Master control and communication system

Name: Master control and communication system
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Description: Master control and communication system

Master control and communication system
Nervous System Master control and communication system Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Nervous System: Functions
Three overlapping functions Sensory receptors monitor changes inside and outside the body Change – a stimulus Gathered information – sensory input CNS Processes and interprets sensory input Makes decisions – integration Dictates a response by activating effector organs Response – motor output Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Basic Divisions of the Nervous System: CNS
Central nervous system (CNS) Brain and spinal cord Integrating and command center Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Basic Divisions of the Nervous System: PNS
Peripheral nervous system (PNS) Outside the CNS Nerves extending from brain and spinal cord Cranial nerves Spinal nerves Link all regions of the body to the CNS Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Sensory Input and Motor Output
Sensory signals picked up by sensory receptors Carried by afferent nerve fibers of PNS to the CNS Motor signals are carried away from the CNS Carried by efferent nerve fibers of PNS to effectors Innervate muscles and glands Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Sensory Input and Motor Output
Divided according to region they serve Somatic body region Visceral body region Results in four main subdivisions Somatic sensory Visceral sensory Somatic motor Visceral motor Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Somatic Sensory Somatic sensory
General somatic senses – receptors are widely spread Touch, pain, vibration, pressure, and temperature Proprioceptive senses – detect stretch in tendons and muscle Body sense – position and movement of body in space Special somatic senses Hearing, balance, vision, and smell Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Visceral Sensory Visceral sensory
General visceral senses – stretch, pain, temperature, nausea, and hunger Widely felt in digestive and urinary tracts, reproductive organs Special visceral senses – taste Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Somatic Motor Somatic motor
General somatic motor – signals contraction of skeletal muscles Under voluntary control Often called “voluntary nervous system” Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Visceral Motor Visceral motor
Regulates the contraction of smooth and cardiac muscle and gland secretion Makes up autonomic nervous system Controls function of visceral organs Often called “involuntary nervous system” Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Peripheral Nervous System Summary
Figure 12.3 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Types of Sensory and Motor Information

Cells are densely packed and intertwined
Nervous Tissue Cells are densely packed and intertwined Two main cell types Neurons – transmit electrical signals Support cells (neuroglial cells) – nonexcitable Surround and wrap neurons Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

The human body contains billions of neurons
The Neuron The human body contains billions of neurons Basic structural unit of the nervous system Specialized cells conduct electrical impulses along the plasma membrane Graded potentials Action potentials Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

The Neuron: Special Characteristics
Longevity – can live and function for a lifetime Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

The Cell Body or Soma (also called Perikaryon)
Size varies from 5–140µm Contains nucleus, organelles plus other structures Chromatophilic bodies (Nissl bodies) Clusters of rough ER and free ribosomes Stain darkly and renew membranes of the cell Neurofibrils – bundles of intermediate filaments Form a network between chromatophilic bodies Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Most neuronal cell bodies
The Cell Body Most neuronal cell bodies Located within the CNS (clustered in nuclei) Protected by bones of the skull and vertebral column Ganglia – clusters of cell bodies in PNS Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Cell Body Structure Figure 12.4
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Processes: Dendrites
Extensively branching from the cell body Transmit electrical signals (graded potentials) toward the cell body Chromatophilic bodies – only extend into the basal part of dendrites Function as receptive sites Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Processes: Axons
Axons (nerve fibers) Neuron has only one, but it can branch Impulse generator and conductor Transmits action potentials away from the cell body Chromatophilic bodies absent No protein synthesis in axon Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Processes: Axons
Neurofilaments, actin microfilaments, and microtubules Provide strength along length of axon Aid in the transport of substances to and from the cell body Axonal transport Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Processes Axons Branches along length are infrequent
Axon collaterals Multiple branches at end of axon Terminal branches (telodendria) End in knobs called axon terminals (also called end bulbs or boutons) Neuron Structure Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Processes: Action Potentials
Nerve impulse (action potential) Generated at the initial segment of the axon Conducted along the axon Releases neurotransmitters at axon terminals Neurotransmitters – excite or inhibit neurons Neuron receives and sends signals Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Site at which neurons communicate
Synapses Site at which neurons communicate Signals pass across synapse in one direction Presynaptic neuron Conducts signal toward a synapse Postsynaptic neuron Transmits electrical activity away from a synapse Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Two Neurons Communicating at a Synapse

