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2011-10-31 12:21:40

A+P 1 Lecture 6
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  1. Neuroglia
    Supporting cells that separate and support neurons

    Schwann cells, amphicytes, astrocytes, oligodenrocytes, microglia, ependymal cells
  2. Schwann cells
    • o Flatten & form sheath around peripheral
    • AXONS

    o Outer surface is the neurolemma

    • o Expel cytoplasm to allow tightly wrapping
    • around AXOLEMMA.
  3. Amphicytes
    satellite cells regulating envir. around neurons

    o Surround neurons cell bodies in ganglia*

    • *Ganglia are clusters of neuron cell bodies in
    • PNS.
  4. Ependymal cells
    - line the Central Canal of spinal cord & the ventricles of brain (enlarged chambers)

    • o Some ependymal cells secrete the CSF
    • (epithelial cells) some monitor CSF composition & there are stem cells in ependyma
  5. Astrocytes
    • o most numerous glia
    • o endothelium lining CNS capillaries
    • o form selectively permeable membrane with tight junctions between them
    • o make blood-brain barrier by wrapping around capillaries
    • o Have microfilaments that make up the framework
    • in the CNS.
    • o Make repairs to stabilize from further injury
    • o guide embryonic neuron development
    • o adjust interstitial environment through:
    • 1. regulation of ions (Na+, K+) & CO2
    • 2. transport of nutrients and gases between neurons & capillaries
    • 3. also absorb & recycle some neurotransmitters; this affects release of chemicals communicating across synapse
    • 4. control blood flow volume in capillaries.
  6. Oligodendrocytes
    - improve axon performance and tie several axons together by the building myelin sheaths (similar to Schwann cells of PNS)

    neuroglia that ties axons together and many sheaths each axon which insulating each from extracellular fluid and speeding up action potential along axon
  7. Microglia
    • migrate through neural tissue into CNS, come from embryonic mesodermal stem cells, engulf cell debris,
    • waste, & pathogens
  8. Anaxonic neuron
    • no myelin
    • dendrites & axons look indistinguishable
    • in brain & special sense organs
    • small neurons
  9. Bipolar neurons
    • - nerve cell body in center
    • - 1 dendrite & 1 axon
    • - in special sense organs
    • - small & rare
  10. Unipolar neurons
    • dendrite & axon are one continuous process
    • nerve body off to one side
    • dendrites end at initial segment & rest is axon
    • processes are afferent fibers
  11. Multipolar neurons
    • - 2 or more dendrites
    • - nerve cell body with one long axon
    • - somatic motor neuron w/ many branched dendrites
    • - most common neuron in CNS
    • - all skeletal motor neurons are this type
  12. Long reflexes (of ANS)
    where sensory information goes to the CNS:

    o Along dorsal roots of the spinal nerves

    o Within sensory branches of cranial nerves

    o Within autonomic nerves that innervate visceral effectors

    o Control activities of an entire organ (IMPT!).
  13. Short reflexes (of ANS)
    o bypass the CNS

    • o Sensory & interneurons (cell bodies are within the autonomic ganglia) that synapse on ganglionic neurons and motor commands are then given by
    • post ganglionic fibers

    o Control patterns of activities in a part of an organ (IMPT!)

    o Short reflexes are in the digestive tract control and they coordinate normal function
  14. Alpha motor neurons
    • largest efferent neuron
    • Activates & contracts extrafusal muscle fibers (aka large muscle fibers)
    • Lower motor neurons of brainstem and spinal cord
    • Cell bodies in the CNS; axons innervate skeletal muscles therefore concidered part of PNS
    • Alpha motor neuron + muscle fiber it innervates = motor unit
    • Alpha motor neurons (aMN) in brainstem (for head & neck) are in clusters called nucleii
    • Injuries by trauma, infection, etc., may kill aMN
    • - Poliomyelitis (virus) selectively kills
    • motor neurons of ventral horn of spinal cord causing paralysis
  15. Gamma motor neuron (3-MN)
    • smallest efferent
    • located in brainstem & spinal cord
    • These are myelinated axons w/ slower
    • conductivity than aMN i.e., have smaller diameter axons.
    • Shorten the muscle spindles (intrafusal) so that as the muscle organ is stimulated, the muscle spindles also contract
    • Are part of fusimotor system by which the CNS controls muscle spindle sensitivity
  16. Beta Motor Neuron (BMN)
    • has functions of alpha & gamma function
    • Are collaterals from aMN to skeletofusimotor fibers
    • Provide both alpha & gamma coactivation
    • Are not very well understood
  17. Interoceptors
    • Monitor digestive, respiratory, cardiovascular, urinary, & reproductive functions
    • Sense of Taste, Deep Pressure and Pain
  18. Exteroceptors
    Information about external environment from touch, (temperature, pressure sensations, and sight, smell, and hearing)
  19. Proprioceptors
    Monitor position & movement of skeletal muscles & joints
  20. Deep sleep
    relaxation of entirebody & minimal cerebral cortex activity w/ up to 30% decline in breathing, heartrate & blood pressure
  21. Rapid Eye Movement sleep (dreaming)
    EEG resembles the awake state - are less receptive to stimuli than deep sleep & muscle tone decreases and experience changes in blood pressure & respiratory rate