The nervous system
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The Nervous System. The Neuron . Consists of a cell body with a nucleus and other organelles and 2 types of extensions: dendrites and axons Dendrites : sensory; they receive incoming messages from other cells and carry the electrical signal to the cell body. Each neuron can have 100s!

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The neuron
The Neuron

  • Consists of a cell body with a nucleus and other organelles and 2 types of extensions: dendrites and axons

    • Dendrites: sensory; they receive incoming messages from other cells and carry the electrical signal to the cell body. Each neuron can have 100s!

    • Axon: only one per neuron; can be several feet long (in large mammals). Transmits an impulse from the cell body outward to another cell.

    • See figure



The neuron1
The Neuron

  • Synapse: the space between 2 neurons

  • Neurotransmitters: chemical messengers sent across the synapse from one neuron to another


Resting potential
Resting Potential

  • Describes the difference in electrical charge across a cell membrane

  • Resting potential is the membrane potential of a neuron at rest; typically -60 to -80mV (millivolts) potential; the inside of the neuron is negative to the outside

  • Figure 48.6 



Action potential
Action Potential

  • An all or nothing response

  • If a stimulus is great enough to excite a neuron, we say the cell “reaches its threshold” and an action potential will occur


Steps in an action potential
Steps in an Action Potential

  • Depolarization: the stimulus opens Na+ channels in the membrane, allowing Na+ to rush inside the cell, changing the membrane potential to a positive value (from negative at rest) = more + inside, - outside

  • Repolarization: the membrane potential is restored when K+ channels open and K+ leaves the cell. The charge is restored to resting potential but the ions are on the wrong sides of the membrane

  • Refractory period: Na-K pump reestablishes the original ion distribution – Na is pumped out of the cell, K is pumped in = ACTIVE TRANSPORT; during this period, a neuron cannot send another impulse