bio final

• Neurons


  Cells that conduct and store information in the nervous system

  
• Synapses


  Connections between neurons where information is passed in chemical form

  
• Central nervous system (CNS)


  Neurons that carry out integration
• Peripheral nervous system (PNS)


  Neurons that carry information to/from CNS

  
• Neurons


  • Cell body
  • Many short dendrites (branched extensions at receiving end)
  • One long axon (extends from neuron to cell it acts on)

  
• Specialized populations of neurons

  • Sensory neurons (transmit information about external stimuli)
  • Interneurons (create local networks connecting neurons in brain or ganglia)
  • Motor neurons (transmit signals to muscle cells)

  
• Neuron excitation and signal transmission

  1. Neuron becomes electrically excited

  2. Excitement passed chemically at synapse

  3. Presynaptic cell releases neurotransmitters

  4. Postsynaptic cell may become electrically excited by neurotransmitters

  
• Resting potential


  Electrical charge difference across neuron membrane when not sending messages, typically -60 to -80 mV

  
• Action potential


  Rapid change in membrane potential from negative to positive that allows neurons to transmit signals

  
• Action potential generation


  1. Depolarization activates voltage-gated Na+ channels

  2. Positive feedback leads to further depolarization

  3. Rapid depolarization opens both Na+ and K+ voltage-gated channels sequentially

  4. Results in rapid hyperpolarization

  
• Action potential propagation


  • Refractory period prohibits regression
  • Propagation speed increases with axon diameter and myelination
• Myelin sheath


  Electrical insulation around axons provided by glial cells, allowing faster saltatory conduction
• Synaptic transmission


  1. Neurotransmitter released into synaptic cleft

  2. Binds to ligand-gated ion channels on postsynaptic membrane

  3. Causes change in postsynaptic membrane potential (excitatory or inhibitory)

  
• Nervous system complexity


  • Varies among animal phyla, reflecting evolutionary history and lifestyle
  • Bilaterally symmetrical animals have a concentrated nervous system with a brain (cephalization)
• Vertebrate CNS


  Brain and spinal cord, made of gray matter (neuron cell bodies) and white matter (myelinated axons)

  
• Vertebrate PNS


  Cranial and spinal nerves, afferent (sensory) and efferent (motor) neurons

  
• Divisions of the autonomic nervous system


  • Sympathetic (arousal and energy generation)
  • Parasympathetic (calming, "rest and digest")
  • Enteric (digestion)

  
• Brain regions


  • Hindbrain (brainstem, cerebellum)
  • Midbrain
  • Forebrain (diencephalon, cerebrum)
• Cerebral cortex


  Center for information processing, with specialized lobes and hemispheres
• Brain development and plasticity

  1. Embryonic development

  2. Neuron die-off

  3. Synapse reconfiguration

  4. Learning and memory through synaptic changes
• Brain disorders provide insights into brain function
• Beluga whales


  Sensing Earth's magnetic fields
• Thermoreceptors


  Detect heat and cold
• Membrane proteins


  • Change shape under different temperatures
• Vipers


  • Have pits to detect body heat (infrared)
• Chemicals that can trick thermoreceptors

  Capsaicin (from peppers) or menthol
• Nociceptors


  Detect "pain", like extreme pressure, chemicals, etc.
• Nociceptors


  • Highest density in skin
• Getting a stimulus to the brain

  1. Reception: Sensory receptor detects stimulus

  2. Transduction: Stimulus can result in a change in membrane potential of receptor cell(s)

  3. Transmission: If receptor potential initiates action potential, impulse is sent to brain

  4. Perception: Brain processing input from sensory neurons

  
• Transduction


  Stimulus can result in a change in membrane potential of receptor cell(s) (called a receptor potential)
• Transmission


  If receptor potential initiates action potential, impulse is sent to brain

  
• Transmission


  Strength of stimulus modulates frequency of action potential
• Transmission


  Integration: Summation on a single receptor cell, Multiple receptor cells acting on a single afferent neuron
• Perception


  Brain processing input from sensory neurons
• Perception


  All perceptions are coded by the paths their action potentials travel
• Transduction modification


  • Amplification: Strengthening the stimulus; adding energy
  • Sensory adaptation: Become unresponsive to constant stimulation
• Gustation


  Taste; detection of chemicals (tastants) in solution
• Taste receptors in mammals

  • Concentrated on taste-buds on tongue
  • Recognize sweet, sour, salty, bitter, & savory (or umami, by glutamate)
  • Many different kinds of cells, each with single receptor
  • Binding receptors cause a change in the ion channels and depolarization may occur
• Taste receptors in insects


  • On bottom of feet and mouth parts
• Olfaction


  Smell; detection of odorants in air