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CHAPTER 11 FUNDAMENTALS OF THE NERVOUS SYSTEM AND NERVOUS TISSUE

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Title: CHAPTER 11 FUNDAMENTALS OF THE NERVOUS SYSTEM AND NERVOUS TISSUE


1
CHAPTER 11 FUNDAMENTALS OF THE NERVOUS SYSTEM
AND NERVOUS TISSUE
2
ORGANIZATION OF THE NERVOUS SYSTEM
  • 1. master control and communication system
  • 2. works with endocrine system for homeostasis
  • 3. rapid acting highly complex short term
  • 4. communication by electrical signals
  • 5. 3 overlapping functions
  • a. sensory input - monitor stimuli (changes)
    externally internally
  • b. integration - processes and interprets input
  • c. motor output - effects a response in muscles
    or glands

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ORGANIZATION
  • 1. Nervous System
  • a. Central Nervous System (CNS)
  • b. Peripheral Nervous System (PNS)
  • 1. spinal nerves
  • 2. cranial nerves

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ORGANIZATION
  • 2. Peripheral nervous system
  • a. Sensory division - afferent receptors---gtCNS
  • 1. somatic afferent - skin, muscles, joints
  • 2. visceral afferent - visceral organs
  • b. Motor division - efferent CNS---gteffectors
  • 1. Somatic nervous system - CNS---gtskeletal
    muscles
  • 2. Autonomic nervous system - CNS---gtsmooth,
    cardiac, glands
  • a. sympathetic
  • b. parasympathetic

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HISTOLOGY OF NERVOUS TISSUE
  • 1. highly cellular
  • 2. 2 cell types
  • a. neurons
  • b. supporting cells

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SUPPORTING CELLS
  • 1. supporting cells - form scaffolding assist,
    segregate, insulate neurons
  • 2. types (a-d) are called neuroglia
  • a. astrocytes
  • b. microglia
  • c. ependymal cells
  • d. oligodendrocytes
  • e. Schwann cells
  • f. satellite cells

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SUPPORTING CELLS
  • 3. 10-50 times more numerous
  • 4. retain ability to reproduce
  • a. gliomas
  • 5. astrocytes
  • a. star shaped
  • b. abundant in CNS
  • c. brace anchor neurons nutrient supply
  • d. living barrier between capillaries and neurons
    (f11.3a, p365)
  • e. control chemical environment around neurons
  • f. buffer K ions in extracellular space

10
SUPPORTING CELLS
  • 6. microglia
  • a. small ovoid
  • b. macrophages in CNS
  • 7. ependymal cells
  • a. line central cavities of brain and spinal cord
  • b. impermeable barrier between CSF and tissue
    fluid bathing CNS cells
  • c. ciliated to circulate CSF

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SUPPORTING CELLS
  • 8. oligodendrocytes
  • a. "few branches"
  • b. form myelin sheath around thicker neuron
    fibers
  • 9. Schwann cells
  • a. form myelin sheaths around PNS fibers
  • b. phagocytic
  • c. vital to peripheral nerve process regeneration
  • 10. satellite cells
  • a. closely associated with Schwann cells
  • b. control chemical environment of PNS neurons

12
NEURONS
  • 1. neuron - nerve cell
  • a. structural functional unit
  • b. conduction
  • c. extreme longevity
  • d. amitotic
  • e. high metabolic rate
  • 2. cell body and processes
  • 3. plasma membrane site of electrical signaling

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NEURONS
  • 4. 3 functional components
  • a. receptive region - input (dendrite)
  • b. conducting component - generates and transmits
    action potential (axon)
  • c. secretory component - output releases
    neurotransmitters (axon)

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NEURONS
  • 5. cell body - perikaryon or soma
  • a. spherical nucleus nucleolus
  • b. biosynthetic center of cell
  • c. Nissl bodies - rough er - protein and membrane
    forming area
  • d. elaborate golgi bodies
  • e. numerous mitochondria
  • f. microtubules - transport
  • g. lipofuscin - by-product of lysosomal activity
  • h. most within the CNS (nuclei) those in PNS
    (ganglia)