Structure of a Synapses
PLAY Synapse Figure 12.8a, b Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Signals Carried by Neurons: Resting Membrane Potential
Plasma membranes of neurons conduct electrical signals Resting neuron – membrane is polarized Inner, cytoplasmic side is negatively charged Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Changes in Membrane Potential
Signals occur as changes in membrane potential Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Stimulation of the neuron  depolarization
Directional Signals Stimulation of the neuron  depolarization Inhibition of the neuron  hyperpolarization Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Action Potentials Figure 12.9a, b

Action Potentials on Axons
Strong depolarizing stimulus applied to the axon hillock triggers Action potential Membrane becomes positive internally Action potential travels the length of the axon Membrane repolarizes itself Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Action Potentials on Axons
Figure 12.9c–e Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Graded Potentials on Dendrites and the Cell Body
Natural stimuli applied to dendrites and the cell body Receptive zone of the neuron Membrane stimulation causes local depolarization A graded potential – inner surface becomes less negative Depolarization spreads from receptive zone to the axon hillock Acts as the trigger that initiates an action potential in the axon Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Synaptic Potentials Excitatory synapses
Neurotransmitters alter the permeability of the postsynaptic membrane Leads to an inflow of positive ions Depolarizes the postsynaptic membrane Drives the postsynaptic neuron toward impulse generation Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Synaptic Potentials Inhibitory synapses
The external surface of the postsynaptic membrane becomes more positive Reduces the ability of the postsynaptic neuron to generate an action potential Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Classification of Neurons
Structural Classification Functional Classification Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Structural Classification of Neurons
Classification based on number of processes Multipolar Bipolar Unipolar (pseudounipolar) Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Multipolar Neurons Possess more than two processes
Numerous dendrites and one axon Figure 12.10a–c Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Bipolar Neurons Possess two processes
Rare neurons – found in some special sensory organs Figure 12.10a–c Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Unipolar (Pseudounipolar) Neurons
Possess one single process Start as bipolar neurons during development Figure 12.10a–c Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Afferent (sensory) neurons – transmit impulses toward the CNS
Afferent neurons Afferent (sensory) neurons – transmit impulses toward the CNS Virtually all are pseudounipolar neurons (some true bipolar) Cell bodies in ganglia outside the CNS Short, single process divides into The central process – runs centrally into the CNS The peripheral process – extends peripherally to the receptors Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Afferent Neurons Periphery CNS Axon terminals Sensory receptors

Efferent (motor) neurons
Efferent Neurons Efferent (motor) neurons Carry impulses away from the CNS to effector organs Most efferent neurons are multipolar Cell bodies are within the CNS Form junctions with effector cells Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Interneurons (association neurons) – most are multipolar
Lie between afferent and efferent neurons Confined to the CNS Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Neurons Classified by Function

Variety of Interneurons
Purkinje cell, stellate cell, granule cell, and basket cell Located in the cerebellum Pyramidal cell – located in the cerebral cortex Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Variety of Interneurons

