Capítulo 12 Tejido Nervioso I Biol 3791 UPR – Aguadilla JA Cardé, Ph. D. © 2015 Pearson Education, Inc.

An Introduction to the Nervous System 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. © 2015 Pearson Education, Inc.

An Introduction to the Nervous System Learning Outcomes 12-4 Explain how the resting membrane potential is created and maintained. 12-5 Describe the events involved in the generation and propagation of an action potential. 12-6 Discuss the factors that affect the speed with which action potentials are propagated. © 2015 Pearson Education, Inc.

An Introduction to the Nervous System Learning Outcomes 12-7 Describe the structure of a synapse, and explain the mechanism involved in synaptic activity. 12-8 Describe the major types of neurotransmitters and neuromodulators, and discuss their effects on postsynaptic membranes. 12-9 Discuss the interactions that enable information processing to occur in neural tissue. © 2015 Pearson Education, Inc.

An Introduction to the Nervous System Includes all neural tissue in the body Neural tissue contains two kinds of cells Neurons Cells that send and receive signals Neuroglia (glial cells) Cells that support and protect neurons © 2015 Pearson Education, Inc.

An Introduction to the Nervous System Organs of the Nervous System Brain and spinal cord Sensory receptors of sense organs (eyes, ears, etc.) Nerves connect nervous system with other systems © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System Anatomical Divisions of the Nervous System Central nervous system (CNS) Peripheral nervous system (PNS) © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System The Central Nervous System (CNS) Consists of the spinal cord and brain Contains neural tissue, connective tissues, and blood vessels Functions of the CNS are 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: intelligence, memory, learning, emotion © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System The Peripheral Nervous System (PNS) Includes all neural tissue outside the CNS Functions of the PNS Deliver sensory information to the CNS Carry motor commands to peripheral tissues and systems © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System The Peripheral Nervous System (PNS) Nerves (also called peripheral nerves) Bundles of axons with connective tissues and blood vessels Carry sensory information and motor commands in PNS Cranial nerves – connect to brain Spinal nerves – attach to spinal cord © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System Functional Divisions of the PNS Afferent division Carries sensory information From PNS sensory receptors to CNS Efferent division Carries motor commands From CNS to PNS muscles and glands © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System Functional Divisions of the PNS Receptors and effectors of afferent division Receptors Detect changes or respond to stimuli Neurons and specialized cells Complex sensory organs (e.g., eyes, ears) Effectors Respond to efferent signals Cells and organs © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System Functional Divisions of the PNS The efferent division Somatic nervous system (SNS) Controls voluntary and involuntary (reflexes) skeletal muscle contractions © 2015 Pearson Education, Inc.

12-1 Divisions of the Nervous System Functional Divisions of the PNS The efferent division Autonomic nervous system (ANS) Controls subconscious actions, contractions of smooth muscle and cardiac muscle, and glandular secretions Sympathetic division has a stimulating effect Parasympathetic division has a relaxing effect © 2015 Pearson Education, Inc.

Figure 12-1 A Functional Overview of the Nervous System. Organization of the Nervous System Central Nervous System (CNS) (brain and spinal cord) Integrate, process, and coordinate sensory data and motor commands Sensory information within afferent division Motor commands within efferent division Peripheral Nervous System (PNS) (neural tissue outside the CNS) includes Somatic nervous system (SNS) Autonomic nervous system (ANS) Parasympathetic division Sympathetic division Receptors Effectors Smooth muscle Cardiac muscle Glands Adipose tissue Special sensory receptors Visceral sensory receptors Somatic sensory receptors monitor smell, taste, vision, balance, and hearing monitor internal organs monitor skeletal muscles, joints, and skin surface Skeletal muscle Skeletal muscle

12-2 Neurons Neurons The basic functional units of the nervous system The structure of neurons The multipolar neuron Common in the CNS Cell body (soma) Short, branched dendrites Long, single axon © 2015 Pearson Education, Inc.

12-2 Neurons The Cell Body Large nucleus and nucleolus Perikaryon (cytoplasm) Mitochondria (produce energy) RER and ribosomes (produce neurotransmitters) © 2015 Pearson Education, Inc.

12-2 Neurons The Cell Body Cytoskeleton Nissl bodies Neurofilaments and neurotubules in place of microfilaments and microtubules Neurofibrils: bundles of neurofilaments that provide support for dendrites and axon Nissl bodies Dense areas of RER and ribosomes Make neural tissue appear gray (gray matter) © 2015 Pearson Education, Inc.

12-2 Neurons Dendrites Highly branched Dendritic spines Many fine processes Receive information from other neurons 80–90 percent of neuron surface area © 2015 Pearson Education, Inc.

12-2 Neurons The axon Is long Carries electrical signal (action potential) to target Axon structure is critical to function © 2015 Pearson Education, Inc.

12-2 Neurons Structures of the Axon Axoplasm Axolemma Cytoplasm of axon Contains neurofibrils, neurotubules, enzymes, organelles Axolemma Specialized cell membrane Covers the axoplasm © 2015 Pearson Education, Inc.

12-2 Neurons Structures of the Axon Axon hillock Initial segment Thick section of cell body Attaches to initial segment Initial segment Attaches to axon hillock © 2015 Pearson Education, Inc.

12-2 Neurons Structures of the Axon Collaterals Telodendria Branches of a single axon Telodendria Fine extensions of distal axon Axon terminals Tips of telodendria © 2015 Pearson Education, Inc.

