous System The CNS: Spinal cord • It extends from the base of the brain and along the length of the vertebral canal formed by the vertebrae. • The spinal cord functions to provide _____________ between the brain and most of the body. • It is the center for ____________. • Gray matter in the center is a __________ shape. • White matter surrounds the gray matter. 11 13.2 The Central Nervous System What does the spinal cord look like? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. white matter gray matter central canal a. gray matter white matter spinal cord vertebra Figure 13.7 The organization of white and gray matter in the spinal cord and the spinal nerves. dorsal root dorsal root ganglion spinal nerve vertebra ventral root b. central canal dorsal root dorsal root ganglion dorsal dorsal root branches gray matter white matter dorsal root ganglion ventral spinal nerve ventral root cut vertebrae meninges c. d. Dorsal view of spinal cord and dorsal roots of spinal nerves. a: © Karl E. Deckart/Phototake; d: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer and Don Kincaid, dissections 12 13.2 The Central Nervous System The CNS: Brain 4 major parts 1. 2. 3. 4. Cerebrum Diencephalon Cerebellum Brain stem 13 13.2 The Central Nervous System The CNS: Overview of the brain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. lateral third ventricle ventricle pineal gland Cerebrum skull meninges corpus callosum Diencephalon thalamus (surrounds the third ventricle) hypothalamus pituitary gland Brain stem midbrain pons Cerebellum fourth ventricle medulla oblongata spinal cord b. Cerebral hemispheres a. Parts of brain Figure 13.8 The human brain. 14 13.2 The Central Nervous System The brain: Cerebrum • Cerebral hemispheres • Cerebral cortex • Primary motor and sensory areas of the cortex • Association areas • Processing centers • Central white matter 15