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The Nervous System (synaptic knobs occur at the ends of axons (cholinergic…

- - - - Potential Difference- the difference in electrical charge between 2 points
      - Irons across the cell membrane
        
        K+; high inside
        
        Na+; high outside
        
        Cl-; high outside
        
        Negatively charged proteins of Anions-; high inside
      - RMP OF NERVE CELL; -70mV
  - - - the threshold potential for a neuron is -55mV
      - a threshold stimulus= +15mV
    - - this is called action potential*
      - represents start of nerve impulse on a neuron
  - - - threshold stimulus (15mV)= yes AP and yes NI
      - threshold stimulus (20mV)= yes AP and yes NI but no greater intensity
      - subthreshold stimulus (5mV)= no AP and no NI
    - - +15 mV= threshold= AP= NI
      - +5 +5 +5= 15mV= threshold= AP= NI
    - - the RMP has to be restored before it can depolarized again
    - - unmyelinated nerve fibers- NI must travel the length of the nerve fiber; slow
      - myelinated nerve fiber (Saltatory Conduction)
        
        NI jumps from node of Ranvier to node of Ranvier
        
        fast
  - - - Synaptic vesicles (filled with neurotransmitter/NT) to release NT via exocytosis into the synaptic cleft
      - NT diffuses across synaptic cleft and depolarizes the post-synaptic neuron's membrane
      - Ca++ channels open and calcium ions rush into axonal terminal causing:
      - An action potential (AP) is triggered and a NI begins in the post-synaptic neuron
      - NI reaches axonal terminal of pre-synaptic knob
  - - - ACh is released by;
        
        all motor neurons {those that stimulate skeletal muscle
        
        some CNS neurons
    - - monoamines (modified amino acids)
        
        are widely distributed in the brain where they play a role in:
        
        emotional behavior
        
        circadian rhythm
        
        are present in some motor neurons of the ANS
        
        include:
        
        dopamine
        
        serotonin
        
        norepinephrine
        
        histamine
        
        epinephrine
    - - Destruction of Neurotransmitter
        
        Enzymes that are present in the synaptic cleft destroy NT
      - Reuptake of Neurotransmitter
        
        NT is transported back into pre-synaptic cleft destroy NT
- - - - c. carry sensory impulses from sensory receptors to CNS
      - d. input information to CNS
      - b. afferent neurons
      - e. Location of receptors-skin and sense organs
        
        somatic receptors
        
        External receptors (touch, pressure, temp, sight, smell, hearing, and touch)
      - a. PNS
    - - Visceral receptors (digestive, respiratory, cardiovascular, urinary, reproductive, taste, deep pressure, and pain)
  - - - Somatic motor neurons (skeletal muscles)
      - Visceral motor neurons (muscle and glands)
        
        Sympathetic (adrenergic)
        
        2.Parasympathetic- cholinergic
  - - - many extensions
      - many dendrites lead toward cell body, one axon leads away from cell body
    - - one fused dendrite leads toward cell body, one axon leads away from cell body
      - two extensions
    - - forms central and peripheral processes
      - only distal ends are dendrites
      - one process from cell body
- - - - short and branched
      - receptive portion of a neuron
      - many per neuron
      - carry impulses toward cell body
    - - long, thin process
      - carry impulses away from cell body
      - one per neuron
      - note terminations of axon branch= axonal terminal; synaptic knobs
      - Axons in PNS
        
        myelin
        
        Interruptions in the myelin sheath between Schwann cells= Nodes of Ranvier
        
        "myelinated nerve fiber"
        
        small axons do not have a myelin sheath
        
        all axons in PNS are associated with Schwann cells
      - Axons in CNS
        
        Myelin is produced by an oligodendrocyte
        
        A bundle of myelinated nerve fibers is white matter
        
        PNS=nerve, PNS=ganglia; CNS= tract/column, CNS= nucleus
    - - cell body injury= death of neuron
      - Neurological Cells- accessory cells of nervous system form supporting network for neurons; neuron glue
        
        PNS= Schwann cells produces myelin and satellite cells nourish neurons
        
        CNS-4 types, provide bulk of brain and spinal cord tissue
        
        Astrocyte
        
        star-shaped
        
        Function-nourishes neurons
        
        Microglia
        
        looks like spider
        
        Function- phagocytosis
        
        Oligodendrocyte
        
        looks like eyeball
        
        Function-produces myelin
        
        Ependymal cell
        
        epithelial-like layer
        
        Function-lines spaces in CNS
        
        brain=ventricles
        
        spinal cord-central canal
- - - - afferent division- brings sensory information to the CNS
      - efferent division- carries motor commands to muscles, glands, and fat cells
        
        somatic nervous system- voluntary control over skelesomatic muscle contractions
        
        autonomic nervous system- automatic, involuntary regulation of smooth muscle, cardiac muscle, and glandular activity