This week: Monday and Tuesday – Nervous System Overview ( Fucntions , Histology, Cell types)
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Transcript of This week: Monday and Tuesday – Nervous System Overview ( Fucntions , Histology, Cell types)
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This week:Monday and Tuesday – Nervous System Overview
(Fucntions, Histology, Cell types)Wednesday and Thursday Nerve Firing
Friday Assess – and Read
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Week 7Near The home Stretch!
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Questions to answer by end of class
1. Name 2 divisions of nervous system2. Name 2 divisions of peripheral nervous
system3. Name 2 divisions of Autonomic Nervous
System4. List functions of (formal) Nervous system
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Today Nervous System Lecture 1
• Functions– Input, output, Interpret!
• Organization – Where cells are found, and by what they do
• Cells– Neurons – Supporting Cells• 6 new cells to ID
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Functions of the Nervous System
1. Sensory input– Info gathered by sensory receptors
2. Integration– Interpretation of sensory input
3. Motor output– Activation of effector organs (muscles and glands)
produces a response
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Figure 11.1
Sensory input
Motor output
Integration
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Divisions of the Nervous System
• Central nervous system (CNS) – Brain and spinal cord– Integration & command center
• Peripheral nervous system (PNS)– Paired spinal and cranial nerves carry messages TO
and FROM the CNS
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Peripheral Nervous System (PNS)
• Two functional divisions1. Sensory (afferent) division• Somatic afferent fibers—convey impulses from skin,
skeletal muscles, and joints • Visceral afferent fibers—convey impulses from visceral
organs 2. Motor (efferent) division • Transmits impulses from the CNS to effector organs
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Efferent (Motor) Division of PNS
1. Somatic nervous system– Conscious control of skeletal muscles
(voluntary Division)
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Motor Division of PNS
2. Autonomic nervous system (ANS)– Visceral motor nerve fibers– Regulates smooth mm, cardiac mm, and glands• Stuff you are too busy to think about
– Two functional subdivisions• Sympathetic• Parasympathetic
involuntary division
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There are 2 divisions of this Autonomic system
– Sympathetic – fight or flight– Parasympathetic – rest and digest
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Figure 11.2
Central nervous system (CNS)Brain and spinal cordIntegrative and control centers
Peripheral nervous system (PNS)Cranial nerves and spinal nervesCommunication lines between theCNS and the rest of the body
Parasympatheticdivision
Conserves energyPromotes house-keeping functionsduring rest
Motor (efferent) divisionMotor nerve fibersConducts impulses from the CNSto effectors (muscles and glands)
Sensory (afferent) divisionSomatic and visceral sensorynerve fibersConducts impulses fromreceptors to the CNS
Somatic nervoussystem
Somatic motor(voluntary)Conducts impulsesfrom the CNS toskeletal muscles
Sympathetic divisionMobilizes bodysystems during activity
Autonomic nervoussystem (ANS)
Visceral motor(involuntary)Conducts impulsesfrom the CNS tocardiac muscles,smooth muscles,and glands
StructureFunctionSensory (afferent)division of PNS Motor (efferent) division of PNS
Somatic sensoryfiber
Visceral sensory fiber
Motor fiber of somatic nervous system
Skin
Stomach Skeletalmuscle
Heart
BladderParasympathetic motor fiber of ANS
Sympathetic motor fiber of ANS
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Histology of Nervous Tissue
• Two principal cell types1. Neurons—excitable cells that transmit electrical
signals
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Histology of Nervous Tissue2. Neuroglia (glial cells)—supporting cells:
• Astrocytes (CNS)• Microglia (CNS)• Ependymal cells (CNS)• Oligodendrocytes (CNS)• Satellite cells (PNS)• Schwann cells (PNS)
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Astrocytes• Most abundant, versatile, and highly branched
glial cells• Cling to neurons, synaptic endings, and
capillaries• Support and brace neurons
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Astrocytes
• Help determine capillary permeability• Guide migration of young neurons• Control the chemical environment– Participate in information processing in the brain
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Figure 11.3a
(a) Astrocytes are the most abundantCNS neuroglia.
Capillary
Neuron
Astrocyte
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Microglia
• Small, egg shaped cells with thorny processes• Migrate toward injured neurons• Phagocytize microorganisms and neuronal
debris• Closest to immune cell you’ll get in CNS
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Figure 11.3b
(b) Microglial cells are defensive cells inthe CNS.
NeuronMicroglialcell
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Ependymal Cells
• Range in shape from squamous to columnar• May be ciliated– Line the central cavities of the brain and spinal
column– Separate the CNS interstitial fluid from the
cerebrospinal fluid in the cavities
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Figure 11.3c
Brain orspinal cordtissue
Ependymalcells
Fluid-filled cavity
(c) Ependymal cells line cerebrospinalfluid-filled cavities.
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Oligodendrocytes
• Branched cells• Processes wrap CNS nerve fibers, forming
insulating myelin sheaths
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Figure 11.3d
(d) Oligodendrocytes have processes that formmyelin sheaths around CNS nerve fibers.
