Human Anatomy and Physiology Chapter 11 PDF

Human Anatomy and Physiology Tenth Edition Chapter 11 Part A Fundamentals of the nervous system and nervous tissue Copyright ©...

Human Anatomy and Physiology Tenth Edition Chapter 11 Part A Fundamentals of the nervous system and nervous tissue Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.1 Functions of Nervous System (1 of 6) Nervous system is master controlling and communicating system of body Cells communicate via electrical and chemical signals – Rapid and specific – Usually cause almost immediate responses Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.1 Functions of Nervous System (2 of 6) Nervous system has three overlapping functions 1. Sensory input  Information gathered by sensory receptors about internal and external changes 2. Integration  Processing and interpretation of sensory input 3. Motor output  Activation of effector organs (muscles and glands) produces a response Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.1 The Nervous System's Functions Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.1 Functions of Nervous System (3 of 6) Nervous system is divided into two principal parts: – Central nervous system (CNS)  Brain and spinal cord of dorsal body cavity  Integration and control center – Interprets sensory input and dictates motor output – Peripheral nervous system (PNS)  The portion of nervous system outside CNS  Consists mainly of nerves that extend from brain and spinal cord – Spinal nerves to and from spinal cord – Cranial nerves to and from brain Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.2 The Nervous System Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.1 Functions of Nervous System (4 of 6) Peripheral nervous system (PNS) has two functional divisions – Sensory (afferent) division  Somatic sensory fibers: convey impulses from skin, skeletal muscles, and joints to CNS  Visceral sensory fibers: convey impulses from visceral organs to CNS – Motor (efferent) division  Transmits impulses from CNS to effector organs – Muscles and glands  Two divisions – Somatic nervous system – Autonomic nervous system Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.1 Functions of Nervous System (5 of 6) Somatic nervous system – Somatic motor nerve fibers conduct impulses from CNS to skeletal muscle – Voluntary nervous system  Conscious control of skeletal muscles Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.1 Functions of Nervous System (6 of 6) Autonomic nervous system – Consists of visceral motor nerve fibers – Regulates smooth muscle, cardiac muscle, and glands – Involuntary nervous system – Two functional subdivisions  Sympathetic  Parasympathetic  Work in opposition to each other Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.3 Organization of the Nervous System Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.2 Neuroglia Nervous tissue consists of two principal cell types – Neuroglia (glial cells): small cells that surround and wrap delicate neurons – Neurons (nerve cells): excitable cells that transmit electrical signals Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuroglia of the CNS (1 of 6) Four main neuroglia support CNS neurons – Astrocytes – Microglial cells – Ependymal cells – Oligodendrocytes Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuroglia of the CNS (2 of 6) Astrocytes – Most abundant, versatile, and highly branched of glial cells – Cling to neurons, synaptic endings, and capillaries Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuroglia of the CNS (3 of 6) Astrocytes – Functions include:  Support and brace neurons  Play role in exchanges between capillaries and neurons  Guide migration of young neurons  Control chemical environment around neurons  Respond to nerve impulses and neurotransmitters  Influence neuronal functioning  Participate in information processing in brain Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.4a Neuroglia Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuroglia of the CNS (4 of 6) Microglial cells – Small, ovoid cells with thorny processes that touch and monitor neurons – Migrate toward injured neurons – Can transform to phagocytize microorganisms and neuronal debris Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.4b Neuroglia Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuroglia of the CNS (5 of 6) Ependymal cells – Range in shape from squamous to columnar – May be ciliated  Cilia beat to circulate CSF – Line the central cavities of the brain and spinal column – Form permeable barrier between cerebrospinal fluid (CSF) in cavities and tissue fluid bathing CNS cells Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.4c Neuroglia Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuroglia of the CNS (6 of 6) Oligodendrocytes – Branched cells – Processes wrap CNS nerve fibers, forming insulating myelin sheaths in thicker nerve fibers Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.4d Neuroglia (1 of 2) Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuroglia of PNS Two major