1. The Nervous System
Allows communication between cells & tissues of the body.
Acts like a telephone or computer network with a complex central control.
Composed of generalized nerve cells called Neurons
Divided into Two General Systems:
*The Central Nervous System (CNS): Command & control region; Consists of the Brain & Spinal Cord
*The Peripheral Nervous System (PNS): Connects the Central Nervous System to the rest of the body.

2. Action Potential

3. Central Nervous System

4. Central Nervous System

6. Peripheral Nervous System

8. General Structure of a Neuron
Cell Body: Contain majority of cell’s cytoplasm & organelles
Dendrites: Extensions which serve in the reception of nerve signals
Axons: Long fibers used to transmit nervous impulses
Surrounded by Schwann Cells (PNS) or Oligodendrocytes (CNS)
Myelin Sheath insulates axons and speeds nerve impulses along the axon as they recharge at the Nodes of Ranvier
End at Synaptic Terminal & push NTs from synaptic vesicles into synapse btwn adjacent nerve or effector cells
The NTs stimulate the adjacent cell and the signal is propagated to the next cell

9. Types of Neurons:
Sensory/Afferent Neurons: Collect messages from sense organs & carry those messages to the spinal cord or brain.
Motor/Efferent Neurons: Carry messages from the spinal cord or brain to muscles and glands
Interneurons: Carry messages from one neuron to another; Only exist in the spinal cord!

11. Neural Function
Neurons function through transmission of a propagating wave of electrochemical potential. This is produced by a diffusion of Sodium(Na+) and Potassium(K+) ions across a neuron’s membranes
In resting potential there is an excess of K+ on the inside of the cell & an excess of Na+ on the outside.
When stimulated, the cell allows the diffusion of ions through its membranes via gated ion channel. This changes the potential across the membrane and is the basis of the electrochemical impulse. Once stimulated, this reaction propagates down the axon.
Na+ and K+ concentrations are then restored via the Sodium Postassium Pump

12. How does a neuron fire?
Resting Potential- fluid outside the axon filled with +++ charged ions. Fluid inside is filled with ---- charged ions. A selectively permeable membrane separates the two.
At this point the ion is charged and ready to fire.
Action Potential- the brief electric charge that moves down the axon.
The Na/K pump moves the charged ions into the axons. Positive ions are pumped in and negative are pumped out (Depolarization)

13. Refractory Period- Na/K pump moves the positive ions back out and the negative ions back in allowing the neuron to fire again (Repolarization)
The neuron has now returned to its resting potential.
Quick Clip
Threshold- minimum level of stimulation needed to trigger a neural impulse.
Some messages are “excitatory” and some are “inhibitory.” Whichever side wins out gets the message delivered. It is “all or nothing”!!!