ANAPHY Semis

• Nervous System


  • Receives sensory input
  • Integrates information
  • Controls muscles and glands
  • Maintains homeostasis
  • Establishes and maintains mental activity
• Main Divisions of Nervous System

  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (all nervous tissue outside the CNS)

  
• Divisions of Peripheral Nervous System

  • Sensory division (conducts action potentials from sensory receptors to the CNS)
  • Motor division (conducts action potentials to effector organs like muscles and glands)
• Divisions of Motor Division

  • Somatic nervous system (transmits action potentials from CNS to skeletal muscles)
  • Autonomic nervous system (transmits action potentials from CNS to cardiac muscle, smooth muscle, and glands)
  • Enteric nervous system (special nervous system found only in digestive tract)

  
• 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 functions that enhance neuron function and maintain normal conditions

  
• Parts of a Neuron

  • Cell body
  • Dendrite
  • Axon

  
• Structural Types of Neurons

  • Multipolar (many dendrites, single axon)
  • Bipolar (one dendrite, one axon)
  • Pseudo-unipolar (single process dividing into two)

  
• Types of Glial Cells

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


  Specialized layers that wrap around axons of some neurons, formed by oligodendrocytes in CNS and Schwann cells in PNS, insulates and increases speed of action potential conduction

  
• Nodes of Ranvier


  Gaps in the myelin sheath where ion movement can occur

  
• Gray Matter


  Nervous tissue with groups of neuron cell bodies and dendrites, little myelin

  
• White Matter


  Nervous tissue with bundles of parallel myelinated axons, whitish in color

  
• Resting Membrane Potential


  Difference in electrical charge across neuron membrane at rest, due to ion concentration gradients and ion channels

  
• Leak Channels


  Always open, allow ions to move down concentration gradient

  
• Gated Channels


  Closed until opened by specific signals like voltage or chemicals
• Sodium-Potassium Pump


  Maintains ion concentration gradients by actively transporting Na+ out and K+ into the cell

  
• Action Potential

  1. Voltage-gated Na+ channels open

  2. Massive Na+ influx causes depolarization

  3. Voltage-gated K+ channels open, K+ efflux causes repolarization

  4. Brief hyperpolarization occurs

  
• Saltatory Conduction


  Action potentials in myelinated axons jump between nodes of Ranvier, faster than continuous conduction in unmyelinated axons
• Synapse


  Junction where axon of one neuron interacts with another neuron, with synaptic cleft between presynaptic and postsynaptic membranes
• Synaptic Transmission

  1. Action potential reaches presynaptic terminal

  2. Ca2+ influx causes neurotransmitter release into synaptic cleft

  3. Neurotransmitters bind to receptors on postsynaptic membrane

  4. Channels open/close, causing depolarization or hyperpolarization
• There are many neurotransmitters, with acetylcholine and norepinephrine being the best known
• Transmitters


  Cause chemically gated channels for Na+, K+, or Cl− to open or close in the postsynaptic membrane

  
• Neurotransmitter type and receptor type


  Determine whether the channel opens or closes
• Response


  May be either stimulation or inhibition of an action potential in the postsynaptic cell
• Na+ channels open


  Postsynaptic cell becomes depolarized, and an action potential will result if threshold is reached

  
• K+ or Cl− channels open


  Inside of the postsynaptic cell tends to become more negative, or hyperpolarized, and an action potential is inhibited from occurring

  
• Well-known neurotransmitters


  • Acetylcholine
  • Norepinephrine
• Neurotransmitters

  Do not normally remain in the synaptic cleft indefinitely, their effects are short duration
• Neurotransmitter removal

  1. Rapidly broken down by enzymes within the synaptic cleft

  2. Transported back into the presynaptic terminal
• Acetylcholinesterase


  Breaks down acetylcholine
• Norepinephrine


  Either actively transported back into the presynaptic terminal or broken down by enzymes
• Reflex


  Involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS
• Reflexes


  • Allow a person to react to stimuli more quickly than is possible if conscious thought is involved
  • Most occur in the spinal cord or brainstem rather than in the higher brain centers
• Reflex arc


  Neuronal pathway by which a reflex occurs
• Reflex arc components

  • Sensory receptor
  • Sensory neuron
  • Interneurons
  • Motor neuron
  • Effector organ (muscles or glands)
• Converging pathway


  Simple pathway in which two or more neurons synapse with the same postsynaptic neuron
• Diverging pathway


  Simple pathway in which an axon from one neuron divides and synapses with more than one other postsynaptic neuron

  
• Summation


  Process where many presynaptic action potentials are needed to cause a sufficiently large postsynaptic local potential to reach threshold and produce an action potential in the target cell

  
• Spatial summation


  Local potentials originate from different locations on the postsynaptic neuron