Fundamentals of Anatomy & Physiology Eleventh Edition Chapter 12 Nervous Tissue Lecture Presentation by Deborah A. Hutchinson Seattle University

Learning Outcomes 12-1 Describe the anatomical and functional divisions of the nervous system. 12-2 Sketch and label the structure of a typical neuron, describe the functions of each component, and classify neurons on the basis of their structure and function. 12-3 Describe the locations and functions of the various types of neuroglia. 12-4 Explain how the resting membrane potential is established and maintained and how the membrane potential can change.

Learning Outcomes 12-5 Describe the events involved in the generation and propagation of an action potential and the factors involved in determining the speed of action potential propagation. 12-6 Describe the structure of a synapse, and explain the mechanism involved in synaptic activity. 12-7 Describe the major types of neurotransmitters and neuromodulators, and discuss their effects on postsynaptic membranes. 12-8 Discuss the interactions that enable information processing to occur in nervous tissue.

Fundamentals of Anatomy & Physiology Eleventh Edition Chapter 12 Quiz 1: Figures 12.2 and 12.5

Figure 12–2 The Anatomy of a Typical Neuron. © 2018 Pearson Education, Inc. Figure 12–2 The Anatomy of a Typical Neuron. Dendrites Perikaryon Nucleus Cell body Telodendria Nissl bodies (RER and free ribosomes) Dendritic branches Mitochondrion Axon a This color-coded diagram shows the four general regions of a neuron. Axon hillock Initial segment of axon Axolemma Axon Telodendria Direction of action potential Golgi apparatus Axon terminals Neurofilament Nucleolus Nucleus Dendrite See Figure 12–15 Presynaptic cell b Details of neuron structure and directional movement of an action potential. Postsynaptic cell

Figure 12–5 Neuroglia in the CNS. © 2018 Pearson Education, Inc. Central canal Gray matter White matter Figure 12–5 Neuroglia in the CNS. CENTRAL CANAL Neuroglia in the CNS Ependymal cell Ependymal cells are simple cuboidal epithelial cells that line fluid-filled passageways within the brain and spinal cord. Neuron Gray matter Neuron Microglial cell Microglia are phagocytes that move through nervous tissue removing unwanted substances. Oligodendrocyte Myelinated axons Oligodendrocytes are cells with sheet-like processes that wrap around axons. Internode Astrocyte Astrocytes are star- shaped cells with projections that anchor to capillaries. They form the blood brain barrier, which isolates the CNS from the general circulation. Myelin (cut) White matter Axon Axolemma Node Unmyelinated axon Basement membrane Capillary A diagram of nervous tissue in the CNS showing relationships between neuroglia and neurons

HOmework

Suggested Homework Monday In class: Notes on 12.1 Home: Review 12.1 Notes Notes on 12.2 Review Quiz Figures (2/7) Tuesday In class: Review/Mark 12.1 and 12.2 Notes Notes on 12.3 Review/Study Quiz Figures (2/7)

Fundamentals of Anatomy & Physiology Eleventh Edition Chapter 12 Nervous Tissue Lecture Presentation by Deborah A. Hutchinson Seattle University

Organization

An Introduction to the Nervous System Includes various organs Brain and spinal cord Receptors of sense organs (eyes, ears, etc.) Nerves that connect to other systems Nervous tissue contains two kinds of cells Neurons for intercellular communication Neuroglia (glial cells) Essential to survival and function of neurons Preserve structure of nervous tissue

Divisions of the Nervous System Anatomical divisions of the nervous system Central nervous system Peripheral nervous system

Divisions of the Nervous System Central nervous system (CNS) Brain and spinal cord Consists of nervous tissue, connective tissue, and blood vessels Functions to process and coordinate sensory data from inside and outside body Motor commands control activities of peripheral organs (e.g., skeletal muscles) Higher functions of brain include intelligence, memory, learning, and emotion

Divisions of the Nervous System Peripheral nervous system (PNS) Includes all nervous tissue outside CNS and ENS Delivers sensory information to the CNS Carries motor commands to peripheral tissues Nerves (peripheral nerves) Bundles of axons with connective tissues and blood vessels Carry sensory information and motor commands Cranial nerves connect to brain Spinal nerves attach to spinal cord

