Neuronal Physiology

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Neuronal Physiology

• JP Slovak
• Texas AM University-Commerce

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• Nerve and muscle cells utilize the membrane
  potential
• Fluctuations take two forms
• graded - short distance signals
• action - serve over long distances
• Nerve and muscle are considered excitable tissues

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Graded potential

• May change membrane potential by 10 mV
• magnitude is related to the triggering event
• Triggering event could be
• stimulus
• ligand-receptor interaction
• spontaneous change in membrane potential

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Graded potential

• Current flows passively between active area and
  inactive area
• direction of current movement of charges
• visualize as a reversal of charges
• the graded potential is decremental
• can function only over short distances

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Action potential

• Spreads throughout membrane in non-decrementally
• Polarization
• Depolarization - moves toward 0 mV
• Hyperpolarization - potential gt resting potential
• Repolarization

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Action potential

• Threshold potential
• 15 mV towards 0mV
• Membrane Channels
• voltage gated
• chemical messenger gated
• mechanically gated

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Action potential

• 1. Increase in Na permeability
• 2. Inside becomes positive 30 mV
• 3. K rushes out of cell
• 4. Resting potential achieved
• 5. Na-K pump restores normal ionic differences
  (Na outside, K inside)

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Action potential

• Neuron
• cell body
• dendrites
• axon
• collaterals
• axon hillock
• axon terminals

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Action potential

• Local current flow
• inactive areas become depolarized
• brings inactive area to threshold
• Na channels are opened leading to action
  potential
• original active area returns to resting potential
• local current spreads to inactive area, causing
  it to become active

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Action potential

• Cycle repeats itself until the action potential
  spreads to the end of the axon
• this occurs in unmyelinated fibers

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Action potential

• Saltatory conduction
• Myelinated fibers
• myelin composed of mainly lipds
• ions cannot permeate the lipid barrier
• myelin acts as insulator
• oligodendrites - myelin forming cells in CNS
• Schwann cells - myelin forming cells in PNS
• nodes of Ranvier

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Action potential

• Diameter influences velocity
• Refractory period -
• Absolute refractory period - sodium channels must
  return to closed state, but capable of opening
• relative refractory period - potassium channels
  are in a closed state.
• refractory period insures unidirectional
  propagation

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Neuronal integration

• Synapse
• presynaptic neuron
• synaptic knob
• synaptic vesicles
• neurotransmitters
• postsynaptic neuron
• synaptic cleft

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Neuronal integration

• Synapse operate in one direction only
• Ca channels in synaptic knob open in response to
  action potential
• this causes exocytosis of neurotransmitter
• interacts with receptor on postsynaptic neuron
• this triggers ion channels in postsynaptic neuron

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Neuronal integration

• Excitatory synapse
• inhibitory synapse
• EPSP (excitatory postsynaptic potential)
• IPSP (inhibitory postsynaptic potential)
• synaptic delay
• a synapse is either excitatory or inhibitory
• neurotransmitters are quickly removed

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Neuronal integration

• Some neurotransmiiters use second messengers
• GPSP (grand postsynaptic potential)
• temporal summation - sum of EPSPs occuring close
  in time
• spatial summation - sum of several inputs that
  spatially close
• action potentials initiated at axon hillock - it
  has the lowest threshold