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NEURONS
  • 6. neuron processes
  • a. cytoplasmic extensions
  • b. tracts in CNS nerves in PNS
  • 7. dendrites - short highly branched
  • a. most organelles also here
  • b. receptive region of cell - provide surface
    area for reception
  • c. conduct impulses toward cell body which are
    short-distance graded potentials

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NEURONS
  • 8. axon - single long
  • a. arises from axon hillock
  • b. nerve fiber - a long axon process
  • c. axon collaterals terminate in telodendria
  • d. function as conducting components - generate
    nerve impulses and transmit away from cell body
  • e. terminals are secretory components for
    neurotransmitters
  • f. lacks Nissl bodies
  • g. cytoskeletal elements allow for transport
    within axon in both directions (anterograde
    retrograde)
  • h. axolemma
  • i. virus bacteria use axonal retrograde
    transport to reach cell body

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NEURONS
  • 9. myelin sheath
  • a. protects and electrically insulates axon
  • b. increase speed of transmission in myelinated
    fibers
  • c. formed by Schwann Cells in PNS that forms a
    tight coil around axon (f11.5, p369)
  • d. formed by oligodendrocytes in CNS
  • e. white matter - myelinated gray matter -
    unmyelinated

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NEURONS
  • 10. neurilemma - portion of Schwann cell with
    nucleus and cytoplasm external to myelin sheath
    outermost layer
  • 11. Nodes of Ranvier - gaps in myelin sheath
  • a. axon collaterals emerge here
  • b. saltatory conduction

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CLASSIFICATION OF NEURONS
  • 1. structural classification (table 11.1,
    p371-372)
  • a. multipolar neurons - most common
  • b. bipolar neurons - rare in adult special
    senses
  • c. unipolar neurons - pseudounipolar neurons
    single fiber functions as both axon and dendrite
  • 1. generates and conducts impulses
  • 2. heavily myelinated
  • 3. indistinguishable microscopically from axons

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CLASSIFICATION
  • 2. functional classification (table 11.1,
    p371-372)
  • a. sensory or afferent neurons - impulses toward
    CNS
  • 1. most are unipolar
  • 2. cell bodies in ganglia
  • b. motor or efferent neurons - impulses away from
    CNS
  • 1. most are multipolar
  • c. association neurons or interneurons - between
    motor and sensory
  • 1. most are multipolar
  • 2. most are within CNS

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NEUROPHYSIOLOGY PRINCIPLES OF ELECTRICITY
  • 1. irritability - response to stimuli
  • 2. voltage - measure of potential energy due to
    separated charges
  • a. potential - measure of voltage between two
    points
  • 3. current - flow of electric charge between
    points

29
PRINCIPLES OF ELECTRICITY
  • 4. resistance - hindrance to charge flow
  • a. insulators
  • b. conductors
  • c. ohm's law
  • current (I) voltage (V) / resistance (R)
  • 5. chemically gated channels - controlled by
    neurotransmitters

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PRINCIPLES OF ELECTRICITY
  • 6. voltage gated channels - respond to changes in
    membrane potential or voltage
  • 7. electrochemical gradient - due to movement of
    ions across a membrane by chemical gradients and
    electrical gradients

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RESTING MEMBRANE POTENTIAL
  • 1. resting membrane potential (f11.7 11.8)
  • a. -70mv
  • b inside membrane negative with respect to
    outside
  • c. membrane is polarized
  • d. high Na outside membrane low K inside
  • e. concentration differences maintained by
  • 1. differential permeability of plasma membrane
  • 2. sodium-potassium pump

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MEMBRANE POTENTIAL
  • 1. changes in membrane potential act as
    communication signals
  • 2. membrane potential changed by
  • a. anything that changes membrane permeability
  • b. alteration of ion concentrations on two sides
    of the membrane
  • 3. graded potentials - signal over short
    distances
  • 4. action potentials - long distance signals

