Nervous Systempages 5253

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Nervous Systempages 52-53

• The human nervous system nerve cells (or neurons)
  
• Neurons
• respond to stimuli
• Conduct impulses
• communicate with each other .

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Neuron

• The nucleus of a neuron is located in the cell
  body. Extending out from the cell body are
  processes called dendrites and axons

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• dendrites conducting impulses toward the cell
  body
• axons conducting impulses away from the cell

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Myelin Sheath

• The Myelin Sheath of a neuron consists of
  fat-containing cells that insulate the axon from
  electrical activity. This insulation acts to
  increase the rate of transmission of signals

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• Neurons can respond to stimuli and conduct
  impulses because a membrane potential is
  established across the cell membrane.

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Establishment of the Resting Membrane Potential

• Membranes are polarized or, in other words,
  exhibit a RESTING MEMBRANE POTENTIAL
• This means that there is an unequal distribution
  of ions (atoms with a positive or negative
  charge) on the two sides of the nerve cell
  membrane.

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• This POTENTIAL generally measures about 70
  millivolts (with the INSIDE of the membrane
  negative with respect to the outside).

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• RESTING MEMBRANE POTENTIAL expressed as -70 mV
  (minus means that the inside is negative relative
  to the outside).
• It is called a RESTING potential because it
  occurs when a membrane is not being stimulated or
  conducting impulses (in other words, it's
  resting).

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What factors contribute to this membrane
potential?

• Two ions are responsible sodium (Na) and
  potassium (K). An unequal distribution of these
  two ions occurs on the two sides of a nerve cell
  membrane because carriers actively transport
  these two ions sodium from the inside to the
  outside and potassium from the outside to the
  inside. The Cell Online Chapter 13 - Animations

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• AS A RESULT there is a higher concentration of Na
  on the outside than the inside and a higher
  concentration of K on the inside than the
  outside.

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• The nerve cell membrane contains GATES or 
  CHANNELS.
• SODIUM GATES and POTASSIUM GATES.
• gates represent the only way that these ions can
  pass through the nerve cell membrane.
• IN A RESTING NERVE CELL MEMBRANE, all the sodium
  gates are closed and some of the potassium gates
  are open.

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Action potential

• http//outreach.mcb.harvard.edu/animations/actionp
  otential.swf
• Action potential propagation
• Remember this action potential delivered by the
  motor neuron. Animation Action Potentials and
  Muscle Contraction

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ACTION POTENTIAL

• An action potential is a very rapid change in
  membrane potential that occurs when a nerve cell
  membrane is stimulated. Specifically, the
  membrane potential goes from the resting
  potential (typically -70 mV) to some positive
  value (typically about 30 mV) in a very short
  period of time (just a few milliseconds).

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• Neurons, Synapses, Action Potentials, and
  Neurotransmission - The Mind Project

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Organization Of The Human Nervous System  
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Central nervous system

• The central nervous system is made up of the
• spinal cord and
• brain

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The spinal cord

• conducts sensory information from the peripheral
  nervous system (both somatic and autonomic) to
  the brain
• conducts motor information from the brain to our
  various effectors
• skeletal muscles
• cardiac muscle
• smooth muscle
• glands
• serves as a minor reflex center

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The brain

• receives sensory input from the spinal cord as
  well as from its own nerves (e.g., olfactory and
  optic nerves)
• devotes most of its volume (and computational
  power) to processing its various sensory inputs
  and initiating appropriate and coordinated
  motor outputs.

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Peripheral nervous system

• The PNS consists of
• sensory neurons running from stimulus receptors
  that inform the CNS of the stimuli
• motor neurons running from the CNS to the muscles
  and glands - called effectors - that take action.

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• The autonomic nervous system has two
  subdivisions, the
• sympathetic nervous system and the
• parasympathetic nervous system.

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• http//users.rcn.com/jkimball.ma.ultranet/BiologyP
  ages/A/autonomic.gif
• synaptic transmission
• Synaptic Transmission

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Some common neurotransmitters