The Neurons

 

·        Functional Classes (Central Nervous System vs. Peripheral Nervous System)

-        There are three classes of neurons:

1.      Sensory neurons:  having to do with internal and external information

2.      Motor neurons:  having to do with the muscles

3.      Other neurons:  also known as ‘inter neurons’

·        Morphology:  how to categorize neurons by shape

-        Unipolar neuron: the kind of neuron in which only one arm (axon) is coming out of the cell body (soma).  At the end of the axon are the dendrites. 

-        Bipolar neuron: when two axons protrude out of a cell body. 

-        Multipolar neuron: when many branches grow out of the cell body.  One branch is always the axon, and the others are dendrites. 

·        Bipolar and Unipolar Neurons

-        found as sensory or motor neurons

-        Bipolar:  has to do mostly with vision and audition

-        Unipolar:  having to do with touch information.  These are located in your spinal cord.

·        Multipolar Neurons

-        The axon in this neuron has a sheath on it called the myelin sheath.  The sheath extends all the way to the ends of the axons, not including the terminal buttons. 

-        On some of the dendrites there are little spines which exist only on these dendrites.

-        Neurons gather information on dendrites and emit info from the axons. 

-        Spines:  learning memory

·        Synapse

-        A synapse is the place where two neurons are connected. 

-        Synapses only occur at the terminal buttons ŕ the terminal buttons usually connect with another neuron on the cell body, the dendrites, and the spines. 

·        Inside a Neuron

-        Nucleus

-        Myelin sheath

-        Microtubules

-        Dendrite

-        Cytoplasm

-        Spines

-        Mitochondria:  the power plants of the cell; they provide the energy for the cell.  The genetic makeup of the mitochondria comes from the mother’s genes.

·        The Glial Cell:  5x more of these than neurons

-        no information flow in these cells

-        Astrocytes:  the city workers of cells; they provide support, cleanup, and nourishment.

-        Oligodendrocytes (CNS) and Schwann Cells (PNS) :  provide the myeliniation

·        Astrocytes

-        The astrocytes hold onto the neurons; they add support

-        They also hold onto blood vessels

·        Oligodendrocytes

-        Schwann Cell (PNS):  everything else but your brain and spinal cord

-        These wrap around the axon, providing the myelin sheath for them. 

 

 

 

 

Neuro-Physiology

 

·        Neurons are electrical devices

-        They are ions, not electrons; sometimes molecules with electrons on them.

-        4 kinds of ions:

ŕ Outside:  Na + , Cl –

ŕ Inside:  A- , K+

-        There is more Na and Cl outside than there is inside, and more A and K inside than there is outside. 

-        Force of Diffusion: the ions tend to flow from areas of high to areas of low concentration.

-        Electrostatic Pressure: when two charges with the same sign repel each other.

-        The inside of the cell body is negative while the outside of it is positive. 

-        The Sodium-Potassium Transporter: pumps out sodium; demands a great deal of energy.  20% of the energy the cell uses is for this purpose. 

·        The Action Potential

-        Resting membrane potential:  -70 mV

-        When membrane potential increases it is called depolarization.

-        When membrane potential decreases it is called hyperpolarization.

-        Action potential: occurs when a great enough current is generated to place the membrane potential at it’s greatest. 

-        If the membrane potential is below the threshold of excitation, nothing occurs; if above it, action potential has been created.

 

v     Everything in the brain, if electrical, is carried by ions.

v     Ion channels exist which open and close by changing the voltage of the cell membrane. 

v     When Na is let into the cell, depolarization occurs; when K is let out of the cell, hyperpolarization occurs.

v     Na channels close when the voltage reaches a certain point.

v     Action potential – the language of neurons.

-        On a dendrite the signal (action potential) will die away. 

-        On an axon, the action potential will travel the full length of the axon without dying out.

*  The action potential slightly decreases when going through the myelin sheath, but is regenerated at the intervals on the axon without the sheath.  These areas are called the Nodes of Ranvier. 

            *  The action potential travels at speeds of 200 mph.