Nervous System - Neurons Biol 105 Chapter 7 Outline I. Nervous system function II. Central and peripheral nervous system III. Nervous system cells IV. Myelinated neurons V. Nerve signal transmission VI. Nerve Synapse Copyright © 2009 Pearson Education, Inc. Nervous Tissues . Nervous tissue functions to conduct messages throughout the body. When nerve cells are stimulated, an electrical signal quickly travels through the nerve cell to the nerve ending, triggering events. Copyright © 2009 Pearson Education, Inc. Nervous System . Includes nervous tissue and sensory organs. Nervous system functions to: . Sense the environment – it receives information from both outside and inside the body. Process the information it receives. Respond to information – send out orders. Copyright © 2009 Pearson Education, Inc. Two Parts of the Nervous System 1. Central Nervous System (CNS) . Brain and Spinal Cord. 2. Peripheral Nervous System (PNS) . Nervous tissue outside brain and spine. Sense organs. Copyright © 2009 Pearson Education, Inc. Central Nervous System Peripheral Copyright © 2009 Pearson Education, Inc. Figure 8.1 The nervous system Copyright © 2009 Pearson Education, Inc. Nervous System Cells . Two types of nervous tissue cells. Neurons – The cells that are responsible for transmitting messages. Neuroglial Cells – Cells that support the neurons. Copyright © 2009 Pearson Education, Inc. Neuroglial Cells . Microglia – Immune system cells, engulf bacteria and cellular debris. Astrocytes – Provide nutrients to neurons. Oligodenrocytes and Schwann Cells – Form myelin sheaths. Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. Parts of a Neuron . Cell body – contains the nucleus, main body of cell. Dendrites – projections from the cell body that carry messages to the cell body. Axon – one projection that carries messages away from the cell body (can be very long). Copyright © 2009 Pearson Education, Inc. Neurons Have Dendrites, a Cell Body, and an Axon Dendrites receive The cell body controls information from the cell’s metabolic other neurons or activities. from the environment. Axon endings release chemicals called neurotransmitters that affect the activity of nearby neurons or an effector (muscle or gland). Nucleus Cell body The cell body An axon conducts the nerve impulse away integrates input Axon from other neurons. from the cell body. endings Receiving portion of Sending portion of neuron neuron Copyright © 2009 Pearson Education, Inc. Figure 7.2 12-12 Copyright © 2009 Pearson Education, Inc. Neurons of the Peripheral Nervous System . Neurons in the PNS are either carrying messages to or from the CNS. Afferent = Sensory neurons = Neurons carrying messages to the CNS. Efferent = Motor neurons = Neurons carrying messages from the CNS. Copyright © 2009 Pearson Education, Inc. Interneurons in the Central Nervous System . Interneurons are located between sensory and motor neurons within the CNS. Interneurons integrate and interpret sensory signals. Copyright © 2009 Pearson Education, Inc. Figure 8.1 The nervous system Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. Sensory Neurons . The afferent or sensory neuron cell bodies are located in dorsal root ganglion. Copyright © 2009 Pearson Education, Inc. Motor Neurons . The efferent or motor neuron cell bodies are located in the gray matter of the spinal cord. Their axons leave the CNS and go to the skeletal muscles. Copyright © 2009 Pearson Education, Inc. The cell bodies of these neurons are located in the dorsal root ganglion 50% 50% 1. Motor 2. Sensory Motor Sensory Copyright © 2009 Pearson Education, Inc. The cell bodies of these neurons are located in the dorsal root ganglion 50% 50% 1. Motor 2. Sensory Motor Sensory Copyright © 2009 Pearson Education, Inc. Neurons of the Nervous System Sensory Muscle receptor (effector) for pain Impulse direction Sensory Cell neuron body Motor neuron Interneuron Copyright © 2009 Pearson Education, Inc. Figure 7.1 12-5 These neuroglial cells provide nutrients to neurons 1. Microglia 25% 25% 25% 25% 2. Astrocytes 3. Oligodenrocytes 4. Schwann cells Microglia Astrocytes Schwann cells Oligodenrocytes Copyright © 2009 Pearson Education, Inc. These neuroglial cells provide nutrients to neurons 1. Microglia 25% 25% 25% 25% 2. Astrocytes 3. Oligodenrocytes 4. Schwann cells Microglia Astrocytes Schwann cells Oligodenrocytes Copyright © 2009 Pearson Education, Inc. These are projections of the neuron cell body that carry messages to the cell body 50% 50% 1. Axons 2. Dendrites Axons Dendrites Copyright © 2009 Pearson Education, Inc. These are projections of the neuron cell body that carry messages to the cell body 50% 50% 1. Axons 2. Dendrites Axons Dendrites Copyright © 2009 Pearson Education, Inc. Which of the following type of neuron would alert the brain that you had touched a hot object? 