Susan Capasso, Ed.D., CGC St. Vincent’s College Suggested Lecture Presentation Copyright © 2009 Pearson Education, Inc. Chapter 7 Neurons: The Matter of the Mind

Copyright © 2009 Pearson Education, Inc. Neurons: The Matter of the Mind  Neurons and neurological cells are the cells of the nervous system  Neurons have dendrites, a cell body, and an axon  The nerve impulse is an electrochemical signal  Synaptic transmission is communication between neurons

Copyright © 2009 Pearson Education, Inc. Neurons and Neurological Cells: The Cells of the Nervous System  The nervous system  Integrates and coordinates many of the body’s activities

Copyright © 2009 Pearson Education, Inc. Cells of the Nervous System  The nervous system is divided into  The central nervous system (CNS)  The brain and spinal cord  The peripheral nervous system (PNS)  All of the nervous tissue in the body besides the brain and spinal cord

Copyright © 2009 Pearson Education, Inc. Cells of the Nervous System  The nervous system is composed of two types of specialized cells 1.Neurons 2.Neuroglial cells

Copyright © 2009 Pearson Education, Inc. Cells of the Nervous System  Neurons  Excitable cells that generate and transmit messages  Neuroglial cells (also called glial cells)  More numerous and provide structural support, growth factors, and insulating sheaths around the nerves  Able to reproduce, unlike neurons

Copyright © 2009 Pearson Education, Inc. Cells of the Nervous System  Sensory (or afferent) neurons  Carry information toward the CNS from sensory receptors  Motor (or efferent) neurons  Carry information away from the CNS to an effector

Copyright © 2009 Pearson Education, Inc. Cells of the Nervous System  Association neurons (or interneurons)  Located between sensory and motor neurons within the CNS, where they integrate and interpret sensory signals  Account for more than 99% of the body’s neurons

Copyright © 2009 Pearson Education, Inc. Cells of the Nervous System Figure 7.1 Interneuron Sensory receptor for pain Muscle (effector) Motor neuron Sensory neuron Cell body Impulse direction

Copyright © 2009 Pearson Education, Inc. Neurons Have Dendrites, a Cell Body, and an Axon  The shape of a typical neuron is specialized for communicating with other cells. It has:  Many short, branching projections called dendrites (one or more)  A single long extension of the neuron called an axon (one)  A cell body (one) which contains the nucleus and other organelles, and functions to maintain the neuron

Copyright © 2009 Pearson Education, Inc. Neurons Have Dendrites, a Cell Body, and an Axon  Dendrites  Carry information toward the cell body of a neuron  A single long axon  Carries information away from the cell body

Copyright © 2009 Pearson Education, Inc. Neurons Have Dendrites, a Cell Body, and an Axon Figure 7.2 The cell body integrates input from other neurons. Dendrites receive information from other neurons or from the environment. The cell body controls the cell’s metabolic activities. An axon conducts the nerve impulse away from the cell body. Axon endings release chemicals called neurotransmitters that affect the activity of nearby neurons or an effector (muscle or gland). Receiving portion of neuron Sending portion of neuron Cell body Axon endings Nucleus

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon  Nerves  Consist of parallel axons, dendrites, or both from many neurons  Covered with tough connective tissue  Classified as sensory, motor or mixed (sensory and motor together) depending on the type of neurons they contain

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon  Most axons not found in the CNS, and some of those within, are electrically insulated by a myelin sheath which increases the rate of conduction of a nerve impulse

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon  In the PNS, Schwann cells form the myelin sheath, insulating it and allowing messages to travel faster as they jump from one node of Ranvier to the next in a type of transmission called saltatory conduction Animation—Myelinated Neurons and Saltatory Conduction PLAY

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon Figure 7.3a (a) Cell body Dendrites Myelin sheath Node of Ranvier Nucleus Schwann cell In saltatory conduction, the nerve impulses jump from one node of Ranvier to the next.

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon Figure 7.3b

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon Figure 7.3c

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon  The myelin sheath also facilitates nerve repair outside the CNS  When an axon in the PNS is cut, the Schwann cells take part in regeneration as they wrap around an axon

Copyright © 2009 Pearson Education, Inc. Dendrites, Cell Body, and Axon  Multiple sclerosis (MS)  Results from the destruction of the myelin sheath that surrounds axons found in the CNS  The resulting scars (scleroses) interfere with the transmission of nerve impulses  Can result in paralysis and loss of sensation, including loss of vision

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Is an Electrochemical Signal  A nerve impulse, or action potential, is a bioelectrical signal involving sodium ions (Na + ) and potassium ions (K + ) that cross the cell membrane through the ion channels  Each ion channel is designed to allow only certain ions to pass through  Sodium channels only allow sodium ions to pass

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Is an Electrochemical Signal Figure 7.4 Extracellular fluid Neuron plasma membrane Cytoplasm Sodium-potassium pump The sodium-potassium pump uses cellular energy (ATP) to pump sodium ions out of the cell and potassium ions into the cell Continually open ion channels “Gated” ion channels Sodium-potassium pump Ion channels Ion channels can be open continuously or opened and closed by a molecular gate Cross section Axon membrane

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse  Ions are also transported across the membrane by the sodium-potassium pump  Special proteins in the cell membrane that actively transport sodium and potassium ions across the membrane

