Lesson 2 - Neurons

• About 100 billion neurons (nerve cells) in the human brain.
• Dendrites – carry information to the cell body from otherneurons
• Cell Body (Soma) – contains nucleus
• Axon – carries information to the next cell
• Myelin Sheath – insulates the axon and speeds up the neuralimpulse
• Synaptic Space (synaptic cleft) – tiny gap between neurons
• Terminal Button – enlarged area at the end of an axon
• The Synapse – composed of the terminal button of one neuron, the synaptic space, and the dendrites or cell body of the receiving neuron
• Synaptic Vesicles – sacs in terminal button that release chemicals into synaptic space
• Neurotransmitters – chemicals released by synaptic vesicles
• Receptor Sites – location on receptor neuron for specificneurotransmitter
• Synapse – the microscopic gap that serves as a communications link between neurons
• Synapses also occur between neurons and the muscles or glands they serve
• Type of Neuron according to function

  Sensory Neurons – carry information from sensory systems to the brain; also referred to as afferent (carry messages from the receptors to the CNS; unipolar)
• Type of Neuron according to function

  Motor Neurons – carry information from the brain to muscles and glands; also referred to as efferent (carry messages from the CNS to muscles and glands; multipolar)
• Type of Neuron according to function

  Interneurons – carry information between other neurons (located in the CNS and are the link between sensory and motor neurons; multipolar)
• Glial cells - Cells that insulate and support neurons
• Glial cells - Create the myelin sheath
• glial cells - remove waste products
• glial cells - provide nourishment and prevent harmful substances from entering the brain
• Neural Communication

  Resting Potential – Nothing is happening. The gates are closed and the positive ions are on the outside with the negative ions on the side of the cell; “Negative Ions inside the Neuron is Natural”
• Neural Communication

  Action Potential (Neural Impulse) – A neural impulse; a brief electrical charge that travels down an axon
• Polarization – when the inside of the Neuron is negatively charged relative to the outside (resting potential)
• Depolarization – when the electrical charge of a cell movestoward zero
• Refractory Period – the time it takes for the positive ions to bepumped out
• Threshold – the level of stimulation required to trigger aneural impulse
• Absolute refractory period - period immediately after an action potential when another action potential cannot occur; 1/1000th of a second
• Relative refractory period - period following absolute refractory period when a neuron will only respond to a stronger than normal impulse
• Graded potential - a shift in the electrical charge in a tiny are of a neuron
• Many subthreshold depolarizations are added together to produce an action potential (a process known as summation)
• All-or-none Law - a neuron either fires or it does not
• Intensity of a stimulus is seen by the frequency of action potentials
• synapse - a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. This tiny gap is called the synaptic gap or cleft.
• neurotransmitters - chemicals released from the sending neuron travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing it to generate an action potential
• reuptake - neurotransmitters in the synapse are reabsorbed into the sending neurons through the process of reuptake. This process applies the brakes on neurotransmitter action.
• lock and key mechanism - neurotransmitters bind to the receptors of the receiving neuron in a key-lock mechanism
• agonists - mimicking or impersonating naturally occurring neurotransmitters, like a hairpin picking a lock, they are able to unlock a cell to produce an effect.
• antagonists - working in the opposite way, antagonists block the receptor, like jamming glue into a keyhole, so that it may not be opened
• Type of Neurotransmitter

  acetylcholine (Ach):

  • Released at the neuromuscular junction
  • Plays an important role in arousal and attention
  • Loss of this neurotransmitter's producing cells is linked to Alzheimer’s Disease
  • Too much = Spasms/Too little = Paralysis
• Type of Neurotransmitter

  dopamine:

  • Affects neurons associated with voluntary movement and pleasure
  • Play a role in learning, memory, and emotions
  • Implicated in Parkinson’s Disease and Schizophrenia