Chap by yaofenjin

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									Nervous System
            Nervous System
• Homeostatic Function
  – Along with the endocrine system, regulate all
    other systems in the body
  – Sense environment and respond
• Organs vertebrates
  – Brain
  – Spinal cord
  – Nerves
                Terminology
• Cephalization: the tendency to localize important
  parts in or near the head
• Ganglia: collections or bundles of neuron cells
  (usually outside the nervous system, but there are
  basal ganglia in the brain)
• Potential: the difference in charge between the
  inside and outside of a nerve
• Synapse: junction between neurons; consists of
  presynaptic membrane, synaptic cleft, and
  postsynaptic membrane
      Speed and Duration:
  Nervous vs. Endocrine System
• Nerves                      • Hormones
  – Communication in            – Communication in
    1/1000 of a second            seconds, minutes, or
  – Effects can be reversed       hours
    or modified almost          – Time needed to reverse
    instantaneously               or modify effects
  – System is ―hardwired‖       – Dependent on nervous
    but can be modified           system
CNS, PNS, and ANS

           • Central Nervous System
             – Brain
             – Spinal Cord
           • Peripheral Nervous
             System
             – Cranial nerves
             – Spinal nerves
           • Autonomic Nervous
             system
             – Sympathetic
             – Parasympathetic
        Nervous Tissue: Neurons
• Parts of neurons
  – Dendrites (receive
    information)
  – Body (a.k.a. soma,
    makes
    neurotransmitters)
  – Axon (a.k.a. nerve,
    send information)
Types of Neurons

• Sensory
  – Input from receptors
  – To CNS
• Interneurons
  – Between neurons in CNS
• Motor
  – Output
  – To effectors
              Myelinated Axons
• Support cells form an insulating covering around the axon
• Nodes of Ranvier
              Myelin Sheath
• Less energy expenditure
• Saltatory conduction
• Nerve regeneration capabilities (PNS only)
Saltatory Conduction
Nervous Tissue: Neuroglia


       Astrocyte
                            Microglia



               Oligodendrocyte forming myelin
               sheath around an axon
                Nerve Impulse
• Electrochemical
   – Ions move across the plasma membrane creating
     voltage differences which change over time
• Resting potential
   – Higher concentration of sodium ions outside, potassium
     ions inside; usually at –65 mV (inside is more negative)
   – Results from sodium-potassium pump, active transport
• Action potential
   – Rapid change in polarity from negative to positive that
     occurs when a threshold stimulation is reached
    Na+/K+ Pump: Resting Potential
•   3 Na+ out, 2 K+ in
•   K+ ―leak‖
•   Net negative charge in cytoplasm
•   Resting potential (-85 to –65 mV)
             Graded Potentials
• Depolarization
  – Signals from incoming axons move the membrane
    potential closer to 0 (less negative)
• Hyperpolarization
  – Signals from incoming axons move the membrane
    potential away from 0 (more negative)
• Spatial summation
  – Both types of polarization are integrated dependent on
    the number of neurons transmitting to the cell
• Temporal summation
  – Both types of polarization are integrated dependent on
    the frequency of stimulation of the neurons transmitting
    to the cell
   Action Potential
• Depolarization
   – Sodium enters the cell through
     channels
   – Polarity goes from –65 mV to
     +40 mV
• Repolarization
   – Reversal of polarity
     (depolarization) closes sodium
     channels, opens potassium
     channels
   – Potassium ions move from
     inside to the outside, causing
     polarity to go from + 40 mV to
     –65 mV (repolarization)
• Refractory period
                 All-Or-None Law
• Action potentials occur maximally
  or not at all
• In other words, either the threshold
  is reached and an action potential
  takes place or it isn’t reached and
  there is no action potential.
• All action potentials look
  essentially the same.
• Frequency of action potentials is
  thus the code of information to the
  receiving cell (temporal
  summation)
   – Spatial summation
Propagation of Action Potentials
• If axon unmyelinated,
  transmission is from one
  portion of
  axomembrane to the
  next (slow)
• If axon is myelinated,
  action potential can
  jump from one node to
  the next: saltatory
  conduction
          Synapse
          Structure
• Axons split into endings tipped by
  axonal bulbs—presynaptic
  membrane is here
   – Ca++ channels open in response to
     action potential
   – Vesicles with neurotransmitter fuse
     with PM
• Neurotransmitter in synaptic cleft
• Postsynaptic membrane can be a
  dendrite, a soma, or another axon
   – Neurotransmitter binds with receptors
   – Chemically gated channels respond
               Neurotransmitters
• Raise membrane potential of postsynaptic
  membrane toward threshold for action potential:
  excitatory
   – Acetylcholine (ACh)
   – Norepinephrine (NE)
   – Dopamine
• Lower membrane potential of postsynaptic
  membrane away from threshold: inhibitory
   – GABA
   – Glycine
            Synaptic Integration
• Neurons integrate excitatory and inhibitory
  signals at the postsynaptic membrane
• Summation of these signals is the
  determining factor for action potential in the
  postsynaptic neuron
  Convergence and Divergence
• Convergence:
  postsynaptic neuron
  receives input from
  many other neurons
• Divergence: one
  neuron transmits to
  many other neurons
        Central Nervous System
• Brain
  – Sensory information received, motor control initiated;
    integration; sentience
  – Protected by 8 cranial bones
  – Surrounded by meninges and cerebrospinal fluid
       • Dura mater, arachnoid mater, pia mater
• Spinal Cord
  –   Center for reflex arc
  –   Integration center for brain and spinal nerves
  –   Protected by vertebrae
  –   Surrounded by meninges and cerebrospinal fluid
       • Lumbar puncture
  Gray Matter and White Matter
• Gray Matter           •   White Matter
• Cell somas            •   Myelinated axons
• Unmyelinated fibers   •   Dorsal tracts  brain
                        •   Ventral tractsbrain
              The Meninges