Glial Cells (Supporting Cells)
Six types of glial cells Four in the CNS Two in the PNS Provide supportive functions for neurons Cover nonsynaptic regions of the neurons Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Supporting Cells (Neuroglial Cells) in the CNS
Neuroglia – usually only refers to supporting cells in the CNS, but can be used for PNS Glial cells have branching processes and a central cell body Outnumber neurons 10 to 1 Make up half the mass of the brain Can divide throughout life Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Types of Glial Cells in the CNS
Astrocytes Microglia Ependymal Cells Oligodendrocytes Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Astrocytes Astrocytes – most abundant glial cell type
Take up and release ions to control the environment around neurons Recapture and recycle neurotransmitters Involved with synapse formation in developing neural tissue Produce molecules necessary for neural growth (BDTF) Propagate calcium signals that may be involved in memory Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Necessary for development and maintenance of theblood brain barrier
Astrocytes Necessary for development and maintenance of theblood brain barrier Figure 12.12a Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Microglia – smallest and least abundant
Phagocytes – the macrophages of the CNS Engulf invading microorganisms and dead neurons Derived from blood cells called monocytes Figure 12.12b Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Ependymal Cells Ependymal cells
Line the central cavity of the spinal cord and brain Bear cilia – help circulate the cerebrospinal fluid Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Oligodendrocytes Oligodendrocytes – have few branches
Wrap their cell processes around axons in CNS Produce myelin sheaths Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Supporting Cells in the PNS
Satellite cells – surround neuron cell bodies within ganglia Schwann cells (neurolemmocytes) – surround axons in the PNS Form myelin sheath around axons of the PNS Figure 12.13 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Segmented structures composed of the lipoprotein myelin
Myelin Sheaths Segmented structures composed of the lipoprotein myelin Surround thicker axons Form an insulating layer Prevent leakage of electrical current Increase the speed of impulse conduction Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Myelin Sheaths in the PNS
Formed by Schwann cells Develop during fetal period and in the first year of postnatal life Schwann cells wrap in concentric layers around the axon Cover the axon in a tightly packed coil of membranes Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Myelin Sheaths in the CNS
Oligodendrocytes form the myelin sheaths in the CNS Have multiple processes Coil around several different axons Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Nerves – cordlike organs in the PNS
Consists of numerous axons wrapped in connective tissue Axon is surrounded by Schwann cells Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Endoneurium – layer of delicate connective tissue surrounding the axon
Nerves Endoneurium – layer of delicate connective tissue surrounding the axon Nerve fascicles – groups of axons bound into bundles Perineurium – connective tissue wrapping surrounding a nerve fascicle Epineurium – whole nerve is surrounded by tough fibrous sheath Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Simplified Design of the Nervous System
Sensory neurons – located dorsally Cell bodies outside the CNS in sensory ganglia Central processes enter dorsal aspect of the spinal cord Motor neurons – located ventrally Axons exit the ventral aspect of the spinal cord Interneurons – located centrally Provide communication between sensory and motor neurons and between levels of the CNS Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Example of Neuronal Organization: Reflexes
Reflex arcs – simple neural pathways Responsible for reflexes Rapid, autonomic motor responses Can be visceral or somatic Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Five Essential Components to the Reflex Arc
Receptor – detects the stimulus Afferent (sensory neuron) – transmits impulses to the CNS Integration center – consists of one or more synapses in the CNS Efferent (motor neuron) – conducts impulses from integration center to an effector Effector – muscle or gland cell Responds to efferent impulses Contraction or secretion Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Example of the Five Components to the Reflex Arc

Types of Reflexes: Number of Classes
Monosynaptic reflex – simplest of all reflexes Just one synapse The fastest of all reflexes Example – knee-jerk reflex Polysynaptic reflex – more common type of reflex Most have a single interneuron between the sensory and motor neuron Example – withdrawal reflexes Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Monosynaptic Reflex Figure 12.18a, b

Polysynaptic Reflex Figure 12.18a, b

Spinal vs Cranial Reflexes
Spinal = spinal cord integration center Ex. Knee-jerk reflex Cranial = brain as integration center Ex. Pupillary light reflex Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Somatic vs Autonomic Reflexes
Somatic = motor neurons to skeletal muscles Ex. Knee-jerk reflex Autonomic = autonomic neurons to smooth muscle and glands Ex. Pupillary light reflex Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Innate vs Learned Reflexes
Innate = born-with Knee-jerk reflex, pupillary reflex Learned = develops based on experiences Pavlov’s dogs salivation in response to bell Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Gray versus White Matter in the Central Nervous System
Gray matter Cell bodies Dendrites Synapses White matter Axons (myelin) Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Gray Matter in the Spinal Cord
H-shaped (butterfly) region – surrounds central cavity Dorsal half contains cell bodies of interneurons Ventral half contains cell bodies of motor neurons Cell bodies are clustered in the gray matter Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

White Matter in the Spinal Cord
Located externally to the gray matter Contains no neuronal cell bodies, but millions of axons Myelin sheath – white color Consists of axons running between different parts of the CNS Tracts – bundles of axons traveling to similar destinations Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Gray Matter in Brain Cortex and nuclei

Disorders of the Nervous System
Multiple sclerosis – common cause of neural disability Varies widely in intensity among those affected Cause is incompletely understood An autoimmune disease Immune system attacks the myelin around axons in the CNS Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

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