nervous

• Nervous System Functions


  • Receiving sensory input
  • Integrating information
  • Controlling muscles and glands
  • Maintaining homeostasis
  • Establishing and maintaining mental activity

  
• Main Divisions of Nervous System

  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)
  • Sensory division
  • Motor division

  
• Main Divisions of Nervous System

  • Somatic nervous system
  • Autonomic nervous system
  • Enteric nervous system

  
• Neurons


  Receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs
• Glial cells


  Supportive cells of the CNS and PNS, do not conduct action potentials but carry out different functions that enhance neuron function and maintain normal conditions within nervous tissue

  
• Parts of a neuron

  • Cell body
  • Dendrite
  • Axon

  
• Structural Types of Neurons

  • Multipolar neurons
  • Bipolar neurons
  • Pseudo-unipolar neurons

  
• Types of Glial Cells

  • Astrocytes
  • Ependymal cells
  • Microglial cells
  • Oligodendrocytes
  • Schwann cells
• Myelin sheath


  Specialized layers that wrap around the axons of some neurons, formed by oligodendrocytes in the CNS and Schwann cells in the PNS, an excellent insulator that prevents almost all ion movement across the cell membrane

  
• Nodes of Ranvier


  Gaps in the myelin sheath where ion movement can occur
• Myelination of an axon increases the speed and efficiency of action potential generation along the axon
• Multiple sclerosis is a disease of the myelin sheath that causes loss of muscle function
• Unmyelinated axons


  Lack myelin sheaths, rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS

  
• Gray matter


  Consists of groups of neuron cell bodies and their dendrites, where there is very little myelin
• White matter


  Consists of bundles of parallel axons with their myelin sheaths, which are whitish in color
• Resting membrane potential


  The small, but measurable, voltage that exists across the cell membrane when the cell is at rest

  
• Leak channels


  Always open so ions can diffuse across the membrane, down their concentration gradient

  
• Gated channels


  Closed until opened by specific signals, including chemically gated channels opened by chemicals such as neurotransmitters and voltage-gated channels opened by a change in the electrical property of the cell membrane

  
• Polarized membrane


  The inside of the membrane has a negative charge relative to the outside of the membrane, which has a positive charge
• Sodium-potassium pump


  Actively transports K+ into the cell and Na+ out of the cell, required to maintain resting membrane potential

  
• The sodium-potassium pump consumes 25% of all the ATP in a typical cell and 70% of the ATP in a neuron

  
• Nerve cells are excitable, the resting membrane potential can change in response to a stimuli

  
• Action potentials


  Changes in membrane potential that nerve cells use to communicate with other cells

  
• The opening and closing of gated ion channels changes the permeability of the membrane to ions and can therefore change the membrane potential, resulting in action potentials

  
• Action potentials are electrical signals that are conducted along the cell membrane similar to electricity travelling along an electrical wire

  
• Membrane potential


  The electrical charge difference across a cell membrane that can change in response to a stimuli

  
• Action potentials


  The changes in membrane potential that nerve cells use to communicate with other cells

  
• Gated membrane channels


  1. Stimuli activate gated channels

  2. Opening and closing of gated ion channels changes membrane permeability

  3. Action potentials may result

  
• Action potential generation


  1. Stimulus applied

  2. Na+ channels open briefly, Na+ diffuses into cell

  3. Depolarization occurs

  4. If depolarization reaches threshold, voltage-gated Na+ channels open

  5. Massive increase in Na+ permeability

  6. Voltage-gated K+ channels open

  7. Repolarization occurs

  8. Hyperpolarization occurs briefly

  
• Action potentials occur in an all-or-none fashion
• The sodium-potassium pump assists in restoring the resting membrane potential

  
• Action potential conduction


  • Continuous conduction in unmyelinated axons
  • Saltatory conduction in myelinated axons

  
• Continuous conduction


  Action potentials travel along the entire membrane

  
• Saltatory conduction


  Action potentials occur in a jumping pattern at the nodes of Ranvier
• Axon diameter


  Determines speed of action potential conduction
• Synapse


  A junction where the axon of one neuron interacts with another neuron
• Synaptic transmission


  1. Action potential reaches presynaptic terminal

  2. Ca2+ enters, causing neurotransmitter release

  3. Neurotransmitters bind to receptors on postsynaptic membrane

  4. Chemically gated channels open/close, causing depolarization or hyperpolarization
• Neurotransmitters


  Chemical substances stored in synaptic vesicles that are released and diffuse across the synaptic cleft
• Neurotransmitters are either broken down by enzymes or transported back into the presynaptic terminal
• Converging pathway


  Two or more neurons synapse with the same postsynaptic neuron