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Chapter 8 Nervous System (8-2 (axons n CNS (a bundle of myelinated nerve…

- - - - PNS
      - Sensory receptors (located at the ends of peripheral neurons) detect changes occuring in their surroundings
      - once stimulated, sensory receptors transmit a sensory impulse to the CNS
      - A sensory impulse is carried on a sensory neuron
    - - CNS (brain and/or spinal cord)
      - involves interpretation of an incoming sensory impulse
      - Integration occurs in interneurons
      - A motor impulse begins...motor function
    - - PNS
      - involves the response of a body part
      - motor impulses are carried from CNS to responsive body parts called effectors
      - A motor impulse is carried on a motor neuron
      - Effectors = 2 types
        
        muscles (that contract)
        
        glands( that secrete a hormone)
- - - - cell body = central portion of a neuron; contains usual organelles, except centrioles
        
        identify: necleus, prominent nucleolus, and many Nissl bodies = RER
      - Neuron processes/ nerve fibers = extensions from cell body; two types
        
        dendrites
        
        many per neuron
        
        short and branched
        
        receptive portion of a neuron
        
        carry impulsestoward cell body
        
        axons
        
        one per neuron
        
        long, thin process
        
        carry impulses away from the cell body
        
        Note terminations of axon branch = axonal terminals; synaptic knobs
    - - large axons are surrounded by a myelin sheath produced by many layers of Schwann Cells
        
        "myelinated nerve fiber"
        
        myelin = lipoprotein
        
        Interruptions in the myelin sheath between shwann cells =nodes of ranvier
      - small axons do not have a myelin sheath
        
        "unmyelinated nerve fibers"
        
        however all axons (in PNS) are associated with schwann cells
  - - - PNS = nerve
      - CNS = tract/ column
    - - PNS = ganglia
      - CNS = nucleus
  - - - olgiodendrocyte
        
        looks like eyeball
        
        function; produces myelin
      - astrocyte
        
        star shaped
        
        function; norishes neurons
      - microglia
        
        looks like spider
        
        function; phagocytosis
      - ependymal cells
        
        epithelial like layer
        
        function; lines spaces in CNS
        
        brain = ventricles
        
        spinal cord = central canal
  - - - PNS
      - afferent neurons
      - carry sensory impluses from sensory receptors to CNS
      - input information to CNS
      - location of receptors = skin & sense organs
        
        somatic receptors
        
        external receptors
        
        visceral receptors
    - - CNS
      - link other neurons together
    - - PNS
      - efferent neurons
      - carry motor impulses away from CNS and to effectors
      - output information from CNS
      - effectors = muscles & glands
        
        somatic motor neurons (skeletal muscles)
        
        visceral motor neurons (muscle & glands)
        
        sympathetic (adrenergic)
        
        parasympathetic (cholinergic)
  - - - many extensions
      - many dendrites leads toward cell body, one axon leads away from cell body
    - - two extensions
      - one fused dendrite leads toward cell body, one axon leads away from cell body
    - - one process from cell body
      - forms central and peripheral processes
      - only distal ends are dendrites
- - - - k; high outside
      - Na; high outside
      - Cl; high outside
      - negatively charged proteins or anions; high outside
  - - - the cell membrane of a neuron must be depolarized in order for a certain ion channels to open and therefor start a nerve impulse
  - - - the threshold potential for a neuron is -55 mv
      - therefor, a threshold stimulus = +15 mv
    - - this event is called the action potential
      - the action potential represents the start of the nerve impulse on a neuron
  - - - destruction of neurotransmitter
        
        enzymes that are present in the synaptic cleft destroy NT
      - reuptae of neurotransmitter
        
        NT is transported back into pre- synaptic knob
- - - - dura mater
        
        outermost membrane
        
        tough, white, fibrous CT
        
        contains many blood vessels and nerves
      - arachnoid mater
        
        middle layer
        
        thin net like membrane
        
        beneath the arachnoid mater lies a wide space
      - pia mater
        
        inner layer that clings to brain surface
        
        very thin delicate CT
        
        many nerves and blood vessels = nourishment
        
        dips into grooves and contours
- - - - posterior dorsal horns
      - lateral horns
      - anterior ventral horns
    - - in general, ascending tracts are located in the posterior dorsal columns and conduct sensory impulses from body parts to brain
      - in general, descending tracts are located in the anterior ventral columns and conduct motor efferent impulses from brain to effectors