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Neurons and Neural Transmission . Neurons – cells responsible for conducting information Information transmission one-way process Afferent (sensory neurons) Efferent (motor neurons) Nerve composed of axons/dendrites of many neurons + blood vessels, neuroglia cells

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Presentation Transcript
slide2
Neurons – cells responsible for conducting information
    • Information transmission one-way process
      • Afferent (sensory neurons)
      • Efferent (motor neurons)
    • Nerve composed of axons/dendrites of many neurons + blood vessels, neuroglia cells
  • Neuroglia (Glia) – responsible for support of neurons
slide3

Most of a neuron’s organelles are in the cell body

  • Most neurons have dendrites, highly branched extensions that receive signals from other neurons
  • The axon is typically a much longer extension that transmits signals to other cells at synapses
  • An axon joins the cell body at the axon hillock
slide4

Conduction along axon: electrical ( disruption of chemiosmotic gradient)

  • Synapses: chemical – involves neurotransmitters
slide5

Resting Potential: 65mv

  • More negative ions inside cell than outside
  • Na ions concentrated outside cell/K ions inside – effect of Na/K pump
  • Membrane channels regulate movement of Na, K ions
  • Na-K pump concentrates Na outside membrane, K inside
slide6
Action potential: Messages transmission as change in membrane potential
  • Stimulus causes gated channels open causing depolarization of membrane
      • Sodium ‘gates’ open so Na+ moves into cell = depolarization

Followed quickly by:

      • Potassium moves out of cell = repolarization
      • Refractory period
  • Once initiated action potential moves progressively away from cell body towards synaptic terminals
slide8

The speed of an action potential increases with the axon’s diameter

  • In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase
  • Myelin sheaths are made by glia— oligodendrocytesin the CNS and Schwann cells in the PNS
  • Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found
  • Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction
slide9

Neurons communicate with other cells at synapses

  • Most are chemical
    • The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal
    • The action potential causes the release of the neurotransmitter
    • The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell
    • Excitory neurotransmitter  dopolarization
    • Inhibitory neurotransmitter  hyperpolarization
slide10

Fig. 48-14

Postsynaptic

neuron

Synaptic

terminals

of pre-

synaptic

neurons

5 µm

slide11

Neurotransmitter in synaptic vesicles located in the synaptic terminal of presynaptic neuron released at arrival of action potential

  • The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell
signal transmission at synapse
Signal Transmission at Synapse
  • Electrical Signal is transformed into Chemical Signal = Neurotransmitter
    • Electrical signal arrives at axon bulb causes opening of Calcium gates and Ca enters cell
    • Excess Ca causes release of neurotransmitter stored in cell (inside vesicles) into synaptic cleft
    • Neurotransmitters diffuse across cleft and interact with receptors on next neuron
signal integration
Signal Integration
  • Many neurons pass signal on to next neuron in the pathway
    • Some send excitatory signals (cause depolarization of neuron)
    • others send inhibitory signals (cause hyperpolarization or more negative charge inside neuron)
    • all or none response: sum of excitatory signals and inhibitory signals determines if an action potential is generated in the next neuron and signal is continued
    • Type signal depends on type neurotransmitter released
slide15
Synapses are interaction/integration points
  • 50+ positive impulses required to fire interneuron
  • integration involves summing of positive and negative signals
  • positive signals result in depolarization
  • negative signals result in hyperpolerization
slide16
Importance of Neurotransmitters
  • Many produced ~ 50
  • Impact mood, memory, ability
  • Used in different behavioral systems
  • Norepinephrine – ‘good’ feeling
  • Serotonin – well being
  • Dopamine – emotions
slide17
Neuortransmitter removed quickly from synapse
  • Effect of neurotransmitter lasts as long as it is present
  • Removed by:
  • Destruction – enzymes
  • Recycling – returned to axon tip
slide18
Example of a Neurotransmitter
  • Acetylcholine
  • Destroyed by acetylcholinesterase
  • Stimulates muscle contraction
  • Pesticides inhibit enzyme – acetylcholinesterase
  • Result of pesticide poisoning is spasms, death
slide19
Neurotransmitters – Another Example
  • Depression:
  • due to low:
    • Serotonin
    • Dopamine
    • Norepinephrine
slide20
Depression
  • Treatment: Drugs that inhibit breakdown of serotonin
  • Specific action:
  • Prozac
  • Zoloft
  • Paxil