Nervefibers
Myelin sheathProcess ofoligodendrocyte
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PNSSatellite Cells and Schwann Cells
• Satellite cells– Surround neuron cell bodies in the PNS
• Schwann cells (neurolemmocytes)– Surround peripheral nerve fibers and form myelin
sheaths– Vital to regeneration of damaged peripheral nerve
fibers
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Figure 11.3e
(e) Satellite cells and Schwann cells (whichform myelin) surround neurons in the PNS.
Schwann cells(forming myelin sheath)
Cell body of neuronSatellitecells
Nerve fiber
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Neurons (Nerve Cells)
• Special characteristics:– Long-lived ( 100 years or more)– Amitotic—with few exceptions– High metabolic rate—constant oxygen and glucose– Plasma membrane functions in:• Electrical signaling • Cell-to-cell interactions during development
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Nerve parts
• Pay attention to axon, dendrites, body
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Cell Body (Perikaryon or Soma)
• Its in the middle! Nucleus • Book gets technical on us…
– Biosynthetic center of a neuron– Spherical nucleus with nucleolus– Well-developed Golgi apparatus– Rough ER called Nissl bodies (chromatophilic substance)
• Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS
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Cell Body (Perikaryon or Soma)– Network of neurofibrils (neurofilaments)
• Axon hillock—cone-shaped area from which axon arises
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Figure 11.4b
Dendrites(receptive regions)
Cell body(biosynthetic centerand receptive region)
Nucleolus
NucleusNissl bodies
Axon(impulse generatingand conducting region)
Axon hillockNeurilemma
Terminalbranches
Node of RanvierImpulsedirection
Schwann cell(one inter-node)
Axonterminals(secretoryregion)
(b)
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Processes
• Dendrites and axons• Bundles of processes are called – Tracts in the CNS– Nerves in the PNS
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Dendrites
• “Cells little feelers”• Scattered branches• Receptive (input) region of a neuron• Convey electrical signals toward the cell body
as graded potentials
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The Axon• One axon per cell arising from the axon hillock• Long axons (nerve fibers)• Occasional branches ~90 degrees (axon
collaterals)
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The Axon
• Numerous terminal branches (telodendria)• Knoblike axon terminals (synaptic knobs or
boutons) – Secretory region of neuron– Release neurotransmitters to excite or inhibit
other cells
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Axons: Function
• Conducting region of a neuron• Generates and transmits nerve impulses
(action potentials) away from the cell body
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Figure 11.4b
Dendrites(receptive regions)
Cell body(biosynthetic centerand receptive region)
Nucleolus
NucleusNissl bodies
Axon(impulse generatingand conducting region)
Axon hillockNeurilemma
Terminalbranches
Node of RanvierImpulsedirection
Schwann cell(one inter-node)
Axonterminals(secretoryregion)
(b)
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Myelin Sheath
• Lipid little blankets!• It functions to:– Protect and electrically insulate the axon– Increase speed of nerve impulse transmission
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Myelin Sheaths in the PNS
• Schwann cells wraps many times around the axon – Myelin sheath—concentric layers of Schwann cell
membrane • Neurilemma—peripheral bulge of Schwann
cell cytoplasm
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Myelin Sheaths in the PNS
• Nodes of Ranvier – Myelin sheath gaps between adjacent Schwann
cells– Sites where axon collaterals can emerge
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Figure 11.5a
(a) Myelination of a nervefiber (axon)
Schwann cellcytoplasmAxon
NeurilemmaMyelin sheath
Schwann cellnucleus
Schwann cellplasma membrane
1
2
3
A Schwann cellenvelopes an axon.
The Schwann cell thenrotates around the axon, wrapping its plasma membrane loosely around it in successive layers.
The Schwann cellcytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath.
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Unmyelinated Axons
• Thin nerve fibers are unmyelinated• One Schwann cell may incompletely enclose
15 or more unmyelinated axons
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Myelin Sheaths in the CNS
• Formed by processes of oligodendrocytes, not the whole cells
• Nodes of Ranvier are present• No neurilemma• Thinnest fibers are unmyelinated
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Figure 11.3d
(d) Oligodendrocytes have processes that formmyelin sheaths around CNS nerve fibers.
Nervefibers
Myelin sheathProcess ofoligodendrocyte
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Stop here!
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White Matter and Gray Matter
• White matter– Dense collections of myelinated fibers
• Gray matter– Mostly neuron cell bodies and unmyelinated fibers
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Structural Classification of Neurons
• Three types:1. Multipolar—1 axon and several dendrites• Most abundant• Motor neurons and interneurons
2. Bipolar—1 axon and 1 dendrite• Rare, e.g., retinal neurons
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Structural Classification of Neurons
3. Unipolar (pseudounipolar)—single, short process that has two branches:• Peripheral process—more distal branch, often
associated with a sensory receptor• Central process—branch entering the CNS
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Table 11.1 (1 of 3)
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Table 11.1 (2 of 3)
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Functional Classification of Neurons
• Three types: 1. Sensory (afferent)• Transmit impulses from sensory receptors toward the
CNS
2. Motor (efferent)• Carry impulses from the CNS to effectors
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Functional Classification of Neurons
3. Interneurons (association neurons)• Shuttle signals through CNS pathways; most are
entirely within the CNS
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Table 11.1 (3 of 3)