Neurons

• Neurons


  The basic building blocks of the nervous system that transmit information

  
• Neurons


  • Cell Body (contains nucleus)
  • Dendrites (specialized for receiving signals)
  • Axon (carries impulse from cell body to terminal end)
  • Myelin Sheath (insulates axon, speeds up impulse)
  • Cell Membrane (selectively permeable "skin", covered with ion channels)
  • Synaptic Terminals/Buttons (have containers that hold neurotransmitters)

  
• Neurons at Rest


  1. Outside the cell, lots of positively charged sodium (Na+) ions

  2. Inside the cell, little sodium, but some potassium (K+)

  3. Ion channels/voltage gates are closed

  4. Sodium pumps maintain this resting state by actively pushing sodium ions out

  5. Cell membrane is polarized
• Neurons in Action


  1. Sodium leaks in and changes the potential across the membrane

  2. Either causes target cell to reach threshold (0mV)

  3. Or sodium pumps push ions out as soon as they leak in, cell stays at rest
• Action Potential


  1. Sodium channels open, sodium rushes in causing depolarization (+40mV) at one spot

  2. Potassium channels open, potassium goes out restoring polarization at that spot

  3. Chain reaction, next sodium channels down the line open up

  4. Travels from cell body end to terminal end
• Refractory Period


  Brief period where resting state is restored by sodium and potassium pumps
• Neurotransmitter Release


  When action potential reaches terminal buttons
• Neurotransmitter Transmission


  1. Neurotransmitter fits like lock and key into receptor sites in next cell

  2. Changes permeability of membrane in post-synaptic neuron so sodium channels get bigger (excitatory) or smaller (inhibitory) and more or less sodium leaks in

  3. Signals received close together in space (spatial summation) or time (temporal summation) combine

  4. Enough excitatory signals close in space and time may cause post-synaptic neuron to reach threshold and have an action potential

  5. Reuptake occurs when NT goes back to synaptic vesicles in pre-synaptic neuron

  6. Autoreception involves the NT landing on a receptor site on the terminal end of the pre-synaptic neuron, always inhibitory

  7. Degradation (enzyme deactivation), NT is broken down by enzymes, limits active time

  
• Many different adjacent pathways for different types of information
• Three Kinds of Neurons


  • Sensory Neurons (transduce physical energy into action potentials)
  • Interneurons (synapse with other neurons at both ends, found only in central nervous system)
  • Motor Neurons (synapse with muscle fiber at terminal end, release acetylcholine)

  
• Simple Reflex


  1. Sensory neurons to nerves to interneurons in spinal cord to motor neurons to muscles (spinal reflex)

  2. Also from interneurons in spinal cord to interneurons in brain, and from brain back to muscles
• There are three types of neurons: sensory (afferent), motor (efferent), and interneuron.
• There are three types of neurons: sensory neurons, motor neurons, and interneurons.
• Neurons are specialized cells that transmit information throughout the nervous system.
• Neurons are specialized cells that transmit information throughout the nervous system.
• The human body has approximately 80 billion neurons.
• Glia cells outnumber neurons by about ten times but do not conduct electrical impulses.
• The three kinds of neurons include sensory neurons that transmit impulses toward the CNS, motor neurons that carry impulses away from the CNS, and interneurons that connect neurons within the CNS.
• Axons can be myelinated or unmyelinated.
• Synapses are gaps between two neurons where neurotransmitters pass messages across.
• Glial cells support and protect neurons, insulate them with myelin sheaths, and form barriers between different parts of the brain.
• Central Nervous System


  Brain and spinal cord
• Peripheral Nervous System (PNS)


  • Sensory neurons carry impulses toward brain or spinal cord
  • Motor neurons carry impulses away from brain or spinal cord, to glands, organs and muscles
• Somatic Nervous System


  Serves the skeletal (voluntary) muscles
• Autonomic Nervous System (ANS)


  • Serves the internal organs and glands
  • Sympathetic division responds to challenges, primary function: Prepare body for action ("fight or flight")
  • Parasympathetic division conserves energy for long-term functions, primary function: Growth and repair ("rest & digest")

  
• Hypothalamus


  • Maintains homeostasis (a stable internal environment)
  • Regulates hunger, thirst, temperature, stress, and sex
  • Sits right over and controls pituitary gland
• Neurotransmitters (NTs)


  Local, fast, travel across synapse
• The nervous system consists of the central nervous system and the peripheral nervous system
• The peripheral nervous system consists of the somatic nervous system and the autonomic nervous system
• The autonomic nervous system consists of the sympathetic division and the parasympathetic division

  
• The brain and spinal cord make up the central nervous system
• The sympathetic division responds to challenges and prepares the body for action ("fight or flight")
• The parasympathetic division conserves energy for long-term functions and promotes growth and repair ("rest and digest")
• Sensation


  Getting information from the environment and bringing it into the brain
• Transduction


  Physical energy into action potentials