50% 50% 1. efferent neuron 2. afferent neuron efferent neuron afferent neuron Copyright © 2009 Pearson Education, Inc. Which of the following type of neuron would alert the brain that you had touched a hot object? 50% 50% 1. efferent neuron 2. afferent neuron efferent neuron afferent neuron Copyright © 2009 Pearson Education, Inc. What type of neuron is the arrow pointing to? 50% 50% 1. Sensory 2. Motor Motor Sensory Copyright © 2009 Pearson Education, Inc. What type of neuron is the arrow pointing to? 50% 50% 1. Sensory 2. Motor Motor Sensory Copyright © 2009 Pearson Education, Inc. Myelinated Neurons . Neurons that have axons covered with neuroglial cells that contain the protein myelin are called myelinated neurons. Copyright © 2009 Pearson Education, Inc. Functions of Myelin Sheaths 1. The main benefit of myelin sheaths is that myelinated neurons are able to carry messages faster than non-myelinated neurons. 2. Myelin sheaths from Schwann cells also help regenerate injured PNS neuron axons. Copyright © 2009 Pearson Education, Inc. Two Types of Cells Myelinate neurons . Schwann cells and Oligodenrocytes are wrapped around neuronal axons. Copyright © 2009 Pearson Education, Inc. Myelinated Neurons . Schwann cells are found in the PNS. Oligodendrocytes are found in the CNS. Nodes of Ranvier are spaces on the axon between the glial cells. Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. Myelin Sheath Copyright © 2009 Pearson Education, Inc. Figure 7.3b Myelin Sheath Copyright © 2009 Pearson Education, Inc. Figure 7.3c Myelinated Neurons Nucleus Dendrites Cell body In saltatory conduction, the nerve impulses jump from one node of Ranvier to the next. Node of Ranvier Schwann cell Myelin sheath (a) Copyright © 2009 Pearson Education, Inc. Figure 7.3a Multiple Sclerosis (MS) . Caused by the destruction of the myelin sheath that surrounds axons found in the CNS. Can result in paralysis and loss of sensation, including loss of vision. Copyright © 2009 Pearson Education, Inc. Nerves . Nerves contain Neuron axons that are bundled together. These bundles contain: . Axons . Blood vessels . Connective tissue Copyright © 2009 Pearson Education, Inc. Nerve Connective tissue surrounding one nerve Blood supply Axons within a connective tissue sheath One axon (d) The anatomy of a nerve Copyright © 2009 Pearson Education, Inc. Figure 8.9d An Ion is an atom that has gained or lost a 1. Neutron 33% 33% 33% 2. Proton 3. Electron Proton Neutron Electron Copyright © 2009 Pearson Education, Inc. An Ion is an atom that has gained or lost a 1. Neutron 33% 33% 33% 2. Proton 3. Electron Proton Neutron Electron Copyright © 2009 Pearson Education, Inc. How can an ion pass through a membrane 20% 20% 20% 20% 20% 1. Simple diffusion 2. Facilitated diffusion 3. Active transport 4. Both 2 and 3 5. All of the above Both 2 and 3 Simple diffusion Active transport All of the above Facilitated diffusion Copyright © 2009 Pearson Education, Inc. How can an ion pass through a membrane 20% 20% 20% 20% 20% 1. Simple diffusion 2. Facilitated diffusion 3. Active transport 4. Both 2 and 3 5. All of the above Both 2 and 3 Simple diffusion Active transport All of the above Facilitated diffusion Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Is an Electrochemical Signal . A nerve impulse, or action potential, involves sodium ions (Na+) and potassium ions (K+) that cross the cell membrane through ion channels. Each ion channel is designed to allow only certain ions to pass through. Copyright © 2009 Pearson Education, Inc. Action Potential Cross section Axon membrane Neuron plasma Extracellular membrane fluid Cytoplasm Continually open ion channels “Gated” ion channels Sodium-potassium pump Ion channels Sodium-potassium pump Ion channels can be open continuously or opened and The sodium-potassium pump closed by a molecular gate uses cellular energy (ATP) to pump sodium ions out of the cell and potassium ions into the cell Copyright © 2009 Pearson Education, Inc. Figure 7.4 Membrane Potential . The difference in charge between the inside and outside of the neuron is the membrane potential. Copyright © 2009 Pearson Education, Inc. Resting Membrane Potential . A neuron that is not conducting a message is said to be “Resting”. When a neuron is resting there is more sodium (Na+) outside the neuron cell and more potassium (K+) inside the cell. The inside of the cell has a negative charge compared to the outside the cell. Copyright © 2009 Pearson Education, Inc. Resting Membrane Potential Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Copyright © 2009 Pearson Education, Inc. Figure 7.5 (1 of 4) Sodium Potassium