Body Systems

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Body Systems

• Nervous System

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Nervous System Functions

• Sensory input sense organs, receptors,
• afferent neurons
• Integration Central Nervous System(CNS)
• interneurons
• Motor output glands, muscles
• efferent neurons

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The Neuron

• Consists of
• Cell body
• Dendrite
• Axon
• Label your diagram

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The Nerve Impulse

• Begins at dendrites, passes through to the cell
  body and then through the axon, terminating at
  the terminal branches before the synapse.

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The Nerve Impulse

• Occurs as a result of both electrical and
  chemical changes across the membrane of the
  neuron.

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Electrochemical nature of membrane
Due to the presence of ions, a positive
electrical charge is present outside the
membrane. (excess of sodium ions) A negative
charge is present inside the membrane. (mostly
potassium ions)
Since both sodium (outside) and potassium
(inside) are both positive ions, how can one side
of the membrane be and the other -?
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• Although diffusion of ions will occur, the
  membrane actively pumps Na/K.
• What do you call the membrane structures through
  which the ions will be pumped through?

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Resting potential- unstimulated (-70 millivolts)

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Action potential channels open, Na ions rush
in, depolarization occurs.
What is the threshold potential?
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Like a domino effect, once stimulated the nerve
impulse is an all or nothing response.
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Repolarization In response to the inflow of
Na, K rushes out of the cell, followed by
closing of the Na channel gates.
Interpret the graph at stage 4 with respect to
the events that are occurring.
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Hyperpolarization More K outflows than is
necessary, thus undershooting threshold, more
than repolarizing the membrane.
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Refractory period Although repolarized, the
neuron has a period when it is unable to fire.
What has to occur to re-establish the original
conditions so that a neuron can fire again?
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After the membrane

• Once the impulse reaches the end of the axon a
  different set of events has to occur to allow the
  impulse to continue to another neuron.
• This requires the crossing of the synapse.

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Most transmissions across a synapse are of a
chemical nature.
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Synapse Summary

• The gated channels for Ca2 respond to the action
  potential by opening up.
• In turn, the Ca2 enters the cell and triggers
  the release of neurotransmitters.
• The neurotransmitter crosses the synapse and
  binds with protein receptors on the next neuron
  membrane.
• Neurotransmitters degrade or are recycled shortly
  after so as not to cause continuous stimulation.

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Neurotransmitters

• Acetylcholine stimulates muscles to contract at
  neuromuscular junctions. At other junctions, acts
  as an inhibitor.
• Epinephrine, norepinephrine, dopamine, serotonin
  (I) all are amino acid derivatives. Work
  between neurons. First three may be excitatory or
  inhibitory.
• GABA inhibitory, within the brain.

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Saltatory Conduction

• Neurons with a myelin sheath (Schwann cells)
  allow a much faster conduction of impulses
  because the impulse jumps between the gaps
  (nodes of Ranvier) of the cells rather than
  traveling along the whole length of the axon.

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The Bigger Picture

• Billions upon billions of neurons and other cells
  make up your nervous system. Appearance can be
  somewhat modified based on location and function.
• CNS brain, spinal cord
• Peripheral all other nerves
• Somatic sensory, motor
• Autonomic sympathetic, parasympathetic

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You are always on your mind!
This diagram illustrates the relative amount of
brain mass devoted to some important parts of the
body. Why do you think some areas require much
more than others?