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MEMBRANE POTENTIAL
  • 5. depolarization - inside of membrane becomes
    less negative with respect to outside
  • a. membrane potential reverses and moves above 0
    to become positive
  • 6. hyperpolarization - membrane potential
    increases becoming more negative than the resting
    potential

38
MEMBRANE POTENTIAL
  • 7. graded potentials
  • a. short lived local changes
  • b. current decrease with distance
  • c. magnitude varies directly with intensity
    (graded)
  • d. triggered by changes in stimulus
  • e. receptor potentials and post-synaptic
    potentials
  • f. ions move inward only outward change in
    current is due to distribution of membrane charges

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MEMBRANE POTENTIAL
  • 8. action potentials
  • a. nerve impulse
  • b. brief reversal of membrane potentials
  • c. only in axons
  • d. change from graded to action potential occurs
    usually at axon hillock

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MEMBRANE POTENTIAL
  • 9. action potential generation encompasses
  • a. increase in sodium permeability and reversal
    of membrane potential
  • 1. threshold level
  • 2. positive feedback Hodgkin's cycle
  • b. decrease in sodium permeability
  • c. increase in potassium permeability and
    repolarization
  • 1. repolarization - return to resting level
  • 10. propagation of action potential
  • a. self-propagating like a "domino effect"

43
MEMBRANE POTENTIAL
  • 11. threshold level - minimum stimulus to
    depolarize membrane
  • 12. all-or-none phenomenon - action potential
    happens completely or it doesn't
  • 13. all impulses are the same once generated
  • a. stimulus is coded by frequency of impulse
    transmission
  • 14. absolute refractory period - neuron cannot
    respond to any stimulus

44
MEMBRANE POTENTIAL
  • 15. relative refractory period - axon threshold
    for impulse generation is elevated
  • a. strong stimulus will cause depolarization
  • b. sodium gates closed potassium gates open
  • 16. rate of propagation depends on
  • a. influence of axon diameter
  • b. influence of myelin sheath
  • 1. saltatory conduction at Nodes of Ranvier

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MEMBRANE POTENTIAL
  • 17. multiple sclerosis - disappearance of myelin
    sheath in CNS impulse conduction eventually
    ceases
  • 18. classification by diameter
  • a. class A - somatic sensory and motor fibers
    largest diameter heavily myelinated 15-103 m/s
  • b. class B - light myelination 3-15 m/s
  • c. class C - small diameter unmyelinated 1 m/s
    or less

47
MEMBRANE POTENTIAL
  • 19. impairment of impulse
  • a. alcohol
  • b. sedatives
  • c. anesthetics
  • d. all reduce membrane permeability to sodium ions

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THE SYNAPSE
  • 1. synapse
  • a. axodendritic synapse
  • b. axosomatic synapse
  • 2. presynaptic neuron
  • 3. postsynaptic neuron
  • 4. typical neuron has 1,000-10,000 axonal
    terminals
  • 5. neuromuscular junctions - synapses between
    neurons and muscle cells
  • 6. neuroglandular synapses

49
SYNAPSE
  • 7. electrical synapses - bridged junctions
    between cytoplasm of adjacent neurons
  • a. provide low resistance electrical pathways
  • b. synchronize activity of interconnected
    neurons
  • 8. chemical synapses - release neurotransmitters
    that open or close ion channels (f11.17, p384)
  • a. prevent impulse from being directly
    transmitted between neurons
  • b. allows for unidirectional communication

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SYNAPSE
  • 9. typical chemical synapse
  • a. axonal terminal filled with synaptic vesicles
  • b. receptor region on postsynaptic membrane
  • 10. synaptic cleft
  • 11. synapse action
  • a. calcium gates open in presynaptic terminals
  • b. neurotransmitter released by exocytosis
  • c. neurotransmitter binds to postsynaptic
    membrane
  • d. ion channels open in postsynaptic membrane