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

Figure 12-2b The Anatomy of a Multipolar 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 12–3 Presynaptic cell b An understanding of neuron function requires knowing its structural components. Postsynaptic cell

12-2 Neurons The Structure of Neurons The synapse Area where a neuron communicates with another cell © 2015 Pearson Education, Inc.

12-2 Neurons The Structure of Neurons The synapse Presynaptic cell Neuron that sends message Postsynaptic cell Cell that receives message The synaptic cleft The small gap that separates the presynaptic membrane and the postsynaptic membrane © 2015 Pearson Education, Inc.

12-2 Neurons The Synapse The synaptic terminal Is expanded area of axon of presynaptic neuron Contains synaptic vesicles of neurotransmitters © 2015 Pearson Education, Inc.

12-2 Neurons Neurotransmitters Are chemical messengers Are released at presynaptic membrane Affect receptors of postsynaptic membrane Are broken down by enzymes Are reassembled at axon terminal © 2015 Pearson Education, Inc.

12-2 Neurons Recycling Neurotransmitters Axoplasmic transport Neurotubules within the axon Transport raw materials Between cell body and axon terminal Powered by mitochondria, kinesin, and dynein © 2015 Pearson Education, Inc.

12-2 Neurons Types of Synapses Neuromuscular junction Synapse between neuron and muscle Neuroglandular junction Synapse between neuron and gland © 2015 Pearson Education, Inc.

Figure 12-3 The Structure of a Typical Synapse. Telodendrion Axon terminal Mitochondrion Synaptic vesicles Presynaptic membrane Postsynaptic membrane Synaptic cleft

12-2 Neurons Structural Classification of Neurons Anaxonic neurons Found in brain and sense organs Bipolar neurons Found in special sensory organs (sight, smell, hearing) Unipolar neurons Found in sensory neurons of PNS Multipolar neurons Common in the CNS Include all skeletal muscle motor neurons © 2015 Pearson Education, Inc.

12-2 Neurons Anaxonic Neurons Bipolar Neurons Small All cell processes look alike Bipolar Neurons Are small One dendrite, one axon © 2015 Pearson Education, Inc.

12-2 Neurons Unipolar Neurons Multipolar Neurons Also called pseudounipolar neurons Have very long axons Fused dendrites and axon Cell body to one side Multipolar Neurons Multiple dendrites, one axon © 2015 Pearson Education, Inc.

Figure 12-4 Structural Classifications of Neurons. Anaxonic neuron Bipolar neuron Unipolar neuron Multipolar neuron Dendrites Dendrites Initial segment Cell body Dendritic branches Axon Dendrite Cell body Cell body Axon Axon Cell body Axon Axon terminals Axon terminals Axon terminals a Anaxonic neurons have more than two processes, and they are all dendrites. b Bipolar neurons have two processes separated by the cell body. c 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. d

Figure 12-4a Structural Classifications of Neurons. Anaxonic neuron Cell body a Anaxonic neurons have more than two processes, and they are all dendrites.

Figure 12-4b Structural Classifications of Neurons. Bipolar neuron Dendritic branches Dendrite Cell body Axon Axon terminals b Bipolar neurons have two processes separated by the cell body.

Figure 12-4c Structural Classifications of Neurons. Unipolar neuron Dendrites Initial segment Axon Cell body Axon Axon terminals Unipolar neurons have a single elongated process, with the cell body located off to the side. c

Figure 12-4d Structural Classifications of Neurons. Multipolar neuron Dendrites Cell body Axon Axon terminals d Multipolar neurons have more than two processes; there is a single axon and multiple dendrites.

12-2 Neurons Three Functional Classifications of Neurons Sensory neurons Afferent neurons of PNS Motor neurons Efferent neurons of PNS Interneurons Association neurons © 2015 Pearson Education, Inc.

12-2 Neurons Functions of Sensory Neurons Monitor internal environment (visceral sensory neurons) Monitor effects of external environment (somatic sensory neurons) Structures of Sensory Neurons Unipolar Cell bodies grouped in sensory ganglia Processes (afferent fibers) extend from sensory receptors to CNS © 2015 Pearson Education, Inc.

12-2 Neurons Three Types of Sensory Receptors Interoceptors Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive) Internal senses (taste, deep pressure, pain) Exteroceptors External senses (touch, temperature, pressure) Distance senses (sight, smell, hearing) Proprioceptors Monitor position and movement (skeletal muscles and joints) © 2015 Pearson Education, Inc.

12-2 Neurons Motor Neurons Carry instructions from CNS to peripheral effectors Via efferent fibers (axons) © 2015 Pearson Education, Inc.

12-2 Neurons Motor Neurons Two major efferent systems Somatic nervous system (SNS) Includes all somatic motor neurons that innervate skeletal muscles Autonomic (visceral) nervous system (ANS) Visceral motor neurons innervate all other peripheral effectors Smooth muscle, cardiac muscle, glands, adipose tissue © 2015 Pearson Education, Inc.

12-2 Neurons Motor Neurons Two groups of efferent axons Signals from CNS motor neurons to visceral effectors pass synapses at autonomic ganglia dividing axons into: Preganglionic fibers Postganglionic fibers © 2015 Pearson Education, Inc.

12-2 Neurons Interneurons Most are located in brain, spinal cord, and autonomic ganglia Between sensory and motor neurons Are responsible for: Distribution of sensory information Coordination of motor activity Are involved in higher functions Memory, planning, learning © 2015 Pearson Education, Inc.