neurons

• Neurons


  The fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between
• Physical activities


  • Playing the piano
  • Driving a car
  • Hitting a tennis ball
• Structure of neuron


  • Soma or cell body
  • Dendrites
  • Axons
  • Terminal buttons
• Soma or cell body

  Contains a nucleus that incorporates the hereditary material that determines how a cell will function
• Dendrites


  Short and thick branches found on the end of a cell body, specialized to receive extracellular influences, either from other cells or from the environment in the form of signals
• Axon


  A long, slim, tube-like extension that carries messages received by the dendrites to other neurons
• Terminal buttons


  Small bulges at the end of axons that send messages to other neurons
• Myelin sheath


  A protective coating of fat and protein that wraps around the axon to insulate it and increase the velocity of electrical impulses
• All-or-none law


  Neurons are either on or off, with nothing in between the on state and the off state
• How neurons fire


  1. Resting state (negative charge)

  2. Positive ions enter cell membrane, changing charge to positive

  3. Action potential travels along axon

  4. Positive ions pumped out, restoring negative charge
• Action potential


  The electrical impulse that travels along the axon of a neuron
• Synapse


  The space between two neurons where the axon of a sending neuron communicates with the dendrites of a receiving neuron using chemical messages
• Neurotransmitters


  Chemical messengers that carry messages across the synapse to a dendrite (and sometimes the cell body) of a receiving neuron
• Excitatory messages


  Make it more likely that a receiving neuron will fire and an action potential will travel down its axon
• Inhibitory messages


  Prevent or decrease the likelihood that the receiving neuron will fire
• Reuptake


  The process where neurons reabsorb the neurotransmitters that are clogging the synapse
• Important neurotransmitters


  • Acetylcholine (ACh)
  • Glutamate
  • Gamma-amino butyric acid (GABA)
• Acetylcholine (ACh)


  Involved in our every move, transmits messages relating to our skeletal muscles, and is involved in memory capabilities
• Glutamate


  Plays a role in memory, with specific biochemical changes at particular synapses
• Gamma-amino butyric acid (GABA)


  The nervous system's primary inhibitory neurotransmitter, moderates a variety of behaviors
• Hundred chemicals have been found to act as neurotransmitters, and neuroscientists believe that more may ultimately be identified
• Acetylcholine (ACh)


  One of the most common neurotransmitters, found throughout the nervous system, involved in our every move, transmits messages relating to our skeletal muscles, involved in memory capabilities, diminished production may be related to Alzheimer's disease
• Glutamate


  Another common excitatory neurotransmitter, plays a role in memory, memories appear to be produced by specific biochemical changes at particular synapses
• Gamma-amino butyric acid (GABA)


  The nervous system's primary inhibitory neurotransmitter, moderates a variety of behaviors, ranging from eating to aggression, several common substances like Valium and alcohol are effective because they permit GABA to operate more efficiently
• Dopamine (DA)


  Another major neurotransmitter, involved in movement, attention, and learning, the discovery that certain drugs can have a significant effect on dopamine release has led to the development of effective treatments for a wide variety of physical and mental ailments, like Parkinson's disease
• Serotonin


  Associated with the regulation of sleep, eating, mood, and pain, a growing body of research points toward a broader role, suggesting its involvement in such diverse behaviors as alcoholism, depression, suicide, impulsivity, aggression, and coping with stress
• Endorphins


  A family of chemicals produced by the brain that are similar in structure to painkilling drugs such as morphine, the production of endorphins reflects the brain's effort to deal with pain as well as to elevate mood, may produce the euphoric feelings that runners sometimes experience after long runs, the act of taking placebos may induce the release of endorphins, leading to the reduction of pain
• The central nervous system (CNS) is composed of the brain and spinal cord
• Spinal cord


  • About the thickness of a pencil, contains a bundle of neurons that leaves the brain and runs down the length of the back, the primary means for transmitting messages between the brain and the rest of the body, controls some simple behaviors on its own, without any help from the brain, like the knee jerk reflex
• Reflex


  An automatic, involuntary response to an incoming stimulus, like withdrawing your hand from a hot stove
• Neurons involved in reflexes

  • Sensory (afferent) neurons
  • Motor (efferent) neurons
• Sensory (afferent) neurons


  Transmit information from the perimeter of the body to the central nervous system and the brain
• Motor (efferent) neurons


  Communicate information in the opposite direction, from the brain and nervous system to muscles and glands
• Quadriplegia


  A condition in which people lose voluntary muscle movement below the neck, resulting from spinal cord injury or severing
• Paraplegia


  A condition in which people are unable to voluntarily move any muscles in the lower half of the body, resulting from spinal cord injury or severing
• Peripheral Nervous System


  • Branches out from the spinal cord and brain and reaches the extremities of the body, made up of neurons with long axons and dendrites, encompasses all the parts of the nervous system other than the brain and spinal cord, includes the somatic division and the autonomic division
• Somatic division


  Specializes in the control of voluntary movements and the communication of information to and from the sense organs
• Autonomic division


  Controls the parts of the body that keep us alive, like the heart, blood vessels, glands, lungs, and other organs that function involuntarily without our awareness
• Activating the divisions of the autonomic nervous system


  1. Sympathetic division acts to prepare the body for action in stressful situations, engaging all of the organism's resources to run away or confront the threat (fight or flight response)

  2. Parasympathetic division acts to calm the body after the emergency has ended, lowering heart rate, stopping sweating, returning the body to its pre-alarm state, directing the body to store energy for use in emergencies
• Endocrine system


  A chemical communication network that sends messages throughout the body via the bloodstream, secretes hormones, chemicals that circulate through the blood and regulate the functioning or growth of the body, closely linked to the hypothalamus