Chapter #11 Nervous system

• The Nervous System


  The system that senses, processes, and reacts to changes in the internal and external environment
• The Nervous System's Functions

  • Touch
  • Taste
  • Smell
  • Hear
  • Sight
  • Thoughts
• Muscle Contraction


  The process by which muscles shorten and generate force
• Motor end plate


  The junction between a motor neuron and a muscle fiber
• Components of the Nervous System

  • CNS (Central Nervous System)
  • PNS (Peripheral Nervous System)
• Fight or flight


  • The body's response to a perceived harmful event, attack, or threat to survival
• Rest & digest


  • The body's parasympathetic nervous system response, allowing the body to rest and recover
• The organization of the Nervous System includes structures and functions
• Neurons (nerve cells)


  Excitable cells that transmit electrical signals
• Neuroglia (glial cells)


  Small cells that surround and wrap delicate neurons, with various functions
• General Characteristics of Neurons

  • Excitability
  • Conductivity
  • Extreme longevity
  • High metabolic rate:
• Neuron: Cell Body (Soma)

  Biosynthetic center of neuron, synthesizes proteins, membranes, chemicals
• Nissl Bodies


  Sites for protein synthesis within the neuron cell body
• Dendrites


  Receptive (input) region of neuron

  
• Axons


  Each neuron has one axon that starts at cone-shaped area called axon hillock, can be short, long, or absent, long axons are called nerve fibers, have occasional branches called axon collaterals, distal endings are called axon terminals
• Most neuron cell bodies are located in the CNS
• Nuclei


  Clusters of neuron cell bodies in the CNS
• Ganglia


  Clusters of neuron cell bodies in the PNS

  
• Tracts


  Bundles of neuron processes in the CNS
• Nerves


  Bundles of neuron processes in the PNS
• Myelin Sheath


  Whitish, protein-lipid substance that protects and insulates the axon, and increases the speed of nerve impulses (saltatory conduction)
• Nonmyelinated fibers


  Axons that do not contain a myelin sheath, conduct impulses more slowly
• Structural Classes of Neurons

  • Multipolar, Bipolar, Unipolar
• Multiple Sclerosis


  Progressive demyelination of neurons in the CNS, an autoimmune disorder
• Guillain-Barré Syndrome


  Loss of myelin from peripheral nerves due to inflammation, causing muscle weakness
• Action Potentials


  The principal way neurons send signals, occur only in muscle cells and axons of neurons, are all-or-none and involve the opening of specific voltage-gated channels

  
• Ion Channels


  Two main types: Leakage (nongated) channels that are always open, and Gated channels that change shape to open/close
• Sodium-Potassium Pump


  Maintains the resting membrane potential by slowly pumping 3 Na+ out for 2 K+ in
• Action potentials


  • Principal way neurons send signals
  • Occur only in muscle cells and axons of neurons
  • Do not decay over distance as graded potentials do, they are all-or-none
  • Involves opening of specific voltage-gated channels

  
• Action Potential: Resting State


  1. Resting membrane potential

  2. Voltage-gated Na+ and K+ channels closed
• Action Potential: Depolarization


  1. Voltage-gated Na+ channels open

  2. Na+ rushes in

  3. Membrane potential rises
• Action Potential: Repolarization


  1. Voltage-gated K+ channels open

  2. K+ rushes out

  3. Membrane potential returns to resting state
• Action Potential: Hyperpolarization


  1. Membrane potential drops below resting potential

  2. Voltage-gated K+ channels still open
• Graded potential


  • 70mV to -55mV
• Graded potentials
• Neuromuscular Junction (NMJ)


  • Axon terminal and muscle fiber separated by synaptic cleft
  • Synaptic vesicles contain neurotransmitter acetylcholine (ACh)
  • Junctional folds contain millions of ACh receptors (motor end plate)
  • NMJ consists of axon terminals, synaptic cleft, and junctional folds

  
• Neurotransmitter


  • Chemical messengers that communicate between neighboring cells (synapses)
  • Examples: Acetylcholine (ACh), Dopamine, Norepinephrine, Glutamate, GABA, Endorphins, Somatostatin
• Impaired action potential impulse propagation can be caused by a number of chemical and physical factors
• Local anesthetics act by blocking voltage-gated Na+ channels
• Cold temperatures or restrictions, continuous pressure will affect blood circulation and delivery of oxygen to neurons