• Dura mater
• Arachnoid mater
• Pia mater
            Blood-Brain Barrier
• Unlike regular capillaries,
  blood borne pathogens
  and formed elements of
  blood cannot enter the
  CNS through the
  capillaries there—this is
  due to the tight junctions
  in the endothelial
  capillaries and due to the
  processes of astrocytes
                              The Brain
• Forebrain: emotions and conscious
  thought
   – Cerebrum
      • Left and Right Cerebral Hemispheres
      • Cerebral Cortex
      • Basal Nuclei
   – Diencephalon
      • Thalamus
      • Hypothalamus
• Midbrain: vision and hearing
• Hindbrain: movement and
  automatic function
   – Cerebellum
   – Pons
   – Medulla Oblongata
 The Ventricles
• Production of CSF
Forebrain: Cerebrum
  (Telencephalon)
         Four Lobes of the Cerebrum


•   Frontal
•   Parietal
•   Occipital
•   Temporal
Cerebral Cortex
Cortex in Action
Basal Nuclei
        The Diencephalon
• Thalamus
• Hypothalamus
The Limbic System: Memory
                  Memory
• Short term memory
  – 7 (plus or minus 2) chunks of information at
    one time
  – 20 second duration
• Long term memory
  – Retrievable
  – Stable
           Sequence of LTP
• Glutamate binds to
  NMDA receptor and to
  AMPA receptor
• EPSP and binding
  causes NMDA Ca++
  channels to open
• Ca++ causes LTP
• Ca++ activates NO
  synthase
• NO acts as retrograde
  messenger
               RESULT: synaptic transmission is stronger
                Brainstem


• Midbrain
• Pons
• Medulla oblongata
            The Cerebellum
• Coordination
• Replication of
  sequenced
  movements
• Sensory input from
  proprioreceptors,
  vision, and
  vestibular apparatus
    Peripheral Nervous System
• Cranial nerves
  – 12 pairs attached to the brain
  – Contain portions of autonomic nervous system
     • Parasympathetic
• Spinal nerves
  – 31 pairs from the spinal cord
  – Preganglionic fibers to the autonomic nervous
    system (sympathetic and parasympathetic)
Cranial Nerves: 12

            I Olfactory
            II Optic
            III Oculomotor
            IV Trochlear
            V Trigeminal
            VI Abducent
            VII Facial
            VIII Vestibulocochlear
            IX Glossopharyngeal
            X Vagus
            XI Accessory
            XII Hypoglossal
Spinal Nerves: 31
                The Reflex Arc
1.   Receptor
2.   Sensory neuron
3.   Interneuron
4.   Motor neuron
5.   Effector
     Autonomic Nervous System
• Sympathetic and Parasympathetic divisions
    – Antagonistic to eachother
•   Functions automatically
•   Innervates all internal organs
•   Utilizes two neurons and a ganglion
•   Critical for homeostasis
Sympathetic vs. Parasympathetic
• Thoracolumbar          • Craniosacral
• Preganglionic fibers   • Preganglionic fibers LONG
  SHORT                  • Neurotransmitter:
• Neurotransmitter:        acetylcholine
  norepinephrine         • ―Relaxation & reproduce‖
• ―Fight or flight‖
Divisions of the ANS
Summary of the PNS

								
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