Ch 48. Nervous Systems

1. Neuron
ww2.cedarcrest.edu/.../tetanus-neuron.gif

• Functional Unit of the nervous system.



• Composed of a Cell body

Dendrite

• Cell extensions that receive incoming messages
  

Axon

• conducts electrical impulses away from the neuron's cell body



• covered by fatty myelin sheath

Synaptic Terminals

• at the end of axons



• relay messages through neruotransmitters

2. Action Potential

http://content.answers.com/main/content/img/oxford/Oxford_Sports/0199210896.action-potential.1.jpg

• axon--->dendrite



• Sodium moves in ( NA+ OUT)



• Potassium moves out (K+ IN)

1. When an axon is at resting potential, it sits at -70mv.



2. When stimulated, sodium gates open which depolarizes the membrane making it less negative.



3. If the membrane reaches -55mv or threshold potential, then an action potential will occur.



4. The sodium gates will close at the peak of the action potential while potassium ions continue to leave the cell.



5. The outward flow of potassium ions decreases the membrane potential or hyperpolarizes the cell.

Nerve Transmission

• Pre-synaptic cells transmit



• Post synaptic cells receive

IPSP-Inhibitory

• opens potassium channels



• potassium does not allow threshold potential because it is less positive than sodium

EPSP-Excitatory

• Sodium gates open which allow threshold potential to be reached



• once threshold potential is reached, an action potential will occur