physio chap 2

• Axon hillock


  Specialized part of the cell body of a neuron that connects to the axon

  
• Axons


  Long slender projection of a nerve cell or neuron, that conducts electrical impulses away from the neuron's cell body
• Myelin Sheath


  • Insulating layer or sheath that forms around nerves, including those in the brain and spinal cord
  • Allows electrical impulses to transmit quickly and efficiently along the nerve cells
• Axon Terminal/Synaptic Terminal


  Pass the information to another neuron
• Synapse


  Small gap between two neurons, where nerve impulses are relayed by a neurotransmitter from the axon of a presynaptic (sending) neuron to the dendrite of a postsynaptic (receiving) neuron

  
• Glia


  Other components of the nervous system that perform many functions
• Microglia


  Removes viruses and fungi from the brain
• Astrocytes


  • Star-shaped glial cells that provide nutrient support to neurons
  • Help to repair damage to nervous system tissue

  
• Oligodendrocytes & Schwann cells


  Build the myelin sheaths that surround and insulate certain vertebrate axons
• Radial Glia


  Guide the migration of neurons and their axons and dendrites during embryonic development
• Blood-Brain Barrier


  Mechanism that excludes most chemicals from entering the brain
• Nerve Impulse


  • Electrical message that is transmitted down the axon of a neuron
  • Does not travel directly down the axon, regenerated points along
  • Speed of nerve impulse is between 1m/s to 100m/s

  
• Electrical Gradient


  Difference of electrical charge in and out of the cell
• Electrical Polarization


  • Maintained by the membrane
  • The inside of the membrane is slightly negative with respect to the outside (app. -70 millivolts)
  • The membrane is selectively permeable, allows some ions to pass more freely than others
  • Sodium, potassium, calcium, and chloride pass through channels in the membrane
  • When membrane is at rest, sodium channels are closed & potassium channels are partially closed allowing slow passage of sodium
• Sodium-Potassium Pump


  • Protein complex that continually pumps three sodium ions out of the cells while drawing two potassium ions into the cell
  • Helps maintain the electrical gradient
  • The electrical gradient and the concentration gradient work to pull sodium ions into the cell
  • The electrical gradient tends to pull potassium ions into the cell
• Resting Potential


  • State of the neuron prior to the sending of a nerve impulse
  • Remains stable until the neuron is stimulated
• 3 Main Types of Gated Channels

  • Voltage Gated Channels
  • Ligand Gated Channels
  • Mechanically Gated Channels
• Hyperpolarization


  Increasing polarization or the difference between the electrical charge of two places
• Depolarization


  Decreasing the polarization towards zero
• Threshold of excitement


  Any stimulation beyond a certain level that results in massive depolarization
• Graded Potential


  Only few channels are open allowing smalls amount of sodium ions to the cell that cause little change to the membrane potential
• Action Potential


  • Rapid depolarization of the neuron
  • The stimulation of neuron past the threshold of excitation triggers a nerve impulse or an action potential
  • After an action potential, sodium channels are quickly closed, and the neuron returns to its resting state by opening potassium channels
  • Potassium ions flow out due to the concentration gradient and take with them their positive charge
  • Sodium-potassium pump later restores the original distribution of ions
• All-or-None Law

  • The amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it
  • Action potentials are equal in intensity and speed within a given neuron
  • If the stimulus is too weak, and the change doesn't hit that level, it's like a false alarm -- the neuron just returns to its resting state

  
• Refractory Period


  • Neuron resists another action potential
  • Help prevent signals from traveling in both directions down the axon at once
  • Absolute Refractory Period: First part of the period which the membrane cannot produce an action potential
  • Relative refractory period: Second part in which it take a stronger than usual stimulus to trigger an action potential

  
• Nodes of Ranvier


  • Interrupted by a short unmyelinated sections of axons
  • Each node of Ranvier, action potential is regenerated by a chain of positively charged ion pushed along by the previous segment
  • Saltatory Conduction: Jumping of an action potential from one node to another
  • Provides rapid conduction of impulses
  • Conserves the energy of the cell

  
• Synapse


  • Specialized junction between two neurons where chemical messages cross from one to other
  • Where the communication occurs between neurons
• Electrical Synapse


  Less common in our own nervous systems
• Chemical Synapse


  • More abundant
  • Slower
  • More precise and selective
  • Use of neurotransmitters

  
• Synaptic Transmission


  The electrochemical messages carried by neurons either increase or decrease, the likelihood that the next cell will continue to transmit

  
• Excitatory Post-Synaptic Potentials (EPSPs)


  Graded potentials that push the neuron closer to threshold and make an action potential more likely

  
• Inhibitory Post-Synaptic Potentials (IPSPs)


  Graded potentials that push the neuron further from threshold, make an action potential harder to achieve
• Synaptic Communication


  Molecules of neurotransmitters are released when an action potential reaches the presynaptic ending or terminal bouton

  
• Examples of Neurotransmitters


  • Acetylcholine (Ach)
  • Dopamine
  • Glutamate
  • Serotonin
  • Norepinephrine
  • Gamma-Aminobutyric acid (GABA)
  • Other Neurotransmitters
• Drug Addiction


  • Chronic, relapsing disease characterized by compulsive drug seeking and use despite negative consequences and by long-lasting changes in the brain
  • Drug use during pregnancy can lead to neonatal abstinence syndrome, a condition in which a baby can suffer from dependence and withdrawal symptoms after birth
• Alcohol


  Effects vary from person to person, depending on a variety of factors including: how much you drink, how often you drink, your age, your health status, your family history
• Ayahuasca


  • Psychoactive tea that originates from the Amazon region
  • Traditional healers in several South American countries use the tea for its reported healing properties
• Psychoactive substances


  Affect the brain and cause people to experience changes in their mood, thinking, and behavior
• Cocaine


  Powerfully addictive stimulant drug made from the leaves of the coca plant native to South America
• GHB (Gammahydroxybutyrate)


  Depressant approved for use in the treatment of narcolepsy, a disorder that causes daytime "sleep attacks"
• Heroin


  Opioid drug made from morphine, a natural substance extracted from the seed pod of the Asian opium poppy plant