neuroglia seen in PNS Satellite cells – Surround neuron cell bodies in PNS – Function similar to astrocytes of CNS Schwann cells (neurolemmocytes) – Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers  Similar function as oligodendrocytes – Vital to regeneration of damaged peripheral nerve fibers Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.4e Neuroglia Copyright © 2016 Pearson Education, Inc. All Rights Reserved 11.3 Neurons Neurons (nerve cells) are structural units of nervous system Large, highly specialized cells that conduct impulses Special characteristics – Extreme longevity (lasts a person’s lifetime) – Amitotic, with few exceptions – High metabolic rate: requires continuous supply of oxygen and glucose All have cell body and one or more processes Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Cell Body (1 of 2) Also called the soma Biosynthetic center of neuron – Synthesizes proteins, membranes, chemicals – Rough ER (chromatophilic substance, or Nissl bodies) Contains spherical nucleus with nucleolus Some contain pigments In most, plasma membrane is part of receptive region that receives input info from other neurons Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Cell Body (2 of 2) Most neuron cell bodies are located in CNS – Nuclei: clusters of neuron cell bodies in CNS – Ganglia: clusters of neuron cell bodies in PNS Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (1 of 10) Armlike processes that extend from cell body – CNS contains both neuron cell bodies and their processes – PNS contains chiefly neuron processes Tracts – Bundles of neuron processes in CNS Nerves – Bundles of neuron processes in PNS Two types of processes – Dendrites – Axon Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.5a Structure of a Motor Neuron (1 of 2) Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (2 of 10) Dendrites – Motor neurons can contain 100s of these short, tapering, diffusely branched processes  Contain same organelles as in cell body – Receptive (input) region of neuron – Convey incoming messages toward cell body as graded potentials (short distance signals) – In many brain areas, finer dendrites are highly specialized to collect information  Contain dendritic spines, appendages with bulbous or spiky ends Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.5b Structure of a Motor Neuron Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (3 of 10) The axon: structure – Each neuron has one axon that starts at cone-shaped area called axon hillock – In some neurons, axons are short or absent; in others, axon comprises almost entire length of cell  Some axons can be over 1 meter long – Long axons are called nerve fibers – Axons branch profusely at their end (terminus)  Can number as many as 10,000 terminal branches – Distal endings are called axon terminals or terminal boutons Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (4 of 10) The axon: functional characteristics – Axon is the conducting region of neuron – Generates nerve impulses and transmits them along axolemma (neuron cell membrane) to axon terminal  Terminal: region that secretes neurotransmitters, which are released into extracellular space  Can excite or inhibit neurons it contacts – Carries on many conversations with different neurons at same time – Axons rely on cell bodies to renew proteins and membranes – Quickly decay if cut or damaged Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (5 of 10) The axon: functional characteristics – Axons have efficient internal transport mechanisms  Molecules and organelles are moved along axons by motor proteins and cytoskeletal elements – Movement occurs in both directions  Anterograde: away from cell body – Examples: mitochondria, cytoskeletal elements, membrane components, enzymes  Retrograde: toward cell body – Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (6 of 10) Myelin sheath – Composed of myelin, a whitish, protein-lipid substance – Function of myelin  Protect and electrically insulate axon  Increase speed of nerve impulse transmission – Myelinated fibers: segmented sheath surrounds most long or large-diameter axons – Nonmyelinated fibers: do not contain sheath  Conduct impulses more slowly Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (7 of 10) Myelination in the PNS – Formed by Schwann cells  Wraps around axon in jelly roll fashion  One cell forms one segment of myelin sheath – Outer collar of perinuclear cytoplasm (formerly called neurilemma): peripheral bulge containing nucleus and most of cytoplasm – Plasma membranes have less protein  No channels or carriers, so good electrical insulators  Interlocking proteins bind adjacent myelin membranes Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.6a PNS Nerve Fiber Myelination Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.6b PNS Nerve Fiber Myelination Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (8 of 10) Myelination in the PNS – Myelin sheath gaps  Gaps between adjacent Schwann cells  Sites where axon collaterals can emerge  Formerly called nodes