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Figure 7.4 Extracellular fluid Neuron plasma membrane Cytoplasm Sodium-potassium pump The sodium-potassium pump uses cellular energy (ATP) to pump sodium ions out of the cell and potassium ions into the cell Continually open ion channels “Gated” ion channels Sodium-potassium pump Ion channels Ion channels can be open continuously or opened and closed by a molecular gate Cross section Axon membrane

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse  When a neuron is not conducting a nerve impulse, it is in a resting state  There is a slight difference in charge across the membrane which is called the resting potential

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Figure 7.5 (1 of 4)

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse  When the neuron is stimulated, there is a sudden reversal of charge across the membrane because the sodium gates open and sodium ions enter the cell  The minimum charge that causes the sodium gates to open is called the threshold

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Figure 7.5 (2 of 4)

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Figure 7.5 (3 of 4)

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse  Next, the potassium gates open and potassium ions rush out of the cell, causing the cell to return to the original state, or repolarize

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Figure 7.5 (4 of 4)

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse  An action potential is the sudden reversal of the charge across the membrane followed immediately by its restoration  These changes occur in a wave along the axon

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse  For a very brief period following an action potential, the nerve cannot be stimulated again  This is called the refractory period

Copyright © 2009 Pearson Education, Inc. The Nerve Impulse Figure 7.6 Animation—The Nerve Impulse PLAY

Copyright © 2009 Pearson Education, Inc. Synaptic Transmission Is Communication between Neurons  Communication between neurons is by neurotransmitters, which are chemicals that cross the gap between two neurons

Copyright © 2009 Pearson Education, Inc. Synaptic Transmission Is Communication between Neurons Figure 7.7a Plasma membrane of an axon ending of a sending (presynaptic) neuron Synaptic cleft Synaptic knob Synaptic vesicle Receptor for neurotransmitter Ion channel Plasma membrane of a receiving (postsynaptic) neuron (a)

Copyright © 2009 Pearson Education, Inc. Synaptic Transmission Is Communication between Neurons Figure 7.7b

Copyright © 2009 Pearson Education, Inc. Synaptic Transmission Is Communication between Neurons Figure 7.9 (1 of 2)

Copyright © 2009 Pearson Education, Inc. Synaptic Transmission Is Communication between Neurons Figure 7.9 (2 of 2)

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  Synapse  The junction between a neuron and another cell  Between two neurons  Presynaptic neuron sends a message to the postsynaptic neuron

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  Calcium ions then cause the membrane of the synaptic vesicles to fuse with the plasma membrane, and to release the neurotransmitter substances  There are many neurotransmitter substances

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  Neurotransmitters diffuse across the synaptic cleft to the other side, where they bind with specific receptors on the postsynaptic cell, which causes the ion channels to open

Copyright © 2009 Pearson Education, Inc. Communication between Neurons Figure 7.8 (1 of 3) Nucleus Impulse Synaptic knob Axon Dendrites Cell body Synaptic cleft Synaptic vesicle Impulse Membrane of postsynaptic neuron Step 1: The impulse reaches the axon ending of the presynaptic membrane. Step 2: Synaptic vesicles release neurotransmitter into the synaptic cleft.

Copyright © 2009 Pearson Education, Inc. Communication between Neurons Figure 7.8 (2 of 3) Neurotransmitter Receptor (of sodium ion channel) on postsynaptic membrane Step 3: Neurotransmitter diffuses across synaptic cleft. Synaptic vesicle

Copyright © 2009 Pearson Education, Inc. Communication between Neurons Figure 7.8 (3 of 3) Step 5: Sodium ion channels open. Step 4: Neurotransmitter molecules bind to receptors on the postsynaptic neuron. Step 6: Sodium ions enter the postsynaptic neuron, causing depolarization and possible action potential.

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  If neurotransmission occurs at an excitatory synapse, and enough receptor sites bind with neurotransmitter substances to cause depolarization to the threshold value, an action potential is generated in the postsynaptic cell

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  However, in an inhibitory synapse, the postsynaptic cell becomes more negatively charged, and there is no action potential generated

Copyright © 2009 Pearson Education, Inc. Summation  A neuron may have as many as 10,000 synapses with other neurons at the same time  Some have excitatory effects and some inhibitory effects  Summation is the combined effects of excitatory and inhibitory effects at any given moment to determine whether an action potential is generated  It provides finer control

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  After the neurotransmitter crosses the membrane, it is quickly broken down or pumped back into the synaptic knob of the presynaptic axon  The enzyme acetylcholinesterase removes acetylcholine from synapses Animation—The Synapse PLAY

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  Acetylcholine  Acts in both the PNS and the CNS as a neurotransmitter  Causes voluntary muscles to contract  Myasthenia gravis is an autoimmune disease that attacks the acetylcholine receptors, resulting in little muscle strength

Copyright © 2009 Pearson Education, Inc. Communication between Neurons  The neurotransmitters dopamine, norepinephrine, and serotonin affect our emotional state  Alzheimer’s disease, depression, and Parkinson’s disease are caused by deficiencies of these chemicals in the brain

Copyright © 2009 Pearson Education, Inc. Communication between Neurons Figure 7.10

Copyright © 2009 Pearson Education, Inc. Communication between Neurons Figure 7.11