Figure 12–1 An Overview of the Nervous System. Central Nervous System (CNS) (brain and spinal cord) Information processing integrates, processes, and coordinates sensory input and motor commands. Peripheral Nervous System (PNS) (nervous tissue outside the CNS and the ENS) Sensory information within afferent division Motor commands within efferent division Somatic nervous system (SNS) Autonomic nervous system (ANS) Parasympathetic division Sympathetic division Smooth muscle Special sensory receptors Visceral sensory receptors Somatic sensory receptors Cardiac muscle monitor smell, taste, vision, balance, and hearing monitor internal organs monitor skeletal muscles, joints, and skin surface Glands Skeletal muscle Adipose tissue Receptors Effectors

Divisions of the Nervous System Functional divisions of the PNS Afferent division Carries sensory information From receptors in peripheral tissues and organs to CNS Efferent division Carries motor commands From CNS to muscles, glands, and adipose tissue

Divisions of the Nervous System Functional divisions of the PNS Receptors Detect changes or respond to stimuli May be neurons or specialized cells May be single cells or complex sensory organs (e.g., eyes, ears) Effectors Target organs that respond to motor commands

Divisions of the Nervous System Efferent division of PNS Somatic nervous system (SNS) Controls skeletal muscle contractions Both voluntary and involuntary (reflexes)

Divisions of the Nervous System Efferent division of PNS Autonomic nervous system (ANS) Controls subconscious actions, contractions of smooth and cardiac muscle, and glandular secretions Sympathetic division has a stimulating effect Parasympathetic division has a relaxing effect

Divisions of the Nervous System Enteric nervous system (ENS) 100 million neurons in walls of digestive tract As many or more than in spinal cord Use the same neurotransmitters as the brain Initiates and coordinates visceral reflexes locally Without instructions from CNS Can be influenced by ANS

Figure 12–1 An Overview of the Nervous System. Central Nervous System (CNS) (brain and spinal cord) Information processing integrates, processes, and coordinates sensory input and motor commands. Peripheral Nervous System (PNS) (nervous tissue outside the CNS and the ENS) Sensory information within afferent division Motor commands within efferent division Somatic nervous system (SNS) Autonomic nervous system (ANS) Parasympathetic division Sympathetic division Smooth muscle Special sensory receptors Visceral sensory receptors Somatic sensory receptors Cardiac muscle monitor smell, taste, vision, balance, and hearing monitor internal organs monitor skeletal muscles, joints, and skin surface Glands Skeletal muscle Adipose tissue Receptors Effectors

Neuron Anatomy

Neurons Neurons Basic functional units of the nervous system Send and receive signals Function in communication, information processing, and control Cell body (soma) Large nucleus and nucleolus Perikaryon (cytoplasm) Mitochondria (produce energy) RER and ribosomes (synthesize proteins)

Neurons Cytoskeleton of perikaryon Neurofilaments and neurotubules Similar to intermediate filaments and microtubules Neurofibrils Bundles of neurofilaments that provide support for dendrites and axon Nissl bodies Dense areas of RER and ribosomes in perikaryon Make nervous tissue appear gray (gray matter) Neurons Neurons

Neurons Dendrites Short and highly branched processes extending from cell body Dendritic spines Fine processes on dendrites Receive information from other neurons 80–90 percent of neuron surface area

Neurons Axon Single, long cytoplasmic process Propagates electrical signals (action potentials) Axoplasm Cytoplasm of axon Contains neurofibrils, neurotubules, enzymes, and organelles

Figure 12–2a The Anatomy of a Typical Neuron. Dendrites Perikaryon Cell body Telodendria Nucleus Axon a This color-coded diagram shows the four general regions of a neuron.

Neurons Structures of the axon Axolemma Plasma membrane of the axon Covers the axoplasm Initial segment Base of axon Axon hillock Thick region that attaches initial segment to cell body

Figure 12–2b The Anatomy of a Typical Neuron. Nissl bodies (RER and free ribosomes) Dendritic branches Mitochondrion Axon hillock Initial segment of axon Axolemma Axon Telodendria Direction of action potential Golgi apparatus Axon terminals Neurofilament Nucleolus Nucleus Dendrite See Figure 12–15 b Details of neuron structure and directional movement of an action potential. Presynaptic cell Postsynaptic cell

Neurons Structures of the axon Collaterals Branches of the axon Telodendria Fine extensions of distal axon Axon terminals (synaptic terminals) Tips of telodendria

Neurons Axonal (axoplasmic) transport Movement of materials between cell body and axon terminals Materials move along neurotubules within axon Powered by mitochondria, kinesin, and dynein

