Lecture nervous system and tissue

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  1. Neuron Function
    neurons are highly irritable

    respond to adequate stimulus by generating an action potential (nerve impulse)

    impulse is always the same regardless of stimulus
  2. Role of membrane ion channels
    Proteins serve as membrane ion channels

    two main types of ion channels

    1. Leakage (nongated) ion channels-always open

    • 2. Gated ion channels (three types)
    • - Chemically gated (ligan gated) channels- open with binding of a specific neurotransmitter

    Voltage gated channels-open and close in response to changes in the membrane potential

    Mechanically gated channels- open and close in response to physical deformation of receptors(like pressure)
  3. Functions of the nervous system
    1. Sensory input: information gathered by sensory receptors about internal and external changes

    2. Integration: interpretation of sensory input

    3. motor output: activation of effector organs (muscles and glands) to poduce a response
  4. Functional divisions of the PNS
    • 1. Sensory (Afferent) division
    • -somatic afferent fibers: convey impulses from the skin, skeletal muscles, organs
    • -Visceral afferent fibers: convey impulses from visceral organs

    • 2. Autonomic (involuntary) nervous system (ANS)
    • -visceral motor nerve fibers
    • -regulates smooth muscle, cardiac muscle, and glands
    • -two functional subdivisions: sympathetic and parasympathetic (usually work in opposition to one another)
  5. Histology of Nervous Tissue
    Two principle cell types:

    1. Neurons- excitable cells that transmit electrical signals

    • 2. Neuroglia (glial cells)-supporting cells
    • - Astrocytes (CNS)
    • -Microglia (CNS)
    • -Ependymal cells (CNS)
    • -Oliodendrocytes (CNS)
    • -Satelite cells(PNS)
    • -Schwann cells (PNS)
  6. Astrocytes
    Most abundant, verstatile, and highly branches glial cells

    cling to neurons, synaptic endings, and capillaries

    support and brace neurons

    help determine capillary permeability

    guide migration of young neurons

    control the chemical enviornment by mopping up leaked potassium and recycling released neurotransmitters

    • participate in information processing in the brain
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  7. Microglia
    Small, ovid cells with thorny processes

    migrate towards injured neurons (monitor neuron health)

    • phagocytize microorganisms and neuronal debris
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  8. Ependymal cells
    range in shape from squamous to colmnar

    • may be ciliated
    • -line the central cavities of the brain and spinal column
    • -seperates the CNS interstitial fluid from the cerebrospinal fluid in the cavities

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  9. oliogodendrocytes
    branches cells

    • processes wrap CNS nerve fibers, forming insulating myelin sheaths
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  10. Satellite cells and Schwann Cells
    • Satellite cells--> like the astrocytes of the PNS
    • -surround neuron cell bodies in PNS

    • Schwann cells (neurolemmocytes)
    • -surround the PN fibers and form myselin sheaths
    • -vital to regeneration of damaged PN fibers
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  11. Neurons
    Structural unit of nervous system

    Long lives (100 years or more)

    Amitotic - with few exceptions (cannot be replaced if damaged)

    high metabolic rate- depends on continous supplu of oxygen and glucose

    • Plasma membranne functions in
    • -electrical signaling
    • -cell to cell interactions during development
  12. Structual classification of neurons
    • 1. Multipolar- 1 axon and several dendrites
    • -most abundant (more than 99% in humans)
    • -motor neurons and interneurons

    • 2. Bipolar- 1 axon and 1 dendrite
    • -rare, ex: retinal neurons

    • 3. Unipolar(pseudounipolar)- single short process that has 2 branches:
    • peripheral process- more distal branch, often associated with a sensory receptor
    • central process- branch entering the CNS
  13. Functional classification of neurons
    • 1. sensory (Afferent)
    • -transmit impulses from sensory receptors towards CNS

    • 2. Motor (efferent)
    • -caarry impulses from the CNS to effectors

    • 3. Interneurons (association neurons)
    • -shuttle signals through the CNS pathways; most are entirely within the CNS
    • -make up over 99% of neurons in the body
    • -lie b/t motor and sensory neurons
  14. Graded Potentials
    Occur when a stimulus causes gated ion channels to open

    magnitude varies directly (graded) with stuimulus strength

    decrease in magnitude with distance as ions flow and diffuse through leakeg channels

    short distance signals
  15. The synapse
    post synaptic neuron--transmits impulses away from the synapse (reciever)

    presynaptic neuron--transmits impulses toward the synapse (sender)
  16. Chemical Synapse
    1. AP reaches the axon termial

    2. voltage gaed Ca2+ channels open and Ca2+ enters the axon terminal

    3. Ca2+ entry causes neurotransmitters containing synaptic vesiscles to release their contents by exocytosis

    4. neurotransmitter diffusions across the synaptic cleft and binds to synaptic receptors on the postsynaptic membrane

    5. binding of neurotransmitter opens ion channels, resulting in graded potentials
  17. Postsynaptic potential (a type of graded potential)
    • Excitatory (EPSP)
    • -short distance
    • -depolarization that spreads to axon hillock
    • -moves membrane potential toward threshhold for generation of AP
    • -neurotransmitter binds to and open chemicalle gated channels that alllow simultaneous flow of Na+ and K+, but Na+ flow is greater, causing depolaraization (toward an AP)

    • Inhibatory (IPSP)
    • -short distace
    • -hyperpolarization that spreads to axon hillock
    • -moves membrane potential away from the threshhold for an AP
    • -neurotransmiter binds to and opens channels for K+ or Cl-, creating a hyperpolarization
  18. Neuotransmitter direct action
    neurotransmitte binds to channel-linked receptor and opens ion channels

    promotes rapid responses

    ex: Ach and amino acods
  19. Neuotransmitter indirect action
    Neurotransmitter binds to a g-protien linked receptor and acts through an intracellular second messenger

    promtotes long lasting effects
  20. G-protien mechanism
    1. neurotransmitter (1st messenger) binds and activates receptor

    2. receptor activates G protiens

    3. G protien activates adenylate cyclase

    4. adenylate cyclase converts ATP to cAmp (2nd messenger)

    5a. cAMP changes membrane permeability by opening or closing ion channels

    5b. cAMP activates enzymes

    5c. cAMP activates specific genes
  21. Reflex arc
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Lecture nervous system and tissue
Lecture nervous system and tissue
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