The Nervous System: Neural Tissue Chapter 13

Human Anatomy, 3rd edition Prentice Hall, © 2001 Introduction Nervous system = control center & communications network Functions –Stimulates movements –Maintains homeostasis (with endocrine system)

Human Anatomy, 3rd edition Prentice Hall, © 2001 Organization of the Nervous System

Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) Nerve fibers that carry information from the central nervous system Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Histology of Nervous Tissue 2 types of cells –Neurons Structural & functional part of nervous system Specialized functions –Neuroglia (glial cells) Gli = glue Support & protection of nervous system

Neuroglia Neuroglia of CNS –Astrocytes –Oligodendrocytes –Microglia –Ependymal cells

Neuroglia of CNS Astrocytes Form the blood- brain barrier Structural framework for CNS Repair damaged neural tissue Control the interstitial environment of the brain Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Neuroglia of CNS Oligodendrocytes Produce myelin sheath around nerve fibers in the central nervous system Marieb, Essentials of Anatomy and Physiology, 8 th edition, 2006

Neuroglia of CNS Microglia Spider-like phagocytes Dispose of debris Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Neuroglia of CNS Ependymal cells Line ventricles of the brain and spinal cord Secrete cerebrospinal fluid Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Human Anatomy, 3rd edition Prentice Hall, © 2001 Neuroglia of CNS

Neuroglia of PNS Schwann cells –Form myelin sheaths of PNS Satellite cells Marieb, Essentials of Anatomy and Physiology, 8 th edition, 2006

Human Anatomy, 3rd edition Prentice Hall, © 2001 Neurons Function –Conduct electrical impulses Structure –Cell body Nucleus with nucleolus Cytoplasm (perikaryon) –Cytoplasmic processes Dendrites Axon

Human Anatomy, 3rd edition Prentice Hall, © 2001 Axon Structure Long, specialized –Collaterals = branches –Telodendria = termination of axons & collaterals Cytoplasm = axoplasm Plasma membrane = axolemma

Human Anatomy, 3rd edition Prentice Hall, © 2001 Anatomy of a Neuron

Nerve Fibers of the PNS An axon and its sheaths –Myelinated axon Axon is surrounded by a myelin sheath –Unmyelinated axon Axon has no myelin sheath

Myelin White matter of nerves, brain, spinal cord Composed primarily of phospholipids Production –Developing Schwann cells wind around axon Neurilemma –Peripheral cytoplasmic layer of the Schwann cell enclosing the myelin sheath Marieb, Essentials of Anatomy and Physiology, 8 th edition, 2006

Human Anatomy, 3rd edition Prentice Hall, © 2001 A Myelinated Axon Function of myelin –Increases speed of impulse conduction –Insulation and maintenance of axon Nodes of Ranvier –Unmyelinated gaps between segments of myelin –Impulses “jump” from node to node

Human Anatomy, 3rd edition Prentice Hall, © 2001 Nerve Fibers of the CNS Unmyelinated Myelinated –Production of myelin is from oligodendrocytes –Nodes of Ranvier are less numerous

Human Anatomy, 3rd edition Prentice Hall, © 2001 Structural Classification of Neurons Based on the number of cytoplasmic processes

Human Anatomy, 3rd edition Prentice Hall, © 2001 Functional Classification of Neurons Based on the direction of impulse transmission –Sensory neurons –Motor neurons –Interneurons (association)

Nerve Impulse A change in charge that travels as a wave along the membrane of a neuron Called an action potential Depends on the movement of sodium ions (Na + ) and potassium ions (K + ) between the interstitial fluid and the inside of the neuron.

Human Anatomy, 3rd edition Prentice Hall, © 2001 Resting Potential Sodium ions are in large concentration along the outside of the cell membrane Potassium ions are in large concentration along the inside of the cell membrane

Beginning of a Nerve Impulse Requires a stimulus of adequate strength Membrane is irritable –Neuron may respond to a stimulus and convert it to an impulse. When? –If above threshold

Starting a Nerve Impulse Depolarization – a stimulus depolarizes the neuron’s membrane A depolarized membrane allows sodium (Na + ) to flow inside the membrane The exchange of ions initiates an action potential in the neuron Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

The Action Potential If the action potential starts, it is propogated over the entire axon Potassium ions rush out of the neuron after sodium ions rush in –Repolarizes the membrane

Return to Resting Potential Sodium-potassium pump restores original configuration –Requires ATP

Nerve Impulse Propagation The impulse continues to move away from the cell body Impulses travel faster when fibers have a myelin sheath Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Continuation of the Nerve Impulse Between Neurons Impulses are able to cross a synapse to another nerve –Neurotransmitter is released from the axon terminal (synaptic knob) into synaptic cleft –The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Synaptic Cleft Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Postsynaptic Membrane Receptor Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006

Human Anatomy, 3rd edition Prentice Hall, © 2001 Synapse

Human Anatomy, 3rd edition Prentice Hall, © 2001 Neural Regeneration After Injury

Human Anatomy, 3rd edition Prentice Hall, © 2001 Neural Regeneration

Human Anatomy, 3rd edition Prentice Hall, © 2001 Neural Regeneration

Human Anatomy, 3rd edition Prentice Hall, © 2001 Neural Regeneration

Nerves Neurons are bundled into fasciculi which are bundled into nerves. –Endoneurium surrounds each nerve fiber (axon) –Groups of fibers are bound into fascicles Surrounded by the perineurium –Fascicles are bound together into a nerve Surrounded by the epineurium Marieb, Essentials of Human Anatomy and Physiology, 8 th edition, 2006