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Transcript
Biology Slide 1 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System Slide 2 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System 35-2 The Nervous System The nervous system • controls/coordinates functions in the body • responds to internal & external stimuli. Slide 3 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System Neurons Neurons Messages carried by the nervous system are electrical signals called impulses. The cells that transmit these impulses are called neurons. Slide 4 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System Neurons Neurons are classified according to where the an impulse travels. • Sensory neurons carry impulses from the sense organs to the spinal cord and brain. • Motor neurons carry impulses from the brain and spinal cord to muscles and glands. • Interneurons connect sensory and motor neurons and carry impulses between them. Slide 5 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System Neurons Structures of a Neuron Nucleus Dendrites Axon terminals Cell body Myelin sheath Axon Nodes Slide 6 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System Neurons The largest part of a typical neuron is the cell body. It contains the nucleus and much of the cytoplasm. Cell body Slide 7 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System Neurons Dendrites carry impulses from the environment toward the cell body. Dendrites Slide 8 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System Neurons Axon - long fiber that carries impulses away from the cell body. The axon ends in axon terminals. Axon terminals Axon Copyright Pearson Prentice Hall Slide 9 of 38 35-2 The Nervous System Neurons Axon is surrounded by an insulating membrane myelin sheath. Nodes - gaps in the myelin sheath. Impulses jump from one node to the next. Myelin sheath Nodes Slide 10 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse How is a nerve impulse transmitted? Slide 11 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse The Moving Impulse An impulse begins when a neuron is stimulated by another neuron or by the environment. Slide 12 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse Slide 13 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse Slide 14 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse Slide 15 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse Slide 16 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse Threshold A stimulus must be of adequate strength to cause a neuron to transmit an impulse. The minimum level of a stimulus that is required to activate a neuron is called the threshold. A stimulus that is weaker than the threshold produces no impulse. Slide 17 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Synapse The Synapse At the end of the neuron, the impulse reaches an axon terminal. The neuron makes contact with another cell at this site. The neuron may pass the impulse along to the second cell. The location at which a neuron can transfer an impulse to another cell is called a synapse. Slide 18 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Synapse A Synapse Slide 19 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Synapse The synaptic cleft separates the axon terminal from the dendrites of the next cell. Synaptic cleft Copyright Pearson Prentice Hall Slide 20 of 38 35-2 The Nervous System Terminals contain vesicles filled with neurotransmitters. The Synapse Vesicle Neurotransmitters are chemicals used by a neuron to transmit an impulse across a synapse to another cell. Neurotransmitter Slide 21 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System As an impulse reaches a terminal, vesicles send neurotransmitters into the synaptic cleft. These diffuse across the cleft and attach to membrane receptors on the next cell. Copyright Pearson Prentice Hall The Synapse Receptor Slide 22 of 38 35-2 The Nervous System The Synapse The next cell is simulated. If the stimulation exceeds the cell’s threshold, a new impulse begins. Slide 23 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Synapse Moments after binding to receptors, neurotransmitters are released from the cell surface. The neurotransmitters may then be broken down by enzymes, or taken up and recycled by the axon terminal. Slide 24 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System DIVISIONS OF THE NERVOUS SYSTEM Slide 25 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Central Nervous System The Central Nervous System • The central nervous system relays messages, processes information, and analyzes information. Slide 26 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Peripheral Nervous System The Peripheral Nervous System • The peripheral nervous system is all of the nerves and associated cells that are not part of the brain and the spinal cord. • The peripheral nervous system includes cranial nerves, spinal nerves, and ganglia. • Ganglia are collections of nerve cell bodies. Slide 27 of 38 Copyright Pearson Prentice Hall 35-2 Click to Launch: Continue to: - or - Slide 28 of 38 Copyright Pearson Prentice Hall 35-2 Neurons that carry impulses from the brain and spinal cord to the muscles are a. interneurons. b. sensory neurons. c. resting neurons. d. motor neurons. Slide 29 of 38 Copyright Pearson Prentice Hall 35-2 The part of the neuron that carries impulses toward the cell body is the a. axon. b. myelin sheath. c. dendrite. d. nodes. Slide 30 of 38 Copyright Pearson Prentice Hall 35-2 The minimum level of a stimulus that is required to activate a neuron is called its a. action potential. b. resting potential. c. threshold. d. synapse. Slide 31 of 38 Copyright Pearson Prentice Hall 35-2 Chemicals that are used by a neuron to transmit impulses are called a. neurotransmitters. b. synapses. c. axons. d. inhibitors. Slide 32 of 38 Copyright Pearson Prentice Hall 35-2 An action potential begins when a. sodium ions flow into the neuron. b. potassium ions flow into the neuron. c. sodium and potassium ions flow into the neuron. d. sodium and potassium ions flow out of the neuron. Slide 33 of 38 Copyright Pearson Prentice Hall END OF SECTION 35-2 The Nervous System The Nerve Impulse The Nerve Impulse The Resting Neuron When resting, the outside of the neuron has a net positive charge. The inside of the neuron has a net negative charge. The cell membrane is electrically charged because there is a difference in electrical charge between its outer and inner surfaces. Slide 35 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse The sodium-potassium pump in the nerve cell membrane pumps sodium (Na+) ions out of the cell and potassium (K+) ions into the cell by means of active transport. As a result, the inside of the cell contains more K+ ions and fewer Na+ ions than the outside. Slide 36 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse Sodium-Potassium Pump Slide 37 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse More K+ ions leak across the membrane than Na+ ions. This produces a negative charge on the inside and a positive charge on the outside. The electrical charge across the cell membrane of a neuron at rest is known as the resting potential. Slide 38 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse The inside of the membrane temporarily becomes more positive than the outside. Slide 39 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse This is called a nerve impulse, or an action potential. Slide 40 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse As the action potential passes, K+ ions flow out restoring the negative potential inside the axon. Slide 41 of 38 Copyright Pearson Prentice Hall 35-2 The Nervous System The Nerve Impulse The impulse continues to move along the axon. An impulse at any point of the membrane causes an impulse at the next point along the membrane. Slide 42 of 38 Copyright Pearson Prentice Hall