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Nervous Tissue 11 Nervous Tissue Lecture Presentation by Lori Garrett © 2018 Pearson Education, Inc. Section 1: Cellular Organization of the Nervous System Learning Outcomes 11.1 Describe the anatomical and functional divisions of the nervous system. 11.2 Sketch and label the structure of a typical neuron, and describe the functions of each component. 11.3 Classify and describe neurons on the basis of their structure and function. © 2018 Pearson Education, Inc. Section 1: Cellular Organization of the Nervous System Learning Outcomes (continued) 11.5 Describe the locations and functions of Schwann cells and satellite cells. 11.4 Describe the locations and functions of neuroglia in the CNS. © 2018 Pearson Education, Inc. Module 11.1: The nervous system has three divisions: the CNS, PNS, and ENS Nervous system—three divisions 1. Central nervous system (CNS) • Brain and spinal cord • Information processing—integrates, processes, coordinates sensory and motor commands 2. Peripheral nervous system (PNS) • All nervous tissue outside CNS, excluding the ENS 3. Enteric nervous system (ENS) • Neural tissues in wall of gastrointestinal tract; helps control digestive function © 2018 Pearson Education, Inc. Module 11.1: Nervous system divisions Subdivisions of the peripheral nervous system . Sensory (afferent) division brings information to CNS from receptors in peripheral tissues and organs • Sensory receptors – Position, touch, pressure, pain, temperature • Special sensory organs – Smell, taste, sight, balance, hearing © 2018 Pearson Education, Inc. Module 11.1: Nervous system divisions . Motor (efferent) division carries motor commands from CNS • Somatic nervous system (SNS) – Voluntary nervous system—conscious control of movement – To skeletal muscles; conscious control of movement • Autonomic nervous system (ANS) – Involuntary nervous system—automatically regulates activities – To smooth muscle, cardiac muscle, glands, adipose tissue © 2018 Pearson Education, Inc. Module 11.1: Nervous system divisions General functions of the nervous system 1. Receptors detect changes in internal or external environment 2. Information is sent to the CNS by the sensory division of the PNS 3. Information processing (integration and distribution of information) occurs in the CNS 4. Motor commands are carried by the motor division of the PNS 5. Effectors respond to those commands and change their activities © 2018 Pearson Education, Inc. Overview of nervous system function © 2018 Pearson Education, Inc. Overview of nervous system function © 2018 Pearson Education, Inc. Overview of nervous system function © 2018 Pearson Education, Inc. Overview of nervous system function 3 © 2018 Pearson Education, Inc. Overview of nervous system function 3 © 2018 Pearson Education, Inc. Module 11.1: Review A. Compare the central and peripheral nervous systems. B. Which division of the PNS brings information to the CNS? C. Name the effectors of the ANS. Learning Outcome: Describe the anatomical and functional divisions of the nervous system. © 2018 Pearson Education, Inc. Module 11.2: Neurons are nerve cells specialized for intercellular communication Neurons . Three general regions 1. Dendrites receive stimuli from environment/other neurons 2. Cell body—contains nucleus, other organelles 3. Axon—carries information toward other cells © 2018 Pearson Education, Inc. Module 11.2: Neurons Dendrites . Highly branched, with dendritic spines . CNS neurons receive most information here Cell body . Perikaryon = cytoplasm; contains organelles that provide energy/synthesize neurotransmitters © 2018 Pearson Education, Inc. Module 11.2: Neurons Cell body (continued) . Cytoskeleton contains • Neurofilaments—similar to intermediate filaments • Neurofibrils—bundles of neurofilaments; extend into and support dendrites and axon © 2018 Pearson Education, Inc. Module 11.2: Neurons Axon components . Axon hillock—origin of axon from cell body . Initial segment—where action potential is initiated . Axolemma—axon’s plasma membrane . Axoplasm—axon’s cytoplasm; contains neurofibrils, neurotubules, vesicles, lysosomes, mitochondria, enzymes Telondendria . = Fine extensions; end at axon terminals (synaptic terminals) © 2018 Pearson Education, Inc. Structure of a neuron © 2018 Pearson Education, Inc. Module 11.2: Neurons Transport of materials . Most organelles are in cell body . Materials travel along axon via neurotubules (neuron microtubules) • Process is axoplasmic transport • Occurs in both directions • Retrograde flow = movement back toward cell body © 2018 Pearson Education, Inc. Module 11.2: Neurons Synapse = Where neuron (presynaptic cell) communicates with another cell (postsynaptic cell) . Most common