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SYNAPSE
  • 12. effects of neurotransmitters terminated by
  • a. degradation by enzymes (ACh)
  • b. removal from the synapse into postsynaptic
    membrane (norepinephrine)
  • c. diffusion away from synapse
  • 13. synaptic delay - time for release of
    neurotransmitter diffusion binding to receptor
  • a. 0.3-0.5 ms
  • b. rate limiting step

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POSTSYNAPTIC POTENTIALS AND SYNAPTIC INTEGRATION
  • 1. excitatory postsynaptic potentials (EPSP)
  • a. neurotransmitter causes depolarization of
    postsynaptic membrane
  • b. trigger an action potential the distal axon
    hillock
  • 2. inhibitory postsynaptic potentials (IPSP)
  • a. neurotransmitter reduces postsynaptic neuron
    ability to generate an action potential

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INTEGRATION
  • 3. summation - process in which cumulative epsp's
    increase ability for depolarization
  • a. temporal summation - one or more presynaptic
    neuron transmit impulses in rapid fire order
  • b. spatial summation - postsynaptic neuron
    stimulated by a large number of neuron terminals
  • c. neurons receive both stimulatory and
    inhibitory impulses

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INTEGRATION
  • 4. synaptic potentiation - repeated or continuous
    use of synapse enhances excitability of
    postsynaptic membrane
  • 5. presynaptic inhibition - release of excitatory
    neurotransmitter is inhibited by activity of
    another neuron
  • 6. neuromodulation - chemicals other than
    neurotransmitters modify neuronal activity

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NEUROTRANSMITTERS
  • 1. means by which neurons communicate
  • 2. neurotransmitters must
  • a. be present in presynaptic terminals
  • b. produce ion fluxes (EPSP IPSP)
  • c. be some means of removing it from synapse

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CLASSIFICATION OF NEUROTRANSMITTERS BY CHEMICAL
STRUCTURE
  • 1. acetylcholine - released at neuromuscular
    junctions
  • a. acetic acid coenzyme A choline-----gtACh
    CoA
  • 2. biogenic amines - include
  • a. catecholamines (dopamine, norepinephrine,
    epinephrine)
  • b. indolamines - (serotinin, histamine)
  • c. mostly in brain
  • d. play a role in emotional behavior biological
    clock

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CLASSIFICATION
  • 3. amino acids - GABA
  • a. only in CNS
  • 4. peptides - neuropeptides
  • a. strings of amino acids
  • b. endorphins enkephalins - natural opiates or
    euphorics
  • c. substance P - mediator of pain signals

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CLASSIFICATION BY FUNCTION
  • 1. excitatory and inhibitory
  • 2. ionotropic - open ion channels
  • 3. metabotropic - act through second messenger
    molecules (cyclic AMP)

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NEURAL INTEGRATION
  • 1. neural integration - neurons function in
    groups
  • 2. neuronal pools - functional groups that
    process and integrate incoming information
  • a. discharge zone - those neurons in the pool
    that receive the bulk of synaptic contacts
  • b. facilitated zone - periphery of the pool

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TYPES OF CIRCUITS
  • 1. circuits - (f11.24, p398) patterns of synaptic
    connections in neuronal pools
  • 2. diverging circuit - one incoming triggers
    increasing numbers
  • a. often amplify
  • 3. converging circuits - several inputs to one
  • a. concentrating effect

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TYPES OF CIRCUITS
  • 4. reverberating circuits - positive feedback
    type
  • a. rhythmic activities
  • 5. parallel after discharge - incoming stimulates
    several neurons in a parallel array to a common
    output
  • a. complex mental processing

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PATTERNS OF NEURAL PROCESSING
  • 1. serial processing - whole system works in an
    all or nothing manner
  • a. reflexes
  • 2. parallel processing - inputs segregated into
    different pathways
  • a. not repetitious

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DEVELOPMENTAL ASPECTS
  • 1. nervous system arises from neural tube and
    neural crest from ectoderm
  • 2. differentiation process
  • a. proliferation
  • b. migration
  • c. cellular differentiation
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