The Human Nervous System 35-1

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The Human Nervous System 35-1

• Name the three parts of a neuron.
• Describe the way in which a nerve impulse occurs.

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Can you label a neuron?

• Cell body
• Nucleus
• Dendrites
• Axon
• Node of Ranvier

• Nucleus - Schwann cell
• Schwann cell
• Myelin sheath
• Synaptic knob
• Terminal Branches

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Myelin Sheath
A faster impulse the action potential jumps
from gap to gap.
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Nerve ImpulseFirst a cell sets up the resting
potential

• negative inside and positive outside
• ATP used to drive sodium/potassium pump
• Potassium can move freely
• Sodium must be pumped
• Potassium diffuses back out.

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Three types of Nerve Cells

• Sensory Neurons
• Inter Neurons
• Motor Neurons

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In a synapse vesicles release neurotransmitters
which cause the next neuron to fire.
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The Impulse

• An Action potential stimulates the membrane.
• Permeability to Na suddenly increases as sodium
  gates open
• Na rushes in and the polarity reverses
• Impulse flows in one direction due to refractory
  period.
• Called all-or-none response.

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The Nerve System
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NERVES
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Fun Facts !

• Average number of neurons in the human brain 100
  billionAverage number of neurons in an octopus
  brain 300 billionRate of neuron growth during
  development of a fetus (in the womb) 250,000
  neurons/minuteDiameter of a neuron 4 to 100
  micronsLongest axon of a neuron around 15 feet
  (Giraffe primary afferent axon from toe to
  neck)Velocity of a signal transmitted through a
  neuron 1.2 to 250 miles/hour
• (remember that these are averages because there
  is lots of variability in the nervous system!!)
• Guess what? There are more nerve cells in the
  human brain than there are stars in the Milky
  Way.

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Fun Facts ! (continued)

• What if we lined up all the neurons in our body?
  How long would that line stretch?
• Well, let's think about this... Let's assume that
  one neuron is about 10 microns long. Remember,
  this is just an example, because neurons come in
  all different sizes. So, if we line up 100
  billion neurons which are 10 microns long . . .
• 100,000,000,000 neurons x 10 microns 1000 km or
  about 600 miles!
• This may help with the math1000 microns
  1milimeter (mm)10 mm 1centimeter (cm)100 cm 1
  meter (m)1000 m 1 kilometer (km)

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Art and text and presentation made by Valerie
Shiba and Jennifer Li
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Xerox 35-1

• 1 e
• 2 i
• 3 d
• 4 n
• 5 g
• 6 l
• 7 j
• 8 a
• 9 j
• 10 m

• 11 b
• 12 a
• 13 h
• 14 k,b
• 15 c
• 16 k
• 17 m
• 18 f
• 19 l

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Xerox 35-1 (Cont.)

• 20 dendrite
• 21 b
• 22 c
• 23 d
• 24 sensory
• 25 negative

• 26 toward
• 27 node
• 28 neurotransmitter
• 29 travel to the next neuron
• 30 the impulse would not work
• 31 increase the speed of the neuron

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Credits

• Initial art, text and presentation made by
  Valerie Shiba and Jennifer Li