type—neurotransmitter released from presynaptic membrane into synaptic cleft (narrow space between the cells); binds receptors on postsynaptic membrane . Neurotransmitters are packaged in synaptic vesicles in axon terminals . Collateral branches allow a single neuron to communicate with more than one other cell. © 2018 Pearson Education, Inc. Types of synapses © 2018 Pearson Education, Inc. Module 11.2: Neurons Neuron replacement . Most CNS neurons lack centrioles—cannot divide • If lost to injury or disease, seldom replaced . Some neural stem cells exist, but most are inactive • Exceptions – Olfactory epithelium (smell) – Retina of the eye (vision) – Hippocampus (memory) © 2018 Pearson Education, Inc. Module 11.2: Review A. Name the structural components of a typical neuron. B. Describe a synapse. C. Compare presynaptic and postsynaptic cells. D. Why is a CNS neuron not usually replaced after it is injured? Learning Outcome: Sketch and label the structure of a typical neuron, and describe the functions of each component. © 2018 Pearson Education, Inc. Module 11.3: Neurons are classified on the basis of structure and function Four major anatomical classes of neurons 1. Anaxonic neurons • Small neurons, lacking features distinguishing axons from dendrites (all cell processes look alike) • Located in brain and special sense organs • Functions are poorly understood © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function 2. Bipolar neurons • Two distinct processes – Dendritic process that branches – Axon • Rare, but occur in special sense organs • Small © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function 3. Unipolar neurons • Dendrites and axons continuous (fused) • Cell body off to one side • Initial segment is where dendrites converge – Remaining part of process is considered “axon” • Includes most sensory neurons in peripheral nervous system – Axons may extend a meter or more—longest carry sensations from toes to spinal cord © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function 4. Multipolar neurons • Two or more dendrites and single axon • Most common neurons in CNS • All motor neurons to skeletal muscles are multipolar • Can be as long as unipolar neurons— longest carry motor signals from spinal cord to muscles that move toes © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function Neuron function within the CNS and PNS Three major functional classes of neurons 1. Sensory neurons ~10 million 2. Interneurons ~20 billion 3. Motor neurons ~500,000 © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function Classification of sensory receptors . Sensory receptors—Detect stimuli; are processes of sensory neurons or cells monitored by sensory neurons • Interoceptors (intero-, inside) – Monitor internal organs/systems – Detect distension (stretch), deep pressure, pain • Proprioceptors – Monitor position/movement of skeletal muscles/joints • Exteroceptors (extero, outside) – Monitor external environment (touch, temperature, pressure, input for special senses) © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function Afferent fibers carry sensory information to CNS . Ganglion = collection of neuron cell bodies in PNS Sensory neurons = mostly unipolar neurons with cell bodies in sensory ganglia • Somatic sensory neurons—monitor outside world and body position/awareness • Visceral sensory neurons—monitor internal conditions and organ systems © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function Interneurons—located in CNS . Usually between sensory and motor neurons . Receive information from PNS and CNS . Also responsible for higher functions (e.g., memory, learning) © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function Somatic motor neurons innervate skeletal muscles; provide conscious control . Cell body lies in CNS; axon extends within a peripheral nerve (nerve = a bundle of axons in the PNS) Visceral motor neurons—part of the autonomic nervous system (parasympathetic and sympathetic divisions); innervate all other effectors (smooth muscle, cardiac muscle, glands, adipose tissue) . Located in CNS and PNS . Autonomic ganglia—location of cell bodies for visceral motor neurons going to peripheral receptors. © 2018 Pearson Education, Inc. Module 11.3: Neuron structure/function Efferent fibers carry information from CNS to effectors (somatic effectors—skeletal muscles; visceral effectors—cardiac or smooth muscle and glands) © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Module 11.3: Review A. Classify neurons based on their structure. B. Classify neurons based on their function. C. Are unipolar neurons in a tissue sample of the PNS more likely to have a sensory or a motor function? Learning Outcome:
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