Bio 209 Ch 12

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Bio 209 Ch 12
2010-07-13 17:46:12
Nervous System

Nervous System Overview
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  1. Describe the structures of the nervous system
    • Central Nervous System (CNS):
    • - Brain
    • - Spinal Cord
    • Peripheral Nervous System (PNS):
    • - Cranial nerves
    • - Spinal Nerves
    • - Sensory Receptors
  2. Describe the functions of the nervous system
    • Sensory Function
    • Integrative Function
    • Motor Function
  3. Describe the subdivisions of the nervous system
    CNS: (1) Brain (2) Spinal cord

    PNS: contains three divisions, Somatic – Autonomic – Enteric
  4. Describe the function of the CNS
    • CNS:
    • (1) Processes sensory information and initiates appropriate response
    • (2) Initiates voluntary muscle contraction such as walking and picking up objects
    • (3) Thoughts, emotions and memories
  5. Describe the function of the PNS

    • - Somatic: consists of sensory neurons that carry sensory information from (skin, skeletal muscle and tendons) and special sensory receptors (vision, smell, taste, hearing) to CNS fibers (these impulses consciously controlled and are voluntary)
    • - Autonomic: consists of sensory neurons carrying info from autonomic sensory receptors (receptors in blood vessels and visceral organs) – motor neurons that carry nerve impulses to smooth muscle, cardiac muscle, glands, adipose tissue (generation of these impulses not normally consciously controlled and are involuntary)
    • - Enteric (brain of the gut)
  6. Name the two cell types found in nervous tissue
    • Neurons
    • Neuroglia
  7. Describe the function of neurons
    Are electrically excitable (respond to a stimulus by generating an action potential)
  8. Stimulus
    Change in the environment that is strong enough to result in an action potential
  9. Action Potential
    electrical signal that travels along the cell membrane of a neuron – there are generated by the flow of ions (mainly Na & K) between interstitial fluid (between cells) and intracellular fluid
  10. Describe the neuron cell structures
    Nucleus & Nucleolus

    Cytoplasm: mitochondria, golgi apparatus, lysosomes, SER, ribosomes, Nissl Bodies (RER of neuron), cytoskeleton

    Dendrites: short processes that receive info from other neurons and receptors

    • Axon: propogates nerve impulse towards another neuron, muscle fiber or gland
    • - Axon Hillock: cone shaped structure that connects axon to cell body
    • - Trigger Zone: located in part of axon closest to axon hillock and generates action potentials

    • Axon Terminals: form part of synapse
    • - Synaptic End Bulbs: bulb like structures at tip of axon terminal and contains synaptic vesicles with neurotransmitter

    Cell Body is the biosynthetic center of the neuron
  11. Describe the function of axonal transport systems
    • (1) Transport material from cell body (biosynthetic center) to axon of axon terminal
    • (2) Transport substances from axon to cell body to be recycled
  12. Describe the structure and function of multipolar neurons
    Mainly dendrites and one axon; can be found mainly in brain and spinal cord
  13. Describe the structure and function of bipolar neurons
    One dendrite, one axon; can be found in retina, ear, olfactory area
  14. Describe the structure and function of unipolar neurons
    Dendrite and axon fused together to form one process; mostly sensory receptors for touch, pressure, pain, temperature
  15. Describe the structure and function of sensory (afferent) neurons
    mostly unipolar and some bipolar neurons; conducts action potential towards CNS through cranial and spinal nerves
  16. Describe the structure and function of motor (efferent) neurons
    mostly motor neurons; conducts action potential away from CNS to effectors (muscle/glands) through cranial and spinal nerves
  17. Describe the structure and function of interneurons (association) neurons
    mostly multipolar neurons: located between sensory and motor neurons
  18. Compare the amount and function of neuroglia and neurons in the CNS
    • (1) Neuroglia DO NOT exhibit electrical excitability (action potentials)
    • (2) Neuroglia are smaller than neurons
    • (3) Neuroglia replaces damaged neurons
  19. Astrocytes
    have processes that surround capillaries - control chemical environment around neurons; help form BBB; BBB prevents harmful substances from entering CNS
  20. Microglia
    in CNS; remove cellular debris, microbes, damaged nervous tissue
  21. Ependymal Cells
    contain cilia - form CSF, assist in circulation of CSF
  22. Oligodendrocytes
    have processes that wrap around several axons to form myelin sheath of CNS neurons
  23. Satellite Cells in the PNS
    located around neuron cell bodies in ganglia, control chemical environment of neurons
  24. Schwann Cells in PNS
    myelin sheath around axon of PNS neurons
  25. Describe the structure and function of myelin sheaths
    Structure: plasma membrane of oligodendrocytes and Schwann cells; plasma membrace wraps around axon several times (like wrapping electrical tape around a wire)