of Ranvier – Nonmyelinated fibers  Thin fibers not wrapped in myelin; surrounded by Schwann cells but no coiling; one cell may surround 15 different fibers Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.5a Structure of a Motor Neuron (2 of 2) Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (9 of 10) Myelin sheaths in the CNS – Formed by processes of oligodendrocytes, not whole cells – Each cell can wrap up to 60 axons at once – Myelin sheath gap is present – No outer collar of perinuclear cytoplasm – Thinnest fibers are unmyelinated, but covered by long extensions of adjacent neuroglia Copyright © 2016 Pearson Education, Inc. All Rights Reserved Neuron Processes (10 of 10) Myelin sheaths in the CNS – White matter: regions of brain and spinal cord with dense collections of myelinated fibers  Usually fiber tracts – Gray matter: mostly neuron cell bodies and nonmyelinated fibers Copyright © 2016 Pearson Education, Inc. All Rights Reserved Figure 11.4d Neuroglia (2 of 2) Copyright © 2016 Pearson Education, Inc. All Rights Reserved Classification of Neurons (1 of 3) Structural classification – Three types grouped by number of processes 1. Multipolar: three or more processes (one axon, others dendrites) – Most common and major neuron type in CNS 2. Bipolar: two processes (one axon, one dendrite) – Rare (ex: retina and olfactory mucosa) 3. Unipolar: one T-like process (two axons) – Also called pseudounipolar Copyright © 2016 Pearson Education, Inc. All Rights Reserved Table 11.1 Comparison of Structural Classes of Neurons (1 of 5) Table 11.1 Comparison of Structural Classes of Neurons Neuron Type Blank Blank Multipolar Bipolar Unipolar (Pseudounipolar) Structural Class: Neuron Blank Blank Type According to the Number of Processes Extending from the Cell Body Many processes extend from Two processes extend from One process extends from the cell the cell body. All are dendrites the cell body. One is a fused body and forms central and except for a single axon. dendrite, the other is an axon. peripheral processes, which together comprise an axon. The neuron has a cell body at the The neuron has a cell body in line end of a long axon. dendrites branch with the axon and the long cordlike In the neuron, the axon extends from the directly from the cell body. fused dendrite, which branches at branched receptive endings to the its free end. branched extensions of the central process. The cell body is off set from the axon. Copyright © 2016 Pearson Education, Inc. All Rights Reserved Table 11.1 Comparison of Structural Classes of Neurons (2 of 5) Neuron Type Blank Blank Multipolar Bipolar Unipolar (Pseudounipolar) Relationship of Anatomy to Blank Blank the Three Functional Regions A multipolar neuron, with receptive, A bipolar neuron, with receptive, A unipolar neuron, with receptive, conducting, and secretory regions conducting, and secretory regions conducting, and secretory regions indicated. indicated. indicated. Copyright © 2016 Pearson Education, Inc. All Rights Reserved Table 11.1 Comparison of Structural Classes of Neurons (3 of 5) Table 11.1 Comparison of Structural Classes of Neurons Neuron Type Blank Blank Multipolar Bipolar Unipolar (Pseudounipolar) Relative Abundance and Blank Blank Location in Human Body Most abundant in body. Major Rare. Found in some special Found mainly in the PNS. neuron type in the CNS. sensory organs (olfactory Common only in dorsal root mucosa, eye, ear). ganglia of the spinal cord and sensory ganglia of cranial nerves. Structural Variations Blank Blank Multipolar: The Purkinje cell of the Bipolar: the olfactory cell has Unipolar: The dorsal root ganglion cell cerebellum has an extensive network limited dendritic branching from an has a cell body offset from the axon. The of dendrites branching from multiple elongated cell body and a single peripheral process of the axon branches leaders rooted at the cell body. A axon terminal. The retinal cell has a into receptive endings, and the central pyramidal cell has dendritic branches fused dendrite, which is longer than process of the axon extends in the extending from the axon at intervals. the axon. opposite direction. Copyright © 2016 Pearson Education, Inc. All Rights Reserved Classification of Neurons (2 of 3) Functional classification of neurons – Three types of neurons grouped by direction in which nerve impulse travels relative to CNS 1. Sensory – Transmit impulses from sensory receptors toward CNS – Almost all are unipolar – Cell bodies are located in ganglia in PNS 2. Motor – Carry impulses from CNS to effectors – Multipolar – Most cell bodies are located in CNS (except some autonomic neurons) Copyright © 2016 Pearson Education, Inc. All Rights Reserved Classification of Neurons (3 of 3) Functional classification of neurons – Three types  Interneurons – Also called association neurons – Lie between motor and sensory neurons – Shuttle signals through CNS pathways – Most are entirely within CNS – 99% of body’s neurons are interneurons Copyright © 2016 Pearson Education, Inc. All Rights Reserved