Classification of Neurons Structural and Functional Classification of Neurons

Figure 12–3 Structural Classifications of Neurons. Anaxonic neuron b Bipolar neuron c Unipolar neuron d Multipolar neuron Anaxonic neurons have more than two processes, and they may all be dendrites; axons are not obvious. Bipolar neurons have two processes separated by the cell body. Unipolar neurons have a single elongated process, with the cell body located off to the side. Multipolar neurons have more than two processes; there is a single axon and multiple dendrites. Dendrites Dendrites Initial segment Dendritic branches Cell body Axon Dendrite Cell body Cell Axon body Cell body Axon Axon Axon terminals Axon terminals Axon terminals

Structural Classification of Neurons Anaxonic neurons Small All cell processes look similar Found in brain and special sense organs

Structural Classification of Neurons Bipolar neurons Small and rare One dendrite and one axon Found in special sense organs (sight, smell, hearing)

Structural Classification of Neurons Unipolar neurons (pseudounipolar neurons) Axon and dendrites are fused Cell body to one side Most sensory neurons of PNS

Structural Classification of Neurons Multipolar neurons Have one long axon and two or more dendrites Common in the CNS All motor neurons that control skeletal muscles

Functional Classification of Neurons Functional classifications of neurons Sensory neurons Motor neurons Interneurons

Functional Classification of Neurons Sensory neurons (afferent neurons) Unipolar Cell bodies grouped in sensory ganglia Processes (afferent fibers) extend from sensory receptors to CNS Somatic sensory neurons Monitor external environment Visceral sensory neurons Monitor internal environment

Functional Classification of Neurons Types of sensory receptors Interoceptors Monitor internal systems (e.g., digestive, urinary) Internal senses (stretch, deep pressure, pain) Exteroceptors Monitor external environment (e.g., temperature) Complex senses (e.g., sight, smell, hearing) Proprioceptors Monitor position and movement of skeletal muscles and joints

Functional Classification of Neurons Motor neurons (efferent neurons) Carry instructions from CNS to peripheral effectors Via efferent fibers (axons) Somatic motor neurons of SNS Innervate skeletal muscles Visceral motor neurons of ANS Innervate all other peripheral effectors Smooth and cardiac muscle, glands, adipose tissue

Functional Classification of Neurons Motor neurons Signals from CNS to visceral effectors cross autonomic ganglia that divide axons into Preganglionic fibers Postganglionic fibers

Functional Classification of Neurons Interneurons Most are in brain and spinal cord Some in autonomic ganglia Located between sensory and motor neurons Responsible for Distribution of sensory information Coordination of motor activity Involved in higher functions Memory, planning, learning

Suggested Homework Tuesday In class: Revise 12.1 and 12.2 Notes Actively Read 12.3 Review Guide on Anatomy eText Video (on Teacher Page) PAL – Histology – Nervous Tissue Home: Finish Notes on 12.3 Review/Study Quiz Figures (2/7)

Neuroglia Neuroglia Support and protect neurons Make up half the volume of the nervous system Many types in CNS and PNS

Neuroglia Types of neuroglia in the CNS Astrocytes Ependymal cells Oligodendrocytes Microglia

Neuroglia Astrocytes Have large cell bodies with many processes Function to Maintain blood brain barrier (BBB) Create three-dimensional framework for CNS Repair damaged nervous tissue Guide neuron development Control interstitial environment

Neuroglia Ependymal cells Form epithelium that lines central canal of spinal cord and ventricles of brain Produce and monitor cerebrospinal fluid (CSF) Have cilia that help circulate CSF

Neuroglia Oligodendrocytes Have small cell bodies with few processes Many cooperate to form a myelin sheath Myelin insulates myelinated axons Increases speed of action potentials Makes nerves appear white

Neuroglia Where axons may branch Oligodendrocytes Internodes—myelinated segments of axon Nodes (nodes of Ranvier) lie between internodes Where axons may branch White matter Regions of CNS with many myelinated axons Gray matter of CNS Contains unmyelinated axons, neuron cell bodies, and dendrites