    Function: insulates axon and increases speed of nerve impulse
  26. Nuclei (Nucleus)
    cluster of neuron cell bodies in CNS
  27. Ganglia (Ganglion)
    cluster of neuron cell bodies in PNS
  28. Tracts
    bundle of axons in CNS
  29. Nerves
    bundle of axons in PNS; most nerves supplying skeletal muscles are myelinated
  30. White Matter
    primarily myelinated axons that gives it its white color
  31. Gray Matter
    neuroglia, neuron cell bodies, dendrites, unmyelinated axons, axon terminals
  32. Action Potential
    communication over long distances generated in axons
  33. Graded Potential
    communication over short distances by stimulus to neuron in dendrites, and to neuron cell body then to axon hillock
  34. Leakage-Gated Channels
    randomly opens and closes
  35. Voltage-Gated Channels
    open and closes in response to a change in membrane potential
  36. Ligand-Gated Channels
    open and close in response to chemical stimuli (neurotransmitters & hormones)
  37. Mechanically-Gated Channels
    opens and closes in response to mechanical stimulation such as vibration, stretch or touch. These receptors are found in skin and in internal organs
  38. Describe the cause of the resting membrane potential in neurons
    • (1) Differences in concentration of ions across plasma membrane:
    • - ECF has more Na than ICF
    • - ICF has more K than ECF
    • - More K leave cells through
    • Leakage-Channels than Na entering à More positive charges leave the cell à Inside of cells becomes slightly negative
    • (2) Inability of most anions to leave the cell
    • (3) Na/K ATPase
    • - Maintains the difference in Na and K ion concentrations
  39. Graded Potential
    change in membrane potential that makes plasma membrane more polarized (inside more negative) or less polarized (inside less negative); caused by opening of ligand-gated/mechanically gated ion channels in dendrites
  40. Depolarization
    less polarized (inside less negative)
  41. Hyperpolarization
    more polarized (inside more negative)
  42. Describe how graded potentials are generated and why they are graded
    • Amplitude of Graded Potential varies according to:
    • (1) Intensity of stimulus
    • (2) Intensity of stimulus determines number of ion channels that open and the length of time ion channels open
  43. Define decremental conduction
    Exhibited by Graded Potentials in which results in a graded potential decreasing in amplitude and dying out a few mm from the point of origin (point where stimulus is applied)
  44. Post-synaptic Potential
    graded-potentials that occur after neurotransmitter binds to receptor on plasma membrane
  45. Receptor (Generator) Potential
    graded-potentials that occur in sensory receptors and sensory neurons
  46. Describe how action potentials are generated
    • (1) Stimulus causes depolarizing graded-potential in dendrites
    • (2) Depolarizing graded-potential travels across neuron
    • (3) Action-Potential occurs if membrane potential at trigger zone is depolarized to threshold (-55mV) – Depolarization to threshold opens voltage-gated Na channels à Action Potential
    • (4) Action-Potential travels down axon
  47. Synapse
    region where communication occurs between two neurons or between a neuron, muscle, or gland
  48. Pre-Synaptic Neuron
    neuron sending signal
  49. Post-Synaptic Neuron
    neuron receiving signal
  50. Describe the structure of electrical synapses and how information is transferred across electrical synapses
    • - Current spreads directly between adjacent cells connections between
    • plasma membranes (Gap Junctions)
    • - Advantages:
    • (1) Faster than chemical synapses
    • (2) Can sync activity of group of neurons or muscle fibers
    • (3) Allows two-way transmission of information whereas chemical synapses transfers info in one direction only