Figure 12–5 Neuroglia in the CNS (Part 2 of 2). Central canal Gray matter White matter Neuroglia in the CNS Oligodendrocyte Oligodendrocytes are cells with sheet-like processes that wrap around axons. Myelinated axons Internode Astrocyte Astrocytes are star- shaped cells with projections that anchor to capillaries. They form the blood brain barrier, which isolates the CNS from the general circulation. Myelin (cut) White matter Axon Axolemma Node Unmyelinated axon Basement membrane Capillary A diagram of nervous tissue in the CNS showing relationships between neuroglia and neurons

Neuroglia Microglia Smallest and least numerous neuroglia Have many fine- branched processes Migrate through nervous tissue Clean up cellular debris, wastes, and pathogens

Figure 12–5 Neuroglia in the CNS (Part 1 of 2). Central canal Gray matter White matter CENTRAL CANAL Neuroglia in the CNS Ependymal cell Ependymal cells are simple cuboidal epithelial cells that line fluid-filled passageways within the brain and spinal cord. Neuron Gray matter Neuron Microglial cell Microglia are phagocytes that move through nervous tissue removing unwanted substances.

Neuroglia Neuroglia of the PNS Insulate neuronal cell bodies and most axons Two types Satellite cells Schwann cells

Figure 12–4 An Introduction to Neuroglia (Part 2 of 2). are found in Peripheral Nervous System contains Satellite cells Schwann cells Surround neuron cell bodies in ganglia; regulate O2, CO2, nutrient, and neurotransmitter levels around neurons in ganglia Surround all axons in PNS; responsible for myelination of peripheral axons; participate in repair process after injury

Neuroglia Neuroglia of the PNS Satellite cells Surround ganglia (clusters of neuronal cell bodies) Regulate interstitial fluid around neurons

Neuroglia Neuroglia of the PNS Schwann cells (neurolemmocytes) Form myelin sheath or indented folds of plasma membrane around axons Neurolemma—outer surface of Schwann cell A myelinating Schwann cell sheaths only one axon Many Schwann cells sheath entire axon

A myelinated axon, showing the organization Figure 12–6a Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath in the PNS (Part 2 of 2). Schwann cell nucleus Myelin covering internode Neurolemma Axon Myelin sheath TEM × 20,600 a A myelinated axon, showing the organization of Schwann cells along the length of the axon.

The enclosing of a group of unmyelinated axons by a Figure 12–6b Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath in the PNS (Part 1 of 2). Schwann cell #1 Schwann cell Schwann cell #2 Schwann cell nucleus Neurolemma Axons Schwann cell #3 nucleus Axons b The enclosing of a group of unmyelinated axons by a single Schwann cell. A series of Schwann cells is required to cover the axons along their entire length.

The enclosing of a group of unmyelinated axons by a Figure 12–6b Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath in the PNS (Part 2 of 2). Neurolemma Axons Schwann cell #3 nucleus Axons Unmyelinated axons TEM × 27,625 b The enclosing of a group of unmyelinated axons by a single Schwann cell. A series of Schwann cells is required to cover the axons along their entire length.

1 2 3 c A Schwann cell first surrounds a portion of the axon within Figure 12–6c Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath in the PNS. 1 A Schwann cell first surrounds a portion of the axon within a groove of its cytoplasm. 2 The Schwann cell then begins to rotate around the axon. 3 As the Schwann cell rotates, myelin is wound around the axon in multiple layers, forming a tightly packed membrane. Schwann cell Myelin Axon Schwann cell cytoplasm c Stages in the formation of a myelin sheath by a single Schwann cell along a portion of a single axon.

Neural Response to Injury Neural responses to injuries Wallerian degeneration Axon distal to injury degenerates Schwann cells Form path for new growth Wrap around new axon Nerve regeneration in CNS Limited by astrocytes, which Produce scar tissue Release chemicals that block regrowth

Figure 12–7 Peripheral Nerve Regeneration after Injury (Part 1 of 4). Fragmentation of axon and myelin occurs in distal stump. Axon Myelin Proximal stump Distal stump

Figure 12–7 Peripheral Nerve Regeneration after Injury (Part 2 of 4). Schwann cells form cord, grow into cut, and unite stumps. Macrophages engulf degenerating axon and myelin. Macrophage Cord of proliferating Schwann cells

Figure 12–7 Peripheral Nerve Regeneration after Injury (Part 3 of 4). Axon sends buds into network of Schwann cells and then starts growing along cord of Schwann cells.

Figure 12–7 Peripheral Nerve Regeneration after Injury (Part 4 of 4). Axon continues to grow into distal stump and is enclosed by Schwann cells.